draft-ietf-tls-protocol-00.txt   draft-ietf-tls-protocol-01.txt 
Transport Layer Security Working Group Tim Dierks
INTERNET-DRAFT Consensus Development
Transport Layer Security Working Group Alan O. Freier Christopher Allen
INTERNET-DRAFT Netscape Communications
Expires May 31, 1997 Philip Karlton
Netscape Communications
Paul C. Kocher
Independent Consultant
Tim Dierks
Consensus Development Consensus Development
November 26, 1996
Expires August 31, 1997 March 6, 1997
The TLS Protocol The TLS Protocol
Version 1.0 Version 1.0
<draft-ietf-tls-protocol-00.txt> <draft-ietf-tls-protocol-01.txt>
Status of this memo Status of this memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet- Drafts. working documents as Internet- Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or made obsolete by other months and may be updated, replaced, or made obsolete by other
skipping to change at page 2, line 6 skipping to change at page 2, line 6
This document specifies Version 1.0 of the Transport Layer Security This document specifies Version 1.0 of the Transport Layer Security
(TLS) protocol, which is at this stage is strictly based on the (TLS) protocol, which is at this stage is strictly based on the
Secure Sockets Layer (SSL) version 3.0 protocol, and is to serve as Secure Sockets Layer (SSL) version 3.0 protocol, and is to serve as
a basis for future discussions. The TLS protocol provides a basis for future discussions. The TLS protocol provides
communications privacy over the Internet. The protocol allows communications privacy over the Internet. The protocol allows
client/server applications to communicate in a way that is designed client/server applications to communicate in a way that is designed
to prevent eavesdropping, tampering, or message forgery. to prevent eavesdropping, tampering, or message forgery.
Table of Contents Table of Contents
Status of this memo 1 Status of this memo 1
Abstract 1 Abstract 1
Table of Contents 2 Table of Contents 2
1. Introduction 4 1. Introduction 3
2. Goals 4 2. Goals 4
3. Goals of this document 5 3. Goals of this document 5
4. Presentation language 6 4. Presentation language 5
4.1 Basic block size 6 4.1. Basic block size 6
4.2 Miscellaneous 6 4.2. Miscellaneous 6
4.3 Vectors 6 4.3. Vectors 6
4.4 Numbers 7 4.4. Numbers 7
4.5 Enumerateds 7 4.5. Enumerateds 7
4.6 Constructed types 8 4.6. Constructed types 8
4.6.1 Variants 9 4.6.1. Variants 8
4.7 Cryptographic attributes 10 4.7. Cryptographic attributes 9
4.8 Constants 11 4.8. Constants 10
5. The TLS Record Protocol 11 5. The TLS Record Protocol 11
5.1 Connection states 11 5.1. Connection states 11
5.2 Record layer 14 5.2. HMAC and the pseudorandom function 14
5.2.1 Fragmentation 14 5.3. Record layer 14
5.2.2 Record compression and decompression 15 5.3.1. Fragmentation 14
5.2.3 Record payload protection 16 5.3.2. Record compression and decompression 15
5.2.3.1 Null or standard stream cipher 16 5.3.3. Record payload protection 16
5.2.3.2 CBC block cipher 17 5.3.3.1. Null or standard stream cipher 17
5.3 Key calculation 18 5.3.3.2. CBC block cipher 17
5.3.1 Export key generation example 19 5.4. Key calculation 18
5.4.1. Export key generation example 20
6. The TLS Handshake Protocol 20 6. The TLS Handshake Protocol 20
6.1 Change cipher spec protocol 21 6.1. Change cipher spec protocol 21
6.2 Alert protocol 21 6.2. Alert protocol 22
6.2.1 Closure alerts 22 6.2.1. Closure alerts 22
6.2.2 Error alerts 22 6.2.2. Error alerts 23
6.3 Handshake protocol overview 23 6.3. Handshake Protocol overview 25
6.4 Handshake protocol 26 6.4. Handshake protocol 28
6.4.1 Hello messages 27 6.4.1. Hello messages 29
6.4.1.1 Hello request 27 6.4.1.1. Hello request 29
6.4.1.2 Client hello 28 6.4.1.2. Client hello 29
6.4.1.3 Server hello 30 6.4.1.3. Server hello 32
6.4.2 Server certificate 31 6.4.2. Server certificate 33
6.4.3 Server key exchange message 32 6.4.3. Server key exchange message 34
6.4.4 Certificate request 35 6.4.4. Certificate request 36
6.4.5 Server hello done 36 6.4.5. Server hello done 37
6.4.6 Client certificate 36 6.4.6. Client certificate 38
6.4.7 Client key exchange message 36 6.4.7. Client key exchange message 38
6.4.7.1 RSA encrypted premaster secret message 37 6.4.7.1. RSA encrypted premaster secret message 39
6.4.7.2 Client Diffie-Hellman public value 38 6.4.7.2. Client Diffie-Hellman public value 39
6.4.8 Certificate verify 38 6.4.8. Certificate verify 40
6.4.9 Finished 39 6.4.9. Finished 40
7. Cryptographic computations 40 7. Cryptographic computations 41
7.1 Computing the master secret 41 7.1. Computing the master secret 42
7.1.1 RSA 41 7.1.1. RSA 42
7.1.2 Diffie-Hellman 41 7.1.2. Diffie-Hellman 42
8. Application data protocol 41 8. Application data protocol 42
A. Protocol constant values 42 A. Protocol constant values 42
A.1 Reserved port assignments 42 A.1. Reserved port assignments 43
A.1.1 Record layer 42 A.2. Record layer 43
A.2 Change cipher specs message 43 A.3. Change cipher specs message 44
A.3 Alert messages 43 A.4. Alert messages 44
A.4 Handshake protocol 44 A.5. Handshake protocol 45
A.4.1 Hello messages 44 A.5.1. Hello messages 45
A.4.2 Server authentication and key exchange messages 45 A.5.2. Server authentication and key exchange messages 46
A.5 Client authentication and key exchange messages 46 A.5.3. Client authentication and key exchange messages 47
A.5.1 Handshake finalization message 47 A.5.4. Handshake finalization message 47
A.6 The CipherSuite 47 A.6. The CipherSuite 48
A.7 The Security Parameters 48 A.7. The Security Parameters 49
B. Glossary 49 B. Glossary 50
C. CipherSuite definitions 52 C. CipherSuite definitions 53
D. Implementation Notes 54 D. Implementation Notes 55
D.1 Temporary RSA keys 54 D.1. Temporary RSA keys 55
D.2 Random Number Generation and Seeding 55 D.2. Random Number Generation and Seeding 55
D.3 Certificates and authentication 55 D.3. Certificates and authentication 56
D.4 CipherSuites 55 D.4. CipherSuites 56
E. Version 2.0 Backward Compatibility 56 E. Backward Compatibility With SSL 56
E.1 Version 2 client hello 56 E.1. Version 2 client hello 58
E.2 Avoiding man-in-the-middle version rollback 58 E.2. Avoiding man-in-the-middle version rollback 59
F. Security analysis 58 F. Security analysis 59
F.1 Handshake protocol 58 F.1. Handshake protocol 59
F.1.1 Authentication and key exchange 58 F.1.1. Authentication and key exchange 60
F.1.1.1 Anonymous key exchange 59 F.1.1.1. Anonymous key exchange 60
F.1.1.2 RSA key exchange and authentication 59 F.1.1.2. RSA key exchange and authentication 61
F.1.1.3 Diffie-Hellman key exchange with authentication 60 F.1.1.3. Diffie-Hellman key exchange with authentication 61
F.1.2 Version rollback attacks 60 F.1.2. Version rollback attacks 62
F.1.3 Detecting attacks against the handshake protocol 61 F.1.3. Detecting attacks against the handshake protocol 62
F.1.4 Resuming sessions 61 F.1.4. Resuming sessions 62
F.1.5 MD5 and SHA 62 F.1.5. MD5 and SHA 63
F.2 Protecting application data 62 F.2. Protecting application data 63
F.3 Final notes 62 F.3. Final notes 63
G. Patent Statement 63 G. Patent Statement 64
References 63 References 64
Credits 65 Credits 66
Comments 67
1. Introduction 1. Introduction
The primary goal of the TLS Protocol is to provide privacy and The primary goal of the TLS Protocol is to provide privacy and
reliability between two communicating applications. The protocol is reliability between two communicating applications. The protocol is
composed of two layers: the TLS Record Protocol and the TLS composed of two layers: the TLS Record Protocol and the TLS
Handshake Protocol. At the lowest level, layered on top of some Handshake Protocol. At the lowest level, layered on top of some
reliable transport protocol (e.g., TCP[TCP]), is the TLS Record reliable transport protocol (e.g., TCP[TCP]), is the TLS Record
Protocol. The TLS Record Protocol provides connection security that Protocol. The TLS Record Protocol provides connection security that
has two basic properties: has two basic properties:
- The connection is private. Symmetric cryptography is used for - The connection is private. Symmetric cryptography is used for
data encryption (e.g., DES[DES], RC4[RC4], etc.) The keys for data encryption (e.g., DES[DES], RC4[RC4], etc.) The keys for
this symmetric encryption are generated uniquely for each this symmetric encryption are generated uniquely for each
connection and are based on a secret negotiated by another connection and are based on a secret negotiated by another
protocol (such as the TLS Handshake Protocol). The Record protocol (such as the TLS Handshake Protocol). The Record
Protocol can also be used with no encryption. | Protocol can also be used without encryption.
- The connection is reliable. Message transport includes a - The connection is reliable. Message transport includes a message
message integrity check using a keyed MAC. Secure hash integrity check using a keyed MAC. Secure hash functions (e.g.,
functions (e.g., SHA, MD5, etc.) are used for MAC SHA, MD5, etc.) are used for MAC computations. The Record
computations. The Record Protocol can operate without a MAC, Protocol can operate without a MAC, but is generally only used
but is generally only used in this mode while another protocol in this mode while another protocol is using the Record Protocol
is using the Record Protocol as a transport for negotiating as a transport for negotiating security parameters.
security parameters.
The TLS Record Protocol is used for encapsulation of various higher The TLS Record Protocol is used for encapsulation of various higher
level protocols. One such encapsulated protocol, the TLS Handshake level protocols. One such encapsulated protocol, the TLS Handshake
Protocol, allows the server and client to authenticate each other Protocol, allows the server and client to authenticate each other
and to negotiate an encryption algorithm and cryptographic keys and to negotiate an encryption algorithm and cryptographic keys
before the application protocol transmits or receives its first byte before the application protocol transmits or receives its first byte
of data. The TLS Handshake Protocol provides connection security of data. The TLS Handshake Protocol provides connection security
that has three basic properties: that has three basic properties:
- The peer's identity can be authenticated using asymmetric, or - The peer's identity can be authenticated using asymmetric, or
public key, cryptography (e.g., RSA[RSA], DSS[DSS], etc.). public key, cryptography (e.g., RSA[RSA], DSS[DSS], etc.). This
This authentication can be made optional, but is generally authentication can be made optional, but is generally required
required for at least one of the peers. for at least one of the peers.
- The negotiation of a shared secret is secure: the negotiated - The negotiation of a shared secret is secure: the negotiated
secret is unavailable to eavesdroppers, and for all | secret is unavailable to eavesdroppers, and for any
authenticated connections, cannot be obtained by an attacker | authenticated connection the secret cannot be obtained, even by
who can place himself in the middle of the connection. | an attacker who can place himself in the middle of the
| connection.
- The negotiation is reliable: no attacker can modify the - The negotiation is reliable: no attacker can modify the
negotiation communication without being detected by the peers. | negotiation communication without being detected by the parties
| to the communication.
One advantage of TLS is that it is application protocol independent. One advantage of TLS is that it is application protocol independent.
A higher level protocol can layer on top of the TLS Protocol | Higher level protocols can layer on top of the TLS Protocol
transparently. transparently.
2. Goals 2. Goals
The goals of TLS Protocol, in order of their priority, are: The goals of TLS Protocol, in order of their priority, are:
1. Cryptographic security 1. Cryptographic security: TLS should be used to establish a secure
TLS should be used to establish a secure connection between connection between two parties.
two parties.
2. Interoperability 2. Interoperability: Independent programmers should be able to
Independent programmers should be able to develop applications develop applications utilizing TLS that will then be able to
utilizing TLS that will then be able to successfully successfully exchange cryptographic parameters without knowledge
exchange cryptographic parameters without knowledge of one of one another's code.
another's code.
Note: Note: It is not the case that all instances of TLS (even in the same
It is not the case that all instances of TLS (even in the same
application domain) will be able to successfully connect. For application domain) will be able to successfully connect. For
instance, if the server supports a particular hardware token, instance, if the server supports a particular hardware token,
and the client does not have access to such a token, then the and the client does not have access to such a token, then the
connection will not succeed. | connection will not succeed. There is no required set of ciphers
| for minimal compliance, so some implementations may be unable to
| communicate.
3. Extensibility 3. Extensibility: TLS seeks to provide a framework into which new
TLS seeks to provide a framework into which new public key and public key and bulk encryption methods can be incorporated as
bulk encryption methods can be incorporated as necessary. This necessary. This will also accomplish two sub-goals: to prevent
will also accomplish two sub-goals: to prevent the need to the need to create a new protocol (and risking the introduction
create a new protocol (and risking the introduction of of possible new weaknesses) and to avoid the need to implement
possible new weaknesses) and to avoid the need to implement an an entire new security library.
entire new security library.
4. Relative efficiency 4. Relative efficiency: Cryptographic operations tend to be highly
Cryptographic operations tend to be highly CPU intensive, CPU intensive, particularly public key operations. For this
particularly public key operations. For this reason, the TLS reason, the TLS protocol has incorporated an optional session
protocol has incorporated an optional session caching scheme caching scheme to reduce the number of connections that need to
to reduce the number of connections that need to be be established from scratch. Additionally, care has been taken
established from scratch. Additionally, care has been taken to to reduce network activity.
reduce network activity.
3. Goals of this document 3. Goals of this document
This document describing the TLS Protocol Version 1.0 Specification | This document and the TLS protocol itself are based on the SSL 3.0
is strictly based on Secure Sockets Layer (SSL) Version 3.0 [SSL3], | Protocol Specification as published by Netscape. The differences
incorporating only errata as well as several clarifications to the | between this protocol and SSL 3.0 are not dramatic, but they are
SSL 3.0 draft, but will have no substantive changes to the "bits on | significant enough that TLS 1.0 and SSL 3.0 do not interoperate
the wire" of the SSL 3.0 protocol. This draft will be the starting | (although TLS 1.0 does incorporate a mechanism by which a TLS
point for future discussions, and from its base the TLS working | implementation can back down to SSL 3.0). This document is intended
group will work together to agree on what changes need to be made. | primarily for readers who will be implementing the protocol and
| those doing cryptographic analysis of it. The spec has been written
Note that in all cases TLS has been substituted for the word SSL in | with this in mind, and it is intended to reflect the needs of those
the presentation language examples. In no way is the presentation | two groups. For that reason, many of the algorithm-dependent data
language of this document any different then with SSL 3.0. This was | structures and rules are included in the body of the text (as
done this way to ease the transition to TLS. | opposed to in an Appendix), providing easier access to them.
This document is intended primarily for readers who will be
implementing the protocol and those doing cryptographic analysis of
it. The spec has been written with this in mind, and it is intended
to reflect the needs of those two groups. For that reason, many of
the algorithm-dependent data structures and rules are included in
the body of the text (as opposed to in an Appendix), providing
easier access to them.
This document is not intended to supply any details of service This document is not intended to supply any details of service
definition nor interface definition, although it does cover select definition nor interface definition, although it does cover select
areas of policy as they are required for the maintenance of solid areas of policy as they are required for the maintenance of solid
security. security.
4. Presentation language 4. Presentation language
This document deals with the formatting of data in an external This document deals with the formatting of data in an external
representation. The following very basic and somewhat casually representation. The following very basic and somewhat casually
defined presentation syntax will be used. The syntax draws from defined presentation syntax will be used. The syntax draws from
several sources in its structure. Although it resembles the several sources in its structure. Although it resembles the
programming language "C" in its syntax and XDR [XDR] in both its programming language "C" in its syntax and XDR [XDR] in both its
syntax and intent, it would be risky to draw too many parallels. The syntax and intent, it would be risky to draw too many parallels. The
purpose of this presentation language is to document TLS only, not purpose of this presentation language is to document TLS only, not
to have general application beyond that particular goal. to have general application beyond that particular goal.
4.1 Basic block size 4.1. Basic block size
The representation of all data items is explicitly specified. The The representation of all data items is explicitly specified. The
basic data block size is one byte (i.e. 8 bits). Multiple byte data basic data block size is one byte (i.e. 8 bits). Multiple byte data
items are concatenations of bytes, from left to right, from top to items are concatenations of bytes, from left to right, from top to
bottom. From the bytestream a multi-byte item (a numeric in the bottom. From the bytestream a multi-byte item (a numeric in the
example) is formed (using C notation) by: example) is formed (using C notation) by:
value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) | ... value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) |
| byte[n-1]; ... | byte[n-1];
This byte ordering for multi-byte values is the commonplace network This byte ordering for multi-byte values is the commonplace network
byte order or big endian format. byte order or big endian format.
4.2 Miscellaneous 4.2. Miscellaneous
Comments begin with "/*" and end with "*/". Comments begin with "/*" and end with "*/".
Optional components are denoted by enclosing them in "[[ ]]" double Optional components are denoted by enclosing them in "[[ ]]" double
brackets. brackets.
Single byte entities containing uninterpreted data are of type Single byte entities containing uninterpreted data are of type
opaque. opaque.
4.3 Vectors 4.3. Vectors
A vector (single dimensioned array) is a stream of homogeneous data A vector (single dimensioned array) is a stream of homogeneous data
elements. The size of the vector may be specified at documentation elements. The size of the vector may be specified at documentation
time or left unspecified until runtime. In either case the length time or left unspecified until runtime. In either case the length
declares the number of bytes, not the number of elements, in the declares the number of bytes, not the number of elements, in the
vector. The syntax for specifying a new type T' that is a fixed vector. The syntax for specifying a new type T' that is a fixed
length vector of type T is length vector of type T is
T T'[n]; T T'[n];
skipping to change at page 7, line 35 skipping to change at page 7, line 21
represent the value 400 (see Section 4.4). On the other hand, longer represent the value 400 (see Section 4.4). On the other hand, longer
can represent up to 800 bytes of data, or 400 uint16 elements, and can represent up to 800 bytes of data, or 400 uint16 elements, and
it may be empty. Its encoding will include a two byte actual length it may be empty. Its encoding will include a two byte actual length
field prepended to the vector. field prepended to the vector.
opaque mandatory<300..400>; opaque mandatory<300..400>;
/* length field is 2 bytes, cannot be empty */ /* length field is 2 bytes, cannot be empty */
uint16 longer<0..800>; uint16 longer<0..800>;
/* zero to 400 16-bit unsigned integers */ /* zero to 400 16-bit unsigned integers */
4.4 Numbers 4.4. Numbers
The basic numeric data type is an unsigned byte (uint8). All larger The basic numeric data type is an unsigned byte (uint8). All larger
numeric data types are formed from fixed length series of bytes numeric data types are formed from fixed length series of bytes
concatenated as described in Section 4.1 and are also unsigned. The concatenated as described in Section 4.1 and are also unsigned. The
following numeric types are predefined. following numeric types are predefined.
uint8 uint16[2]; uint8 uint16[2];
uint8 uint24[3]; uint8 uint24[3];
uint8 uint32[4]; uint8 uint32[4];
uint8 uint64[8]; uint8 uint64[8];
4.5 Enumerateds | All values, here and elsewhere in the specification, are stored in
| "network" or "big-endian" order; the uint32 represented by the hex
| bytes 01 02 03 04 is equivalent to the decimal value 16909060.
4.5. Enumerateds
An additional sparse data type is available called enum. A field of An additional sparse data type is available called enum. A field of
type enum can only assume the values declared in the definition. type enum can only assume the values declared in the definition.
Each definition is a different type. Only enumerateds of the same Each definition is a different type. Only enumerateds of the same
type may be assigned or compared. Every element of an enumerated type may be assigned or compared. Every element of an enumerated
must be assigned a value, as demonstrated in the following example. must be assigned a value, as demonstrated in the following example.
Since the elements of the enumerated are not ordered, they can be Since the elements of the enumerated are not ordered, they can be
assigned any unique value, in any order. assigned any unique value, in any order.
enum { e1(v1), e2(v2), ... , en(vn), [[(n)]] } Te; enum { e1(v1), e2(v2), ... , en(vn), [[(n)]] } Te;
skipping to change at page 8, line 35 skipping to change at page 8, line 25
well specified. well specified.
Color color = Color.blue; /* overspecified, legal */ Color color = Color.blue; /* overspecified, legal */
Color color = blue; /* correct, type implicit */ Color color = blue; /* correct, type implicit */
For enumerateds that are never converted to external representation, For enumerateds that are never converted to external representation,
the numerical information may be omitted. the numerical information may be omitted.
enum { low, medium, high } Amount; enum { low, medium, high } Amount;
4.6 Constructed types 4.6. Constructed types
Structure types may be constructed from primitive types for Structure types may be constructed from primitive types for
convenience. Each specification declares a new, unique type. The convenience. Each specification declares a new, unique type. The
syntax for definition is much like that of C. syntax for definition is much like that of C.
struct { struct {
T1 f1; T1 f1;
T2 f2; T2 f2;
... ...
Tn fn; Tn fn;
} [[T]]; } [[T]];
The fields within a structure may be qualified using the type's name The fields within a structure may be qualified using the type's name
using a syntax much like that available for enumerateds. For using a syntax much like that available for enumerateds. For
example, T.f2 refers to the second field of the previous example, T.f2 refers to the second field of the previous
declaration. Structure definitions may be embedded. declaration. Structure definitions may be embedded.
4.6.1 Variants 4.6.1. Variants
Defined structures may have variants based on some knowledge that is Defined structures may have variants based on some knowledge that is
available within the environment. The selector must be an enumerated available within the environment. The selector must be an enumerated
type that defines the possible variants the structure defines. There type that defines the possible variants the structure defines. There
must be a case arm for every element of the enumeration declared in must be a case arm for every element of the enumeration declared in
the select. The body of the variant structure may be given a label the select. The body of the variant structure may be given a label
for reference. The mechanism by which the variant is selected at for reference. The mechanism by which the variant is selected at
runtime is not prescribed by the presentation language. runtime is not prescribed by the presentation language.
struct { struct {
skipping to change at page 9, line 28 skipping to change at page 9, line 14
.... ....
Tn fn; Tn fn;
select (E) { select (E) {
case e1: Te1; case e1: Te1;
case e2: Te2; case e2: Te2;
.... ....
case en: Ten; case en: Ten;
} [[fv]]; } [[fv]];
} [[Tv]]; } [[Tv]];
For example For example:
enum { apple, orange } VariantTag; enum { apple, orange } VariantTag;
struct { struct {
uint16 number; uint16 number;
opaque string<0..10>; /* variable length */ opaque string<0..10>; /* variable length */
} V1; } V1;
struct { struct {
uint32 number; uint32 number;
opaque string[10]; /* fixed length */ opaque string[10]; /* fixed length */
} V2; } V2;
skipping to change at page 10, line 5 skipping to change at page 9, line 40
} VariantRecord; } VariantRecord;
Variant structures may be qualified (narrowed) by specifying a value Variant structures may be qualified (narrowed) by specifying a value
for the selector prior to the type. For example, a for the selector prior to the type. For example, a
orange VariantRecord orange VariantRecord
is a narrowed type of a VariantRecord containing a variant_body of is a narrowed type of a VariantRecord containing a variant_body of
type V2. type V2.
4.7 Cryptographic attributes 4.7. Cryptographic attributes
The four cryptographic operations digital signing, stream cipher The four cryptographic operations digital signing, stream cipher
encryption, block cipher encryption, and public key encryption are encryption, block cipher encryption, and public key encryption are
designated digitally-signed, stream-ciphered, block-ciphered, and designated digitally-signed, stream-ciphered, block-ciphered, and
public-key-encrypted, respectively. A field's cryptographic public-key-encrypted, respectively. A field's cryptographic
processing is specified by prepending an appropriate key word processing is specified by prepending an appropriate key word
designation before the field's type specification. Cryptographic designation before the field's type specification. Cryptographic
keys are implied by the current session state (see Section 5.1). keys are implied by the current session state (see Section 5.1).
In digital signing, one-way hash functions are used as input for a In digital signing, one-way hash functions are used as input for a
skipping to change at page 11, line 5 skipping to change at page 10, line 37
} UserType; } UserType;
The contents of hash are used as input for the signing algorithm, The contents of hash are used as input for the signing algorithm,
then the entire structure is encrypted with a stream cipher. The then the entire structure is encrypted with a stream cipher. The
length of this structure, in bytes would be equal to 2 bytes for length of this structure, in bytes would be equal to 2 bytes for
field1 and field2, plus two bytes for the length of the signature, field1 and field2, plus two bytes for the length of the signature,
plus the length of the output of the signing algorithm. This is plus the length of the output of the signing algorithm. This is
known due to the fact that the algorithm and key used for the known due to the fact that the algorithm and key used for the
signing are known prior to encoding or decoding this structure. signing are known prior to encoding or decoding this structure.
4.8 Constants 4.8. Constants
Typed constants can be defined for purposes of specification by Typed constants can be defined for purposes of specification by
declaring a symbol of the desired type and assigning values to it. declaring a symbol of the desired type and assigning values to it.
Under-specified types (opaque, variable length vectors, and Under-specified types (opaque, variable length vectors, and
structures that contain opaque) cannot be assigned values. No fields structures that contain opaque) cannot be assigned values. No fields
of a multi-element structure or vector may be elided. of a multi-element structure or vector may be elided.
For example, For example,
struct { struct {
uint8 f1; uint8 f1;
uint8 f2; uint8 f2;
} Example1; } Example1;
Example1 Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */
ex1 = {1, 4};/* assigns f1 = 1, f2 = 4 */
5. The TLS Record Protocol 5. The TLS Record Protocol
The TLS Record Protocol is a layered protocol. At each layer, The TLS Record Protocol is a layered protocol. At each layer,
messages may include fields for length, description, and content. messages may include fields for length, description, and content.
The Record Protocol takes messages to be transmitted, fragments the The Record Protocol takes messages to be transmitted, fragments the
data into manageable blocks, optionally compresses the data, applies data into manageable blocks, optionally compresses the data, applies
a MAC, encrypts, and transmits the result. Received data is a MAC, encrypts, and transmits the result. Received data is
decrypted, verified, decompressed, and reassembled, then delivered decrypted, verified, decompressed, and reassembled, then delivered
to higher level clients. to higher level clients.
5.1 Connection states | Four record protocol clients are described in this document: the
| handshake protocol, the alert protocol, the change cipher spec
| protocol, and the application data protocol. In order to allow
| extension of the TLS protocol, additional record types can be
| supported by the record protocol. Any new record types should
| allocate type values immediately beyond the ContentType values for
| the four record types described here (see Appendix A.2). If a TLS
| implementation receives a record type it does not understand, it
| should just ignore it. Any protocol designed for use over TLS must
| be carefully designed to deal with all possible attacks against it.
An TLS connection state is the operating environment of the TLS 5.1. Connection states
A TLS connection state is the operating environment of the TLS
Record Protocol. It specifies a compression algorithm, encryption Record Protocol. It specifies a compression algorithm, encryption
algorithm, and MAC algorithm. In addition, the parameters for these algorithm, and MAC algorithm. In addition, the parameters for these
algorithms are known: the MAC secret and the bulk encryption keys algorithms are known: the MAC secret and the bulk encryption keys
and IVs for the connection in both the read and the write and IVs for the connection in both the read and the write
directions. Logically, there are always four connection states directions. Logically, there are always four connection states
outstanding: the current read and write states, and the pending read outstanding: the current read and write states, and the pending read
and write states. All records are processed under the current read and write states. All records are processed under the current read
and write states. The security parameters for the pending states can and write states. The security parameters for the pending states can
be set by the TLS Handshake Protocol, and the Handshake Protocol can be set by the TLS Handshake Protocol, and the Handshake Protocol can
selectively make either of the pending states current, in which case selectively make either of the pending states current, in which case
skipping to change at page 12, line 13 skipping to change at page 11, line 55
that no encryption, compression, or MAC will be used. that no encryption, compression, or MAC will be used.
The security parameters for a TLS Connection read and write state The security parameters for a TLS Connection read and write state
are set by providing the following values: are set by providing the following values:
connection end connection end
Whether this entity is considered the "client" or the "server" Whether this entity is considered the "client" or the "server"
in this connection. in this connection.
bulk encryption algorithm bulk encryption algorithm
An algorithm to be used for bulk encryption. This An algorithm to be used for bulk encryption. This specification
specification includes the key size of this algorithm, how includes the key size of this algorithm, how much of that key is
much of that key is secret, whether it is a block or stream secret, whether it is a block or stream cipher, the block size
cipher, the block size of the cipher (if appropriate), and of the cipher (if appropriate), and whether it is considered an
whether it is considered an "export" cipher. "export" cipher.
MAC algorithm MAC algorithm
An algorithm to be used for message authentication. This An algorithm to be used for message authentication. This
specification includes the size of the hash to be returned by | specification includes the size of the hash which is returned by
the MAC algorithm, and a pad size which is to be used when | the MAC algorithm.
whitening the hash.
compression algorithm compression algorithm
An algorithm to be used for data compression. This An algorithm to be used for data compression. This specification
specification must include all information the algorithm must include all information the algorithm requires to do
requires to do compression. compression.
master secret master secret
A 48 byte secret shared between the two peers in the A 48 byte secret shared between the two peers in the connection.
connection.
client random client random
A 32 byte value provided by the client. A 32 byte value provided by the client.
server random server random
A 32 byte value provided by the server. A 32 byte value provided by the server.
These parameters are defined in the presentation language as: These parameters are defined in the presentation language as:
enum { null(0), (255) } CompressionMethod;
enum { server, client } ConnectionEnd; enum { server, client } ConnectionEnd;
enum { null, rc4, rc2, des, 3des, des40 } BulkCipherAlgorithm; enum { null, rc4, rc2, des, 3des, des40 } BulkCipherAlgorithm;
enum { stream, block } CipherType; enum { stream, block } CipherType;
enum { true, false } IsExportable; enum { true, false } IsExportable;
enum { null, md5, sha } MACAlgorithm; enum { null, md5, sha } MACAlgorithm;
enum { null(0), (255) } CompressionMethod;
/* The algorithms specified in CompressionMethod, /* The algorithms specified in CompressionMethod,
BulkCipherAlgorithm, and MACAlgorithm may be added to. */ BulkCipherAlgorithm, and MACAlgorithm may be added to. */
struct { struct {
ConnectionEnd entity; ConnectionEnd entity;
BulkCipherAlgorithm bulk_cipher_algorithm; BulkCipherAlgorithm bulk_cipher_algorithm;
CipherType cipher_type; CipherType cipher_type;
uint8 key_size; uint8 key_size;
uint8 key_material_length; uint8 key_material_length;
IsExportable is_exportable; IsExportable is_exportable;
MACAlgorithm mac_algorithm; MACAlgorithm mac_algorithm;
uint8 hash_size; uint8 hash_size;
uint8 whitener_length;
CompressionMethod compression_algorithm; CompressionMethod compression_algorithm;
opaque master_secret[48]; opaque master_secret[48];
opaque client_random[32]; opaque client_random[32];
opaque server_random[32]; opaque server_random[32];
} SecurityParameters; } SecurityParameters;
The record layer will use the security parameters to generate the The record layer will use the security parameters to generate the
following six items: following six items:
client write MAC secret client write MAC secret
server write MAC secret server write MAC secret
client write key client write key
server write key server write key
client write IV (for block ciphers only) client write IV (for block ciphers only)
server write IV (for block ciphers only) server write IV (for block ciphers only)
The client write parameters are used by the server when receiving The client write parameters are used by the server when receiving
and processing records and vice-versa. The algorithm used for and processing records and vice-versa. The algorithm used for
generating these items from the security parameters is described in generating these items from the security parameters is described in
section 5.3. section 5.4.
Once the security parameters have been set and the keys have been Once the security parameters have been set and the keys have been
generated, the connection states can be instantiated by making them generated, the connection states can be instantiated by making them
the current states. These current states must be updated for each the current states. These current states must be updated for each
record processed. Each connection state includes the following record processed. Each connection state includes the following
elements: elements:
compression state compression state
The current state of the compression algorithm. The current state of the compression algorithm.
cipher state cipher state
The current state of the encryption algorithm. This will The current state of the encryption algorithm. This will consist
consist of the scheduled key for that connection. In addition, of the scheduled key for that connection. In addition, for block
for block ciphers, this will initially contain the IV for that | ciphers running in CBC mode, this will initially contain the IV
connection state and be updated to contain the ciphertext of | for that connection state and be updated to contain the
the last block encrypted or decrypted as records are | ciphertext of the last block encrypted or decrypted as records
processed. For stream ciphers, this will contain whatever the | are processed. For block ciphers in other modes, whatever state
necessary state information is to allow the stream to continue | is necessary to sustain encryption or decryption must be
to encrypt or decrypt data. | maintained. For stream ciphers, this will contain whatever the
| necessary state information is to allow the stream to continue
| to encrypt or decrypt data.
MAC secret MAC secret
The MAC secret for this connection as generated above. The MAC secret for this connection as generated above.
sequence number sequence number
Each connection state contains a sequence number, which is Each connection state contains a sequence number, which is
maintained seperately for read and write states. The sequence maintained seperately for read and write states. The sequence
number must be set to zero whenever a connection state is made number must be set to zero whenever a connection state is made
the active state. Sequence numbers are of type uint64 and may the active state. Sequence numbers are of type uint64 and may
not exceed 2^64-1. A sequence number is incremented after each not exceed 2^64-1. A sequence number is incremented after each
record: specifically, the first record which is transmitted record: specifically, the first record which is transmitted
under a particular connection state should use sequence number under a particular connection state should use sequence number
0. 0.
5.2 Record layer 5.2. HMAC and the pseudorandom function
| A number of operations in the TLS record and handshake layer
| required a keyed MAC; this is a secure digest of some data protected
| by a secret. Forging the MAC is infeasible without knowledge of the
| MAC secret. Finding two data messages which have the same MAC is
| also cryptographically infeasible. The construction we use for this
| operation is known as HMAC, described in [HMAC].
| HMAC can be used with a variety of different hash algorithms. TLS
| uses it with two different algorithms: MD5 and SHA-1, denoting these
| as HMAC_MD5(secret, data) and HMAC_SHA(secret, data). In order to
| extend the security even further, an additional construction is
| defined which uses both MD5 and SHA-1: HMAC_mix(secret, data) =
| HMAC_MD5(secret, HMAC_SHA(secret, data)). This provides some
| protection against either of the algorithms being completely broken.
| In addition, TLS needs the ability to generate a chunk of random
| data of arbitrary length from a secret and a seed. To do this, a
| pseudorandom function (PRF) is defined. This function generates data
| by repeatedly applying HMAC_mix to the secret and seed, generating
| 16 bytes at a time.
| PRF(secret, seed) = HMAC_mix(secret, 'A' + seed) +
| HMAC_mix(secret, 'BB' + seed) +
| HMAC_mix(secret, 'CCC' + seed) + ...
| Where + indicates concatenation
| Where each iteration of PRF generates 16 bytes of output and
| consists of the HMAC_mix of the secret and the seed, where the seed
| is varied by prepending a string of bytes, where the first iteration
| uses a one byte string with the single value 'A' (0x40), the second
| uses a two byte string containing the value 'B' (0x41) twice, and so
| on. This can be repeated to generate up to 26 16-byte blocks, which
| is more than TLS ever requires.
5.3. Record layer
The TLS Record Layer receives uninterpreted data from higher layers The TLS Record Layer receives uninterpreted data from higher layers
in non-empty blocks of arbitrary size. in non-empty blocks of arbitrary size.
5.2.1 Fragmentation 5.3.1. Fragmentation
The record layer fragments information blocks into TLSPlaintext The record layer fragments information blocks into TLSPlaintext
records of 2^14 bytes or less. Client message boundaries are not records of 2^14 bytes or less. Client message boundaries are not
preserved in the record layer (i.e., multiple client messages of the preserved in the record layer (i.e., multiple client messages of the
same ContentType may be coalesced into a single TLSPlaintext record, same ContentType may be coalesced into a single TLSPlaintext record,
or may be fragmented across several records). or may be fragmented across several records).
struct { struct {
uint8 major, minor; uint8 major, minor;
} ProtocolVersion; } ProtocolVersion;
skipping to change at page 14, line 45 skipping to change at page 15, line 22
} ContentType; } ContentType;
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
opaque fragment[TLSPlaintext.length]; opaque fragment[TLSPlaintext.length];
} TLSPlaintext; } TLSPlaintext;
type type
The higher level protocol used to process the enclosed The higher level protocol used to process the enclosed fragment.
fragment.
version version
The version of the protocol being employed. This document The version of the protocol being employed. This document
describes TLS Version 1.0, which uses the version { 3, 0 }, | describes TLS Version 1.0, which uses the version { 3, 1 }. The
as it is identical to SSL Version 3.0 (See Appendix A.1.1). | version value 3.1 is historical: TLS version 1.0 is a minor
| modification to the SSL 3.0 protocol, which bears the version
| value 3.0. (See Appendix A.1.1).
length length
The length (in bytes) of the following TLSPlaintext.fragment. The length (in bytes) of the following TLSPlaintext.fragment.
The length should not exceed 2^14. The length should not exceed 2^14.
fragment fragment
The application data. This data is transparent and treated as The application data. This data is transparent and treated as an
an independent block to be dealt with by the higher level independent block to be dealt with by the higher level protocol
protocol specified by the type field. specified by the type field.
Note: Note: Data of different TLS Record layer content types may be
Data of different TLS Record layer content types may be
interleaved. Application data is generally of lower precedence interleaved. Application data is generally of lower precedence
for transmission than other content types. for transmission than other content types.
5.2.2 Record compression and decompression 5.3.2. Record compression and decompression
All records are compressed using the compression algorithm defined All records are compressed using the compression algorithm defined
in the current session state. There is always an active compression in the current session state. There is always an active compression
algorithm, however initially it is defined as algorithm; however, initially it is defined as
CompressionMethod.null. The compression algorithm translates an CompressionMethod.null. The compression algorithm translates a
TLSPlaintext structure into an TLSCompressed structure. Compression TLSPlaintext structure into a TLSCompressed structure. Compression
functions are initialized with default state information whenever a functions are initialized with default state information whenever a
connection state is made active. connection state is made active.
Compression must be lossless and may not increase the content length Compression must be lossless and may not increase the content length
by more than 1024 bytes. If the decompression function encounters an by more than 1024 bytes. If the decompression function encounters a
TLSCompressed.fragment that would decompress to a length in excess TLSCompressed.fragment that would decompress to a length in excess
of 2^14 bytes, it should report a fatal decompression failure error. of 2^14 bytes, it should report a fatal decompression failure error.
struct { struct {
ContentType type; /* same as TLSPlaintext.type */ ContentType type; /* same as TLSPlaintext.type */
ProtocolVersion version;/* same as TLSPlaintext.version */ ProtocolVersion version;/* same as TLSPlaintext.version */
uint16 length; uint16 length;
opaque fragment[TLSCompressed.length]; opaque fragment[TLSCompressed.length];
} TLSCompressed; } TLSCompressed;
length length
The length (in bytes) of the following TLSCompressed.fragment. The length (in bytes) of the following TLSCompressed.fragment.
The length should not exceed 2^14 + 1024. The length should not exceed 2^14 + 1024.
fragment fragment
The compressed form of TLSPlaintext.fragment. The compressed form of TLSPlaintext.fragment.
Note: Note: A CompressionMethod.null operation is an identity operation; no
A CompressionMethod.null operation is an identity operation; fields are altered.
no fields are altered. (See Appendix A.4.1)
Implementation note: Implementation note:
Decompression functions are responsible for ensuring that Decompression functions are responsible for ensuring that
messages cannot cause internal buffer overflows. messages cannot cause internal buffer overflows.
5.2.3 Record payload protection 5.3.3. Record payload protection
The encryption and MAC functions translate an TLSCompressed The encryption and MAC functions translate a TLSCompressed structure
structure into an TLSCiphertext. The decryption functions reverse into a TLSCiphertext. The decryption functions reverse the process.
the process. Transmissions also include a sequence number so that Transmissions also include a sequence number so that missing,
missing, altered, or extra messages are detectable. altered, or extra messages are detectable.
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
select (CipherSpec.cipher_type) { select (CipherSpec.cipher_type) {
case stream: GenericStreamCipher; case stream: GenericStreamCipher;
case block: GenericBlockCipher; case block: GenericBlockCipher;
} fragment; } fragment;
} TLSCiphertext; } TLSCiphertext;
skipping to change at page 16, line 35 skipping to change at page 17, line 8
version version
The version field is identical to TLSCompressed.version. The version field is identical to TLSCompressed.version.
length length
The length (in bytes) of the following TLSCiphertext.fragment. The length (in bytes) of the following TLSCiphertext.fragment.
The length may not exceed 2^14 + 2048. The length may not exceed 2^14 + 2048.
fragment fragment
The encrypted form of TLSCompressed.fragment, with the MAC. The encrypted form of TLSCompressed.fragment, with the MAC.
5.2.3.1 Null or standard stream cipher 5.3.3.1. Null or standard stream cipher
Stream ciphers (including BulkCipherAlgorithm.null - see Appendix Stream ciphers (including BulkCipherAlgorithm.null - see Appendix
A.7) convert TLSCompressed.fragment structures to and from stream A.7) convert TLSCompressed.fragment structures to and from stream
TLSCiphertext.fragment structures. TLSCiphertext.fragment structures.
stream-ciphered struct { stream-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[CipherSpec.hash_size]; opaque MAC[CipherSpec.hash_size];
} GenericStreamCipher; } GenericStreamCipher;
The MAC is generated as: The MAC is generated as:
hash(MAC_write_secret + pad_2 + | HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.version +
hash(MAC_write_secret + pad_1 + seq_num + | TLSCompressed.type + TLSCompressed.length +
TLSCompressed.type + TLSCompressed.length + | TLSCompressed.fragment));
TLSCompressed.fragment));
where "+" denotes concatenation. where "+" denotes concatenation.
pad_1
The character 0x36 repeated SecurityParameters.whitener_length
times.
pad_2
The character 0x5c repeated SecurityParameters.whitener_length
times.
seq_num seq_num
The sequence number for this record. The sequence number for this record.
hash hash
The hashing algorithm specified by The hashing algorithm specified by
SecurityParameters.mac_algorithm. SecurityParameters.mac_algorithm.
Note that the MAC is computed before encryption. The stream cipher Note that the MAC is computed before encryption. The stream cipher
encrypts the entire block, including the MAC. For stream ciphers encrypts the entire block, including the MAC. For stream ciphers
that do not use a synchronization vector (such as RC4), the stream that do not use a synchronization vector (such as RC4), the stream
cipher state from the end of one record is simply used on the cipher state from the end of one record is simply used on the
subsequent packet. If the CipherSuite is TLS_NULL_WITH_NULL_NULL, subsequent packet. If the CipherSuite is TLS_NULL_WITH_NULL_NULL,
encryption consists of the identity operation (i.e., the data is not encryption consists of the identity operation (i.e., the data is not
encrypted and the MAC size is zero implying that no MAC is used). encrypted and the MAC size is zero implying that no MAC is used).
TLSCiphertext.length is TLSCompressed.length plus TLSCiphertext.length is TLSCompressed.length plus
CipherSpec.hash_size. CipherSpec.hash_size.
5.2.3.2 CBC block cipher 5.3.3.2. CBC block cipher
For block ciphers (such as RC2 or DES), the encryption and MAC For block ciphers (such as RC2 or DES), the encryption and MAC
functions convert TLSCompressed.fragment structures to and from functions convert TLSCompressed.fragment structures to and from
block TLSCiphertext.fragment structures. block TLSCiphertext.fragment structures.
block-ciphered struct { block-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[CipherSpec.hash_size]; opaque MAC[CipherSpec.hash_size];
uint8 padding[GenericBlockCipher.padding_length]; uint8 padding[GenericBlockCipher.padding_length];
uint8 padding_length; uint8 padding_length;
} GenericBlockCipher; } GenericBlockCipher;
The MAC is generated as described in Section 5.3.3.1.
The MAC is generated as described in Section 5.2.3.1.
padding padding
Padding that is added to force the length of the plaintext to Padding that is added to force the length of the plaintext to be
be a multiple of the block cipher's block length. | an even multiple of the block cipher's block length. The padding
| may be any length up to 255 bytes long, as long as it results in
| the TLSCiphertext.length being an even multiple of the block
| length. Lengths longer than necessary might be desirable to
| frustrate attacks on a protocol based on analysis of the lengths
| of exchanged messages. The padding data must be filled with the
| padding length repeated to fill the array.
padding_length padding_length
The length of the padding must be less than the cipher's block The length of the padding must be less than the cipher's block
length and may be zero. The padding length should be such that length and may be zero. The padding length should be such that
the total size of the GenericBlockCipher structure is a the total size of the GenericBlockCipher structure is a multiple
multiple of the cipher's block length. of the cipher's block length.
The encrypted data length (TLSCiphertext.length) is one more than The encrypted data length (TLSCiphertext.length) is one more than
the sum of TLSCompressed.length, CipherSpec.hash_size, and the sum of TLSCompressed.length, CipherSpec.hash_size, and
padding_length. padding_length.
Note: Example: If the block length is 8 bytes, the content length
With CBC block chaining the initialization vector (IV) for the | (TLSCompressed.length) is 61 bytes, and the MAC length is 20
first record is generated with the other keys and secrets when | bytes, the length before padding is 82 bytes. Thus, the
the security parameters are set. The IV for subsequent records | padding length modulo 8 must be equal to 6 in order to make
is the last ciphertext block from the previous record. | the total length an even multiple of 8 bytes (the block
| length). The padding length can be 6, 14, 22, and so on,
| through 254. If the padding length were the minimum necessary,
| 6, the padding would be 6 bytes, each containing the value 6.
5.3 Key calculation |Note: With block ciphers in CBC mode (Cipher Block Chaining) the
initialization vector (IV) for the first record is generated
with the other keys and secrets when the security parameters are
set. The IV for subsequent records is the last ciphertext block
from the previous record.
5.4. Key calculation
The Record Protocol requires an algorithm to generate keys, IVs, and The Record Protocol requires an algorithm to generate keys, IVs, and
MAC secrets from the security parameters provided by the handshake MAC secrets from the security parameters provided by the handshake
protocol. protocol.
The master secret is hashed into a sequence of secure bytes, which The master secret is hashed into a sequence of secure bytes, which
are assigned to the MAC secrets, keys, and non-export IVs required are assigned to the MAC secrets, keys, and non-export IVs required
by the current connection state (see Appendix A.7). CipherSpecs by the current connection state (see Appendix A.7). CipherSpecs
require a client write MAC secret, a server write MAC secret, a require a client write MAC secret, a server write MAC secret, a
client write key, a server write key, a client write IV, and a client write key, a server write key, a client write IV, and a
server write IV, which are generated from the master secret in that server write IV, which are generated from the master secret in that
order. Unused values are empty. order. Unused values are empty.
When generating keys and MAC secrets, the master secret is used as When generating keys and MAC secrets, the master secret is used as
an entropy source, and the random values provide unencrypted salt an entropy source, and the random values provide unencrypted salt
material and IVs for exportable ciphers. material and IVs for exportable ciphers.
To generate the key material, compute To generate the key material, compute
key_block = | key_block = PRF(SecurityParameters.master_secret,
MD5(master_secret + SHA('A' + SecurityParameters.master_secret + | SecurityParameters.master_secret +
SecurityParameters.server_random + | SecurityParameters.server_random +
SecurityParameters.client_random)) + | SecurityParameters.client_random);
MD5(master_secret + SHA('BB' + SecurityParameters.master_secret +
SecurityParameters.server_random +
SecurityParameters.client_random)) +
MD5(master_secret + SHA('CCC' + SecurityParameters.master_secret +
SecurityParameters.server_random +
SecurityParameters.client_random)) + [...];
until enough output has been generated. Then the key_block is until enough output has been generated. Then the key_block is
partitioned as follows. partitioned as follows:
client_write_MAC_secret[SecurityParameters.hash_size] client_write_MAC_secret[SecurityParameters.hash_size]
server_write_MAC_secret[SecurityParameters.hash_size] server_write_MAC_secret[SecurityParameters.hash_size]
client_write_key[SecurityParameters.key_material] client_write_key[SecurityParameters.key_material]
server_write_key[SecurityParameters.key_material] server_write_key[SecurityParameters.key_material]
client_write_IV[SecurityParameters.IV_size] /* non-export ciphers */ client_write_IV[SecurityParameters.IV_size]
server_write_IV[SecurityParameters.IV_size] /* non-export ciphers */ server_write_IV[SecurityParameters.IV_size]
Any extra key_block material is discarded. The client_write_IV and server_write_IV are only generated for
non-export block ciphers. For exportable block ciphers, the
initialization vectors are generated later, as described below. Any
extra key_block material is discarded.
Implementation note: Implementation note:
The cipher spec which is defined in this document which The cipher spec which is defined in this document which requires
requires the most material is 3DES_EDE_CBC_SHA: it requires 2 the most material is 3DES_EDE_CBC_SHA: it requires 2 x 24 byte
x 24 byte keys, 2 x 20 byte MAC secrets, and 2 x 8 byte IVs, keys, 2 x 20 byte MAC secrets, and 2 x 8 byte IVs, for a total
for a total of 104 bytes of key material. This will require of 104 bytes of key material. This will require iterating the
iterating the key generation algorithm seven times, through | PRF algorithm seven times, through 'GGGGGGG'.
'GGGGGGG'.
Exportable encryption algorithms (for which CipherSpec.is_exportable Exportable encryption algorithms (for which CipherSpec.is_exportable
is true) require additional processing as follows to derive their is true) require additional processing as follows to derive their
final write keys: final write keys:
final_client_write_key = MD5(client_write_key + | final_client_write_key =
SecurityParameters.client_random + | PRF(SecurityParameters.client_write_key,
SecurityParameters.server_random); | SecurityParameters.client_random +
final_server_write_key = MD5(server_write_key + | SecurityParameters.server_random);
SecurityParameters.server_random + | final_server_write_key =
SecurityParameters.client_random); | PRF(SecurityParameters.server_write_key,
| SecurityParameters.client_random +
| SecurityParameters.server_random);
Note that this implies that exportable algorithms cannot have final | Exportable encryption algorithms derive their IVs solely from the
write keys larger than the output of MD5 (16 bytes). | random messages:
Exportable encryption algorithms derive their IVs from the random | iv_block = PRF("", SecurityParameters.client_random +
messages: | SecurityParameters.server_random);
client_write_IV = MD5(SecurityParameters.client_random + | The iv_block is partitioned into two initialization vectors as the
SecurityParameters.server_random); | key_block was above:
server_write_IV = MD5(SecurityParameters.server_random +
SecurityParameters.client_random);
MD5 outputs are trimmed to the appropriate size by discarding the | client_write_IV[SecurityParameters.IV_size]
trailing bytes. (The key or IV is taken from the first bytes of the | server_write_IV[SecurityParameters.IV_size]
MD5 output.)
5.3.1 Export key generation example | Note that the PRF is used without a secret in this case: this just
| means that the secret has a length of zero bytes and contributes
| nothing to the hashing in the PRF.
5.4.1. Export key generation example
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 requires five random bytes for TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 requires five random bytes for
each of the two encryption keys and 16 bytes for each of the MAC each of the two encryption keys and 16 bytes for each of the MAC
keys, for a total of 42 bytes of key material. MD5 produces 16 bytes keys, for a total of 42 bytes of key material. MD5 produces 16 bytes
of output per call, so three calls to MD5 are required. The MD5 | of output per call, so the PRF will iterate three times internally.
outputs are concatenated into a 48-byte key_block with the first MD5 | The PRF output is stored in the key_block. The key_block is
call providing bytes zero through 15, the second providing bytes 16 | partitioned, and the write keys are salted because this is an
through 31, etc. The key_block is partitioned, and the write keys | exportable encryption algorithm.
are salted because this is an exportable encryption algorithm.
| key_block = PRF(master_secret,
| master_secret +
| server_random +
| client_random)[0..41]
client_write_MAC_secret = key_block[0..15] client_write_MAC_secret = key_block[0..15]
server_write_MAC_secret = key_block[16..31] server_write_MAC_secret = key_block[16..31]
client_write_key = key_block[32..36] client_write_key = key_block[32..36]
server_write_key = key_block[37..41] server_write_key = key_block[37..41]
final_client_write_key = MD5(client_write_key + | final_client_write_key = PRF(client_write_key,
ClientHello.random + | client_random +
ServerHello.random)[0..15]; | server_random)[0..15]
final_server_write_key = MD5(server_write_key + | final_server_write_key = PRF(server_write_key,
ServerHello.random + | client_random +
ClientHello.random)[0..15]; | server_random)[0..15]
client_write_IV = MD5(ClientHello.random + | iv_block = PRF("", client_random +
ServerHello.random)[0..7]; | server_random)[0..15]
server_write_IV = MD5(ServerHello.random + | client_write_IV = iv_block[0..7]
ClientHello.random)[0..7]; | server_write_IV = iv_block[8..15]
6. The TLS Handshake Protocol 6. The TLS Handshake Protocol
The TLS Handshake Protocol consists of a suite of three The TLS Handshake Protocol consists of a suite of three
sub-protocols which are used to allow peers to agree upon security sub-protocols which are used to allow peers to agree upon security
parameters for the record layer, authenticate themselves, parameters for the record layer, authenticate themselves,
instantiate negotiated security parameters, and report error instantiate negotiated security parameters, and report error
conditions to each other. conditions to each other.
The Handshake Protocol is responsible for negotiating a session, The Handshake Protocol is responsible for negotiating a session,
which consists of the following items: which consists of the following items:
session identifier session identifier
An arbitrary byte sequence chosen by the server to identify an An arbitrary byte sequence chosen by the server to identify an
active or resumable session state. active or resumable session state.
peer certificate peer certificate
X509.v3[X509] certificate of the peer. This element of the X509v3[X509] certificate of the peer. This element of the state
state may be null. may be null.
compression method compression method
The algorithm used to compress data prior to encryption. The algorithm used to compress data prior to encryption.
cipher spec cipher spec
Specifies the bulk data encryption algorithm (such as null, Specifies the bulk data encryption algorithm (such as null, DES,
DES, etc.) and a MAC algorithm (such as MD5 or SHA). It also etc.) and a MAC algorithm (such as MD5 or SHA). It also defines
defines cryptographic attributes such as the hash_size. (See cryptographic attributes such as the hash_size. (See Appendix
Appendix A.7 for formal definition) A.7 for formal definition)
master secret master secret
48-byte secret shared between the client and server. 48-byte secret shared between the client and server.
is resumable is resumable
A flag indicating whether the session can be used to initiate A flag indicating whether the session can be used to initiate
new connections. new connections.
These items are then used to create security parameters for use by These items are then used to create security parameters for use by
the Record Layer when protecting application data. Many connections the Record Layer when protecting application data. Many connections
can be instantiated using the same session through the resumption can be instantiated using the same session through the resumption
feature of the TLS Handshake Protocol. feature of the TLS Handshake Protocol.
6.1 Change cipher spec protocol 6.1. Change cipher spec protocol
The change cipher spec protocol exists to signal transitions in The change cipher spec protocol exists to signal transitions in
ciphering strategies. The protocol consists of a single message, ciphering strategies. The protocol consists of a single message,
which is encrypted and compressed under the current (not the which is encrypted and compressed under the current (not the
pending) connection state. The message consists of a single byte of pending) connection state. The message consists of a single byte of
value 1. value 1.
struct { struct {
enum { change_cipher_spec(1), (255) } type; enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec; } ChangeCipherSpec;
skipping to change at page 21, line 29 skipping to change at page 22, line 5
protected under the newly negotiated CipherSpec and keys. Reception protected under the newly negotiated CipherSpec and keys. Reception
of this message causes the receiver to instruct the Record Layer to of this message causes the receiver to instruct the Record Layer to
immediately copy the read pending state into the read current state. immediately copy the read pending state into the read current state.
Immediately after sending this message, the sender should instruct Immediately after sending this message, the sender should instruct
the record layer to make the write pending state the write active the record layer to make the write pending state the write active
state. (See section 5.1.) The change cipher spec message is sent state. (See section 5.1.) The change cipher spec message is sent
during the handshake after the security parameters have been agreed during the handshake after the security parameters have been agreed
upon, but before the verifying finished message is sent (see section upon, but before the verifying finished message is sent (see section
6.4.9). 6.4.9).
6.2 Alert protocol 6.2. Alert protocol
One of the content types supported by the TLS Record layer is the One of the content types supported by the TLS Record layer is the
alert type. Alert messages convey the severity of the message and a alert type. Alert messages convey the severity of the message and a
description of the alert. Alert messages with a level of fatal description of the alert. Alert messages with a level of fatal
result in the immediate termination of the connection. In this case, result in the immediate termination of the connection. In this case,
other connections corresponding to the session may continue, but the other connections corresponding to the session may continue, but the
session identifier must be invalidated, preventing the failed session identifier must be invalidated, preventing the failed
session from being used to establish new connections. Like other session from being used to establish new connections. Like other
messages, alert messages are encrypted and compressed, as specified messages, alert messages are encrypted and compressed, as specified
by the current connection state. by the current connection state.
enum { warning(1), fatal(2), (255) } AlertLevel; enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum {
close_notify(0), close_notify(0),
unexpected_message(10), unexpected_message(10),
bad_record_mac(20), bad_record_mac(20),
| decryption_failed(21),
| record_overflow(22),
decompression_failure(30), decompression_failure(30),
handshake_failure(40), handshake_failure(40),
no_certificate(41), no_certificate(41),
bad_certificate(42), bad_certificate(42),
unsupported_certificate(43), unsupported_certificate(43),
certificate_revoked(44), certificate_revoked(44),
certificate_expired(45), certificate_expired(45),
certificate_unknown(46), certificate_unknown(46),
illegal_parameter (47), illegal_parameter (47),
| unknown_ca(48),
| access_denied(49),
| decode_error(50),
| decrypt_error(51),
| export_restriction(60),
| protocol_version(70),
| insufficient_security(71),
| internal_error(80),
| user_canceled(90),
| no_renegotiation(100),
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
6.2.1 Closure alerts 6.2.1. Closure alerts
The client and the server must share knowledge that the connection The client and the server must share knowledge that the connection
is ending in order to avoid a truncation attack. Either party may is ending in order to avoid a truncation attack. Either party may
initiate the exchange of closing messages. initiate the exchange of closing messages.
close_notify close_notify
This message notifies the recipient that the sender will not This message notifies the recipient that the sender will not
send any more messages on this connection. The session becomes send any more messages on this connection. The session becomes
unresumable if any connection is terminated without proper unresumable if any connection is terminated without proper
close_notify messages with level equal to warning. close_notify messages with level equal to warning.
skipping to change at page 22, line 34 skipping to change at page 23, line 21
Either party may initiate a close by sending a close_notify alert. Either party may initiate a close by sending a close_notify alert.
Any data received after a closure alert is ignored. Any data received after a closure alert is ignored.
Each party is required to send a close_notify alert before closing Each party is required to send a close_notify alert before closing
the write side of the connection. It is required that the other the write side of the connection. It is required that the other
party respond with a close_notify alert of its own and close down party respond with a close_notify alert of its own and close down
the connection immediately, discarding any pending writes. It is not the connection immediately, discarding any pending writes. It is not
required for the initiator of the close to wait for the responding required for the initiator of the close to wait for the responding
close_notify alert before closing the read side of the connection. close_notify alert before closing the read side of the connection.
NB: NB: It is assumed that closing a connection reliably delivers
It is assumed that closing a connection reliably delivers
pending data before destroying the transport. pending data before destroying the transport.
6.2.2 Error alerts 6.2.2. Error alerts
Error handling in the TLS Handshake protocol is very simple. When an Error handling in the TLS Handshake protocol is very simple. When an
error is detected, the detecting party sends a message to the other error is detected, the detecting party sends a message to the other
party. Upon transmission or receipt of an fatal alert message, both party. Upon transmission or receipt of an fatal alert message, both
parties immediately close the connection. Servers and clients are parties immediately close the connection. Servers and clients are
required to forget any session-identifiers, keys, and secrets required to forget any session-identifiers, keys, and secrets
associated with a failed connection. The following error alerts are associated with a failed connection. The following error alerts are
defined: defined:
unexpected_message unexpected_message
An inappropriate message was received. This alert is always An inappropriate message was received. This alert is always
fatal and should never be observed in communication between fatal and should never be observed in communication between
proper implementations. proper implementations.
bad_record_mac bad_record_mac
This alert is returned if a record is received with an This alert is returned if a record is received with an incorrect
incorrect MAC. This message is always fatal. MAC. This message is always fatal.
| decryption_failed
| A TLSCiphertext decrypted in an invalid way: either it wasn`t an
| even multiple of the block length or its padding values, when
| checked, weren`t correct. This message is always fatal.
| record_overflow
| A TLSCiphertext record was received which had a length more than
| 2^14+2048 bytes, or a record decrypted to a TLSCompressed record
| with more than 2^14+1024 bytes. This message is always fatal.
decompression_failure decompression_failure
The decompression function received improper input (e.g. data The decompression function received improper input (e.g. data
that would expand to excessive length). This message is always that would expand to excessive length). This message is always
fatal. fatal.
handshake_failure handshake_failure
Reception of a handshake_failure alert message indicates that Reception of a handshake_failure alert message indicates that
the sender was unable to negotiate an acceptable set of the sender was unable to negotiate an acceptable set of security
security parameters given the options available. This is a parameters given the options available. This is a fatal error.
fatal error.
no_certificate no_certificate
A no_certificate alert message may be sent in response to a A no_certificate alert message may be sent in response to a
certification request if no appropriate certificate is certification request if no appropriate certificate is
available. available.
bad_certificate bad_certificate
A certificate was corrupt, contained signatures that did not A certificate was corrupt, contained signatures that did not
verify correctly, etc. verify correctly, etc.
skipping to change at page 23, line 46 skipping to change at page 24, line 36
A certificate has expired or is not currently valid. A certificate has expired or is not currently valid.
certificate_unknown certificate_unknown
Some other (unspecified) issue arose in processing the Some other (unspecified) issue arose in processing the
certificate, rendering it unacceptable. certificate, rendering it unacceptable.
illegal_parameter illegal_parameter
A field in the handshake was out of range or inconsistent with A field in the handshake was out of range or inconsistent with
other fields. This is always fatal. other fields. This is always fatal.
| unknown_ca
| A valid certificate chain or partial chain was received, but the
| certificate was not accepted because the CA certificate could
| not be located or couldn`t be matched with a known, trusted CA.
| This message is always fatal.
| access_denied
| A valid certificate was received, but when access control was
| applied, the sender decided not to proceed with negotiation.
| This message is always fatal.
| decode_error
| A message could not be decoded because some field was out of the
| specified range or the length of the message was incorrect. This
| message is always fatal.
| export_restriction
| A negotiation not in compliance with export restrictions was
| detected; for example, attemption to transfer a 1024 bit
| ephemeral RSA key for the RSA_EXPORT handshake method. This
| message is always fatal.
| protocol_version
| The protocol version the client has attempted to negotiate is
| recognized, but not supported. (For example, old protocol
| versions might be avoided for security reasons). This message is
| always fatal.
| insufficient_security
| Returned instead of handshake_failure when a negotiation has
| failed specifically because the server requires ciphers more
| secure than those supported by the client. This message is
| always fatal.
| internal_error
| An internal error unrelated to the peer or the correctness of
| the protocol makes it impossible to continue (such as a memory
| allocation failure). This message is always fatal.
| user_cancelled
| This handshake is being cancelled for some reason unrelated to a
| protocol failure. If the user cancels an operation after the
| handshake is complete, just closing the connection by sending a
| close_notify is more appropriate. This alert should be followed
| by a close_notify. This message is generally a warning.
| no_renegotiation
| Sent by the client in response to a hello request or by the
| server in response to a client hello after initial handshaking.
| Either of these would normally lead to renegotiation; when that
| is not appropriate, the reciepient should respond with this
| alert; at that point, the original reqester can decide whether
| to proceed with the connection. One case where this would be
| appropriate would be where a server has spawned a process to
| satisfy a request; the process might receive secuirty parameters
| (key length, authentication, etc.) at startup and it might be
| difficult to communicate changes to these parameters after that
| point. This message is always a warning.
For all errors where an alert level is not explicitly specified, the For all errors where an alert level is not explicitly specified, the
sending party may determine at its discretion whether this is a sending party may determine at its discretion whether this is a
fatal error or not; if an alert with a level of warning is received, fatal error or not; if an alert with a level of warning is received,
the receiving party may decide at its discretion whether to treat the receiving party may decide at its discretion whether to treat
this as a fatal error or not. However, all messages which are this as a fatal error or not. However, all messages which are
transmitted with a level of fatal must be treated as fatal messages. transmitted with a level of fatal must be treated as fatal messages.
6.3 Handshake Protocol overview 6.3. Handshake Protocol overview
The cryptographic parameters of the session state are produced by The cryptographic parameters of the session state are produced by
the TLS Handshake Protocol, which operates on top of the TLS Record the TLS Handshake Protocol, which operates on top of the TLS Record
Layer. When a TLS client and server first start communicating, they Layer. When a TLS client and server first start communicating, they
agree on a protocol version, select cryptographic algorithms, agree on a protocol version, select cryptographic algorithms,
optionally authenticate each other, and use public-key encryption optionally authenticate each other, and use public-key encryption
techniques to generate shared secrets. techniques to generate shared secrets.
The TLS Handshake Protocol has three goals: | The TLS Handshake Protocol has the following goals:
- Exchange hello messages to agree on algorithms, exchange - Exchange hello messages to agree on algorithms, exchange random
random values, and check for session resumption. values, and check for session resumption.
- Exchange the necessary cryptographic parameters to allow - Exchange the necessary cryptographic parameters to allow the
the client and server to agree on a premaster secret. client and server to agree on a premaster secret.
- Exchange certificates and cryptographic information to - Exchange certificates and cryptographic information to allow the
allow the client and server to authenticate themselves. client and server to authenticate themselves.
- Generate a master secret from the premaster secret and - Generate a master secret from the premaster secret and exchanged
exchanged random values. random values.
- Provide security paramers to the record layer. - Provide security paramers to the record layer.
- Allow the client and server to verify that their peer has - Allow the client and server to verify that their peer has
calculated the same security parameters and that the calculated the same security parameters and that the handshake
handshake occured without tampering by an attacker. occured without tampering by an attacker.
These goals are achieved by the handshake protocol, which can be These goals are achieved by the handshake protocol, which can be
summarized as follows: The client sends a client hello message to summarized as follows: The client sends a client hello message to
which the server must respond with a server hello message, or else a which the server must respond with a server hello message, or else a
fatal error will occur and the connection will fail. The client fatal error will occur and the connection will fail. The client
hello and server hello are used to establish security enhancement hello and server hello are used to establish security enhancement
capabilities between client and server. The client hello and server capabilities between client and server. The client hello and server
hello establish the following attributes: Protocol Version, Session hello establish the following attributes: Protocol Version, Session
ID, Cipher Suite, and Compression Method. Additionally, two random ID, Cipher Suite, and Compression Method. Additionally, two random
values are generated and exchanged: ClientHello.random and values are generated and exchanged: ClientHello.random and
skipping to change at page 25, line 7 skipping to change at page 26, line 54
Following the hello messages, the server will send its certificate, Following the hello messages, the server will send its certificate,
if it is to be authenticated. Additionally, a server key exchange if it is to be authenticated. Additionally, a server key exchange
message may be sent, if it is required (e.g. if their server has no message may be sent, if it is required (e.g. if their server has no
certificate, or if its certificate is for signing only). If the certificate, or if its certificate is for signing only). If the
server is authenticated, it may request a certificate from the server is authenticated, it may request a certificate from the
client, if that is appropriate to the cipher suite selected. Now the client, if that is appropriate to the cipher suite selected. Now the
server will send the server hello done message, indicating that the server will send the server hello done message, indicating that the
hello-message phase of the handshake is complete. The server will hello-message phase of the handshake is complete. The server will
then wait for a client response. If the server has sent a then wait for a client response. If the server has sent a
certificate request Message, the client must send either the certificate request message, the client must send either the
certificate message or a no_certificate alert. The client key certificate message or a no_certificate alert. The client key
exchange message is now sent, and the content of that message will exchange message is now sent, and the content of that message will
depend on the public key algorithm selected between the client hello depend on the public key algorithm selected between the client hello
and the server hello. If the client has sent a certificate with and the server hello. If the client has sent a certificate with
signing ability, a digitally-signed certificate verify message is signing ability, a digitally-signed certificate verify message is
sent to explicitly verify the certificate. sent to explicitly verify the certificate.
At this point, a change cipher spec message is sent by the client, At this point, a change cipher spec message is sent by the client,
and the client copies the pending Cipher Spec into the current and the client copies the pending Cipher Spec into the current
Cipher Spec. The client then immediately sends the finished message Cipher Spec. The client then immediately sends the finished message
skipping to change at page 25, line 45 skipping to change at page 27, line 39
CertificateVerify* CertificateVerify*
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
Application Data <-------> Application Data Application Data <-------> Application Data
* Indicates optional or situation-dependent messages that are not * Indicates optional or situation-dependent messages that are not
always sent. always sent.
Note: Note: To help avoid pipeline stalls, ChangeCipherSpec is an
To help avoid pipeline stalls, ChangeCipherSpec is an independent TLS Protocol content type, and is not actually a TLS
independent TLS Protocol content type, and is not actually an handshake message.
TLS handshake message.
When the client and server decide to resume a previous session or When the client and server decide to resume a previous session or
duplicate an existing session (instead of negotiating new security duplicate an existing session (instead of negotiating new security
parameters) the message flow is as follows: parameters) the message flow is as follows:
The client sends a ClientHello using the Session ID of the session The client sends a ClientHello using the Session ID of the session
to be resumed. The server then checks its session cache for a match. to be resumed. The server then checks its session cache for a match.
If a match is found, and the server is willing to re-establish the If a match is found, and the server is willing to re-establish the
connection under the specified session state, it will send a connection under the specified session state, it will send a
ServerHello with the same Session ID value. At this point, both ServerHello with the same Session ID value. At this point, both
skipping to change at page 26, line 19 skipping to change at page 28, line 11
directly to finished messages. Once the re-establishment is directly to finished messages. Once the re-establishment is
complete, the client and server may begin to exchange application complete, the client and server may begin to exchange application
layer data. (See flow chart below.) If a Session ID match is not layer data. (See flow chart below.) If a Session ID match is not
found, the server generates a new session ID and the TLS client and found, the server generates a new session ID and the TLS client and
server perform a full handshake. server perform a full handshake.
Client Server Client Server
ClientHello --------> ClientHello -------->
ServerHello ServerHello
[change cipher spec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
change cipher spec [ChangeCipherSpec]
Finished --------> Finished -------->
Application Data <-------> Application Data Application Data <-------> Application Data
The contents and significance of each message will be presented in The contents and significance of each message will be presented in
detail in the following sections. detail in the following sections.
6.4 Handshake protocol 6.4. Handshake protocol
The TLS Handshake Protocol is one of the defined higher level The TLS Handshake Protocol is one of the defined higher level
clients of the TLS Record Protocol. This protocol is used to clients of the TLS Record Protocol. This protocol is used to
negotiate the secure attributes of a session. Handshake messages are negotiate the secure attributes of a session. Handshake messages are
supplied to the TLS Record Layer, where they are encapsulated within supplied to the TLS Record Layer, where they are encapsulated within
one or more TLSPlaintext structures, which are processed and one or more TLSPlaintext structures, which are processed and
transmitted as specified by the current active session state. transmitted as specified by the current active session state.
enum { enum {
hello_request(0), client_hello(1), server_hello(2), hello_request(0), client_hello(1), server_hello(2),
skipping to change at page 27, line 10 skipping to change at page 29, line 4
case server_hello: ServerHello; case server_hello: ServerHello;
case certificate: Certificate; case certificate: Certificate;
case server_key_exchange: ServerKeyExchange; case server_key_exchange: ServerKeyExchange;
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case server_hello_done: ServerHelloDone; case server_hello_done: ServerHelloDone;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange; case client_key_exchange: ClientKeyExchange;
case finished: Finished; case finished: Finished;
} body; } body;
} Handshake; } Handshake;
The handshake protocol messages are presented in the order they must The handshake protocol messages are presented in the order they must
be sent; sending handshake messages in an unexpected order results be sent; sending handshake messages in an unexpected order results
in a fatal error. | in a fatal error. Unneeded handshake messages can be omitted,
| however. The one exception is the Hello request message, which may
| be sent by the server at any time.
6.4.1 Hello messages 6.4.1. Hello messages
The hello phase messages are used to exchange security enhancement The hello phase messages are used to exchange security enhancement
capabilities between the client and server. When a new session capabilities between the client and server. When a new session
begins, the Record Layer's connection state encryption, hash, and begins, the Record Layer's connection state encryption, hash, and
compression algorithms are initialized to null. The current compression algorithms are initialized to null. The current
connection state is used for renegotiation messages. connection state is used for renegotiation messages.
6.4.1.1 Hello request 6.4.1.1. Hello request
When this message will be sent: When this message will be sent:
The hello request message may be sent by the server at any time. The hello request message may be sent by the server at any time.
Meaning of this message: Meaning of this message:
Hello request is a simple notification that the client should
Hello request is a simple notification that the client should begin begin the negotiation process anew by sending a client hello
the negotiation process anew by sending a client hello message when message when convenient. This message will be ignored by the
convenient. This message will be ignored by the client if the client client if the client is currently negotiating a session. This
is currently negotiating a session. This message may be ignored by message may be ignored by the client if it does not wish to
the client if it does not wish to renegotiate a session. Since renegotiate a session. Since handshake messages are intended to
handshake messages are intended to have transmission precedence over have transmission precedence over application data, it is
application data, it is expected that the negotiation will begin expected that the negotiation will begin before no more than a
before no more than a few records are received from the client. If few records are received from the client. If the server sends a
the server sends a hello request but does not recieve a client hello hello request but does not recieve a client hello in response,
in response, it may close the connection with a fatal alert. it may close the connection with a fatal alert.
After sending a hello request, servers should not repeat the request After sending a hello request, servers should not repeat the request
until the subsequent handshake negotiation is complete. until the subsequent handshake negotiation is complete.
Structure of this message: Structure of this message:
struct { } HelloRequest; struct { } HelloRequest;
Note: Note: This message should never be included in the message hashes
This message should never be included in the message hashes
which are maintained throughout the handshake and used in the which are maintained throughout the handshake and used in the
finished messages and the certificate verify message. finished messages and the certificate verify message.
6.4.1.2 Client hello 6.4.1.2. Client hello
When this message will be sent: When this message will be sent:
When a client first connects to a server it is required to send
When a client first connects to a server it is required to send the the client hello as its first message. The client can also send
client hello as its first message. The client can also send a client a client hello in response to a hello request or on its own
hello in response to a hello request or on its own initiative in initiative in order to renegotiate the security parameters in an
order to renegotiate the security parameters in an existing existing connection.
connection.
Structure of this message: Structure of this message:
The client hello message includes a random structure, which is
The client hello message includes a random structure, which is used used later in the protocol.
later in the protocol.
struct { struct {
uint32 gmt_unix_time; uint32 gmt_unix_time;
opaque random_bytes[28]; opaque random_bytes[28];
} Random; } Random;
gmt_unix_time gmt_unix_time
The current time and date in standard UNIX 32-bit format The current time and date in standard UNIX 32-bit format
according to the sender's internal clock. Clocks are not according to the sender's internal clock. Clocks are not
required to be set correctly by the basic TLS Protocol; higher required to be set correctly by the basic TLS Protocol; higher
skipping to change at page 28, line 42 skipping to change at page 30, line 31
random_bytes random_bytes
28 bytes generated by a secure random number generator. 28 bytes generated by a secure random number generator.
The client hello message includes a variable length session The client hello message includes a variable length session
identifier. If not empty, the value identifies a session between the identifier. If not empty, the value identifies a session between the
same client and server whose security parameters the client wishes same client and server whose security parameters the client wishes
to reuse. The session identifier may be from an earlier connection, to reuse. The session identifier may be from an earlier connection,
this connection, or another currently active connection. The second this connection, or another currently active connection. The second
option is useful if the client only wishes to update the random option is useful if the client only wishes to update the random
structures and derived values of a connection, while the third structures and derived values of a connection, while the third
option makes it possible to establish several simultaneous | option makes it possible to establish several independent secure
independent secure connections without repeating the full handshake | connections without repeating the full handshake protocol. These
protocol. The actual contents of the SessionID are defined by the | independant connections may occur sequentially or simultaneously; a
server. | SessionID becomes valid when the handshake negotiating it completes
| with the exchange of Finished messages and persists until removed
| due to aging or because a fatal error was encountered on a
| connection associated with the session. The actual contents of the
| SessionID are defined by the server.
opaque SessionID<0..32>; opaque SessionID<0..32>;
Warning: Warning:
Servers must not place confidential information in session | Because the SessionID is transmitted without encryption or
identifiers or let the contents of fake session identifiers | immediate MAC protection, servers must not place confidential
cause any breach of security. | information in session identifiers or let the contents of fake
| session identifiers cause any breach of security. (Note that the
| contents of the handshake as a whole, including the SessionID,
| is protected by the Finished messages exchanged at the end of
| the handshake.)
The CipherSuite list, passed from the client to the server in the The CipherSuite list, passed from the client to the server in the
client hello message, contains the combinations of cryptographic client hello message, contains the combinations of cryptographic
algorithms supported by the client in order of the client's algorithms supported by the client in order of the client's
preference (first choice first). Each CipherSuite defines a key preference (first choice first). Each CipherSuite defines a key
exchange algorithm, a bulk encryption algorithm (including secret exchange algorithm, a bulk encryption algorithm (including secret
key length) and a MAC algorithm. The server will select a cipher key length) and a MAC algorithm. The server will select a cipher
suite or, if no acceptable choices are presented, return a handshake suite or, if no acceptable choices are presented, return a handshake
failure alert and close the connection. failure alert and close the connection.
uint8 CipherSuite[2]; /* Cryptographic suite selector */ uint8 CipherSuite[2]; /* Cryptographic suite selector */
The client hello includes a list of compression algorithms supported The client hello includes a list of compression algorithms supported
by the client, ordered according to the client's preference. by the client, ordered according to the client's preference.
Issue:
Which compression methods to support is under investigation.
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suites<2..2^16-1>; CipherSuite cipher_suites<2..2^16-1>;
CompressionMethod compression_methods<1..2^8-1>; CompressionMethod compression_methods<1..2^8-1>;
} ClientHello; } ClientHello;
client_version client_version
The version of the TLS protocol by which the client wishes to The version of the TLS protocol by which the client wishes to
communicate during this session. This should be the latest communicate during this session. This should be the latest
(highest valued) version supported by the client. For this (highest valued) version supported by the client. For this
version of the specification, the version will be 3.0 (See | version of the specification, the version will be 3.1 (See
Appendix E for details about backward compatibility). Appendix E for details about backward compatibility).
random random
A client-generated random structure. A client-generated random structure.
session_id session_id
The ID of a session the client wishes to use for this The ID of a session the client wishes to use for this
connection. This field should be empty if no session_id is connection. This field should be empty if no session_id is
available or the client wishes to generate new security available or the client wishes to generate new security
parameters. parameters.
cipher_suites cipher_suites
This is a list of the cryptographic options supported by the This is a list of the cryptographic options supported by the
client, with the client's first preference first. If the client, with the client's first preference first. If the
session_id field is not empty (implying a session resumption session_id field is not empty (implying a session resumption
request) this vector must include at least the cipher_suite request) this vector must include at least the cipher_suite from
from that session. Values are defined in Appendix A.6. that session. Values are defined in Appendix A.6.
compression_methods compression_methods
This is a list of the compression methods supported by the This is a list of the compression methods supported by the
client, sorted by client preference. If the session_id field client, sorted by client preference. If the session_id field is
is not empty (implying a session resumption request) it not empty (implying a session resumption request) it must
must include the compression_method from that session. include the compression_method from that session. This vector
must contain, and all implementations must support,
This vector must contain, and all implementations must CompressionMethod.null. Thus, a client and server will always be
support, CompressionMethod.null. Thus, a client and server able to agree on a compression method.
will always be able to agree on a compression method.
After sending the client hello message, the client waits for a After sending the client hello message, the client waits for a
server hello message. Any other handshake message returned by the server hello message. Any other handshake message returned by the
server except for a hello request is treated as a fatal error. server except for a hello request is treated as a fatal error.
Forward compatibility note: Forward compatibility note:
In the interests of forward compatibility, it is permitted for In the interests of forward compatibility, it is permitted for a
a client hello message to include extra data after the client hello message to include extra data after the compression
compression methods. This data must be included in the methods. This data must be included in the handshake hashes, but
handshake hashes, but must otherwise be ignored. This is the must otherwise be ignored. This is the only handshake message
only handshake message for which this is legal; for all other for which this is legal; for all other messages, the amount of
messages, the amount of data in the message must match the data in the message must match the description of the message
description of the message precisely. precisely.
6.4.1.3 Server hello 6.4.1.3. Server hello
When this message will be sent: When this message will be sent:
The server will send this message in response to a client hello The server will send this message in response to a client hello
message when it was able to find an acceptable set of algorithms. If message when it was able to find an acceptable set of
it cannot find such a match, it will respond with a handshake algorithms. If it cannot find such a match, it will respond with
failure alert. a handshake failure alert.
Structure of this message: Structure of this message:
struct { struct {
ProtocolVersion server_version; ProtocolVersion server_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suite; CipherSuite cipher_suite;
CompressionMethod compression_method; CompressionMethod compression_method;
} ServerHello; } ServerHello;
server_version server_version
This field will contain the lower of that suggested by the This field will contain the lower of that suggested by the
skipping to change at page 30, line 44 skipping to change at page 32, line 38
ProtocolVersion server_version; ProtocolVersion server_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suite; CipherSuite cipher_suite;
CompressionMethod compression_method; CompressionMethod compression_method;
} ServerHello; } ServerHello;
server_version server_version
This field will contain the lower of that suggested by the This field will contain the lower of that suggested by the
client in the client hello and the highest supported by the client in the client hello and the highest supported by the
server. For this version of the specification, the version is | server. For this version of the specification, the version is
be 3.0 (See Appendix E for details about backward | 3.1 (See Appendix E for details about backward compatibility).
compatibility).
random random
This structure is generated by the server and must be This structure is generated by the server and must be different
different from (and independent of) ClientHello.random. from (and independent of) ClientHello.random.
session_id session_id
This is the identity of the session corresponding to this This is the identity of the session corresponding to this
connection. If the ClientHello.session_id was non-empty, the connection. If the ClientHello.session_id was non-empty, the
server will look in its session cache for a match. If a match server will look in its session cache for a match. If a match is
is found and the server is willing to establish the new found and the server is willing to establish the new connection
connection using the specified session state, the server will using the specified session state, the server will respond with
respond with the same value as was supplied by the client. This the same value as was supplied by the client. This indicates a
indicates a resumed session and dictates that the parties must resumed session and dictates that the parties must proceed
proceed directly to the finished messages. Otherwise this field directly to the finished messages. Otherwise this field will
will contain a different value identifying the new session. The contain a different value identifying the new session. The
server may return an empty session_id to indicate that the server may return an empty session_id to indicate that the
session will not be cached and therefore cannot be resumed. session will not be cached and therefore cannot be resumed.
cipher_suite cipher_suite
The single cipher suite selected by the server from the list in The single cipher suite selected by the server from the list in
ClientHello.cipher_suites. For resumed sessions this field is ClientHello.cipher_suites. For resumed sessions this field is
the value from the state of the session being resumed. the value from the state of the session being resumed.
compression_method compression_method
The single compression algorithm selected by the server from The single compression algorithm selected by the server from the
the list in ClientHello.compression_methods. For resumed list in ClientHello.compression_methods. For resumed sessions
sessions this field is the value from the resumed session this field is the value from the resumed session state.
state.
6.4.2 Server certificate 6.4.2. Server certificate
When this message will be sent: When this message will be sent:
The server must send a certificate whenever the agreed-upon key The server must send a certificate whenever the agreed-upon key
exchange method is not an anonymous one. This message will always exchange method is not an anonymous one. This message will
immediately follow the server hello message. always immediately follow the server hello message.
Meaning of this message: Meaning of this message:
The certificate type must be appropriate for the selected cipher The certificate type must be appropriate for the selected cipher
suite's key exchange algorithm, and is generally an X.509.v3 suite's key exchange algorithm, and is generally an X.509v3
certificate. It must contain a key which matches the key exchange certificate. It must contain a key which matches the key
method, as follows. Unless otherwise specified, the signing exchange method, as follows. Unless otherwise specified, the
algorithm for the certificate must be the same as the algorithm for signing algorithm for the certificate must be the same as the
the certificate key. Unless otherwise specified, the public key may algorithm for the certificate key. Unless otherwise specified,
be of any length. the public key may be of any length.
Key Exchange Algorithm Certificate Key Type Key Exchange Algorithm Certificate Key Type
RSA RSA public key; the certificate must RSA RSA public key; the certificate must
allow the key to be used for encryption. allow the key to be used for encryption.
RSA_EXPORT RSA public key of length greater than RSA_EXPORT RSA public key of length greater than
512 bits which can be used for signing, 512 bits which can be used for signing,
or a key of 512 bits or shorter which or a key of 512 bits or shorter which
Can be used for encryption or signing. Can be used for encryption or signing.
skipping to change at page 32, line 22 skipping to change at page 34, line 10
to sign the certificate should be DSS. to sign the certificate should be DSS.
DH_RSA Diffie-Hellman key. The algorithm used DH_RSA Diffie-Hellman key. The algorithm used
to sign the certificate should be RSA. to sign the certificate should be RSA.
As CipherSuites which specify new key exchange methods are specified As CipherSuites which specify new key exchange methods are specified
for the TLS Protocol, they will imply certificate format and the for the TLS Protocol, they will imply certificate format and the
required encoded keying information. required encoded keying information.
Structure of this message: Structure of this message:
opaque ASN.1Cert<1..2^24-1>; opaque ASN.1Cert<1..2^24-1>;
struct { struct {
ASN.1Cert certificate_list<1..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
certificate_list certificate_list
This is a sequence (chain) of X.509.v3 certificates, ordered | This is a sequence (chain) of X.509v3 certificates. The sender's
with the sender's certificate first followed by any certificate | certificate must come first in the list. Each following
authority certificates proceeding sequentially upward, with a | certificate must directly certify the one preceding it. Because
self-signed certificate for the root CA coming last in the | certificate validation requires that root keys be distributed
list. | independantly, the self-signed certificate which specifies the
| root certificate authority may optionally be omitted from the
| chain, under the assumption that the remote end must already
| possess it in order to validate it in any case.
The same message type and structure will be used for the client's The same message type and structure will be used for the client's
response to a certificate request message. | response to a certificate request message. Note that a client may
| send no certificates if it does not have an appropriate certificate
| to send in response to the server's authentication request.
Note: Note: PKCS #7 [PKCS7] is not used as the format for the certificate
PKCS #7 [PKCS7] is not used as the format for the certificate
vector because PKCS #6 [PKCS6] extended certificates are not vector because PKCS #6 [PKCS6] extended certificates are not
used. Also PKCS #7 defines a SET rather than a SEQUENCE, making used. Also PKCS #7 defines a SET rather than a SEQUENCE, making
the task of parsing the list more difficult. the task of parsing the list more difficult.
6.4.3 Server key exchange message 6.4.3. Server key exchange message
When this message will be sent: When this message will be sent:
| This message will be sent immediately after the server
| certificate message (or the server hello message, if this is an
| anonymous negotiation).
This message will be sent after the server certificate message (or The server key exchange message is sent by the server only when
the server hello message, if the server certificate is not sent), the server certificate message (if sent) does not contain enough
but before the server hello done message. The server key exchange data to allow the client to exchange a premaster secret. This is
message may be sent before or after this message. true for the following key exchange methods:
The server key exchange message is sent by the server only when the
server certificate message (if sent) does not contain enough data to
allow the client to exchange a premaster secret. This is true for
the following key exchange methods:
RSA_EXPORT (if the public key in the server certificate is RSA_EXPORT (if the public key in the server certificate is
longer than 512 bits) longer than 512 bits)
DHE_DSS DHE_DSS
DHE_DSS_EXPORT DHE_DSS_EXPORT
DHE_RSA DHE_RSA
DHE_RSA_EXPORT DHE_RSA_EXPORT
DH_anon DH_anon
It is not legal to send the server key exchange message for the It is not legal to send the server key exchange message for the
following key exchange methods: following key exchange methods:
RSA RSA
RSA_EXPORT (when the public key in the server certificate RSA_EXPORT (when the public key in the server certificate is
is less than or equal to 512 bits in length) less than or equal to 512 bits in length)
DH_DSS DH_DSS
DH_RSA DH_RSA
Meaning of this message: Meaning of this message:
This message conveys cryptographic information to allow the
This message conveys cryptographic information to allow the client client to communicate the premaster secret: either an RSA public
to communicate the premaster secret: either an RSA public key to key to encrypt the premaster secret with, or a Diffie-Hellman
encrypt the premaster secret with, or a Diffie-Hellman public key public key with which the client can complete a key exchange
with which the client can complete a key exchange (with the result (with the result being the premaster secret.)
being the premaster secret.)
As additional CipherSuites are defined for TLS which include new key As additional CipherSuites are defined for TLS which include new key
exchange algorithms, the server key exchange message will be sent if exchange algorithms, the server key exchange message will be sent if
and only if the certificate type associated with the key exchange and only if the certificate type associated with the key exchange
algorithm does not provide enough information for the client to algorithm does not provide enough information for the client to
exchange a premaster secret. exchange a premaster secret.
Note: Note: According to current US export law, RSA moduli larger than 512
According to current US export law, RSA moduli larger than 512 bits may not be used for key exchange in software exported from
bits may not be used for key exchange in software exported the US. With this message, the larger RSA keys encoded in
from the US. With this message, the larger RSA keys encoded in certificates may be used to sign temporary shorter RSA keys for
certificates may be used to sign temporary shorter RSA keys the RSA_EXPORT key exchange method.
for the RSA_EXPORT key exchange method.
Structure of this message: Structure of this message:
enum { rsa, diffie_hellman } KeyExchangeAlgorithm;
enum { rsa, diffie_hellman }
KeyExchangeAlgorithm;
struct { struct {
opaque rsa_modulus<1..2^16-1>; opaque rsa_modulus<1..2^16-1>;
opaque rsa_exponent<1..2^16-1>; opaque rsa_exponent<1..2^16-1>;
} ServerRSAParams; } ServerRSAParams;
rsa_modulus rsa_modulus
The modulus of the server's temporary RSA key. The modulus of the server's temporary RSA key.
rsa_exponent rsa_exponent
skipping to change at page 35, line 10 skipping to change at page 36, line 51
digitally-signed struct { digitally-signed struct {
opaque md5_hash[16]; opaque md5_hash[16];
opaque sha_hash[20]; opaque sha_hash[20];
}; };
case dsa: case dsa:
digitally-signed struct { digitally-signed struct {
opaque sha_hash[20]; opaque sha_hash[20];
}; };
} Signature; } Signature;
6.4.4 Certificate request 6.4.4. Certificate request
When this message will be sent: When this message will be sent:
A non-anonymous server can optionally request a certificate from
| the client, if appropriate for the selected cipher suite. This
| message, if sent, will immediately follow the Server Key
A non-anonymous server can optionally request a certificate from the | Exchange message (if it is sent; otherwise, the Server
client, if appropriate for the selected cipher suite. | Certificate message).
This message may be sent between the server certificate message and
the server hello done message. It may legally precede or follow the
server key exchange message. It is sent at the discretion of the
server, when legal.
Structure of this message: Structure of this message:
enum { enum {
rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),
rsa_ephemeral_dh(5), dss_ephemeral_dh(6), rsa_ephemeral_dh(5), dss_ephemeral_dh(6),
(255) (255)
} ClientCertificateType; } ClientCertificateType;
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
skipping to change at page 35, line 43 skipping to change at page 37, line 28
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
DistinguishedName certificate_authorities<3..2^16-1>; DistinguishedName certificate_authorities<3..2^16-1>;
} CertificateRequest; } CertificateRequest;
certificate_types certificate_types
This field is a list of the types of certificates requested, This field is a list of the types of certificates requested,
sorted in order of the server's preference. sorted in order of the server's preference.
certificate_authorities certificate_authorities
A list of the distinguished names of acceptable certificate A list of the distinguished names of acceptable certificate
authorities. | authorities. These distinguished names may specify a desired
| distinguished name for a root CA or for a subordinate CA;
| thus, this message can be used both to describe known roots
| and a desired authorization space.
Note: Note: DistinguishedName is derived from [X509].
DistinguishedName is derived from [X509].
Note: Note: It is a fatal handshake_failure alert for an anonymous server to
It is a fatal handshake_failure alert for an anonymous server request client identification.
to request client identification.
6.4.5 Server hello done 6.4.5. Server hello done
When this message will be sent: When this message will be sent:
The server hello done message is sent by the server to indicate
The server hello done message is sent by the server to indicate the the end of the server hello and associated messages. After
end of the server hello and associated messages. After sending this sending this message the server will wait for a client response.
message the server will wait for a client response.
Meaning of this message: Meaning of this message:
This message means that the server is done sending messages to This message means that the server is done sending messages to
support the key exchange, and the client can proceed with its phase support the key exchange, and the client can proceed with its
of the key exchange. phase of the key exchange.
Upon receipt of the server hello done message the client should Upon receipt of the server hello done message the client should
verify that the server provided a valid certificate if required and verify that the server provided a valid certificate if required
check that the server hello parameters are acceptable. and check that the server hello parameters are acceptable.
Structure of this message: Structure of this message:
struct { } ServerHelloDone; struct { } ServerHelloDone;
6.4.6 Client certificate 6.4.6. Client certificate
When this message will be sent: When this message will be sent:
This is the first message the client can send after receiving a This is the first message the client can send after receiving a
server hello done message. This message is only sent if the server server hello done message. This message is only sent if the
requests a certificate. If no suitable certificate is available, the server requests a certificate. If no suitable certificate is
client should send a no_certificate alert instead. This alert is | available, the client should send a certificate message
only a warning, however the server may respond with a fatal | containing no certificates. If client authentication is required
handshake failure alert if client authentication is required. Client | by the server for the handshake to continue, it may respond with
certificates are sent using the Certificate structure defined in | a fatal handshake failure alert. Client certificates are sent
Section 5.6.2. | using the Certificate structure defined in Section 6.4.2.
Note: Note: When using a static Diffie-Hellman based key exchange method
When using a static Diffie-Hellman based key exchange method
(DH_DSS or DH_RSA), if client authentication is requested, the (DH_DSS or DH_RSA), if client authentication is requested, the
Diffie-Hellman group and generator encoded in the client's Diffie-Hellman group and generator encoded in the client's
certificate must match the server specified Diffie-Hellman certificate must match the server specified Diffie-Hellman
parameters if the client's parameters are to be used for the parameters if the client's parameters are to be used for the key
key exchange. exchange.
6.4.7 Client key exchange message 6.4.7. Client key exchange message
When this message will be sent: When this message will be sent:
This message is always sent by the client. It will immediately This message is always sent by the client. It will immediately
follow the client certificate message, if it is sent, or the | follow the client certificate message, if it is sent. Otherwise
no_certificate alert, if a certificate was requested but an | it will be the first message sent by the client after it
appropriate one was not available. Otherwise it will be the first | receives the server hello done message.
message sent by the client after it receives the server hello done
message.
Meaning of this message: Meaning of this message:
With this message, the premaster secret is set, either though
With this message, the premaster secret is set, either though direct direct transmisson of the RSA-encrypted secret, or by the
transmisson of the RSA-encrypted secret, or by the transmission of transmission of Diffie-Hellman parameters which will allow each
Diffie-Hellman parameters which will allow each side to agree upon side to agree upon the same premaster secret. When the key
the same premaster secret. When the key exchange method is DH_RSA or exchange method is DH_RSA or DH_DSS, client certification has
DH_DSS, client certification has been requested, and the client was been requested, and the client was able to respond with a
able to respond with a certificate which contained a Diffie-Hellman certificate which contained a Diffie-Hellman public key whose
public key whose parameters (group and generator) matched those parameters (group and generator) matched those specified by the
specified by the server in its certificate, this message will not server in its certificate, this message will not contain any
contain any data. data.
Structure of this message: Structure of this message:
The choice of messages depends on which key exchange method has
The choice of messages depends on which key exchange method has been been selected. See Section 6.4.3 for the KeyExchangeAlgorithm
selected. See Section 6.4.3 for the KeyExchangeAlgorithm definition. definition.
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case rsa: EncryptedPreMasterSecret; case rsa: EncryptedPreMasterSecret;
case diffie_hellman: ClientDiffieHellmanPublic; case diffie_hellman: ClientDiffieHellmanPublic;
} exchange_keys; } exchange_keys;
} ClientKeyExchange; } ClientKeyExchange;
6.4.7.1 RSA encrypted premaster secret message 6.4.7.1. RSA encrypted premaster secret message
Meaning of this message: Meaning of this message:
If RSA is being used for key agreement and authentication, the If RSA is being used for key agreement and authentication, the
client generates a 48-byte premaster secret, encrypts it using the client generates a 48-byte premaster secret, encrypts it using
public key from the server's certificate or the temporary RSA key the public key from the server's certificate or the temporary
provided in a server key exchange message, and sends the result in RSA key provided in a server key exchange message, and sends the
an encrypted premaster secret message. This structure is a variant result in an encrypted premaster secret message. This structure
of the client key exchange message, not a message in itself. is a variant of the client key exchange message, not a message
in itself.
Structure of this message: Structure of this message:
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
opaque random[46]; opaque random[46];
} PreMasterSecret; } PreMasterSecret;
client_version client_version
The latest (newest) version supported by the client. This is The latest (newest) version supported by the client. This is
used to detect version roll-back attacks. | used to detect version roll-back attacks. Upon receiving the
| premaster secret, the server should check that this value
| matches the value transmitted by the client in the client
| hello message.
random random
46 securely-generated random bytes. 46 securely-generated random bytes.
struct { struct {
public-key-encrypted PreMasterSecret pre_master_secret; public-key-encrypted PreMasterSecret pre_master_secret;
} EncryptedPreMasterSecret; } EncryptedPreMasterSecret;
pre_master_secret pre_master_secret
This random value is generated by the client and is used to This random value is generated by the client and is used to
generate the master secret, as specified in Section 7.1. generate the master secret, as specified in Section 7.1.
6.4.7.2 Client Diffie-Hellman public value 6.4.7.2. Client Diffie-Hellman public value
Meaning of this message: Meaning of this message:
This structure conveys the client's Diffie-Hellman public value
This structure conveys the client's Diffie-Hellman public value (Yc) (Yc) if it was not already included in the client's certificate.
if it was not already included in the client's certificate. The The encoding used for Yc is determined by the enumerated
encoding used for Yc is determined by the enumerated PublicValueEncoding. This structure is a variant of the client
PublicValueEncoding. This structure is a variant of the client key key exchange message, not a message in itself.
exchange message, not a message in itself.
Structure of this message: Structure of this message:
enum { implicit, explicit } PublicValueEncoding; enum { implicit, explicit } PublicValueEncoding;
implicit implicit
If the client certificate already contains a suitable If the client certificate already contains a suitable
Diffie-Hellman key, then Yc is implicit and does not need to Diffie-Hellman key, then Yc is implicit and does not need to
be sent again. | be sent again. In this case, the Client Key Exchange message
| will be sent, but will be empty.
explicit explicit
Yc needs to be sent. Yc needs to be sent.
struct { struct {
select (PublicValueEncoding) { select (PublicValueEncoding) {
case implicit: struct { }; case implicit: struct { };
case explicit: opaque dh_Yc<1..2^16-1>; case explicit: opaque dh_Yc<1..2^16-1>;
} dh_public; } dh_public;
} ClientDiffieHellmanPublic; } ClientDiffieHellmanPublic;
dh_Yc dh_Yc
The client's Diffie-Hellman public value (Yc). The client's Diffie-Hellman public value (Yc).
6.4.8 Certificate verify 6.4.8. Certificate verify
When this message will be sent: When this message will be sent:
This message is used to provide explicit verification of a
This message is used to provide explicit verification of a client client certificate. This message is only sent following a client
certificate. This message is only sent following a client
certificate that has signing capability (i.e. all certificates certificate that has signing capability (i.e. all certificates
except those containing fixed Diffie-Hellman parameters). When sent, except those containing fixed Diffie-Hellman parameters). When
it will immediately follow the client key exchange message. sent, it will immediately follow the client key exchange
message.
Structure of this message: Structure of this message:
struct { struct {
Signature signature; Signature signature;
} CertificateVerify; } CertificateVerify;
The Signature type is defined in 6.4.3. The Signature type is defined in 6.4.3.
CertificateVerify.signature.md5_hash CertificateVerify.signature.md5_hash
MD5(master_secret + pad_2 + MD5(handshake_messages + | HMAC_MD5(master_secret, handshake_messages);
master_secret + pad_1));
Certificate.signature.sha_hash Certificate.signature.sha_hash
SHA(master_secret + pad_2 + SHA(handshake_messages + | HMAC_SHA(master_secret, handshake_messages);
master_secret + pad_1));
pad_1
The character 0x36 repeated 48 times for MD5 or 40 times for SHA.
pad_2
The character 0x5c repeated 48 times for MD5 or 40 times for SHA.
Here handshake_messages refers to all handshake messages sent or Here handshake_messages refers to all handshake messages sent or
received starting at client hello up to but not including this received starting at client hello up to but not including this
message, including the type and length fields of the handshake message, including the type and length fields of the handshake
messages. This is the concatenation of all the Handshake structures messages. This is the concatenation of all the Handshake structures
as defined in 6.4 exchanged thus far. as defined in 6.4 exchanged thus far.
6.4.9 Finished 6.4.9. Finished
When this message will be sent: When this message will be sent:
A finished message is always sent immediately after a change
A finished message is always sent immediately after a change cipher cipher spec message to verify that the key exchange and
spec message to verify that the key exchange and authentication authentication processes were successful. It is essential that a
processes were successful. It is essential that a change cipher spec change cipher spec message be received between the other
message be received between the other handshake messages and the handshake messages and the Finished message.
Finished message.
Meaning of this message: Meaning of this message:
The finished message is the first protected with the
The finished message is the first protected with the just-negotiated just-negotiated algorithms, keys, and secrets. No acknowledgment
algorithms, keys, and secrets. No acknowledgment of the finished of the finished message is required; parties may begin sending
message is required; parties may begin sending encrypted data encrypted data immediately after sending the finished message.
immediately after sending the finished message. Recipients of Recipients of finished messages must verify that the contents
finished messages must verify that the contents are correct. are correct.
enum { client(0x434C4E54), server(0x53525652) } Sender; enum { client(0x434C4E54), server(0x53525652) } Sender;
struct { struct {
opaque md5_hash[16]; opaque md5_hash[16];
opaque sha_hash[20]; opaque sha_hash[20];
} Finished; } Finished;
md5_hash md5_hash
MD5(master_secret + pad2 + MD5(handshake_messages + Sender + | HMAC_MD5(master_secret, handshake_messages + Sender);
master_secret + pad1));
sha_hash sha_hash
SHA(master_secret + pad2 + SHA(handshake_messages + Sender + | HMAC_SHA(master_secret, handshake_messages + Sender);
master_secret + pad1));
handshake_messages handshake_messages
All of the data from all handshake messages up to but not All of the data from all handshake messages up to but not
including this message. This is only data visible at the including this message. This is only data visible at the
handshake layer and does not include record layer headers. handshake layer and does not include record layer headers.
This is the concatenation of all the Handshake structures as This is the concatenation of all the Handshake structures as
defined in 6.4 exchanged thus far. defined in 6.4 exchanged thus far.
It is a fatal error if a finished message is not preceeded by a It is a fatal error if a finished message is not preceeded by a
change cipher spec message at the appropriate point in the change cipher spec message at the appropriate point in the
handshake. handshake.
The hash contained in finished messages sent by the server The hash contained in finished messages sent by the server
incorporate Sender.server; those sent by the client incorporate incorporate Sender.server; those sent by the client incorporate
Sender.client. The value handshake_messages includes all handshake Sender.client. The value handshake_messages includes all handshake
messages starting at client hello up to, but not including, this messages starting at client hello up to, but not including, this
finished message. This may be different from handshake_messages in finished message. This may be different from handshake_messages in
Section 5.6.8 because it would include the certificate verify Section 6.4.8 because it would include the certificate verify
message (if sent). Also, the handshake_messages for the finished message (if sent). Also, the handshake_messages for the finished
message sent by the client will be different from that for the message sent by the client will be different from that for the
finished message sent by the server, because the one which is sent finished message sent by the server, because the one which is sent
second will include the prior one. second will include the prior one.
Note: Note: Change cipher spec messages are not handshake messages and are
Change cipher spec messages are not handshake messages and are | not included in the hash computations. Also, Hello Request
not included in the hash computations. | messages are omitted from handshake hashes.
7. Cryptographic computations 7. Cryptographic computations
In order to begin connection protection, the TLS Record Protocol In order to begin connection protection, the TLS Record Protocol
requires specification of a suite of algorithms, a master secret, requires specification of a suite of algorithms, a master secret,
and the client and server random values. The authentication, and the client and server random values. The authentication,
encryption, and MAC algorithms are determined by the cipher_suite encryption, and MAC algorithms are determined by the cipher_suite
selected by the server and revealed in the server hello message. The selected by the server and revealed in the server hello message. The
compression algorithm is negotiated in the hello messages, and the compression algorithm is negotiated in the hello messages, and the
random values are exchanged in the hello messages. All that remains random values are exchanged in the hello messages. All that remains
is to calculate the master secret. is to calculate the master secret.
7.1 Computing the master secret 7.1. Computing the master secret
For all key exchange methods, the same algorithm is used to convert For all key exchange methods, the same algorithm is used to convert
the pre_master_secret into the master_secret. The pre_master_secret the pre_master_secret into the master_secret. The pre_master_secret
should be deleted from memory once the master_secret has been should be deleted from memory once the master_secret has been
computed. computed.
master_secret = | master_secret = PRF(pre_master_secret, pre_master_secret +
MD5(pre_master_secret + SHA('A' + pre_master_secret + | ClientHello.random + ServerHello.random);
ClientHello.random + ServerHello.random)) +
MD5(pre_master_secret + SHA('BB' + pre_master_secret +
ClientHello.random + ServerHello.random)) +
MD5(pre_master_secret + SHA('CCC' + pre_master_secret +
ClientHello.random + ServerHello.random));
The master secret is always exactly 48 bytes in length. The length The master secret is always exactly 48 bytes in length. The length
of the premaster secret will vary depending on key exchange method. of the premaster secret will vary depending on key exchange method.
7.1.1 RSA 7.1.1. RSA
When RSA is used for server authentication and key exchange, a When RSA is used for server authentication and key exchange, a
48-byte pre_master_secret is generated by the client, encrypted 48-byte pre_master_secret is generated by the client, encrypted
under the server's public key, and sent to the server. The server under the server's public key, and sent to the server. The server
uses its private key to decrypt the pre_master_secret. Both parties uses its private key to decrypt the pre_master_secret. Both parties
then convert the pre_master_secret into the master_secret, as then convert the pre_master_secret into the master_secret, as
specified above. specified above.
RSA digital signatures are performed using PKCS #1 [PKCS1] block RSA digital signatures are performed using PKCS #1 [PKCS1] block
type 1. RSA public key encryption is performed using PKCS #1 block type 1. RSA public key encryption is performed using PKCS #1 block
type 2. type 2.
7.1.2 Diffie-Hellman 7.1.2. Diffie-Hellman
A conventional Diffie-Hellman computation is performed. The A conventional Diffie-Hellman computation is performed. The
negotiated key (Z) is used as the pre_master_secret, and is negotiated key (Z) is used as the pre_master_secret, and is
converted into the master_secret, as specified above. converted into the master_secret, as specified above.
Note: Note: Diffie-Hellman parameters are specified by the server, and may
Diffie-Hellman parameters are specified by the server, and may
be either ephemeral or contained within the server's be either ephemeral or contained within the server's
certificate. certificate.
8. Application data protocol 8. Application data protocol
Application data messages are carried by the Record Layer and are Application data messages are carried by the Record Layer and are
fragmented, compressed and encrypted based on the current connection fragmented, compressed and encrypted based on the current connection
state. The messages are treated as transparent data to the record state. The messages are treated as transparent data to the record
layer. layer.
Appendix A
A. Protocol constant values A. Protocol constant values
This section describes protocol types and constants. This section describes protocol types and constants.
A.1 Reserved port assignments A.1. Reserved port assignments
At the present time TLS is implemented using TCP/IP as the base At the present time TLS is implemented using TCP/IP as the base
networking technology. The IANA reserved the following Internet | networking technology, although the protocol should be useful over
Protocol [IP] port numbers for use in conjunction with the SSL 3.0 | any transport which can provide a reliable stream connection. The
Protocol, which we presume will be used by TLS as well. IANA reserved the following Internet Protocol [IP] port numbers for
use in conjunction with the SSL 3.0 Protocol, which we presume will
be used by TLS as well.
443 Reserved for use by Hypertext Transfer Protocol with SSL (https) 443 Reserved for use by Hypertext Transfer Protocol with SSL (https)
465 Reserved for use by Simple Mail Transfer Protocol with 465 Reserved for use by Simple Mail Transfer Protocol with SSL
SSL (ssmtp). (ssmtp).
563 Reserved for use by Network News Transfer Protocol with SSL 563 Reserved for use by Network News Transfer Protocol with SSL
(snntp). (snntp).
636 Reserved for Light Directory Access Protocol with SSL (ssl-ldap) 636 Reserved for Light Directory Access Protocol with SSL (ssl-ldap)
990 Reserved (pending) for File Transfer Protocol with SSL (ftps) 990 Reserved (pending) for File Transfer Protocol with SSL (ftps)
995 Reserved for Post Office Protocol with SSL (spop3) 995 Reserved for Post Office Protocol with SSL (spop3)
A.1.1 Record layer A.2. Record layer
struct { struct {
uint8 major, minor; uint8 major, minor;
} ProtocolVersion; } ProtocolVersion;
ProtocolVersion version = { 3,0 }; | ProtocolVersion version = { 3, 1 }; /* TLS v1.0 */
enum { enum {
change_cipher_spec(20), alert(21), handshake(22), change_cipher_spec(20), alert(21), handshake(22),
application_data(23), (255) application_data(23), (255)
} ContentType; } ContentType;
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
skipping to change at page 43, line 30 skipping to change at page 44, line 24
opaque MAC[CipherSpec.hash_size]; opaque MAC[CipherSpec.hash_size];
} GenericStreamCipher; } GenericStreamCipher;
block-ciphered struct { block-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[CipherSpec.hash_size]; opaque MAC[CipherSpec.hash_size];
uint8 padding[GenericBlockCipher.padding_length]; uint8 padding[GenericBlockCipher.padding_length];
uint8 padding_length; uint8 padding_length;
} GenericBlockCipher; } GenericBlockCipher;
A.2 Change cipher specs message A.3. Change cipher specs message
struct { struct {
enum { change_cipher_spec(1), (255) } type; enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec; } ChangeCipherSpec;
A.3 Alert messages A.4. Alert messages
enum { warning(1), fatal(2), (255) } AlertLevel; enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum {
close_notify(0), close_notify(0),
unexpected_message(10), unexpected_message(10),
bad_record_mac(20), bad_record_mac(20),
decompression_failure(30), decompression_failure(30),
handshake_failure(40), handshake_failure(40),
no_certificate(41), no_certificate(41),
skipping to change at page 44, line 13 skipping to change at page 45, line 5
certificate_unknown(46), certificate_unknown(46),
illegal_parameter (47), illegal_parameter (47),
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
A.4 Handshake protocol A.5. Handshake protocol
enum { enum {
hello_request(0), client_hello(1), server_hello(2), hello_request(0), client_hello(1), server_hello(2),
certificate(11), server_key_exchange (12), certificate(11), server_key_exchange (12),
certificate_request(13), server_done(14), certificate_request(13), server_done(14),
certificate_verify(15), client_key_exchange(16), certificate_verify(15), client_key_exchange(16),
finished(20), (255) finished(20), (255)
} HandshakeType; } HandshakeType;
struct { struct {
skipping to change at page 44, line 40 skipping to change at page 45, line 32
case certificate: Certificate; case certificate: Certificate;
case server_key_exchange: ServerKeyExchange; case server_key_exchange: ServerKeyExchange;
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case server_done: ServerHelloDone; case server_done: ServerHelloDone;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange; case client_key_exchange: ClientKeyExchange;
case finished: Finished; case finished: Finished;
} body; } body;
} Handshake; } Handshake;
A.4.1 Hello messages A.5.1. Hello messages
struct { } HelloRequest; struct { } HelloRequest;
struct { struct {
uint32 gmt_unix_time; uint32 gmt_unix_time;
opaque random_bytes[28]; opaque random_bytes[28];
} Random; } Random;
opaque SessionID<0..32>; opaque SessionID<0..32>;
skipping to change at page 45, line 20 skipping to change at page 46, line 10
} ClientHello; } ClientHello;
struct { struct {
ProtocolVersion server_version; ProtocolVersion server_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suite; CipherSuite cipher_suite;
CompressionMethod compression_method; CompressionMethod compression_method;
} ServerHello; } ServerHello;
A.4.2 Server authentication and key exchange messages A.5.2. Server authentication and key exchange messages
opaque ASN.1Cert<2^24-1>; opaque ASN.1Cert<2^24-1>;
struct { struct {
ASN.1Cert certificate_list<1..2^24-1>; ASN.1Cert certificate_list<1..2^24-1>;
} Certificate; } Certificate;
enum { rsa, diffie_hellman } KeyExchangeAlgorithm; enum { rsa, diffie_hellman } KeyExchangeAlgorithm;
struct { struct {
skipping to change at page 46, line 4 skipping to change at page 46, line 43
case diffie_hellman: case diffie_hellman:
ServerDHParams params; ServerDHParams params;
Signature signed_params; Signature signed_params;
case rsa: case rsa:
ServerRSAParams params; ServerRSAParams params;
Signature signed_params; Signature signed_params;
}; };
} ServerKeyExchange; } ServerKeyExchange;
enum { anonymous, rsa, dsa } SignatureAlgorithm; enum { anonymous, rsa, dsa } SignatureAlgorithm;
digitally-signed struct {
select(SignatureAlgorithm) { select (SignatureAlgorithm)
case anonymous: struct { }; { case anonymous: struct { };
case rsa: case rsa:
digitally-signed struct {
opaque md5_hash[16]; opaque md5_hash[16];
opaque sha_hash[20]; opaque sha_hash[20];
};
case dsa: case dsa:
digitally-signed struct {
opaque sha_hash[20]; opaque sha_hash[20];
}; };
} Signature; } Signature;
enum { enum {
RSA_sign(1), DSS_sign(2), RSA_fixed_DH(3), RSA_sign(1), DSS_sign(2), RSA_fixed_DH(3),
DSS_fixed_DH(4), RSA_ephemeral_DH(5), DSS_ephemeral_DH(6), DSS_fixed_DH(4), RSA_ephemeral_DH(5), DSS_ephemeral_DH(6),
(255) (255)
} CertificateType; } CertificateType;
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
CertificateType certificate_types<1..2^8-1>; CertificateType certificate_types<1..2^8-1>;
skipping to change at page 46, line 30 skipping to change at page 47, line 19
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
CertificateType certificate_types<1..2^8-1>; CertificateType certificate_types<1..2^8-1>;
DistinguishedName certificate_authorities<3..2^16-1>; DistinguishedName certificate_authorities<3..2^16-1>;
} CertificateRequest; } CertificateRequest;
struct { } ServerHelloDone; struct { } ServerHelloDone;
A.5 Client authentication and key exchange messages A.5.3. Client authentication and key exchange messages
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case rsa: EncryptedPreMasterSecret; case rsa: EncryptedPreMasterSecret;
case diffie_hellman: DiffieHellmanClientPublicValue; case diffie_hellman: DiffieHellmanClientPublicValue;
} exchange_keys; } exchange_keys;
} ClientKeyExchange; } ClientKeyExchange;
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
skipping to change at page 47, line 10 skipping to change at page 47, line 50
select (PublicValueEncoding) { select (PublicValueEncoding) {
case implicit: struct {}; case implicit: struct {};
case explicit: opaque DH_Yc<1..2^16-1>; case explicit: opaque DH_Yc<1..2^16-1>;
} dh_public; } dh_public;
} ClientDiffieHellmanPublic; } ClientDiffieHellmanPublic;
struct { struct {
Signature signature; Signature signature;
} CertificateVerify; } CertificateVerify;
A.5.1 Handshake finalization message A.5.4. Handshake finalization message
struct { struct {
opaque md5_hash[16]; opaque md5_hash[16];
opaque sha_hash[20]; opaque sha_hash[20];
} Finished; } Finished;
A.6 The CipherSuite A.6. The CipherSuite
The following values define the CipherSuite codes used in the client The following values define the CipherSuite codes used in the client
hello and server hello messages. hello and server hello messages.
A CipherSuite defines a cipher specifications supported in TLS A CipherSuite defines a cipher specification supported in TLS
Version 1.0. Version 1.0.
CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 }; CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 };
The following CipherSuite definitions require that the server The following CipherSuite definitions require that the server
provide an RSA certificate that can be used for key exchange. The provide an RSA certificate that can be used for key exchange. The
server may request either an RSA or a DSS signature-capable server may request either an RSA or a DSS signature-capable
certificate in the certificate request message. certificate in the certificate request message.
CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 }; CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 };
skipping to change at page 47, line 50 skipping to change at page 48, line 38
CipherSuite TLS_RSA_WITH_DES_CBC_SHA = { 0x00,0x09 }; CipherSuite TLS_RSA_WITH_DES_CBC_SHA = { 0x00,0x09 };
CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A }; CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A };
The following CipherSuite definitions are used for The following CipherSuite definitions are used for
server-authenticated (and optionally client-authenticated) server-authenticated (and optionally client-authenticated)
Diffie-Hellman. DH denotes cipher suites in which the server's Diffie-Hellman. DH denotes cipher suites in which the server's
certificate contains the Diffie-Hellman parameters signed by the certificate contains the Diffie-Hellman parameters signed by the
certificate authority (CA). DHE denotes ephemeral Diffie-Hellman, certificate authority (CA). DHE denotes ephemeral Diffie-Hellman,
where the Diffie-Hellman parameters are signed by a DSS or RSA where the Diffie-Hellman parameters are signed by a DSS or RSA
certificate, which has been signed by the CA. The signing algorithm certificate, which has been signed by the CA. The signing algorithm
used is specified after the DH or DHE parameter. In all cases, the | used is specified after the DH or DHE parameter. The server can
client must have the same type of certificate, and must use the | request an RSA or DSS signature-capable certificate from the client
Diffie-Hellman parameters chosen by the server. | for client authentication or it may request a Diffie-Hellman
| certificate. Any Diffie-Hellman certificate provided by the client
| must use the parameters (group and generator) described by the
| server.
CipherSuite TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0B }; CipherSuite TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0B };
CipherSuite TLS_DH_DSS_WITH_DES_CBC_SHA = { 0x00,0x0C }; CipherSuite TLS_DH_DSS_WITH_DES_CBC_SHA = { 0x00,0x0C };
CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D }; CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D };
CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E }; CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E };
CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F }; CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F };
CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 }; CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 };
CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 }; CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 };
CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 }; CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 };
CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 }; CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 };
skipping to change at page 48, line 17 skipping to change at page 49, line 4
CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D }; CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D };
CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E }; CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E };
CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F }; CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F };
CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 }; CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 };
CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 }; CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 };
CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 }; CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 };
CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 }; CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 };
CipherSuite TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x14 }; CipherSuite TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x14 };
CipherSuite TLS_DHE_RSA_WITH_DES_CBC_SHA = { 0x00,0x15 }; CipherSuite TLS_DHE_RSA_WITH_DES_CBC_SHA = { 0x00,0x15 };
CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 }; CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 };
The following cipher suites are used for completely anonymous The following cipher suites are used for completely anonymous
Diffie-Hellman communications in which neither party is Diffie-Hellman communications in which neither party is
authenticated. Note that this mode is vulnerable to authenticated. Note that this mode is vulnerable to
man-in-the-middle attacks and is therefore strongly discouraged. | man-in-the-middle attacks and is therefore deprecated.
CipherSuite TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x17 }; CipherSuite TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x17 };
CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 }; CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 };
CipherSuite TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x19 }; CipherSuite TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x19 };
CipherSuite TLS_DH_anon_WITH_DES_CBC_SHA = { 0x00,0x1A }; CipherSuite TLS_DH_anon_WITH_DES_CBC_SHA = { 0x00,0x1A };
CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B }; CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B };
Note: Note: All cipher suites whose first byte is 0xFF are considered
All cipher suites whose first byte is 0xFF are considered
private and can be used for defining local/experimental private and can be used for defining local/experimental
algorithms. Interoperability of such types is a local matter. algorithms. Interoperability of such types is a local matter.
Note: Note: Additional cipher suites will be considered for implementation
Additional cipher suites will be considered for implementation
only with submission of notarized letters from two independent only with submission of notarized letters from two independent
entities. Netscape Communications Corp. will act as an interim entities. Netscape Communications Corp. will act as an interim
registration office, until a public standards body assumes registration office, until a public standards body assumes
control of TLS. control of TLS.
A.7 The Security Parameters A.7. The Security Parameters
These security parameters are determined by the TLS Handshake These security parameters are determined by the TLS Handshake
Protocol and provided as parameters to the TLS Record Layer in order Protocol and provided as parameters to the TLS Record Layer in order
to initialize a connection state. SecurityParameters includes: to initialize a connection state. SecurityParameters includes:
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
enum { server, client } ConnectionEnd; enum { server, client } ConnectionEnd;
enum { null, rc4, rc2, des, 3des, des40 } enum { null, rc4, rc2, des, 3des, des40 } BulkCipherAlgorithm;
BulkCipherAlgorithm;
enum { stream, block } CipherType; enum { stream, block } CipherType;
enum { true, false } IsExportable; enum { true, false } IsExportable;
enum { null, md5, sha } MACAlgorithm; enum { null, md5, sha } MACAlgorithm;
/* The algorithms specified in CompressionMethod, /* The algorithms specified in CompressionMethod,
BulkCipherAlgorithm, and MACAlgorithm may be added to. */ BulkCipherAlgorithm, and MACAlgorithm may be added to. */
struct { struct {
ConnectionEnd entity; ConnectionEnd entity;
BulkCipherAlgorithm bulk_cipher_algorithm; BulkCipherAlgorithm bulk_cipher_algorithm;
skipping to change at page 49, line 27 skipping to change at page 50, line 10
IsExportable is_exportable; IsExportable is_exportable;
MACAlgorithm mac_algorithm; MACAlgorithm mac_algorithm;
uint8 hash_size; uint8 hash_size;
uint8 whitener_length; uint8 whitener_length;
CompressionMethod compression_algorithm; CompressionMethod compression_algorithm;
opaque master_secret[48]; opaque master_secret[48];
opaque client_random[32]; opaque client_random[32];
opaque server_random[32]; opaque server_random[32];
} SecurityParameters; } SecurityParameters;
Appendix B
B. Glossary B. Glossary
application protocol application protocol
An application protocol is a protocol that normally layers An application protocol is a protocol that normally layers
directly on top of the transport layer (e.g., TCP/IP). directly on top of the transport layer (e.g., TCP/IP). Examples
Examples include HTTP, TELNET, FTP, and SMTP. include HTTP, TELNET, FTP, and SMTP.
asymmetric cipher asymmetric cipher
See public key cryptography. See public key cryptography.
authentication authentication
Authentication is the ability of one entity to determine the Authentication is the ability of one entity to determine the
identity of another entity. identity of another entity.
block cipher block cipher
A block cipher is an algorithm that operates on plaintext in A block cipher is an algorithm that operates on plaintext in
groups of bits, called blocks. 64 bits is a typical block size. groups of bits, called blocks. 64 bits is a typical block size.
bulk cipher bulk cipher
A symmetric encryption algorithm used to encrypt large A symmetric encryption algorithm used to encrypt large
quantities of data. quantities of data.
cipher block chaining | cipher block chaining (CBC)
Mode (CBC) CBC is a mode in which every plaintext block | CBC is a mode in which every plaintext block encrypted with a
encrypted with the block cipher is first exclusive-ORed with | block cipher is first exclusive-ORed with the previous
the previous ciphertext block (or, in the case of the first | ciphertext block (or, in the case of the first block, with the
block, with the initialization vector). | initialization vector). For decryption, every block is first
| decrypted, then exclusive-ORed with the previous ciphertext
| block (or IV).
certificate certificate
As part of the X.509 protocol (a.k.a. ISO Authentication As part of the X.509 protocol (a.k.a. ISO Authentication
framework), certificates are assigned by a trusted Certificate framework), certificates are assigned by a trusted Certificate
Authority and provide verification of a party's identity and Authority and provide verification of a party's identity and may
may also supply its public key. also supply its public key.
client client
The application entity that initiates a connection to a server The application entity that initiates a connection to a server
client write key client write key
The key used to encrypt data written by the client. The key used to encrypt data written by the client.
client write MAC secret client write MAC secret
The secret data used to authenticate data written by the The secret data used to authenticate data written by the client.
client.
connection connection
A connection is a transport (in the OSI layering model A connection is a transport (in the OSI layering model
definition) that provides a suitable type of service. For TLS, definition) that provides a suitable type of service. For TLS,
such connections are peer to peer relationships. The such connections are peer to peer relationships. The connections
connections are transient. Every connection is associated with are transient. Every connection is associated with one session.
one session.
Data Encryption Standard Data Encryption Standard
DES is a very widely used symmetric encryption algorithm. DES is a very widely used symmetric encryption algorithm. DES is
DES is a block cipher. (DES) | a block cipher with a 56 bit key and an 8 byte block size. Note
| that in TLS, for key generation purposes, DES is treated as
| having an 8 byte key length (64 bits), but it still only
| provides 56 bits of protection. DES can also be operated in a
| mode where three independant keys and three encryptions are used
| for each block of data; this uses 168 bits of key (24 bytes in
| the TLS key generation method) and provides the equivalent of
| 112 bits of security. [DES], [3DES]
Digital Signature Standard Digital Signature Standard (DSS)
(DSS) A standard for digital signing, including the Digital A standard for digital signing, including the Digital Signing
Signing Algorithm, approved by the National Institute of Algorithm, approved by the National Institute of Standards and
Standards and Technology, defined in NIST FIPS PUB 186, Technology, defined in NIST FIPS PUB 186, "Digital Signature
"Digital Signature Standard," published May, 1994 by the U.S. Standard," published May, 1994 by the U.S. Dept. of Commerce.
Dept. of Commerce. [DSS]
digital signatures digital signatures
Digital signatures utilize public key cryptography and one-way Digital signatures utilize public key cryptography and one-way
hash functions to produce a signature of the data that can be hash functions to produce a signature of the data that can be
authenticated, and is difficult to forge or repudiate. authenticated, and is difficult to forge or repudiate.
handshake handshake
An initial negotiation between client and server that An initial negotiation between client and server that
establishes the parameters of their transactions. establishes the parameters of their transactions.
Initialization Vector Initialization Vector (IV)
(IV) When a block cipher is used in CBC mode, the When a block cipher is used in CBC mode, the initialization
initialization vector is exclusive-ORed with the first vector is exclusive-ORed with the first plaintext block prior to
plaintext block prior to encryption. encryption.
IDEA IDEA
A 64-bit block cipher designed by Xuejia Lai and James Massey. A 64-bit block cipher designed by Xuejia Lai and James Massey.
[IDEA]
Message Authentication Code Message Authentication Code (MAC)
(MAC) A Message Authentication Code is a one-way hash computed A Message Authentication Code is a one-way hash computed from a
from a message and some secret data. Its purpose is to detect | message and some secret data. It is difficult to forge without
if the message has been altered. | knowing the secret data and it is difficult to find messages
| which hash to the same MAC. Its purpose is to detect if the
| message has been altered.
master secret master secret
Secure secret data used for generating encryption keys, MAC Secure secret data used for generating encryption keys, MAC
secrets, and IVs. secrets, and IVs.
MD5 MD5
MD5 [7] is a secure hashing function that converts an MD5 is a secure hashing function that converts an arbitrarily
arbitrarily long data stream into a digest of fixed size. | long data stream into a digest of fixed size (16 bytes). [MD5]
public key cryptography public key cryptography
A class of cryptographic techniques employing two-key ciphers. A class of cryptographic techniques employing two-key ciphers.
Messages encrypted with the public key can only be decrypted Messages encrypted with the public key can only be decrypted
with the associated private key. Conversely, messages signed with the associated private key. Conversely, messages signed
with the private key can be verified with the public key. with the private key can be verified with the public key.
one-way hash function one-way hash function
A one-way transformation that converts an arbitrary amount of A one-way transformation that converts an arbitrary amount of
data into a fixed-length hash. It is computation- ally hard to data into a fixed-length hash. It is computationally hard to
reverse the transformation or to find collisions. MD5 and SHA reverse the transformation or to find collisions. MD5 and SHA
are examples of one-way hash functions. are examples of one-way hash functions.
RC2, RC4 RC2, RC4
Proprietary bulk ciphers from RSA Data Security, Inc. (There Proprietary bulk ciphers from RSA Data Security, Inc. (There is
is no good reference to these as they are unpublished works; no good reference to these as they are unpublished works;
however, see [RSADSI]). RC2 is block cipher and RC4 is a however, see [RSADSI]). RC2 is block cipher and RC4 is a stream
stream cipher. cipher.
RSA RSA
A very widely used public-key algorithm that can be used for A very widely used public-key algorithm that can be used for
either encryption or digital signing. either encryption or digital signing. [RSA]
salt salt
Non-secret random data used to make export encryption keys Non-secret random data used to make export encryption keys
resist precomputation attacks. resist precomputation attacks.
server server
The server is the application entity that responds to requests The server is the application entity that responds to requests
for connections from clients. The server is passive, waiting for connections from clients. The server is passive, waiting for
for requests from clients. requests from clients.
session session
A TLS session is an association between a client and a server. A TLS session is an association between a client and a server.
Sessions are created by the handshake protocol. Sessions Sessions are created by the handshake protocol. Sessions define
define a set of cryptographic security parameters, which can a set of cryptographic security parameters, which can be shared
be shared among multiple connections. Sessions are used to among multiple connections. Sessions are used to avoid the
avoid the expensive negotiation of new security parameters for expensive negotiation of new security parameters for each
each connection. connection.
session identifier session identifier
A session identifier is a value generated by a server that A session identifier is a value generated by a server that
identifies a particular session. identifies a particular session.
server write key server write key
The key used to encrypt data written by the server. The key used to encrypt data written by the server.
server write MAC secret server write MAC secret
The secret data used to authenticate data written by the The secret data used to authenticate data written by the server.
server.
SHA SHA
The Secure Hash Algorithm is defined in FIPS PUB 180-1. It The Secure Hash Algorithm is defined in FIPS PUB 180-1. It
produces a 20-byte output [SHA]. | produces a 20-byte output. Note that all references to SHA
| actually use the modified SHA-1 algorithm. [SHA]
SSL SSL
Netscape's Secure Socket Layer protocol [SSL3]. TLS is based Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on
on SSL Version 3.0 SSL Version 3.0
stream cipher/ stream cipher
An encryption algorithm that converts a key into a An encryption algorithm that converts a key into a
cryptographically-strong keystream, which is then cryptographically-strong keystream, which is then exclusive-ORed
exclusive-ORed with the plaintext. with the plaintext.
symmetric cipher symmetric cipher
See bulk cipher. See bulk cipher.
Appendix C | Transport Layer Security (TLS)
| This protocol; also, the Transport Layer Security working group
| of the Internet Engineering Task Force (IETF). See "Comments" at
| the end of this document.
C. CipherSuite definitions C. CipherSuite definitions
CipherSuite Is Key Cipher Hash CipherSuite Is Key Cipher Hash
Exportable Exchange Exportable Exchange
TLS_NULL_WITH_NULL_NULL * NULL NULL NULL TLS_NULL_WITH_NULL_NULL * NULL NULL NULL
TLS_RSA_WITH_NULL_MD5 * RSA NULL MD5 TLS_RSA_WITH_NULL_MD5 * RSA NULL MD5
TLS_RSA_WITH_NULL_SHA * RSA NULL SHA TLS_RSA_WITH_NULL_SHA * RSA NULL SHA
TLS_RSA_EXPORT_WITH_RC4_40_MD5 * RSA_EXPORT RC4_40 MD5 TLS_RSA_EXPORT_WITH_RC4_40_MD5 * RSA_EXPORT RC4_40 MD5
skipping to change at page 53, line 4 skipping to change at page 53, line 52
TLS_RSA_WITH_IDEA_CBC_SHA RSA IDEA_CBC SHA TLS_RSA_WITH_IDEA_CBC_SHA RSA IDEA_CBC SHA
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA * RSA_EXPORT DES40_CBC SHA TLS_RSA_EXPORT_WITH_DES40_CBC_SHA * RSA_EXPORT DES40_CBC SHA
TLS_RSA_WITH_DES_CBC_SHA RSA DES_CBC SHA TLS_RSA_WITH_DES_CBC_SHA RSA DES_CBC SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE_CBC SHA TLS_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE_CBC SHA
TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA * DH_DSS_EXPORT DES40_CBC SHA TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA * DH_DSS_EXPORT DES40_CBC SHA
TLS_DH_DSS_WITH_DES_CBC_SHA DH_DSS DES_CBC SHA TLS_DH_DSS_WITH_DES_CBC_SHA DH_DSS DES_CBC SHA
TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA DH_DSS 3DES_EDE_CBC SHA TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA DH_DSS 3DES_EDE_CBC SHA
TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA * DH_RSA_EXPORT DES40_CBC SHA TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA * DH_RSA_EXPORT DES40_CBC SHA
TLS_DH_RSA_WITH_DES_CBC_SHA DH_RSA DES_CBC SHA TLS_DH_RSA_WITH_DES_CBC_SHA DH_RSA DES_CBC SHA
TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA DH_RSA 3DES_EDE_CBC SHA TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA DH_RSA 3DES_EDE_CBC SHA
TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA * DHE_DSS_EXPORT DES40_CBC SHA TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA * DHE_DSS_EXPORT DES40_CBC SHA
TLS_DHE_DSS_WITH_DES_CBC_SHA DHE_DSS DES_CBC SHA TLS_DHE_DSS_WITH_DES_CBC_SHA DHE_DSS DES_CBC SHA
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA
TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA * DHE_RSA_EXPORT DES40_CBC SHA TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA * DHE_RSA_EXPORT DES40_CBC SHA
TLS_DHE_RSA_WITH_DES_CBC_SHA DHE_RSA DES_CBC SHA TLS_DHE_RSA_WITH_DES_CBC_SHA DHE_RSA DES_CBC SHA
TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA
TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 * DH_anon_EXPORT RC4_40 MD5 TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 * DH_anon_EXPORT RC4_40 MD5
TLS_DH_anon_WITH_RC4_128_MD5 DH_anon RC4_128 MD5 TLS_DH_anon_WITH_RC4_128_MD5 DH_anon RC4_128 MD5
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA DH_anon DES40_CBC SHA TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA DH_anon DES40_CBC SHA
TLS_DH_anon_WITH_DES_CBC_SHA DH_anon DES_CBC SHA TLS_DH_anon_WITH_DES_CBC_SHA DH_anon DES_CBC SHA
TLS_DH_anon_WITH_3DES_EDE_CBC_SHA DH_anon 3DES_EDE_CBC SHA TLS_DH_anon_WITH_3DES_EDE_CBC_SHA DH_anon 3DES_EDE_CBC SHA
* Indicates IsExportable is True * Indicates IsExportable is True
Key Description Key size limit Key
Exchange Exchange
Algorithm Algorithm Description Key size limit
DHE_DSS Ephemeral DH with DSS signatures None DHE_DSS Ephemeral DH with DSS signatures None
DHE_DSS_EXPORT Ephemeral DH with DSS signatures DH = 512 bits DHE_DSS_EXPORT Ephemeral DH with DSS signatures DH = 512 bits
DHE_RSA Ephemeral DH with RSA signatures None DHE_RSA Ephemeral DH with RSA signatures None
DHE_RSA_EXPORT Ephemeral DH with RSA signatures DH = 512 bits, DHE_RSA_EXPORT Ephemeral DH with RSA signatures DH = 512 bits,
RSA = none RSA = none
DH_anon Anonymous DH, no signatures None DH_anon Anonymous DH, no signatures None
DH_anon_EXPORT Anonymous DH, no signatures DH = 512 bits DH_anon_EXPORT Anonymous DH, no signatures DH = 512 bits
DH_DSS DH with DSS-based certificates None DH_DSS DH with DSS-based certificates None
DH_DSS_EXPORT DH with DSS-based certificates DH = 512 bits DH_DSS_EXPORT DH with DSS-based certificates DH = 512 bits
DH_RSA DH with RSA-based certificates None DH_RSA DH with RSA-based certificates None
DH_RSA_EXPORT DH with RSA-based certificates DH = 512 bits, DH_RSA_EXPORT DH with RSA-based certificates DH = 512 bits,
RSA = none RSA = none
NULL No key exchange N/A NULL No key exchange N/A
RSA RSA key exchange None RSA RSA key exchange None
RSA_EXPORT RSA key exchange RSA = 512 bits RSA_EXPORT RSA key exchange RSA = 512 bits
Key size limit Key size limit
The key size limit gives the size of the largest public key The key size limit gives the size of the largest public key that
that can be legally used for encryption in cipher suites that can be legally used for encryption in cipher suites that are
are exportable. exportable.
Cipher Cipher IsExpo Key Exp. Effect IV Block Key Expanded Effective IV Block
Type rtable Material Key Mat ive Key Size Size Cipher Type Material Key Material Key Bits Size Size
erial Bits
NULL Stream * 0 0 0 0 N/A NULL * Stream 0 0 0 0 N/A
IDEA_CBC Block 16 16 128 8 8 IDEA_CBC Block 16 16 128 8 8
RC2_CBC_40 Block * 5 16 40 8 8 RC2_CBC_40 * Block 5 16 40 8 8
RC4_40 Stream * 5 16 40 0 N/A RC4_40 * Stream 5 16 40 0 N/A
RC4_128 Stream 16 16 128 0 N/A RC4_128 Stream 16 16 128 0 N/A
DES40_CBC Block * 5 8 40 8 8 DES40_CBC * Block 5 8 40 8 8
DES_CBC Block 8 8 56 8 8 DES_CBC Block 8 8 56 8 8
3DES_EDE_CBC Block 24 24 168 8 8 3DES_EDE_CBC Block 24 24 168 8 8
* Indicates IsExportable is true. * Indicates IsExportable is true.
Key Material Key Material
The number of bytes from the key_block that are used for The number of bytes from the key_block that are used for
generating the write keys. generating the write keys.
Expanded Key Material Expanded Key Material
The number of bytes actually fed into the encryption algorithm The number of bytes actually fed into the encryption algorithm
Effective Key Bits Effective Key Bits
skipping to change at page 54, line 14 skipping to change at page 55, line 9
* Indicates IsExportable is true. * Indicates IsExportable is true.
Key Material Key Material
The number of bytes from the key_block that are used for The number of bytes from the key_block that are used for
generating the write keys. generating the write keys.
Expanded Key Material Expanded Key Material
The number of bytes actually fed into the encryption algorithm The number of bytes actually fed into the encryption algorithm
Effective Key Bits Effective Key Bits
How much entropy material is in the key material being fed How much entropy material is in the key material being fed into
into the encryption routines. the encryption routines.
Hash Hash Size Padding Hash Hash Padding
function Size function Size Size
NULL 0 0 NULL 0 0
MD5 16 48 MD5 16 48
SHA 20 40 SHA 20 40
Appendix D Appendix D
D. Implementation Notes D. Implementation Notes
The TLS protocol cannot prevent many common security mistakes. This The TLS protocol cannot prevent many common security mistakes. This
section provides several recommendations to assist implementers. section provides several recommendations to assist implementers.
D.1 Temporary RSA keys D.1. Temporary RSA keys
US Export restrictions limit RSA keys used for encryption to 512 US Export restrictions limit RSA keys used for encryption to 512
bits, but do not place any limit on lengths of RSA keys used for bits, but do not place any limit on lengths of RSA keys used for
signing operations. Certificates often need to be larger than 512 signing operations. Certificates often need to be larger than 512
bits, since 512-bit RSA keys are not secure enough for high-value bits, since 512-bit RSA keys are not secure enough for high-value
transactions or for applications requiring long-term security. Some transactions or for applications requiring long-term security. Some
certificates are also designated signing-only, in which case they certificates are also designated signing-only, in which case they
cannot be used for key exchange. cannot be used for key exchange.
When the public key in the certificate cannot be used for When the public key in the certificate cannot be used for
skipping to change at page 55, line 8 skipping to change at page 55, line 52
possible. Note that while it is acceptable to use the same temporary possible. Note that while it is acceptable to use the same temporary
key for multiple transactions, it must be signed each time it is key for multiple transactions, it must be signed each time it is
used. used.
RSA key generation is a time-consuming process. In many cases, a RSA key generation is a time-consuming process. In many cases, a
low-priority process can be assigned the task of key generation. low-priority process can be assigned the task of key generation.
Whenever a new key is completed, the existing temporary key can be Whenever a new key is completed, the existing temporary key can be
replaced with the new one. replaced with the new one.
D.2 Random Number Generation and Seeding D.2. Random Number Generation and Seeding
TLS requires a cryptographically-secure pseudorandom number TLS requires a cryptographically-secure pseudorandom number
generator (PRNG). Care must be taken in designing and seeding PRNGs. generator (PRNG). Care must be taken in designing and seeding PRNGs.
PRNGs based on secure hash operations, most notably MD5 and/or SHA, PRNGs based on secure hash operations, most notably MD5 and/or SHA,
are acceptable, but cannot provide more security than the size of are acceptable, but cannot provide more security than the size of
the random number generator state. (For example, MD5-based PRNGs the random number generator state. (For example, MD5-based PRNGs
usually provide 128 bits of state.) usually provide 128 bits of state.)
To estimate the amount of seed material being produced, add the To estimate the amount of seed material being produced, add the
number of bits of unpredictable information in each seed byte. For number of bits of unpredictable information in each seed byte. For
example, keystroke timing values taken from a PC- compatible's 18.2 example, keystroke timing values taken from a PC compatible's 18.2
Hz timer provide 1 or 2 secure bits each, even though the total size Hz timer provide 1 or 2 secure bits each, even though the total size
of the counter value is 16 bits or more. To seed a 128-bit PRNG, one of the counter value is 16 bits or more. To seed a 128-bit PRNG, one
would thus require approximately 100 such timer values. would thus require approximately 100 such timer values.
Note: Warning: The seeding functions in RSAREF and versions of BSAFE prior to
The seeding functions in RSAREF and versions of BSAFE prior to
3.0 are order-independent. For example, if 1000 seed bits are 3.0 are order-independent. For example, if 1000 seed bits are
supplied, one at a time, in 1000 separate calls to the seed supplied, one at a time, in 1000 separate calls to the seed
function, the PRNG will end up in a state which depends only function, the PRNG will end up in a state which depends only
on the number of 0 or 1 seed bits in the seed data (i.e., on the number of 0 or 1 seed bits in the seed data (i.e.,
there are 1001 possible final states). Applications using there are 1001 possible final states). Applications using
BSAFE or RSAREF must take extra care to ensure proper seeding. BSAFE or RSAREF must take extra care to ensure proper seeding.
| This may be accomplished by accumulating seed bits into a
| buffer and processing them all at once or by processing an
| incrementing counter with every seed bit; either method will
| reintroduce order dependance into the seeding process.
D.3 Certificates and authentication D.3. Certificates and authentication
Implementations are responsible for verifying the integrity of Implementations are responsible for verifying the integrity of
certificates and should generally support certificate revocation certificates and should generally support certificate revocation
messages. Certificates should always be verified to ensure proper messages. Certificates should always be verified to ensure proper
signing by a trusted Certificate Authority (CA). The selection and signing by a trusted Certificate Authority (CA). The selection and
addition of trusted CAs should be done very carefully. Users should addition of trusted CAs should be done very carefully. Users should
be able to view information about the certificate and root CA. be able to view information about the certificate and root CA.
D.4 CipherSuites D.4. CipherSuites
TLS supports a range of key sizes and security levels, including TLS supports a range of key sizes and security levels, including
some which provide no or minimal security. A proper implementation some which provide no or minimal security. A proper implementation
will probably not support many cipher suites. For example, 40-bit will probably not support many cipher suites. For example, 40-bit
encryption is easily broken, so implementations requiring strong encryption is easily broken, so implementations requiring strong
security should not allow 40-bit keys. Similarly, anonymous security should not allow 40-bit keys. Similarly, anonymous
Diffie-Hellman is strongly discouraged because it cannot prevent Diffie-Hellman is strongly discouraged because it cannot prevent
man-in-the- middle attacks. Applications should also enforce minimum man-in-the- middle attacks. Applications should also enforce minimum
and maximum key sizes. For example, certificate chains containing and maximum key sizes. For example, certificate chains containing
512-bit RSA keys or signatures are not appropriate for high-security 512-bit RSA keys or signatures are not appropriate for high-security
applications. applications.
Appendix E E. Backward Compatibility With SSL
E. Version 2.0 Backward Compatibility | For historical reasons and in order to avoid a profligate
| consumption of reserved port numbers, application protocols which
| are secured by TLS 1.0, SSL 3.0, and SSL 2.0 all frequently share
| the same connection port: for example, the https protocol (HTTP
| secured by SSL or TLS) uses port 443 regardless of which security
Version 3.0 clients that support Version 2.0 servers must send | protocol it is using. Thus, some mechanism must be determined to
Version 2.0 client hello messages [SSL-2]. Version 3.0 servers | distinguish and negotiate among the various protocols.
should accept either client hello format. The only deviations from
the Version 2.0 specification are the ability to specify a version
with a value of three and the support for more ciphering types in
the CipherSpec.
Warning: | TLS version 1.0 and SSL 3.0 are very similar; thus, supporting both
The ability to send Version 2.0 client hello messages will be | is easy. TLS clients who wish to negotiate with SSL 3.0 servers
| should send client hello messages using the SSL 3.0 record format
| and client hello structure, sending {3, 1} for the version field to
| note that they support TLS 1.0. If the server supports only SSL 3.0,
| it will respond with an SSL 3.0 server hello; if it supports TLS,
| with a TLS server hello. The negotiation then proceeds as
| appropriate for the negotiated protocol.
| Similarly, a TLS server which wishes to interoperate with SSL 3.0
| clients should accept SSL 3.0 client hello messages and respond with
| an SSL 3.0 server hello if an SSL 3.0 client hello is received which
| has a version field of {3, 0}, denoting that this client does not
| support TLS.
| Whenever a client already knows the highest protocol known to a
| server (for example, when resuming a session), it should initiate
| the connection in that native protocol.
| TLS 1.0 clients that support SSL Version 2.0 servers must send SSL
| Version 2.0 client hello messages [SSL-2]. TLS servers should accept
| either client hello format if they wish to support SSL 2.0 clients
| on the same connection port. The only deviations from the Version
| 2.0 specification are the ability to specify a version with a value
| of three and the support for more ciphering types in the CipherSpec.
Warning: The ability to send Version 2.0 client hello messages will be
phased out with all due haste. Implementers should make every phased out with all due haste. Implementers should make every
effort to move forward as quickly as possible. Version 3.0 effort to move forward as quickly as possible. Version 3.0
provides better mechanisms for moving to newer versions. provides better mechanisms for moving to newer versions.
The following cipher specifications are carryovers from SSL Version The following cipher specifications are carryovers from SSL Version
2.0. These are assumed to use RSA for key exchange and 2.0. These are assumed to use RSA for key exchange and
authentication. authentication.
V2CipherSpec SSL_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 }; | V2CipherSpec TLS_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 };
V2CipherSpec SSL_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 }; | V2CipherSpec TLS_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 };
V2CipherSpec SSL_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 }; | V2CipherSpec TLS_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 };
V2CipherSpec SSL_RC2_CBC_128_CBC_EXPORT40_WITH_MD5 | V2CipherSpec TLS_RC2_CBC_128_CBC_EXPORT40_WITH_MD5
= { 0x04,0x00,0x80 }; | = { 0x04,0x00,0x80 };
V2CipherSpec SSL_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 }; | V2CipherSpec TLS_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 };
V2CipherSpec SSL_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 }; | V2CipherSpec TLS_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 };
V2CipherSpec SSL_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 }; | V2CipherSpec TLS_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 };
Cipher specifications introduced in Version 3.0 can be included in | Cipher specifications native to TLS can be included in Version 2.0
Version 2.0 client hello messages using the syntax below. Any | client hello messages using the syntax below. Any V2CipherSpec
V2CipherSpec element with its first byte equal to zero will be | element with its first byte equal to zero will be ignored by Version
ignored by Version 2.0 servers. Clients sending any of the above | 2.0 servers. Clients sending any of the above V2CipherSpecs should
V2CipherSpecs should also include the Version 3.0 equivalent (see | also include the TLS equivalent (see Appendix A.6):
Appendix A.6):
V2CipherSpec (see Version 3.0 name) = { 0x00, CipherSuite }; | V2CipherSpec (see TLS name) = { 0x00, CipherSuite };
E.1 Version 2 client hello E.1. Version 2 client hello
The Version 2.0 client hello message is presented below using this The Version 2.0 client hello message is presented below using this
document's presentation model. The true definition is still assumed document's presentation model. The true definition is still assumed
to be the SSL Version 2.0 specification. to be the SSL Version 2.0 specification.
uint8 V2CipherSpec[3]; uint8 V2CipherSpec[3];
struct { struct {
unit8 msg_type; unit8 msg_type;
Version version; Version version;
uint16 cipher_spec_length; uint16 cipher_spec_length;
uint16 session_id_length; uint16 session_id_length;
uint16 challenge_length; uint16 challenge_length;
V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length]; V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length];
opaque session_id[V2ClientHello.session_id_length]; opaque session_id[V2ClientHello.session_id_length];
Random challenge; Random challenge;
} V2ClientHello; } V2ClientHello;
msg_type msg_type
This field, in conjunction with the version field, identifies This field, in conjunction with the version field, identifies a
a version 2 client hello message. The value should be one (1). version 2 client hello message. The value should be one (1).
version version
The highest version of the protocol supported by the client The highest version of the protocol supported by the client
(equals ProtocolVersion.version, see Appendix A.1.1). (equals ProtocolVersion.version, see Appendix A.1.1).
cipher_spec_length cipher_spec_length
This field is the total length of the field cipher_specs. It This field is the total length of the field cipher_specs. It
cannot be zero and must be a multiple of the V2CipherSpec cannot be zero and must be a multiple of the V2CipherSpec length
length (3). (3).
session_id_length session_id_length
This field must have a value of either zero or 16. If zero, This field must have a value of either zero or 16. If zero, the
the client is creating a new session. If 16, the session_id client is creating a new session. If 16, the session_id field
field will contain the 16 bytes of session identification. will contain the 16 bytes of session identification.
challenge_length challenge_length
The length in bytes of the client's challenge to the server to The length in bytes of the client's challenge to the server to
authenticate itself. This value must be 32. authenticate itself. This value must be 32.
cipher_specs cipher_specs
This is a list of all CipherSpecs the client is willing and This is a list of all CipherSpecs the client is willing and able
able to use. There must be at least one CipherSpec acceptable to use. There must be at least one CipherSpec acceptable to the
to the server. server.
session_id session_id
If this field's length is not zero, it will contain the If this field's length is not zero, it will contain the
identification for a session that the client wishes to resume. identification for a session that the client wishes to resume.
challenge challenge
The client challenge to the server for the server to identify The client challenge to the server for the server to identify
itself is a (nearly) arbitrary length random. The Version 3.0 itself is a (nearly) arbitrary length random. The Version 3.0
server will right justify the challenge data to become the server will right justify the challenge data to become the
ClientHello.random data (padded with leading zeroes, if ClientHello.random data (padded with leading zeroes, if
necessary), as specified in this Version 3.0 protocol. If the necessary), as specified in this Version 3.0 protocol. If the
length of the challenge is greater than 32 bytes, only the length of the challenge is greater than 32 bytes, only the last
last 32 bytes are used. It is legitimate (but not necessary) 32 bytes are used. It is legitimate (but not necessary) for a V3
for a V3 server to reject a V2 ClientHello that has fewer than server to reject a V2 ClientHello that has fewer than 16 bytes
16 bytes of challenge data. of challenge data.
Note: |Note: Requests to resume a TLS session should use a TLS client hello.
Requests to resume an SSL 3.0 session should use an SSL 3.0
client hello.
E.2 Avoiding man-in-the-middle version rollback E.2. Avoiding man-in-the-middle version rollback
When SSL Version 3.0 clients fall back to Version 2.0 compatibility | When TLS clients fall back to Version 2.0 compatibility mode, they
mode, they use special PKCS #1 block formatting. This is done so | should use special PKCS #1 block formatting. This is done so that
that Version 3.0 servers will reject Version 2.0 sessions with | TLS servers will reject Version 2.0 sessions with TLS-capable
Version 3.0-capable clients. | clients.
When Version 3.0 clients are in Version 2.0 compatibility mode, they | When TLS clients are in Version 2.0 compatibility mode, they set the
set the right-hand (least-significant) 8 random bytes of the PKCS right-hand (least-significant) 8 random bytes of the PKCS padding
padding (not including the terminal null of the padding) for the RSA (not including the terminal null of the padding) for the RSA
encryption of the ENCRYPTED-KEY- DATA field of the CLIENT-MASTER-KEY encryption of the ENCRYPTED-KEY- DATA field of the CLIENT-MASTER-KEY
to 0x03 (the other padding bytes are random). After decrypting the to 0x03 (the other padding bytes are random). After decrypting the
ENCRYPTED- KEY-DATA field, servers that support TLS should issue ENCRYPTED-KEY-DATA field, servers that support TLS should issue an
an error if these eight padding bytes are 0x03. Version 2.0 servers error if these eight padding bytes are 0x03. Version 2.0 servers
receiving blocks padded in this manner will proceed normally. receiving blocks padded in this manner will proceed normally.
Appendix F Appendix F
F. Security analysis F. Security analysis
The TLS protocol is designed to establish a secure connection The TLS protocol is designed to establish a secure connection
between a client and a server communicating over an insecure between a client and a server communicating over an insecure
channel. This document makes several traditional assumptions, channel. This document makes several traditional assumptions,
including that attackers have substantial computational resources including that attackers have substantial computational resources
and cannot obtain secret information from sources outside the and cannot obtain secret information from sources outside the
protocol. Attackers are assumed to have the ability to capture, protocol. Attackers are assumed to have the ability to capture,
modify, delete, replay, and otherwise tamper with messages sent over modify, delete, replay, and otherwise tamper with messages sent over
the communication channel. This appendix outlines how TLS has been the communication channel. This appendix outlines how TLS has been
designed to resist a variety of attacks. designed to resist a variety of attacks.
F.1 Handshake protocol F.1. Handshake protocol
The handshake protocol is responsible for selecting a CipherSpec and The handshake protocol is responsible for selecting a CipherSpec and
generating a MasterSecret, which together comprise the primary generating a MasterSecret, which together comprise the primary
cryptographic parameters associated with a secure session. The cryptographic parameters associated with a secure session. The
handshake protocol can also optionally authenticate parties who have handshake protocol can also optionally authenticate parties who have
certificates signed by a trusted certificate authority. certificates signed by a trusted certificate authority.
F.1.1 Authentication and key exchange F.1.1. Authentication and key exchange
TLS supports three authentication modes: authentication of both TLS supports three authentication modes: authentication of both
parties, server authentication with an unauthenticated client, and parties, server authentication with an unauthenticated client, and
total anonymity. Whenever the server is authenticated, the channel total anonymity. Whenever the server is authenticated, the channel
should be secure against man-in- the-middle attacks, but completely should be secure against man-in- the-middle attacks, but completely
anonymous sessions are inherently vulnerable to such attacks. anonymous sessions are inherently vulnerable to such attacks.
Anonymous servers cannot authenticate clients, since the client Anonymous servers cannot authenticate clients, since the client
signature in the certificate verify message may require a server signature in the certificate verify message may require a server
certificate to bind the signature to a particular server. If the certificate to bind the signature to a particular server. If the
server is authenticated, its certificate message must provide a server is authenticated, its certificate message must provide a
valid certificate chain leading to an acceptable certificate valid certificate chain leading to an acceptable certificate
authority. Similarly, authenticated clients must supply an authority. Similarly, authenticated clients must supply an
acceptable certificate to the server. Each party is responsible for acceptable certificate to the server. Each party is responsible for
verifying that the other's certificate is valid and has not expired verifying that the other's certificate is valid and has not expired
or been revoked. or been revoked.
The general goal of the key exchange process is to create a The general goal of the key exchange process is to create a
pre_master_secret known to the communicating parties and not to pre_master_secret known to the communicating parties and not to
attackers. The pre_master_secret will be used to generate the attackers. The pre_master_secret will be used to generate the
master_secret (see Section 6.1). The master_secret is required to master_secret (see Section 7.1). The master_secret is required to
generate the finished messages, encryption keys, and MAC secrets | generate the certificate verify and finished messages, encryption
(see Sections 5.6.9 and 6.2.2). By sending a correct finished keys, and MAC secrets (see Sections 6.4.8, 6.4.9 and 5.4). By
message, parties thus prove that they know the correct sending a correct finished message, parties thus prove that they
pre_master_secret. know the correct pre_master_secret.
F.1.1.1 Anonymous key exchange F.1.1.1. Anonymous key exchange
Completely anonymous sessions can be established using RSA or Completely anonymous sessions can be established using RSA or
Diffie-Hellman for key exchange. With anonymous RSA, the client Diffie-Hellman for key exchange. With anonymous RSA, the client
encrypts a pre_master_secret with the server's uncertified public encrypts a pre_master_secret with the server's uncertified public
key extracted from the server key exchange message. The result is key extracted from the server key exchange message. The result is
sent in a client key exchange message. Since eavesdroppers do not sent in a client key exchange message. Since eavesdroppers do not
know the server's private key, it will be infeasible for them to know the server's private key, it will be infeasible for them to
decode the pre_master_secret. (Note that no anonymous RSA Cipher decode the pre_master_secret. (Note that no anonymous RSA Cipher
Suites are defined in this document). Suites are defined in this document).
With Diffie-Hellman, the server's public parameters are contained in With Diffie-Hellman, the server's public parameters are contained in
the server key exchange message and the client's are sent in the the server key exchange message and the client's are sent in the
client key exchange message. Eavesdroppers who do not know the client key exchange message. Eavesdroppers who do not know the
private values should not be able to find the Diffie-Hellman result private values should not be able to find the Diffie-Hellman result
(i.e. the pre_master_secret). (i.e. the pre_master_secret).
Warning: Warning: Completely anonymous connections only provide protection
Completely anonymous connections only provide protection
against passive eavesdropping. Unless an independent against passive eavesdropping. Unless an independent
tamper-proof channel is used to verify that the finished tamper-proof channel is used to verify that the finished
messages were not replaced by an attacker, server messages were not replaced by an attacker, server
authentication is required in environments where active authentication is required in environments where active
man-in-the-middle attacks are a concern. man-in-the-middle attacks are a concern.
F.1.1.2 RSA key exchange and authentication F.1.1.2. RSA key exchange and authentication
With RSA, key exchange and server authentication are combined. The With RSA, key exchange and server authentication are combined. The
public key may be either contained in the server's certificate or public key may be either contained in the server's certificate or
may be a temporary RSA key sent in a server key exchange message. may be a temporary RSA key sent in a server key exchange message.
When temporary RSA keys are used, they are signed by the server's When temporary RSA keys are used, they are signed by the server's
RSA or DSS certificate. The signature includes the current RSA or DSS certificate. The signature includes the current
ClientHello.random, so old signatures and temporary keys cannot be ClientHello.random, so old signatures and temporary keys cannot be
replayed. Servers may use a single temporary RSA key for multiple replayed. Servers may use a single temporary RSA key for multiple
negotiation sessions. negotiation sessions.
Note: Note: The temporary RSA key option is useful if servers need large
The temporary RSA key option is useful if servers need large certificates but must comply with government-imposed size limits
certificates but must comply with government-imposed size on keys used for key exchange.
limits on keys used for key exchange.
After verifying the server's certificate, the client encrypts a After verifying the server's certificate, the client encrypts a
pre_master_secret with the server's public key. By successfully pre_master_secret with the server's public key. By successfully
decoding the pre_master_secret and producing a correct finished decoding the pre_master_secret and producing a correct finished
message, the server demonstrates that it knows the private key message, the server demonstrates that it knows the private key
corresponding to the server certificate. corresponding to the server certificate.
When RSA is used for key exchange, clients are authenticated using When RSA is used for key exchange, clients are authenticated using
the certificate verify message (see Section 5.6.8). The client signs the certificate verify message (see Section 6.4.8). The client signs
a value derived from the master_secret and all preceding handshake a value derived from the master_secret and all preceding handshake
messages. These handshake messages include the server certificate, messages. These handshake messages include the server certificate,
which binds the signature to the server, and ServerHello.random, which binds the signature to the server, and ServerHello.random,
which binds the signature to the current handshake process. which binds the signature to the current handshake process.
F.1.1.3 Diffie-Hellman key exchange with authentication F.1.1.3. Diffie-Hellman key exchange with authentication
When Diffie-Hellman key exchange is used, the server can either When Diffie-Hellman key exchange is used, the server can either
supply a certificate containing fixed Diffie-Hellman parameters or supply a certificate containing fixed Diffie-Hellman parameters or
can use the server key exchange message to send a set of temporary can use the server key exchange message to send a set of temporary
Diffie-Hellman parameters signed with a DSS or RSA certificate. Diffie-Hellman parameters signed with a DSS or RSA certificate.
Temporary parameters are hashed with the hello.random values before Temporary parameters are hashed with the hello.random values before
signing to ensure that attackers do not replay old parameters. In signing to ensure that attackers do not replay old parameters. In
either case, the client can verify the certificate or signature to either case, the client can verify the certificate or signature to
ensure that the parameters belong to the server. ensure that the parameters belong to the server.
skipping to change at page 60, line 49 skipping to change at page 62, line 6
pre_master_secret from staying in memory any longer than necessary, pre_master_secret from staying in memory any longer than necessary,
it should be converted into the master_secret as soon as possible. it should be converted into the master_secret as soon as possible.
Client Diffie- Hellman parameters must be compatible with those Client Diffie- Hellman parameters must be compatible with those
supplied by the server for the key exchange to work. supplied by the server for the key exchange to work.
If the client has a standard DSS or RSA certificate or is If the client has a standard DSS or RSA certificate or is
unauthenticated, it sends a set of temporary parameters to the unauthenticated, it sends a set of temporary parameters to the
server in the client key exchange message, then optionally uses a server in the client key exchange message, then optionally uses a
certificate verify message to authenticate itself. certificate verify message to authenticate itself.
F.1.2 Version rollback attacks F.1.2. Version rollback attacks
Because TLS includes substantial improvements over SSL Version 2.0, Because TLS includes substantial improvements over SSL Version 2.0,
attackers may try to make TLS-capable clients and servers fall back attackers may try to make TLS-capable clients and servers fall back
to Version 2.0. This attack can occur if (and only if) two to Version 2.0. This attack can occur if (and only if) two
TLS-capable parties use an SSL 2.0 handshake. TLS-capable parties use an SSL 2.0 handshake.
Although the solution using non-random PKCS #1 block type 2 message Although the solution using non-random PKCS #1 block type 2 message
padding is inelegant, it provides a reasonably secure way for padding is inelegant, it provides a reasonably secure way for
Version 3.0 servers to detect the attack. This solution is not Version 3.0 servers to detect the attack. This solution is not
secure against attackers who can brute force the key and substitute secure against attackers who can brute force the key and substitute
a new ENCRYPTED-KEY-DATA message containing the same key (but with a new ENCRYPTED-KEY-DATA message containing the same key (but with
normal padding) before the application specified wait threshold has normal padding) before the application specified wait threshold has
expired. Parties concerned about attacks of this scale should not be expired. Parties concerned about attacks of this scale should not be
using 40-bit encryption keys anyway. Altering the padding of the using 40-bit encryption keys anyway. Altering the padding of the
least-significant 8 bytes of the PKCS padding does not impact least-significant 8 bytes of the PKCS padding does not impact
security, since this is essentially equivalent to increasing the | security for the size of the signed hashes and RSA key lengths used
input block size by 8 bytes. | in the protocol, since this is essentially equivalent to increasing
| the input block size by 8 bytes.
F.1.3 Detecting attacks against the handshake protocol F.1.3. Detecting attacks against the handshake protocol
An attacker might try to influence the handshake exchange to make An attacker might try to influence the handshake exchange to make
the parties select different encryption algorithms than they would the parties select different encryption algorithms than they would
normally choose. Because many implementations will support 40-bit normally choose. Because many implementations will support 40-bit
exportable encryption and some may even support null encryption or exportable encryption and some may even support null encryption or
MAC algorithms, this attack is of particular concern. MAC algorithms, this attack is of particular concern.
For this attack, an attacker must actively change one or more For this attack, an attacker must actively change one or more
handshake messages. If this occurs, the client and server will handshake messages. If this occurs, the client and server will
compute different values for the handshake message hashes. As a compute different values for the handshake message hashes. As a
result, the parties will not accept each others' finished messages. result, the parties will not accept each others' finished messages.
Without the master_secret, the attacker cannot repair the finished Without the master_secret, the attacker cannot repair the finished
messages, so the attack will be discovered. messages, so the attack will be discovered.
F.1.4 Resuming sessions F.1.4. Resuming sessions
When a connection is established by resuming a session, new When a connection is established by resuming a session, new
ClientHello.random and ServerHello.random values are hashed with the ClientHello.random and ServerHello.random values are hashed with the
session's master_secret. Provided that the master_secret has not session's master_secret. Provided that the master_secret has not
been compromised and that the secure hash operations used to produce been compromised and that the secure hash operations used to produce
the encryption keys and MAC secrets are secure, the connection the encryption keys and MAC secrets are secure, the connection
should be secure and effectively independent from previous should be secure and effectively independent from previous
connections. Attackers cannot use known encryption keys or MAC connections. Attackers cannot use known encryption keys or MAC
secrets to compromise the master_secret without breaking the secure secrets to compromise the master_secret without breaking the secure
hash operations (which use both SHA and MD5). hash operations (which use both SHA and MD5).
skipping to change at page 62, line 5 skipping to change at page 63, line 11
Sessions cannot be resumed unless both the client and server agree. Sessions cannot be resumed unless both the client and server agree.
If either party suspects that the session may have been compromised, If either party suspects that the session may have been compromised,
or that certificates may have expired or been revoked, it should or that certificates may have expired or been revoked, it should
force a full handshake. An upper limit of 24 hours is suggested for force a full handshake. An upper limit of 24 hours is suggested for
session ID lifetimes, since an attacker who obtains a master_secret session ID lifetimes, since an attacker who obtains a master_secret
may be able to impersonate the compromised party until the may be able to impersonate the compromised party until the
corresponding session ID is retired. Applications that may be run in corresponding session ID is retired. Applications that may be run in
relatively insecure environments should not write session IDs to relatively insecure environments should not write session IDs to
stable storage. stable storage.
F.1.5 MD5 and SHA F.1.5. MD5 and SHA
TLS uses hash functions very conservatively. Where possible, both TLS uses hash functions very conservatively. Where possible, both
MD5 and SHA are used in tandem to ensure that non- catastrophic MD5 and SHA are used in tandem to ensure that non-catastrophic flaws
flaws in one algorithm will not break the overall protocol. in one algorithm will not break the overall protocol.
F.2 Protecting application data F.2. Protecting application data
The master_secret is hashed with the ClientHello.random and The master_secret is hashed with the ClientHello.random and
ServerHello.random to produce unique data encryption keys and MAC ServerHello.random to produce unique data encryption keys and MAC
secrets for each connection. secrets for each connection.
Outgoing data is protected with a MAC before transmission. To Outgoing data is protected with a MAC before transmission. To
prevent message replay or modification attacks, the MAC is computed prevent message replay or modification attacks, the MAC is computed
from the MAC secret, the sequence number, the message length, the from the MAC secret, the sequence number, the message length, the
message contents, and two fixed character strings. The message type message contents, and two fixed character strings. The message type
field is necessary to ensure that messages intended for one TLS field is necessary to ensure that messages intended for one TLS
skipping to change at page 62, line 36 skipping to change at page 63, line 42
other's output, since they use independent MAC secrets. Similarly, other's output, since they use independent MAC secrets. Similarly,
the server-write and client-write keys are independent so stream the server-write and client-write keys are independent so stream
cipher keys are used only once. cipher keys are used only once.
If an attacker does break an encryption key, all messages encrypted If an attacker does break an encryption key, all messages encrypted
with it can be read. Similarly, compromise of a MAC key can make with it can be read. Similarly, compromise of a MAC key can make
message modification attacks possible. Because MACs are also message modification attacks possible. Because MACs are also
encrypted, message-alteration attacks generally require breaking the encrypted, message-alteration attacks generally require breaking the
encryption algorithm as well as the MAC. encryption algorithm as well as the MAC.
Note: Note: MAC secrets may be larger than encryption keys, so messages can
MAC secrets may be larger than encryption keys, so messages remain tamper resistant even if encryption keys are broken.
can remain tamper resistant even if encryption keys are broken.
F.3 Final notes F.3. Final notes
For TLS to be able to provide a secure connection, both the client For TLS to be able to provide a secure connection, both the client
and server systems, keys, and applications must be secure. In and server systems, keys, and applications must be secure. In
addition, the implementation must be free of security errors. addition, the implementation must be free of security errors.
The system is only as strong as the weakest key exchange and The system is only as strong as the weakest key exchange and
authentication algorithm supported, and only trustworthy authentication algorithm supported, and only trustworthy
cryptographic functions should be used. Short public keys, 40-bit cryptographic functions should be used. Short public keys, 40-bit
bulk encryption keys, and anonymous servers should be used with bulk encryption keys, and anonymous servers should be used with
great caution. Implementations and users must be careful when great caution. Implementations and users must be careful when
skipping to change at page 63, line 19 skipping to change at page 64, line 22
This version of the TLS protocol relies on the use of patented This version of the TLS protocol relies on the use of patented
public key encryption technology for authentication and encryption. public key encryption technology for authentication and encryption.
The Internet Standards Process as defined in RFC 1310 requires a The Internet Standards Process as defined in RFC 1310 requires a
written statement from the Patent holder that a license will be made written statement from the Patent holder that a license will be made
available to applicants under reasonable terms and conditions prior available to applicants under reasonable terms and conditions prior
to approving a specification as a Proposed, Draft or Internet to approving a specification as a Proposed, Draft or Internet
Standard. The Massachusetts Institute of Technology has granted RSA Standard. The Massachusetts Institute of Technology has granted RSA
Data Security, Inc., exclusive sub-licensing rights to the following Data Security, Inc., exclusive sub-licensing rights to the following
patent issued in the United States: patent issued in the United States:
Cryptographic Communications System and Method ("RSA"), Cryptographic Communications System and Method ("RSA"), No.
No. 4,405,829 4,405,829
The Board of Trustees of the Leland Stanford Junior University have The Board of Trustees of the Leland Stanford Junior University have
granted Caro-Kann Corporation, a wholly owned subsidiary granted Caro-Kann Corporation, a wholly owned subsidiary
corporation, exclusive sub-licensing rights to the following patents corporation, exclusive sub-licensing rights to the following patents
issued in the United States, and all of their corresponding foreign issued in the United States, and all of their corresponding foreign
patents: patents:
Cryptographic Apparatus and Method ("Diffie-Hellman"), No. Cryptographic Apparatus and Method ("Diffie-Hellman"), No.
4,200,770 4,200,770
skipping to change at page 63, line 47 skipping to change at page 64, line 50
and patent applications, nor on the appropriateness of the terms of and patent applications, nor on the appropriateness of the terms of
the assurance. The Internet Society and other groups mentioned above the assurance. The Internet Society and other groups mentioned above
have not made any determination as to any other intellectual have not made any determination as to any other intellectual
property rights which may apply to the practice of this standard. property rights which may apply to the practice of this standard.
Any further consideration of these matters is the user's own Any further consideration of these matters is the user's own
responsibility. responsibility.
References References
[SSL3] Frier, Karton and Kocher, [SSL3] Frier, Karton and Kocher,
internet-draft-tls-ssl-version3-00.txt: "The SSL 3.0 Protocol", internet-draft-tls-ssl-version3-00.txt: "The SSL 3.0 Protocol", Nov
Nov 18 1996. 18 1996.
[DH1] W. Diffie and M. E. Hellman, "New Directions in Cryptography," [DH1] W. Diffie and M. E. Hellman, "New Directions in Cryptography,"
IEEE Transactions on Information Theory, V. IT-22, n. 6, Jun 1977, IEEE Transactions on Information Theory, V. IT-22, n. 6, Jun 1977,
pp. 74-84. pp. 74-84.
[3DES] W. Tuchman, "Hellman Presents No Shortcut Solutions To DES," [3DES] W. Tuchman, "Hellman Presents No Shortcut Solutions To DES,"
IEEE Spectrum, v. 16, n. 7, July 1979, pp40-41. IEEE Spectrum, v. 16, n. 7, July 1979, pp40-41.
[DES] ANSI X3.106, "American National Standard for Information [DES] ANSI X3.106, "American National Standard for Information
Systems-Data Link Encryption," American National Standards Systems-Data Link Encryption," American National Standards
skipping to change at page 64, line 51 skipping to change at page 65, line 54
[RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for [RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for
Obtaining Digital Signatures and Public-Key Cryptosystems," Obtaining Digital Signatures and Public-Key Cryptosystems,"
Communications of the ACM, v. 21, n. 2, Feb 1978, pp. 120- 126. Communications of the ACM, v. 21, n. 2, Feb 1978, pp. 120- 126.
[RSADSI] Contact RSA Data Security, Inc., Tel: 415-595-8782 [SCH] B. [RSADSI] Contact RSA Data Security, Inc., Tel: 415-595-8782 [SCH] B.
Schneier. Applied Cryptography: Protocols, Algorithms, and Source Schneier. Applied Cryptography: Protocols, Algorithms, and Source
Code in C, Published by John Wiley & Sons, Inc. 1994. Code in C, Published by John Wiley & Sons, Inc. 1994.
[SHA] NIST FIPS PUB 180-1, "Secure Hash Standard," National [SHA] NIST FIPS PUB 180-1, "Secure Hash Standard," National
Institute of Standards and Technology, U.S. Department of Commerce, Institute of Standards and Technology, U.S. Department of Commerce,
DRAFT, 31 May 1994. [TCP] ISI for DARPA, RFC 793: Transport Control DRAFT, 31 May 1994.
Protocol, September 1981.
[TEL] J. Postel and J. Reynolds, RFC 854/5, May, 1993. [X509] CCITT. [TCP] ISI for DARPA, RFC 793: Transport Control Protocol, September
Recommendation X.509: "The Directory - Authentication Framework". 1981.
1988.
[TEL] J. Postel and J. Reynolds, RFC 854/5, May, 1993.
[X509] CCITT. Recommendation X.509: "The Directory - Authentication
Framework". 1988.
[XDR] R. Srinivansan, Sun Microsystems, RFC-1832: XDR: External Data [XDR] R. Srinivansan, Sun Microsystems, RFC-1832: XDR: External Data
Representation Standard, August 1995. Representation Standard, August 1995.
Credits
Working Group Chair Working Group Chair
Win Treese Win Treese
Open Market Open Market
treeseopenmarket.com treeseopenmarket.com
Editors Editors
Tim Dierks Christopher Allen Tim Dierks Christopher Allen
Consensus Development Consensus Development Consensus Development Consensus Development
skipping to change at page 66, line 22 skipping to change at page 67, line 32
Stuart Haber Don Stephenson Stuart Haber Don Stephenson
Bellcore Sun Microsystems Bellcore Sun Microsystems
stuart@bellcore.com don.stephenson@eng.sun.com stuart@bellcore.com don.stephenson@eng.sun.com
Burt Kaliski Joe Tardo Burt Kaliski Joe Tardo
RSA Data Security, Inc. General Magic RSA Data Security, Inc. General Magic
burt@rsa.com tardo@genmagic.com burt@rsa.com tardo@genmagic.com
Comments Comments
Comments on this draft should be sent to the editors, Tim Comments on this draft should be sent to the editors, Tim Dierks
Dierks <timd@consensus.com> and Christopher Allen <timd@consensus.com> and Christopher Allen
<christophera@consensus.com>, or to the IETF Transport Layer <christophera@consensus.com>, or to the IETF Transport Layer
Security (TLS) Working Group. Security (TLS) Working Group.
The discussion list for IETF-TLS is at IETF-TLS@W3.ORG. You The discussion list for IETF-TLS is at IETF-TLS@W3.ORG. You
subscribe and unsubscribe by sending to IETF-TLS-REQUEST@W3.ORG subscribe and unsubscribe by sending to IETF-TLS-REQUEST@W3.ORG with
with subscribe or unsubscribe in the SUBJECT of the message. subscribe or unsubscribe in the SUBJECT of the message.
Archives of the list are at Archives of the list are at:
<http://lists.w3.org/Archives/Public/ietf-tls> <http://lists.w3.org/Archives/Public/ietf-tls>
 End of changes. 

This html diff was produced by rfcdiff 1.23, available from http://www.levkowetz.com/ietf/tools/rfcdiff/