draft-ietf-tls-protocol-02.txt   draft-ietf-tls-protocol-03.txt 
Transport Layer Security Working Group Tim Dierks Transport Layer Security Working Group Tim Dierks
INTERNET-DRAFT Consensus Development INTERNET-DRAFT Consensus Development
Expires September 22, 1997 Christopher Allen Expires September 22, 1997 Christopher Allen
Consensus Development Consensus Development
March 24, 1997 May 21, 1997
The TLS Protocol The TLS Protocol
Version 1.0 Version 1.0
<draft-ietf-tls-protocol-02.txt> <draft-ietf-tls-protocol-03.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 23 skipping to change at page 2, line 23
4. Presentation language 5 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 8 4.6.1. Variants 8
4.7. Cryptographic attributes 9 4.7. Cryptographic attributes 9
4.8. Constants 10 4.8. Constants 10
5. The TLS Record Protocol 11 5. HMAC and the pseudorandom function 11
5.1. Connection states 11 6. The TLS Record Protocol 12
5.2. HMAC and the pseudorandom function 14 6.1. Connection states 13
5.3. Record layer 15 6.2. Record layer 15
5.3.1. Fragmentation 15 6.2.1. Fragmentation 15
5.3.2. Record compression and decompression 16 6.2.2. Record compression and decompression 16
5.3.3. Record payload protection 17 6.2.3. Record payload protection 17
5.3.3.1. Null or standard stream cipher 17 6.2.3.1. Null or standard stream cipher 18
5.3.3.2. CBC block cipher 18 6.2.3.2. CBC block cipher 18
5.4. Key calculation 19 6.3. Key calculation 19
5.4.1. Export key generation example 21 6.3.1. Export key generation example 21
6. The TLS Handshake Protocol 21 7. The TLS Handshake Protocol 21
6.1. Change cipher spec protocol 22 7.1. Change cipher spec protocol 22
6.2. Alert protocol 22 7.2. Alert protocol 23
6.2.1. Closure alerts 23 7.2.1. Closure alerts 24
6.2.2. Error alerts 24 7.2.2. Error alerts 24
6.3. Handshake Protocol overview 26 7.3. Handshake Protocol overview 27
6.4. Handshake protocol 29 7.4. Handshake protocol 29
6.4.1. Hello messages 30 7.4.1. Hello messages 30
6.4.1.1. Hello request 30 7.4.1.1. Hello request 30
6.4.1.2. Client hello 31 7.4.1.2. Client hello 31
6.4.1.3. Server hello 33 7.4.1.3. Server hello 33
6.4.2. Server certificate 34 7.4.2. Server certificate 34
6.4.3. Server key exchange message 36 7.4.3. Server key exchange message 36
6.4.4. Certificate request 38 7.4.4. Certificate request 38
6.4.5. Server hello done 39 7.4.5. Server hello done 39
6.4.6. Client certificate 39 7.4.6. Client certificate 39
6.4.7. Client key exchange message 40 7.4.7. Client key exchange message 40
6.4.7.1. RSA encrypted premaster secret message 40 7.4.7.1. RSA encrypted premaster secret message 40
6.4.7.2. Client Diffie-Hellman public value 41 7.4.7.2. Client Diffie-Hellman public value 41
6.4.8. Certificate verify 41 7.4.8. Certificate verify 42
6.4.9. Finished 42 7.4.9. Finished 42
7. Cryptographic computations 43 8. Cryptographic computations 43
7.1. Computing the master secret 43 8.1. Computing the master secret 43
7.1.1. RSA 44 8.1.1. RSA 44
7.1.2. Diffie-Hellman 44 8.1.2. Diffie-Hellman 44
8. Application data protocol 44 9. Application data protocol 44
A. Protocol constant values 44 A. Protocol constant values 44
A.1. Reserved port assignments 44 A.1. Reserved port assignments 44
A.2. Record layer 45 A.2. Record layer 45
A.3. Change cipher specs message 46 A.3. Change cipher specs message 46
A.4. Alert messages 46 A.4. Alert messages 46
A.5. Handshake protocol 46 A.5. Handshake protocol 47
A.5.1. Hello messages 47 A.5.1. Hello messages 47
A.5.2. Server authentication and key exchange messages 47 A.5.2. Server authentication and key exchange messages 48
A.5.3. Client authentication and key exchange messages 49 A.5.3. Client authentication and key exchange messages 49
A.5.4. Handshake finalization message 49 A.5.4. Handshake finalization message 50
A.6. The CipherSuite 49 A.6. The CipherSuite 50
A.7. The Security Parameters 51 A.7. The Security Parameters 51
B. Glossary 51 B. Glossary 52
C. CipherSuite definitions 55 C. CipherSuite definitions 55
D. Implementation Notes 57 D. Implementation Notes 57
D.1. Temporary RSA keys 57 D.1. Temporary RSA keys 58
D.2. Random Number Generation and Seeding 57 D.2. Random Number Generation and Seeding 58
D.3. Certificates and authentication 58 D.3. Certificates and authentication 59
D.4. CipherSuites 58 D.4. CipherSuites 59
E. Backward Compatibility With SSL 58 E. Backward Compatibility With SSL 59
E.1. Version 2 client hello 59 E.1. Version 2 client hello 60
E.2. Avoiding man-in-the-middle version rollback 61 E.2. Avoiding man-in-the-middle version rollback 61
F. Security analysis 61 F. Security analysis 62
F.1. Handshake protocol 61 F.1. Handshake protocol 62
F.1.1. Authentication and key exchange 61 F.1.1. Authentication and key exchange 62
F.1.1.1. Anonymous key exchange 62 F.1.1.1. Anonymous key exchange 63
F.1.1.2. RSA key exchange and authentication 62 F.1.1.2. RSA key exchange and authentication 63
F.1.1.3. Diffie-Hellman key exchange with authentication 63 F.1.1.3. Diffie-Hellman key exchange with authentication 64
F.1.2. Version rollback attacks 63 F.1.2. Version rollback attacks 64
F.1.3. Detecting attacks against the handshake protocol 64 F.1.3. Detecting attacks against the handshake protocol 65
F.1.4. Resuming sessions 64 F.1.4. Resuming sessions 65
F.1.5. MD5 and SHA 64 F.1.5. MD5 and SHA 65
F.2. Protecting application data 65 F.2. Protecting application data 65
F.3. Final notes 65 F.3. Final notes 66
G. Patent Statement 65 G. Patent Statement 66
References 66 References 67
Credits 68 Credits 69
Comments 69 Comments 70
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 data
reliability between two communicating applications. The protocol is | integrity 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 without encryption. Protocol can also be used without encryption.
- The connection is reliable. Message transport includes a message - The connection is reliable. Message transport includes a message
integrity check using a keyed MAC. Secure hash functions (e.g., integrity check using a keyed MAC. Secure hash functions (e.g.,
SHA, MD5, etc.) are used for MAC computations. The Record SHA, MD5, etc.) are used for MAC computations. The Record
Protocol can operate without a MAC, but is generally only used Protocol can operate without a MAC, but is generally only used
in this mode while another protocol is using the Record Protocol in this mode while another protocol is using the Record Protocol
as a transport for negotiating security parameters. as a transport for negotiating 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
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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.). This public key, cryptography (e.g., RSA[RSA], DSS[DSS], etc.). This
authentication can be made optional, but is generally required authentication can be made optional, but is generally 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 any secret is unavailable to eavesdroppers, and for any
| authenticated connection the secret cannot be obtained, even by authenticated connection the secret cannot be obtained, even by
| an attacker who can place himself in the middle of the an attacker who can place himself in the middle of the
| connection. 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 parties negotiation communication without being detected by the parties
| to the communication. 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.
| Higher level protocols can layer on top of the TLS Protocol ] Higher level protocols can layer on top of the TLS Protocol
] transparently. The TLS standard, however, does not specify how ] transparently. The TLS standard, however, does not specify how
] protocols add security with TLS; the decisions on how to initiate ] protocols add security with TLS; the decisions on how to initiate
] TLS handshaking and how to interpret the authentication certificates ] TLS handshaking and how to interpret the authentication certificates
] exchanged are left up to the judgement of the designers and ] exchanged are left up to the judgment of the designers and
] implementors of protocols which run on top of TLS. ] implementors of protocols which run on top of TLS.
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: TLS should be used to establish a secure 1. Cryptographic security: TLS should be used to establish a secure
connection between two parties. connection between two parties.
2. Interoperability: Independent programmers should be able to 2. Interoperability: Independent programmers should be able to
develop applications utilizing TLS that will then be able to develop applications utilizing TLS that will then be able to
successfully exchange cryptographic parameters without knowledge successfully exchange cryptographic parameters without knowledge
of one another's code. of one another's code.
Note: It is not the case that all instances of TLS (even in the same Note: 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. There is no required set of ciphers ] connection will not succeed. There is no required set of ciphers
| for minimal compliance, so some implementations may be unable to ] for minimal compliance, so some implementations may be unable to
| communicate. ] communicate.
3. Extensibility: TLS seeks to provide a framework into which new 3. Extensibility: TLS seeks to provide a framework into which new
public key and bulk encryption methods can be incorporated as public key and bulk encryption methods can be incorporated as
necessary. This will also accomplish two sub-goals: to prevent necessary. This will also accomplish two sub-goals: to prevent
the need to create a new protocol (and risking the introduction the need to create a new protocol (and risking the introduction
of possible new weaknesses) and to avoid the need to implement of possible new weaknesses) and to avoid the need to implement
an entire new security library. an entire new security library.
4. Relative efficiency: Cryptographic operations tend to be highly 4. Relative efficiency: Cryptographic operations tend to be highly
CPU intensive, particularly public key operations. For this CPU intensive, particularly public key operations. For this
reason, the TLS protocol has incorporated an optional session reason, the TLS protocol has incorporated an optional session
caching scheme to reduce the number of connections that need to caching scheme to reduce the number of connections that need to
be established from scratch. Additionally, care has been taken be established from scratch. Additionally, care has been taken
to reduce network activity. to reduce network activity.
3. Goals of this document 3. Goals of this document
| This document and the TLS protocol itself are based on the SSL 3.0 ] This document and the TLS protocol itself are based on the SSL 3.0
| Protocol Specification as published by Netscape. The differences ] Protocol Specification as published by Netscape. The differences
| between this protocol and SSL 3.0 are not dramatic, but they are ] between this protocol and SSL 3.0 are not dramatic, but they are
| significant enough that TLS 1.0 and SSL 3.0 do not interoperate ] significant enough that TLS 1.0 and SSL 3.0 do not interoperate
| (although TLS 1.0 does incorporate a mechanism by which a TLS ] (although TLS 1.0 does incorporate a mechanism by which a TLS
| implementation can back down to SSL 3.0). This document is intended ] implementation can back down to SSL 3.0). This document is intended
| primarily for readers who will be implementing the protocol and ] primarily for readers who will be implementing the protocol and
| those doing cryptographic analysis of it. The spec has been written ] those doing cryptographic analysis of it. The specification has been
| with this in mind, and it is intended to reflect the needs of those ] written with this in mind, and it is intended to reflect the needs
| two groups. For that reason, many of the algorithm-dependent data ] of those two groups. For that reason, many of the
| structures and rules are included in the body of the text (as ] algorithm-dependent data structures and rules are included in the
| opposed to in an Appendix), providing easier access to them. ] 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
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length field of zero is referred to as an empty vector. length field of zero is referred to as an empty vector.
T T'<floor..ceiling>; T T'<floor..ceiling>;
In the following example, mandatory is a vector that must contain In the following example, mandatory is a vector that must contain
between 300 and 400 bytes of type opaque. It can never be empty. The between 300 and 400 bytes of type opaque. It can never be empty. The
actual length field consumes two bytes, a uint16, sufficient to actual length field consumes two bytes, a uint16, sufficient to
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. The length of an encoded vector must
| be an even multiple of the length of a single element (for example,
| a 17 byte vector of uint16 would be illegal).
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];
| All values, here and elsewhere in the specification, are stored in ] All values, here and elsewhere in the specification, are stored in
| "network" or "big-endian" order; the uint32 represented by the hex ] "network" or "big-endian" order; the uint32 represented by the hex
| bytes 01 02 03 04 is equivalent to the decimal value 16909060. ] bytes 01 02 03 04 is equivalent to the decimal value 16909060.
4.5. Enumerateds 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.
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For example, For example,
struct { struct {
uint8 f1; uint8 f1;
uint8 f2; uint8 f2;
} Example1; } Example1;
Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */ Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */
5. The TLS Record Protocol 5. 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 in the handshake with two different algorithms: MD5 and
] SHA-1, denoting these as HMAC_MD5(secret, data) and HMAC_SHA(secret,
] data). Additional hash algorithms can be defined by cipher suites
] and used to protect record data, but MD5 and SHA-1 are hard coded
] into the description of the handshaking for this version of the
] protocol.
] In addition, a construction is required to do expansion of secrets
] into blocks of data for the purposes of key generation or
] validation. This pseudo-random function (PRF) takes as input a
| secret, a seed, and an identifying label and produces an output of
| arbitrary length.
] In order to make the PRF as secure as possible, it uses two hash
] algorithms in a way which should guarantee its security if either
] algorithm remains secure.
] First, we define a data expansion function, P_hash(secret, data)
] which uses a single hash function to expand a secret and seed into
] an arbitrary quantity of output:
] P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +
] HMAC_hash(secret, A(2) + seed) +
] HMAC_hash(secret, A(3) + seed) + ...
] Where + indicates concatenation.
] A() is defined as:
] A(0) = seed
] A(i) = HMAC_hash(secret, A(i-1))
] P_hash can be iterated as many times as is necessary to produce the
] required quantity of data. For example, if P_SHA-1 was being used to
] create 64 bytes of data, it would have to be iterated 4 times
] (through A(4)), creating 80 bytes of output data; the last 16 bytes
] of the final iteration would then be discarded, leaving 64 bytes of
] output data.
] TLS's PRF is created by splitting the secret into two halves and
] using one half to generate data with P_MD5 and the other half to
] generate data with P_SHA1, then exclusive-or'ing the outputs of
] these two expansion functions together.
] S1 and S2 are the two halves of the secret and each is the same
] length. S1 is taken from the first half of the secret, S2 from the
] second half. Their length is created by rounding up the length of
] the overall secret divided by two; thus, if the original secret is
] an odd number of bytes long, the last byte of S1 will be the same as
] the first byte of S2.
] L_S = length in bytes of secret;
] L_S1 = L_S2 = ceil(L_S / 2);
] The secret is partitioned into two halves (with the possibility of
] one shared byte) as described above, S1 taking the first L_S1 bytes
] and S2 the last L_S2 bytes.
] The PRF is then defined as the result of mixing the two pseudorandom
] streams by exclusive-or'ing them together.
| PRF(secret, label, seed) = P_MD5(S1, label + seed) XOR
| P_SHA-1(S2, label + seed);
] Note that because MD5 produces 16 byte outputs and SHA-1 produces 20
] byte outputs, the boundaries of their internal iterations will not
] be aligned; to generate a 80 byte output will involve P_MD5 being
] iterated through A(5), while P_SHA-1 will only iterate through A(4).
6. 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.
| Four record protocol clients are described in this document: the ] Four record protocol clients are described in this document: the
| handshake protocol, the alert protocol, the change cipher spec ] handshake protocol, the alert protocol, the change cipher spec
| protocol, and the application data protocol. In order to allow ] protocol, and the application data protocol. In order to allow
| extension of the TLS protocol, additional record types can be ] extension of the TLS protocol, additional record types can be
| supported by the record protocol. Any new record types should ] 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.
5.1. Connection states ] 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.
| Note that because the type and length of a record are not protected
| by encryption, care should be take to minimize the value of traffic
| analysis of these values.
6.1. Connection states
A TLS connection state is the operating environment of the TLS 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
the appropriate current state is disposed of and replaced with the the appropriate current state is disposed of and replaced with the
pending state; the pending state is then reinitialized to an empty pending state; the pending state is then reinitialized to an empty
state. It is illegal to make a state which has not been initialized state. It is illegal to make a state which has not been initialized
with security parameters a current state (although those security | with security parameters a current state. The initial current state
parameters may specify that no compression, encryption or MAC | always specifies that no encryption, compression, or MAC will be
algorithm is to be used). The initial current state always specifies | 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 specification An algorithm to be used for bulk encryption. This specification
includes the key size of this algorithm, how much of that key is includes the key size of this algorithm, how much of that key is
secret, whether it is a block or stream cipher, the block size secret, whether it is a block or stream cipher, the block size
of the cipher (if appropriate), and whether it is considered an of the cipher (if appropriate), and 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 which is returned by specification includes the size of the hash which is returned by
| the MAC algorithm. the MAC algorithm.
compression algorithm compression algorithm
An algorithm to be used for data compression. This specification An algorithm to be used for data compression. This specification
must include all information the algorithm requires to do must include all information the algorithm requires to do
compression. compression.
master secret master secret
A 48 byte secret shared between the two peers in the connection. A 48 byte secret shared between the two peers in the connection.
client random client random
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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 5.4. section 6.3.
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 consist The current state of the encryption algorithm. This will consist
of the scheduled key for that connection. In addition, for block of the scheduled key for that connection. In addition, for block
| ciphers running in CBC mode, this will initially contain the IV | ciphers running in CBC mode (the only mode specified for TLS),
| for that connection state and be updated to contain the | this will initially contain the IV for that connection state and
| ciphertext of the last block encrypted or decrypted as records | be updated to contain the ciphertext of the last block encrypted
| are processed. For block ciphers in other modes, whatever state | or decrypted as records are processed. For stream ciphers, this
| is necessary to sustain encryption or decryption must be | will contain whatever the necessary state information is to
| maintained. For stream ciphers, this will contain whatever the | allow the stream to continue to encrypt or decrypt data.
| 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 separately 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. HMAC and the pseudorandom function 6.2. Record layer
| 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 in the handshake with two different algorithms: MD5 and
] SHA-1, denoting these as HMAC_MD5(secret, data) and HMAC_SHA(secret,
] data). Additional hash algorithms can be defined by cipher suites
] and used to protect record data, but these hashes are hard coded
] into the description of the handshaking for this version of the
] protocol.
] In addition, a construction is required to do expansion of secrets
] into blocks of data for the purposes of key generation or
] validation. This pseudo-random function (PRF) takes as input a
] secret and a seed and produces an output of arbitrary length.
] In order to make the PRF as secure as possible, it uses two hash
] algorithms in a way which should guarantee its security if either
] algorithm remains secure.
] First, we define a data expansion function, P_hash(secret, data)
] which uses a single hash function to expand a secret and seed into
] an arbitrary quantity of output:
] P_hash(secret, seed) = HMAC_hash(secret, A(1) + data) +
] HMAC_hash(secret, A(2) + data) +
] HMAC_hash(secret, A(3) + data) + ...
] Where + indicates concatenation.
] A() is defined as:
] A(0) = seed
] A(i) = HMAC_hash(secret, A(i-1))
] P_hash can be iterated as many times as is necessary to produce the
] required quantity of data. For example, if P_SHA-1 was being used to
] create 64 bytes of data, it would have to be iterated 4 times
] (through A(4)), creating 80 bytes of output data; the last 16 bytes
] of the final iteration would then be discarded, leaving 64 bytes of
] output data.
] TLS's PRF is created by splitting the secret into two halves and
] using one half to generate data with P_MD5 and the other half to
] generate data with P_SHA1, then exclusive-or'ing the outputs of
] these two expansion functions together.
] S1 and S2 are the two halves of the secret and each is the same
] length. S1 is taken from the first half of the secret, S2 from the
] second half. Their length is created by rounding up the length of
] the overall secret divided by two; thus, if the original secret is
] an odd number of bytes long, the last byte of S1 will be the same as
] the first byte of S2.
] L_S = length in bytes of secret;
] L_S1 = L_S2 = ceil(L_S / 2);
] The secret is partitioned into two halves (with the possibility of
] one shared byte) as described above, S1 taking the first L_S1 bytes
] and S2 the last L_S2 bytes.
] The PRF is then defined as the result of mixing the two pseudorandom
] streams by exclusive-or'ing them together.
] PRF(secret, seed) = P_MD5(S1, seed) XOR P_SHA-1(S2, seed);
] Note that because MD5 produces 16 byte outputs and SHA-1 produces 20
] byte outputs, the boundaries of their internal iterations will not
] be aligned; to generate a 80 byte output will involve P_MD5 being
] iterated through A(5), while P_SHA-1 will only iterate through A(4).
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.
5.3.1. Fragmentation 6.2.1. 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 a single message may be fragmented across several records).
struct { struct {
uint8 major, minor; uint8 major, minor;
} ProtocolVersion; } ProtocolVersion;
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;
opaque fragment[TLSPlaintext.length]; opaque fragment[TLSPlaintext.length];
} TLSPlaintext; } TLSPlaintext;
type type
The higher level protocol used to process the enclosed fragment. The higher level protocol used to process the enclosed fragment.
skipping to change at page 16, line 16 skipping to change at page 16, line 26
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 fragment. The higher level protocol used to process the enclosed 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, 1 }. The ] describes TLS Version 1.0, which uses the version { 3, 1 }. The
| version value 3.1 is historical: TLS version 1.0 is a minor ] version value 3.1 is historical: TLS version 1.0 is a minor
| modification to the SSL 3.0 protocol, which bears the version ] modification to the SSL 3.0 protocol, which bears the version
| value 3.0. (See Appendix A.1.1). ] 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 an The application data. This data is transparent and treated as an
independent block to be dealt with by the higher level protocol independent block to be dealt with by the higher level protocol
specified by the type field. specified by the type field.
Note: Data of different TLS Record layer content types may be Note: 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.
5.3.2. Record compression and decompression 6.2.2. 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 a CompressionMethod.null. The compression algorithm translates a
TLSPlaintext structure into a 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
skipping to change at page 17, line 18 skipping to change at page 17, line 27
fragment fragment
The compressed form of TLSPlaintext.fragment. The compressed form of TLSPlaintext.fragment.
Note: A CompressionMethod.null operation is an identity operation; no Note: A CompressionMethod.null operation is an identity operation; no
fields are altered. fields are altered.
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.
5.3.3. Record payload protection 6.2.3. Record payload protection
The encryption and MAC functions translate a TLSCompressed structure The encryption and MAC functions translate a TLSCompressed structure
into a TLSCiphertext. The decryption functions reverse the process. into a TLSCiphertext. The decryption functions reverse the process.
Transmissions also include a sequence number so that missing, | Transmissions also include a sequence number so that missing, extra
altered, or extra messages are detectable. | or repeated 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 17, line 48 skipping to change at page 18, 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.
5.3.3.1. Null or standard stream cipher 6.2.3.1. 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:
| HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.version + | HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.type +
| TLSCompressed.type + TLSCompressed.length + | TLSCompressed.version + TLSCompressed.length +
| TLSCompressed.fragment)); TLSCompressed.fragment));
where "+" denotes concatenation. where "+" denotes concatenation.
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.
5.3.3.2. CBC block cipher 6.2.3.2. 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 6.2.3.1.
The MAC is generated as described in Section 5.3.3.1.
padding padding
Padding that is added to force the length of the plaintext to be Padding that is added to force the length of the plaintext to be
| an even multiple of the block cipher's block length. The padding ] 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 ] 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 ] the TLSCiphertext.length being an even multiple of the block
| length. Lengths longer than necessary might be desirable to ] length. Lengths longer than necessary might be desirable to
| frustrate attacks on a protocol based on analysis of the lengths ] frustrate attacks on a protocol based on analysis of the lengths
| of exchanged messages. Each uint8 in the padding data vector
| of exchanged messages. The padding data must be filled with the | must be filled with the padding length value.
| 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 padding length should be such that the total size of the
length and may be zero. The padding length should be such that | GenericBlockCipher structure is a multiple of the cipher's block
the total size of the GenericBlockCipher structure is a multiple | length. Legal values range from zero to 255, inclusive.
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.
Example: If the block length is 8 bytes, the content length Example: If the block length is 8 bytes, the content length
| (TLSCompressed.length) is 61 bytes, and the MAC length is 20 ] (TLSCompressed.length) is 61 bytes, and the MAC length is 20
| bytes, the length before padding is 82 bytes. Thus, the ] bytes, the length before padding is 82 bytes. Thus, the
| padding length modulo 8 must be equal to 6 in order to make ] padding length modulo 8 must be equal to 6 in order to make
| the total length an even multiple of 8 bytes (the block ] the total length an even multiple of 8 bytes (the block
| length). The padding length can be 6, 14, 22, and so on, ] length). The padding length can be 6, 14, 22, and so on,
| through 254. If the padding length were the minimum necessary, ] through 254. If the padding length were the minimum necessary,
| 6, the padding would be 6 bytes, each containing the value 6. ] 6, the padding would be 6 bytes, each containing the value 6.
|Note: With block ciphers in CBC mode (Cipher Block Chaining) the Note: With block ciphers in CBC mode (Cipher Block Chaining) the
initialization vector (IV) for the first record is generated initialization vector (IV) for the first record is generated
with the other keys and secrets when the security parameters are with the other keys and secrets when the security parameters are
set. The IV for subsequent records is the last ciphertext block set. The IV for subsequent records is the last ciphertext block
from the previous record. from the previous record.
5.4. Key calculation 6.3. 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 = PRF(SecurityParameters.master_secret, ] key_block = PRF(SecurityParameters.master_secret,
| "key expansion",
] SecurityParameters.server_random + ] SecurityParameters.server_random +
] SecurityParameters.client_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] client_write_IV[SecurityParameters.IV_size]
server_write_IV[SecurityParameters.IV_size] server_write_IV[SecurityParameters.IV_size]
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The client_write_IV and server_write_IV are only generated for The client_write_IV and server_write_IV are only generated for
non-export block ciphers. For exportable block ciphers, the non-export block ciphers. For exportable block ciphers, the
initialization vectors are generated later, as described below. Any initialization vectors are generated later, as described below. Any
extra key_block material is discarded. extra key_block material is discarded.
Implementation note: Implementation note:
The cipher spec which is defined in this document which requires The cipher spec which is defined in this document which requires
the most material is 3DES_EDE_CBC_SHA: it requires 2 x 24 byte the most material is 3DES_EDE_CBC_SHA: it requires 2 x 24 byte
keys, 2 x 20 byte MAC secrets, and 2 x 8 byte IVs, for a total keys, 2 x 20 byte MAC secrets, and 2 x 8 byte IVs, for a total
] of 104 bytes of key material. | of 104 bytes of key material.
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 = ] final_client_write_key =
| PRF(SecurityParameters.client_write_key, ] PRF(SecurityParameters.client_write_key,
| SecurityParameters.client_random + | "client write key",
| SecurityParameters.server_random); ] SecurityParameters.client_random +
| final_server_write_key = ] SecurityParameters.server_random);
| PRF(SecurityParameters.server_write_key, ] final_server_write_key =
| SecurityParameters.client_random + ] PRF(SecurityParameters.server_write_key,
| SecurityParameters.server_random); | "server write key",
] SecurityParameters.client_random +
] SecurityParameters.server_random);
| Exportable encryption algorithms derive their IVs solely from the ] Exportable encryption algorithms derive their IVs solely from the
] random values from the hello messages: ] random values from the hello messages:
| iv_block = PRF("", SecurityParameters.client_random + | iv_block = PRF("", "IV block", SecurityParameters.client_random
| SecurityParameters.server_random); ] + SecurityParameters.server_random);
| The iv_block is partitioned into two initialization vectors as the ] The iv_block is partitioned into two initialization vectors as the
| key_block was above: ] key_block was above:
| client_write_IV[SecurityParameters.IV_size] ] client_write_IV[SecurityParameters.IV_size]
| server_write_IV[SecurityParameters.IV_size] ] server_write_IV[SecurityParameters.IV_size]
| Note that the PRF is used without a secret in this case: this just ] 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 ] means that the secret has a length of zero bytes and contributes
| nothing to the hashing in the PRF. ] nothing to the hashing in the PRF.
5.4.1. Export key generation example 6.3.1. 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. The PRF output is | keys, for a total of 42 bytes of key material. The PRF output is
] stored in the key_block. The key_block is partitioned, and the write | stored in the key_block. The key_block is partitioned, and the write
] keys are salted because this is an exportable encryption algorithm. | keys are salted because this is an exportable encryption algorithm.
| key_block = PRF(master_secret, ] key_block = PRF(master_secret,
| master_secret + | "key expansion",
| server_random + ] master_secret +
| client_random)[0..41] ] 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 = PRF(client_write_key, ] final_client_write_key = PRF(client_write_key,
| client_random + | "client write key",
| server_random)[0..15] ] client_random +
| final_server_write_key = PRF(server_write_key, ] server_random)[0..15]
| client_random + ] final_server_write_key = PRF(server_write_key,
| server_random)[0..15] | "server write key",
| iv_block = PRF("", client_random + ] client_random +
| server_random)[0..15] ] server_random)[0..15]
| client_write_IV = iv_block[0..7] | iv_block = PRF("", "IV block", client_random +
| server_write_IV = iv_block[8..15] ] server_random)[0..15]
] client_write_IV = iv_block[0..7]
] server_write_IV = iv_block[8..15]
6. The TLS Handshake Protocol 7. 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:
skipping to change at page 22, line 19 skipping to change at page 22, line 37
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 7.1. 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;
The change cipher spec message is sent by both the client and server The change cipher spec message is sent by both the client and server
to notify the receiving party that subsequent records will be to notify the receiving party that subsequent records will be
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 6.1.) 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). 7.4.9).
6.2. Alert protocol 7.2. 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), ] decryption_failed(21),
| record_overflow(22), ] record_overflow(22),
decompression_failure(30), decompression_failure(30),
handshake_failure(40), handshake_failure(40),
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), ] unknown_ca(48),
| access_denied(49), ] access_denied(49),
| decode_error(50), ] decode_error(50),
| decrypt_error(51), ] decrypt_error(51),
| export_restriction(60), ] export_restriction(60),
| protocol_version(70), ] protocol_version(70),
| insufficient_security(71), ] insufficient_security(71),
| internal_error(80), ] internal_error(80),
| user_canceled(90), ] user_canceled(90),
| no_renegotiation(100), ] no_renegotiation(100),
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
6.2.1. Closure alerts 7.2.1. 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.
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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: It is assumed that closing a connection reliably delivers NB: 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 7.2.2. 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 incorrect This alert is returned if a record is received with an incorrect
MAC. This message is always fatal. MAC. This message is always fatal.
| decryption_failed ] decryption_failed
| A TLSCiphertext decrypted in an invalid way: either it wasn`t an ] A TLSCiphertext decrypted in an invalid way: either it wasn`t an
| even multiple of the block length or its padding values, when ] even multiple of the block length or its padding values, when
| checked, weren`t correct. This message is always fatal. ] checked, weren`t correct. This message is always fatal.
| record_overflow ] record_overflow
| A TLSCiphertext record was received which had a length more than ] A TLSCiphertext record was received which had a length more than
| 2^14+2048 bytes, or a record decrypted to a TLSCompressed record ] 2^14+2048 bytes, or a record decrypted to a TLSCompressed record
| with more than 2^14+1024 bytes. This message is always fatal.
] 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 security the sender was unable to negotiate an acceptable set of security
parameters given the options available. This is a fatal error. parameters given the options available. This is a fatal error.
no_certificate
A no_certificate alert message may be sent in response to a
certification request if no appropriate certificate is
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.
unsupported_certificate unsupported_certificate
A certificate was of an unsupported type. A certificate was of an unsupported type.
certificate_revoked certificate_revoked
A certificate was revoked by its signer. A certificate was revoked by its signer.
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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 ] unknown_ca
| A valid certificate chain or partial chain was received, but the ] A valid certificate chain or partial chain was received, but the
| certificate was not accepted because the CA certificate could ] certificate was not accepted because the CA certificate could
| not be located or couldn`t be matched with a known, trusted CA. ] not be located or couldn`t be matched with a known, trusted CA.
| This message is always fatal. ] This message is always fatal.
| access_denied ] access_denied
| A valid certificate was received, but when access control was ] A valid certificate was received, but when access control was
| applied, the sender decided not to proceed with negotiation. ] applied, the sender decided not to proceed with negotiation.
| This message is always fatal. ] This message is always fatal.
| decode_error ] decode_error
| A message could not be decoded because some field was out of the ] A message could not be decoded because some field was out of the
| specified range or the length of the message was incorrect. This ] specified range or the length of the message was incorrect. This
| message is always fatal. ] message is always fatal.
| export_restriction | decrypt_error
| A negotiation not in compliance with export restrictions was | A handshake cryptographic operation failed, including being
| detected; for example, attemption to transfer a 1024 bit | unable to correctly verify a signature, decrypt a key exchange,
| ephemeral RSA key for the RSA_EXPORT handshake method. This
| message is always fatal.
| protocol_version | or validate a finished message.
| 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 ] export_restriction
| Returned instead of handshake_failure when a negotiation has ] A negotiation not in compliance with export restrictions was
| failed specifically because the server requires ciphers more ] detected; for example, attempting to transfer a 1024 bit
| secure than those supported by the client. This message is ] ephemeral RSA key for the RSA_EXPORT handshake method. This
| always fatal. ] message is always fatal.
| internal_error ] protocol_version
| An internal error unrelated to the peer or the correctness of ] The protocol version the client has attempted to negotiate is
| the protocol makes it impossible to continue (such as a memory ] recognized, but not supported. (For example, old protocol
| allocation failure). This message is always fatal. ] versions might be avoided for security reasons). This message is
] always fatal.
| user_cancelled ] insufficient_security
| This handshake is being cancelled for some reason unrelated to a ] Returned instead of handshake_failure when a negotiation has
| protocol failure. If the user cancels an operation after the ] failed specifically because the server requires ciphers more
| handshake is complete, just closing the connection by sending a ] secure than those supported by the client. This message is
| close_notify is more appropriate. This alert should be followed ] always fatal.
| by a close_notify. This message is generally a warning.
| no_renegotiation ] internal_error
| Sent by the client in response to a hello request or by the ] An internal error unrelated to the peer or the correctness of
| server in response to a client hello after initial handshaking. ] the protocol makes it impossible to continue (such as a memory
| Either of these would normally lead to renegotiation; when that ] allocation failure). This message is always fatal.
| is not appropriate, the reciepient should respond with this
| alert; at that point, the original reqester can decide whether ] user_canceled
| to proceed with the connection. One case where this would be ] This handshake is being canceled for some reason unrelated to a
| appropriate would be where a server has spawned a process to ] protocol failure. If the user cancels an operation after the
| satisfy a request; the process might receive secuirty parameters ] handshake is complete, just closing the connection by sending a
| (key length, authentication, etc.) at startup and it might be ] close_notify is more appropriate. This alert should be followed
| difficult to communicate changes to these parameters after that ] by a close_notify. This message is generally a warning.
| point. This message is always 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 recipient should respond with this
] alert; at that point, the original requester 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 security 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 7.3. 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 the following goals: | The TLS Handshake Protocol involves the following steps:
- Exchange hello messages to agree on algorithms, exchange random - Exchange hello messages to agree on algorithms, exchange random
values, and check for session resumption. values, and check for session resumption.
- Exchange the necessary cryptographic parameters to allow the - Exchange the necessary cryptographic parameters to allow 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 allow the - Exchange certificates and cryptographic information to allow the
client and server to authenticate themselves. client and server to authenticate themselves.
- Generate a master secret from the premaster secret and exchanged - Generate a master secret from the premaster secret and exchanged
random values. random values.
- Provide security paramers to the record layer. - Provide security parameters 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 handshake calculated the same security parameters and that the handshake
occured without tampering by an attacker. occurred without tampering by an attacker.
] Note that higher layers should not be overly reliant on TLS always ] Note that higher layers should not be overly reliant on TLS always
] negotiating the strongest possible connection between two peers: ] negotiating the strongest possible connection between two peers:
] there are a number of ways a man in the middle attacker can attempt ] there are a number of ways a man in the middle attacker can attempt
] to make two entities drop down to the least secure method they ] to make two entities drop down to the least secure method they
] support. The protocol has been designed to minimize this risk, but ] support. The protocol has been designed to minimize this risk, but
] there are still attacks available: for example, an attacker could ] there are still attacks available: for example, an attacker could
] block access to the port a secure service runs on, or attempt to get ] block access to the port a secure service runs on, or attempt to get
] the peers to negotiate an unauthenticated connection. The ] the peers to negotiate an unauthenticated connection. The
] fundamental rule is that higher levels must be cognizant of what ] fundamental rule is that higher levels must be cognizant of what
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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
ServerHello.random. ServerHello.random.
The actual key exchange uses up to four messages: the server The actual key exchange uses up to four messages: the server
certificate, the server key exchange, the client certificate, and certificate, the server key exchange, the client certificate, and
the client key exchange. New key exchange methods can be created by the client key exchange. New key exchange methods can be created by
specifing a format for these messages and defining the use of the specifying a format for these messages and defining the use of the
messages to allow the client and server to agree upon a shared messages to allow the client and server to agree upon a shared
secret. This secret should be quite long; currently defined key secret. This secret should be quite long; currently defined key
exchange methods exchange secrets which range from 48 to 128 bytes exchange methods exchange secrets which range from 48 to 128 bytes
in length. in length.
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 the certificate
certificate message or a no_certificate alert. The client key | message. The client key exchange message is now sent, and the
exchange message is now sent, and the content of that message will content of that message will depend on the public key algorithm
depend on the public key algorithm selected between the client hello selected between the client hello and the server hello. If the
and the server hello. If the client has sent a certificate with client has sent a certificate with signing ability, a
signing ability, a digitally-signed certificate verify message is digitally-signed certificate verify message is sent to explicitly
sent to explicitly verify the certificate. 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
under the new algorithms, keys, and secrets. In response, the server under the new algorithms, keys, and secrets. In response, the server
will send its own change cipher spec message, transfer the pending will send its own change cipher spec message, transfer the pending
to the current Cipher Spec, and send its finished message under the to the current Cipher Spec, and send its finished message under the
new Cipher Spec. At this point, the handshake is complete and the new Cipher Spec. At this point, the handshake is complete and the
client and server may begin to exchange application layer data. (See client and server may begin to exchange application layer data. (See
flow chart below.) flow chart below.)
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<-------- ServerHelloDone <-------- ServerHelloDone
Certificate* Certificate*
ClientKeyExchange ClientKeyExchange
CertificateVerify* CertificateVerify*
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
Application Data <-------> Application Data Application Data <-------> Application Data
| Fig. 1 - Message flow for a full handshake
* Indicates optional or situation-dependent messages that are not * Indicates optional or situation-dependent messages that are not
always sent. always sent.
Note: To help avoid pipeline stalls, ChangeCipherSpec is an Note: 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 a TLS
handshake message. 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:
skipping to change at page 29, line 31 skipping to change at page 29, line 46
Client Server Client Server
ClientHello --------> ClientHello -------->
ServerHello ServerHello
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
Application Data <-------> Application Data Application Data <-------> Application Data
| Fig. 2 - Message flow for an abbreviated handshake
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 7.4. 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 30, line 15 skipping to change at page 30, line 33
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 below in the order
be sent; sending handshake messages in an unexpected order results they must be sent; sending handshake messages in an unexpected order
| in a fatal error. Unneeded handshake messages can be omitted, results in a fatal error. Unneeded handshake messages can be
| however. The one exception is the Hello request message, which may | omitted, however. Note one exception to the ordering: the
| be sent by the server at any time. | Certificate message is used twice in the handshake (from server to
| client, then from client to server), but described only in its first
| position. The one message which is not bound by these ordering rules
| in the Hello Request message, which can be sent at any time, but
| which should be ignored by the client if it arrives in the middle of
| a handshake.
6.4.1. Hello messages 7.4.1. 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 7.4.1.1. 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 the negotiation process anew by sending a client hello begin the negotiation process anew by sending a client hello
message when convenient. This message will be ignored by the message when convenient. This message will be ignored by the
client if the client is currently negotiating a session. This client if the client is currently negotiating a session. This
message may be ignored by the client if it does not wish to message may be ignored by the client if it does not wish to
renegotiate a session. Since handshake messages are intended to | renegotiate a session, or the client may, if it wishes, respond
have transmission precedence over application data, it is | with a no_renegotiation alert. Since handshake messages are
expected that the negotiation will begin before no more than a intended to have transmission precedence over application data,
few records are received from the client. If the server sends a it is expected that the negotiation will begin before no more
hello request but does not recieve a client hello in response, than a few records are received from the client. If the server
it may close the connection with a fatal alert. sends a hello request but does not receive a client hello in
response, 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: This message should never be included in the message hashes Note: 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 7.4.1.2. 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 client hello as its first message. The client can also send the client hello as its first message. The client can also send
a client hello in response to a hello request or on its own a client hello in response to a hello request or on its own
initiative in order to renegotiate the security parameters in an initiative in order to renegotiate the security parameters in an
existing connection. existing 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 later in the protocol. used 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 | (seconds since the midnight starting Jan 1, 1970, GMT) according
required to be set correctly by the basic TLS Protocol; higher to the sender's internal clock. Clocks are not required to be
level or application protocols may define additional set correctly by the basic TLS Protocol; higher level or
requirements. application protocols may define additional requirements.
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 independent secure option makes it possible to establish several independent secure
| connections without repeating the full handshake protocol. These connections without repeating the full handshake protocol. These
| independant connections may occur sequentially or simultaneously; a ] independent connections may occur sequentially or simultaneously; a
| SessionID becomes valid when the handshake negotiating it completes ] SessionID becomes valid when the handshake negotiating it completes
| with the exchange of Finished messages and persists until removed ] with the exchange of Finished messages and persists until removed
| due to aging or because a fatal error was encountered on a ] due to aging or because a fatal error was encountered on a
| connection associated with the session. The actual contents of the ] connection associated with the session. The actual contents of the
| SessionID are defined by the server. SessionID are defined by the server.
opaque SessionID<0..32>; opaque SessionID<0..32>;
Warning: Warning:
| Because the SessionID is transmitted without encryption or ] Because the SessionID is transmitted without encryption or
| immediate MAC protection, servers must not place confidential ] immediate MAC protection, servers must not place confidential
| information in session identifiers or let the contents of fake ] information in session identifiers or let the contents of fake
| session identifiers cause any breach of security. (Note that the ] session identifiers cause any breach of security. (Note that the
| contents of the handshake as a whole, including the SessionID, ] content of the handshake as a whole, including the SessionID, is
] protected by the Finished messages exchanged at the end of the
| is protected by the Finished messages exchanged at the end of ] handshake.)
| 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 (favorite 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.
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
] It also contains a vendor identification string, intended to
] identify the manufacturer, platform, and/or version of the TLS
] implementation running on the Client. While these are the intended
] uses, this field is not specified and may contain any data thought
] useful by the implementor, or no data at all. This string consists
] of between 0 and 64 ISO Latin 1 characters.
] opaque VendorID<0..64>; /* Vendor-specified ID string */
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>;
] VendorID client_vendor;
} 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 3.1 (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.
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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 is client, sorted by client preference. If the session_id field is
not empty (implying a session resumption request) it must not empty (implying a session resumption request) it must
include the compression_method from that session. This vector include the compression_method from that session. This vector
must contain, and all implementations must support, must contain, and all implementations must support,
CompressionMethod.null. Thus, a client and server will always be CompressionMethod.null. Thus, a client and server will always be
able to agree on a compression method. able to agree on a compression method.
] client_vendor
] This freeform string contains ISO Latin 1 characters specifying
] the implementation of TLS being used by the client. This is
] intended solely for compatibility and debugging work and should
] not be used by the server as a part of the protocol.
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 a In the interests of forward compatibility, it is permitted for a
client hello message to include extra data after the compression client hello message to include extra data after the compression
methods. This data must be included in the handshake hashes, but methods. This data must be included in the handshake hashes, but
must otherwise be ignored. This is the only handshake message must otherwise be ignored. This is the only handshake message
for which this is legal; for all other messages, the amount of for which this is legal; for all other messages, the amount of
data in the message must match the description of the message data in the message must match the description of the message
precisely. precisely.
6.4.1.3. Server hello 7.4.1.3. 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 message when it was able to find an acceptable set of
algorithms. If it cannot find such a match, it will respond with algorithms. If it cannot find such a match, it will respond with
a handshake 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;
] VendorID server_vendor;
} 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
| 3.1 (See Appendix E for details about backward compatibility). ] 3.1 (See Appendix E for details about backward compatibility).
random random
This structure is generated by the server and must be different This structure is generated by the server and must be 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 is server will look in its session cache for a match. If a match is
found and the server is willing to establish the new connection found and the server is willing to establish the new connection
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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 The single compression algorithm selected by the server from the
list in ClientHello.compression_methods. For resumed sessions list in ClientHello.compression_methods. For resumed sessions
this field is the value from the resumed session state. this field is the value from the resumed session state.
] server_vendor 7.4.2. Server certificate
] This freeform string contains ISO Latin 1 characters specifying
] the implementation of TLS being used by the server. This is
] intended solely for compatibility and debugging work and should
] not be used by the client as a part of the protocol.
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 exchange method is not an anonymous one. This message will
always 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.509v3 suite's key exchange algorithm, and is generally an X.509v3
certificate. It must contain a key which matches the key certificate. It must contain a key which matches the key
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the public key may 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 either encryption or
signing.
DHE_DSS DSS public key. DHE_DSS DSS public key.
DHE_DSS_EXPORT DSS public key. DHE_DSS_EXPORT DSS public key.
DHE_RSA RSA public key which can be used for DHE_RSA RSA public key which can be used for
signing. signing.
DHE_RSA_EXPORT RSA public key which can be used for DHE_RSA_EXPORT RSA public key which can be used for
signing. signing.
DH_DSS Diffie-Hellman key. The algorithm used DH_DSS Diffie-Hellman key. The algorithm used
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.
] All certificate profiles, key and cryptographic formats are defined ] All certificate profiles, key and cryptographic formats are defined
] by the IETF PKIX working group [PKIX]. | by the IETF PKIX working group [PKIX]. When a key usage extension is
| present, the digitalSignature bit must be set for the key to be
| eligible for signing, as described above, and the keyEncipherment
| bit must be present to allow encryption, as described above. The
| keyAgreement bit must be set on Diffie-Hellman certificates.
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<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
certificate_list certificate_list
| This is a sequence (chain) of X.509v3 certificates. The sender's ] This is a sequence (chain) of X.509v3 certificates. The sender's
| certificate must come first in the list. Each following ] certificate must come first in the list. Each following
| certificate must directly certify the one preceding it. Because ] certificate must directly certify the one preceding it. Because
| certificate validation requires that root keys be distributed ] certificate validation requires that root keys be distributed
| independantly, the self-signed certificate which specifies the ] independently, the self-signed certificate which specifies the
| root certificate authority may optionally be omitted from the ] root certificate authority may optionally be omitted from the
| chain, under the assumption that the remote end must already ] chain, under the assumption that the remote end must already
] possess it in order to validate it in any case.
| 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. Note that a client may ] response to a certificate request message. Note that a client may
| send no certificates if it does not have an appropriate certificate ] send no certificates if it does not have an appropriate certificate
| to send in response to the server's authentication request. ] to send in response to the server's authentication request.
Note: PKCS #7 [PKCS7] is not used as the format for the certificate Note: 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 7.4.3. 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 ] This message will be sent immediately after the server
| certificate message (or the server hello message, if this is an ] certificate message (or the server hello message, if this is an
| anonymous negotiation). ] anonymous negotiation).
The server key exchange message is sent by the server only when The server key exchange message is sent by the server only when
the server certificate message (if sent) does not contain enough the server certificate message (if sent) does not contain enough
data to allow the client to exchange a premaster secret. This is data to allow the client to exchange a premaster secret. This is
true for the following key exchange methods: 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
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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 7.4.4. Certificate request
When this message will be sent: When this message will be sent:
A non-anonymous server can optionally request a certificate from A non-anonymous server can optionally request a certificate from
| the client, if appropriate for the selected cipher suite. This ] the client, if appropriate for the selected cipher suite. This
| message, if sent, will immediately follow the Server Key ] message, if sent, will immediately follow the Server Key
| Exchange message (if it is sent; otherwise, the Server ] Exchange message (if it is sent; otherwise, the Server
| Certificate message). ] Certificate message).
] 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),
(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>;
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.
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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. These distinguished names may specify a desired ] authorities. These distinguished names may specify a desired
| distinguished name for a root CA or for a subordinate CA; ] distinguished name for a root CA or for a subordinate CA;
| thus, this message can be used both to describe known roots ] thus, this message can be used both to describe known roots
| and a desired authorization space. ] and a desired authorization space.
Note: DistinguishedName is derived from [X509]. Note: DistinguishedName is derived from [X509].
Note: It is a fatal handshake_failure alert for an anonymous server to Note: It is a fatal handshake_failure alert for an anonymous server to
request client identification. request client identification.
6.4.5. Server hello done 7.4.5. 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 end of the server hello and associated messages. After the end of the server hello and associated messages. After
sending this message the server will wait for a client response. sending this 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 support the key exchange, and the client can proceed with its
phase 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 verify that the server provided a valid certificate if required
and 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 7.4.6. 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 hello done message. This message is only sent if the
server requests a certificate. If no suitable certificate is server requests a certificate. If no suitable certificate is
| available, the client should send a certificate message ] available, the client should send a certificate message
| containing no certificates. If client authentication is required ] containing no certificates. If client authentication is required
| by the server for the handshake to continue, it may respond with ] by the server for the handshake to continue, it may respond with
| a fatal handshake failure alert. Client certificates are sent ] a fatal handshake failure alert. Client certificates are sent
| using the Certificate structure defined in Section 6.4.2.
] using the Certificate structure defined in Section 7.4.2.
Note: When using a static Diffie-Hellman based key exchange method Note: 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 key parameters if the client's parameters are to be used for the key
exchange. exchange.
6.4.7. Client key exchange message 7.4.7. 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. Otherwise ] follow the client certificate message, if it is sent. Otherwise
| it will be the first message sent by the client after it ] it will be the first message sent by the client after it
| receives the server hello done message. ] 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 transmisson of the RSA-encrypted secret, or by the direct transmission of the RSA-encrypted secret, or by the
transmission of Diffie-Hellman parameters which will allow each transmission of Diffie-Hellman parameters which will allow each
side to agree upon the same premaster secret. When the key side to agree upon the same premaster secret. When the key
exchange method is DH_RSA or DH_DSS, client certification has exchange method is DH_RSA or DH_DSS, client certification has
been requested, and the client was able to respond with a been requested, and the client was able to respond with a
certificate which contained a Diffie-Hellman public key whose certificate which contained a Diffie-Hellman public key whose
parameters (group and generator) matched those specified by the parameters (group and generator) matched those specified by the
server in its certificate, this message will not contain any server in its certificate, this message will not 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 selected. See Section 6.4.3 for the KeyExchangeAlgorithm been selected. See Section 7.4.3 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 7.4.7.1. 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 client generates a 48-byte premaster secret, encrypts it using
the public key from the server's certificate or the temporary the public key from the server's certificate or the temporary
RSA key provided in a server key exchange message, and sends the RSA key provided in a server key exchange message, and sends the
result in an encrypted premaster secret message. This structure result in an encrypted premaster secret message. This structure
is a variant of the client key exchange message, not a message is a variant of the client key exchange message, not a message
in itself. 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. Upon receiving the ] used to detect version roll-back attacks. Upon receiving the
] premaster secret, the server should check that this value
| premaster secret, the server should check that this value ] matches the value transmitted by the client in the client
| matches the value transmitted by the client in the client ] hello message.
| 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 8.1.
6.4.7.2. Client Diffie-Hellman public value 7.4.7.2. 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) if it was not already included in the client's certificate. (Yc) if it was not already included in the client's certificate.
The encoding used for Yc is determined by the enumerated The 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 exchange message, not a message in itself. key 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. In this case, the Client Key Exchange message ] be sent again. In this case, the Client Key Exchange message
| will be sent, but will be empty. ] 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;
skipping to change at page 41, line 47 skipping to change at page 42, line 4
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 7.4.8. 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 certificate. This message is only sent following a client 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 except those containing fixed Diffie-Hellman parameters). When
sent, it will immediately follow the client key exchange sent, it will immediately follow the client key exchange
message. 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
| HMAC_MD5(master_secret, handshake_messages); | MD5(handshake_messages);
Certificate.signature.sha_hash Certificate.signature.sha_hash
| HMAC_SHA(master_secret, handshake_messages); | SHA(handshake_messages);
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 7.4 exchanged thus far.
6.4.9. Finished 7.4.9. 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 spec message to verify that the key exchange and cipher spec message to verify that the key exchange and
authentication processes were successful. It is essential that a authentication processes were successful. It is essential that a
change cipher spec message be received between the other change cipher spec message be received between the other
handshake messages and the Finished message. handshake messages and the 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 algorithms, keys, and secrets. Recipients of ] just-negotiated algorithms, keys, and secrets. Recipients of
] finished messages must verify that the contents are correct. ] finished messages must verify that the contents are correct.
] Once a side has sent its Finished message and received and ] Once a side has sent its Finished message and received and
] validated the Finished message from its peer, it may begin to ] validated the Finished message from its peer, it may begin to
] send and receive application data over the connection. ] send and receive application data over the connection.
enum { client(0x434C4E54), server(0x53525652) } Sender; | struct {
| opaque verify_data[12];
| } Finished;
struct { | verify_data
opaque md5_hash[16]; | PRF(master_secret, finished_label, MD5(handshake_messages) +
opaque sha_hash[20]; | SHA-1(handshake_messages)) [0..11];
} Finished;
md5_hash | finished_label
| HMAC_MD5(master_secret, handshake_messages + Sender); | For Finished messages sent by the client, the string "client
sha_hash | finished". For Finished messages sent by the server, the
| HMAC_SHA(master_secret, handshake_messages + Sender); | string "server finished".
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 7.4 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 preceded 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 6.4.8 because it would include the certificate verify Section 7.4.8 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: Change cipher spec messages are not handshake messages and are |Note: Change cipher spec messages, alerts and any other record types
| not included in the hash computations. Also, Hello Request are not handshake messages and are not included in the hash
| messages are omitted from handshake hashes. ] computations. Also, Hello Request messages are omitted from
] handshake hashes.
7. Cryptographic computations 8. 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 8.1. 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 = PRF(pre_master_secret, | master_secret = PRF(pre_master_secret, "master secret",
] ClientHello.random + ServerHello.random); | ClientHello.random + ServerHello.random) [0..47];
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 8.1.1. 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 8.1.2. 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: Diffie-Hellman parameters are specified by the server, and may Note: 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 9. 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.
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, although the protocol should be useful over ] networking technology, although the protocol should be useful over
| any transport which can provide a reliable stream connection. The ] any transport which can provide a reliable stream connection. The
IANA reserved the following Internet Protocol [IP] port numbers for IANA reserved the following Internet Protocol [IP] port numbers for
use in conjunction with the SSL 3.0 Protocol, which we presume will use in conjunction with the SSL 3.0 Protocol, which we presume will
be used by TLS as well. be used by TLS as well.
| While we describe these existing port assignments for completeness,
| in general, protocol designers and implementors should be the ones
| to decide on how security can be incorporated into their protocol
| using TLS, including the mechanisms for negotiating to start TLS and
| the requirements and meaning of that connection (such as
| interpretation of exchanged certificates).
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 SSL 465 Reserved for use by Simple Mail Transfer Protocol with 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.2. Record layer A.2. Record layer
struct { struct {
uint8 major, minor; uint8 major, minor;
} ProtocolVersion; } ProtocolVersion;
| ProtocolVersion version = { 3, 1 }; /* TLS v1.0 */ 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;
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} ChangeCipherSpec; } ChangeCipherSpec;
A.4. 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),
] decryption_failed(21),
] record_overflow(22),
decompression_failure(30), decompression_failure(30),
handshake_failure(40), handshake_failure(40),
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;
A.5. 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_hello_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 {
HandshakeType msg_type; HandshakeType msg_type;
uint24 length; uint24 length;
select (HandshakeType) { select (HandshakeType) {
case hello_request: HelloRequest; case hello_request: HelloRequest;
case client_hello: ClientHello; case client_hello: ClientHello;
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_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;
A.5.1. Hello messages A.5.1. Hello messages
struct { } HelloRequest; struct { } HelloRequest;
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opaque SessionID<0..32>; opaque SessionID<0..32>;
uint8 CipherSuite[2]; uint8 CipherSuite[2];
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<0..2^16-1>; CipherSuite cipher_suites<2..2^16-1>;
CompressionMethod compression_methods<0..2^8-1>; CompressionMethod compression_methods<0..2^8-1>;
] VendorID client_vendor;
} 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;
] VendorID server_vendor;
} ServerHello; } ServerHello;
A.5.2. 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 {
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;
struct { struct {
opaque DH_p<1..2^16-1>; opaque DH_p<1..2^16-1>;
opaque DH_g<1..2^16-1>; opaque DH_g<1..2^16-1>;
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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;
] 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),
] (255) (255)
] } ClientCertificateType; } ClientCertificateType;
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
CertificateType 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;
struct { } ServerHelloDone; struct { } ServerHelloDone;
A.5.3. 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;
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} dh_public; } dh_public;
} ClientDiffieHellmanPublic; } ClientDiffieHellmanPublic;
struct { struct {
Signature signature; Signature signature;
} CertificateVerify; } CertificateVerify;
A.5.4. Handshake finalization message A.5.4. Handshake finalization message
struct { struct {
opaque md5_hash[16]; | opaque verify_data[12];
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 specification supported in TLS A CipherSuite defines a cipher specification supported in TLS
Version 1.0. Version 1.0.
| TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a
| TLS connection during the first handshake on that channel, but
| should not be negotiated, as it provides no more protection than an
| unsecured connection.
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 };
CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 }; CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 };
CipherSuite TLS_RSA_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x03 }; CipherSuite TLS_RSA_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x03 };
skipping to change at page 50, line 23 skipping to change at page 50, line 50
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. The server can ] used is specified after the DH or DHE parameter. The server can
| request an RSA or DSS signature-capable certificate from the client ] request an RSA or DSS signature-capable certificate from the client
| for client authentication or it may request a Diffie-Hellman ] for client authentication or it may request a Diffie-Hellman
| certificate. Any Diffie-Hellman certificate provided by the client ] certificate. Any Diffie-Hellman certificate provided by the client
| must use the parameters (group and generator) described by the ] must use the parameters (group and generator) described by the
| server. ] 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 };
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 deprecated. 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: All cipher suites whose first byte is 0xFF are considered Note: 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: Additional cipher suites will be considered for implementation Note: 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. Consensus Development Corp. will act as an interim ] entities. Consensus Development 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 cipher suites. control of TLS cipher suites.
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 } BulkCipherAlgorithm; enum { null, rc4, rc2, des, 3des, des40, idea }
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;
CipherType cipher_type; CipherType cipher_type;
uint8 key_size; uint8 key_size;
skipping to change at page 51, line 41 skipping to change at page 52, line 18
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;
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
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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 common 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 (CBC) cipher block chaining (CBC)
| CBC is a mode in which every plaintext block encrypted with a CBC is a mode in which every plaintext block encrypted with a
| block cipher is first exclusive-ORed with the previous block cipher is first exclusive-ORed with the previous
| ciphertext block (or, in the case of the first block, with the ciphertext block (or, in the case of the first block, with the
| initialization vector). For decryption, every block is first ] initialization vector). For decryption, every block is first
| decrypted, then exclusive-ORed with the previous ciphertext ] decrypted, then exclusive-ORed with the previous ciphertext
| block (or IV). ] 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 may | Authority and provide a strong binding between a party's
also supply its public key. | identity or some other attributes and its public key.
client client
The application entity that initiates a connection to a server | The application entity that initiates a TLS connection to a
| server. This may or may not imply that the client initiated the
| underlying transport connection. The primary operational
| difference between the server and client is that the server is
| generally authenticated, while the client is only optionally
| authenticated.
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 client. The secret data used to authenticate data written by the 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 connections such connections are peer to peer relationships. The connections
are transient. Every connection is associated with one session. are transient. Every connection is associated with one session.
Data Encryption Standard Data Encryption Standard
DES is a very widely used symmetric encryption algorithm. DES is DES is a very widely used symmetric encryption algorithm. DES is
| a block cipher with a 56 bit key and an 8 byte block size. Note ] 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 ] that in TLS, for key generation purposes, DES is treated as
| having an 8 byte key length (64 bits), but it still only ] having an 8 byte key length (64 bits), but it still only
| provides 56 bits of protection. DES can also be operated in a ] provides 56 bits of protection. DES can also be operated in a
| mode where three independant keys and three encryptions are used ] mode where three independent keys and three encryptions are used
| for each block of data; this uses 168 bits of key (24 bytes in ] for each block of data; this uses 168 bits of key (24 bytes in
] the TLS key generation method) and provides the equivalent of
| the TLS key generation method) and provides the equivalent of ] 112 bits of security. [DES], [3DES]
| 112 bits of security. [DES], [3DES]
Digital Signature Standard (DSS) Digital Signature Standard (DSS)
A standard for digital signing, including the Digital Signing A standard for digital signing, including the Digital Signing
Algorithm, approved by the National Institute of Standards and Algorithm, approved by the National Institute of Standards and
Technology, defined in NIST FIPS PUB 186, "Digital Signature Technology, defined in NIST FIPS PUB 186, "Digital Signature
Standard," published May, 1994 by the U.S. Dept. of Commerce. Standard," published May, 1994 by the U.S. Dept. of Commerce.
[DSS] [DSS]
digital signatures digital signatures
Digital signatures utilize public key cryptography and one-way Digital signatures utilize public key cryptography and one-way
skipping to change at page 53, line 35 skipping to change at page 54, line 16
When a block cipher is used in CBC mode, the initialization When a block cipher is used in CBC mode, the initialization
vector is exclusive-ORed with the first plaintext block prior to vector is exclusive-ORed with the first 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] [IDEA]
Message Authentication Code (MAC) Message Authentication Code (MAC)
A Message Authentication Code is a one-way hash computed from a A Message Authentication Code is a one-way hash computed from a
| message and some secret data. It is difficult to forge without ] message and some secret data. It is difficult to forge without
| knowing the secret data and it is difficult to find messages ] knowing the secret data and it is difficult to find messages
| which hash to the same MAC. Its purpose is to detect if the ] which hash to the same MAC. Its purpose is to detect if the
| message has been altered. 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 is a secure hashing function that converts an arbitrarily MD5 is a secure hashing function that converts an arbitrarily
| long data stream into a digest of fixed size (16 bytes). [MD5] 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 computationally 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
Proprietary bulk ciphers from RSA Data Security, Inc. (There is | A proprietary block cipher from RSA Data Security, Inc.
no good reference to these as they are unpublished works; | [RSADSI].
however, see [RSADSI]). RC2 is block cipher and RC4 is a stream
cipher. | RC4
| A stream cipher licensed by RSA Data Security [RSADSI]. A
| compatible cipher is described in [RC4].
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. [RSA] 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 for connections from clients. See also under client.
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 define Sessions are created by the handshake protocol. Sessions define
a set of cryptographic security parameters, which can be shared a set of cryptographic security parameters, which can be shared
among multiple connections. Sessions are used to avoid the among multiple connections. Sessions are used to avoid the
expensive negotiation of new security parameters for each expensive negotiation of new security parameters for each
connection. connection.
session identifier session identifier
skipping to change at page 54, line 46 skipping to change at page 55, line 29
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 server. The secret data used to authenticate data written by the 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. Note that all references to SHA ] produces a 20-byte output. Note that all references to SHA
| actually use the modified SHA-1 algorithm. [SHA] ] actually use the modified SHA-1 algorithm. [SHA]
SSL SSL
Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on Netscape's Secure Socket Layer protocol [SSL3]. TLS is based 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 exclusive-ORed cryptographically-strong keystream, which is then exclusive-ORed
with the plaintext. with the plaintext.
symmetric cipher symmetric cipher
See bulk cipher. See bulk cipher.
| Transport Layer Security (TLS) ] Transport Layer Security (TLS)
| This protocol; also, the Transport Layer Security working group ] This protocol; also, the Transport Layer Security working group
| of the Internet Engineering Task Force (IETF). See "Comments" at ] of the Internet Engineering Task Force (IETF). See "Comments" at
| the end of this document. ] 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
TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5 TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5
TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 * RSA_EXPORT RC2_CBC_40 MD5 TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 * RSA_EXPORT RC2_CBC_40 MD5
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
skipping to change at page 56, line 37 skipping to change at page 57, line 19
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.
| Type
| Indicates whether this is a stream cipher or a block cipher
| running in CBC mode.
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 into How much entropy material is in the key material being fed into
the encryption routines. the encryption routines.
| IV Size
| How much data needs to be generated for the initialization
| vector. Zero for stream ciphers; equal to the block size for
| block ciphers.
| Block Size
| The amount of data a block cipher enciphers in one chunk; a
| block cipher running in CBC mode can only encrypt an even
| multiple of its block size.
Hash Hash Padding Hash Hash Padding
function Size 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 implementors.
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.
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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.
Warning: The seeding functions in RSAREF and versions of BSAFE prior to Warning: 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 ] This may be accomplished by accumulating seed bits into a
| buffer and processing them all at once or by processing an ] 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. ] incrementing counter with every seed bit; either method will
] reintroduce order dependence 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.
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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.
E. Backward Compatibility With SSL E. Backward Compatibility With SSL
| For historical reasons and in order to avoid a profligate ] For historical reasons and in order to avoid a profligate
| consumption of reserved port numbers, application protocols which ] consumption of reserved port numbers, application protocols which
| are secured by TLS 1.0, SSL 3.0, and SSL 2.0 all frequently share ] 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 ] the same connection port: for example, the https protocol (HTTP
| secured by SSL or TLS) uses port 443 regardless of which security ] secured by SSL or TLS) uses port 443 regardless of which security
| protocol it is using. Thus, some mechanism must be determined to ] protocol it is using. Thus, some mechanism must be determined to
| distinguish and negotiate among the various protocols. ] distinguish and negotiate among the various protocols.
| TLS version 1.0 and SSL 3.0 are very similar; thus, supporting both ] TLS version 1.0 and SSL 3.0 are very similar; thus, supporting both
| is easy. TLS clients who wish to negotiate with SSL 3.0 servers ] 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 ] should send client hello messages using the SSL 3.0 record format
| and client hello structure, sending {3, 1} for the version field to ] 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, ] 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, ] it will respond with an SSL 3.0 server hello; if it supports TLS,
| with a TLS server hello. The negotiation then proceeds as ] with a TLS server hello. The negotiation then proceeds as
| appropriate for the negotiated protocol. ] appropriate for the negotiated protocol.
| Similarly, a TLS server which wishes to interoperate with SSL 3.0 ] Similarly, a TLS server which wishes to interoperate with SSL 3.0
| clients should accept SSL 3.0 client hello messages and respond with ] 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 ] 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 ] has a version field of {3, 0}, denoting that this client does not
| support TLS. ] support TLS.
| Whenever a client already knows the highest protocol known to a ] Whenever a client already knows the highest protocol known to a
| server (for example, when resuming a session), it should initiate ] server (for example, when resuming a session), it should initiate
| the connection in that native protocol. ] the connection in that native protocol.
| TLS 1.0 clients that support SSL Version 2.0 servers must send SSL ] 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 ] Version 2.0 client hello messages [SSL2]. TLS servers should accept
| either client hello format if they wish to support SSL 2.0 clients ] either client hello format if they wish to support SSL 2.0 clients
| on the same connection port. The only deviations from the Version ] on the same connection port. The only deviations from the Version
| 2.0 specification are the ability to specify a version with a value ] 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. ] 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 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. Implementors 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 TLS_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 }; V2CipherSpec TLS_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 };
| V2CipherSpec TLS_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 }; V2CipherSpec TLS_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 };
| V2CipherSpec TLS_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 }; V2CipherSpec TLS_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 };
| V2CipherSpec TLS_RC2_CBC_128_CBC_EXPORT40_WITH_MD5 V2CipherSpec TLS_RC2_CBC_128_CBC_EXPORT40_WITH_MD5
| = { 0x04,0x00,0x80 }; = { 0x04,0x00,0x80 };
| V2CipherSpec TLS_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 }; V2CipherSpec TLS_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 };
| V2CipherSpec TLS_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 }; V2CipherSpec TLS_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 };
| V2CipherSpec TLS_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 }; V2CipherSpec TLS_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 };
| Cipher specifications native to TLS can be included in Version 2.0 Cipher specifications native to TLS can be included in Version 2.0
| client hello messages using the syntax below. Any V2CipherSpec client hello messages using the syntax below. Any V2CipherSpec
| element with its first byte equal to zero will be ignored by Version element with its first byte equal to zero will be ignored by Version
| 2.0 servers. Clients sending any of the above V2CipherSpecs should 2.0 servers. Clients sending any of the above V2CipherSpecs should
| also include the TLS equivalent (see Appendix A.6): also include the TLS equivalent (see Appendix A.6):
| V2CipherSpec (see TLS 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;
skipping to change at page 61, line 5 skipping to change at page 61, line 50
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 last length of the challenge is greater than 32 bytes, only the last
32 bytes are used. It is legitimate (but not necessary) for a V3 32 bytes are used. It is legitimate (but not necessary) for a V3
server to reject a V2 ClientHello that has fewer than 16 bytes server to reject a V2 ClientHello that has fewer than 16 bytes
of challenge data. of challenge data.
|Note: Requests to resume a TLS session should use a TLS client hello. Note: Requests to resume a TLS session should use a TLS client hello.
E.2. Avoiding man-in-the-middle version rollback E.2. Avoiding man-in-the-middle version rollback
| When TLS clients fall back to Version 2.0 compatibility mode, they When TLS clients fall back to Version 2.0 compatibility mode, they
| should use special PKCS #1 block formatting. This is done so that should use special PKCS #1 block formatting. This is done so that
| TLS servers will reject Version 2.0 sessions with TLS-capable TLS servers will reject Version 2.0 sessions with TLS-capable
| clients. clients.
| When TLS clients are in Version 2.0 compatibility mode, they set the When TLS clients are in Version 2.0 compatibility mode, they set the
right-hand (least-significant) 8 random bytes of the PKCS padding right-hand (least-significant) 8 random bytes of the PKCS 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 an ENCRYPTED-KEY-DATA field, servers that support TLS should issue 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
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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. If the server is
signature in the certificate verify message may require a server authenticated, its certificate message must provide a valid
certificate to bind the signature to a particular server. If the certificate chain leading to an acceptable certificate authority.
server is authenticated, its certificate message must provide a Similarly, authenticated clients must supply an acceptable
valid certificate chain leading to an acceptable certificate certificate to the server. Each party is responsible for verifying
authority. Similarly, authenticated clients must supply an that the other's certificate is valid and has not expired or been
acceptable certificate to the server. Each party is responsible for revoked.
verifying that the other's certificate is valid and has not expired
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 7.1). The master_secret is required to master_secret (see Section 8.1). The master_secret is required to
| generate the certificate verify and finished messages, encryption generate the certificate verify and finished messages, encryption
keys, and MAC secrets (see Sections 6.4.8, 6.4.9 and 5.4). By keys, and MAC secrets (see Sections 7.4.8, 7.4.9 and 6.3). By
sending a correct finished message, parties thus prove that they sending a correct finished message, parties thus prove that they
know the correct 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
skipping to change at page 63, line 12 skipping to change at page 64, line 6
certificates but must comply with government-imposed size limits certificates but must comply with government-imposed size limits
on keys used for key exchange. 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 6.4.8). The client signs the certificate verify message (see Section 7.4.8). 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
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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 for the size of the signed hashes and RSA key lengths used security for the size of the signed hashes and RSA key lengths used
| in the protocol, since this is essentially equivalent to increasing in the protocol, since this is essentially equivalent to increasing
| the input block size by 8 bytes. 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
skipping to change at page 67, line 8 skipping to change at page 67, line 49
[DSS] NIST FIPS PUB 186, "Digital Signature Standard," National [DSS] NIST FIPS PUB 186, "Digital Signature Standard," National
Institute of Standards and Technology, U.S. Department of Commerce, Institute of Standards and Technology, U.S. Department of Commerce,
18 May 1994. 18 May 1994.
[FTP] J. Postel and J. Reynolds, RFC 959: File Transfer Protocol, [FTP] J. Postel and J. Reynolds, RFC 959: File Transfer Protocol,
October 1985. October 1985.
[HTTP] T. Berners-Lee, R. Fielding, H. Frystyk, Hypertext Transfer [HTTP] T. Berners-Lee, R. Fielding, H. Frystyk, Hypertext Transfer
Protocol -- HTTP/1.0, October, 1995. Protocol -- HTTP/1.0, October, 1995.
] [HMAC] H. Krawczyk, RFC 2104, HMAC: Keyed-Hashing for Message | [HMAC] H. Krawczyk, M. Bellare, and R. Canetti, RFC 2104, HMAC:
] Authentication, February, 1997. | Keyed-Hashing for Message Authentication, February, 1997.
[IDEA] X. Lai, "On the Design and Security of Block Ciphers," ETH [IDEA] X. Lai, "On the Design and Security of Block Ciphers," ETH
Series in Information Processing, v. 1, Konstanz: Hartung-Gorre Series in Information Processing, v. 1, Konstanz: Hartung-Gorre
Verlag, 1992. Verlag, 1992.
[MD2] R. Rivest. RFC 1319: The MD2 Message Digest Algorithm. April [MD2] R. Rivest. RFC 1319: The MD2 Message Digest Algorithm. April
1992. 1992.
[MD5] R. Rivest. RFC 1321: The MD5 Message Digest Algorithm. April [MD5] R. Rivest. RFC 1321: The MD5 Message Digest Algorithm. April
1992. 1992.
skipping to change at page 67, line 34 skipping to change at page 68, line 24
[PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate Syntax [PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate Syntax
Standard," version 1.5, November 1993. Standard," version 1.5, November 1993.
[PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax [PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax
Standard," version 1.5, November 1993. Standard," version 1.5, November 1993.
] [PKIX] R. Housley, W. Ford, W. Polk, D. Solo, Internet Public Key ] [PKIX] R. Housley, W. Ford, W. Polk, D. Solo, Internet Public Key
] Infrastructure: Part I: X.509 Certificate and CRL Profile, ] Infrastructure: Part I: X.509 Certificate and CRL Profile,
] <draft-ietf-pkix-ipki-part1-03.txt>, December 1996. ] <draft-ietf-pkix-ipki-part1-03.txt>, December 1996.
| [RC4] R. Thayer, A Stream Cipher Encryption Algorithm,
| <draft-thayer-cipher-00.txt>, February 1997.
[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. DRAFT, 31 May 1994.
| [SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications
| Corp., Feb 9th, 1995.
[SSL3] Frier, Karton and Kocher, [SSL3] Frier, Karton and Kocher,
internet-draft-tls-ssl-version3-00.txt: "The SSL 3.0 Protocol", Nov internet-draft-tls-ssl-version3-00.txt: "The SSL 3.0 Protocol", Nov
18 1996. 18 1996.
[TCP] ISI for DARPA, RFC 793: Transport Control Protocol, September [TCP] ISI for DARPA, RFC 793: Transport Control Protocol, September
1981. 1981.
[TEL] J. Postel and J. Reynolds, RFC 854/5, May, 1993. [TEL] J. Postel and J. Reynolds, RFC 854/5, May, 1993.
[X509] CCITT. Recommendation X.509: "The Directory - Authentication [X509] CCITT. Recommendation X.509: "The Directory - Authentication
skipping to change at page 68, line 17 skipping to change at page 69, line 11
[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 Credits
Working Group Chair Working Group Chair
Win Treese Win Treese
Open Market Open Market
treeseopenmarket.com | treese@openmarket.com
Editors Editors
Tim Dierks Christopher Allen Christopher Allen Tim Dierks
Consensus Development Consensus Development Consensus Development Consensus Development
timd@consensus.com christophera@consensus.com christophera@consensus.com timd@consensus.com
Authors Authors
Tim Dierks Philip L. Karlton
Consensus Development Netscape Communications
timd@consensus.com karlton@netscape.com
Alan O. Freier Paul C. Kocher Alan O. Freier Paul C. Kocher
Netscape Communications Independent Consultant Netscape Communications Independent Consultant
freier@netscape.com pck@netcom.com freier@netscape.com pck@netcom.com
Philip L. Karlton Tim Dierks
Netscape Communications Consensus Development
karlton@netscape.com timd@consensus.com
Other contributors Other contributors
Martin Abadi Robert Relyea Martin Abadi Robert Relyea
Digital Equipment Corporation Netscape Communications Digital Equipment Corporation Netscape Communications
ma@pa.dec.com relyea@netscape.com ma@pa.dec.com relyea@netscape.com
Taher Elgamal Jim Roskind | Ran Canetti Jim Roskind
Netscape Communications Netscape Communications | IBM Watson Research Center Netscape Communications
elgamal@netscape.com jar@netscape.com | canetti@watson.ibm.com jar@netscape.com
Anil Gangolli Micheal J. Sabin, Ph. D. Taher Elgamal Micheal J. Sabin, Ph. D.
Netscape Communications Consulting Engineer Netscape Communications Consulting Engineer
gangolli@netscape.com msabin@netcom.com elgamal@netscape.com msabin@netcom.com
| Anil Gangolli Dan Simon
| Netscape Communications Microsoft
| gangolli@netscape.com dansimon@microsoft.com
Kipp E.B. Hickman Tom Weinstein Kipp E.B. Hickman Tom Weinstein
Netscape Communications Netscape Communications Netscape Communications Netscape Communications
kipp@netscape.com tomw@netscape.com kipp@netscape.com tomw@netscape.com
Early reviewers | Hugo Krawczyk
Robert Baldwin Clyde Monma | IBM Watson Research Center
RSA Data Security, Inc. Bellcore | hugo@watson.ibm.com
baldwin@rsa.com clyde@bellcore.com
George Cox Eric Murray
Intel Corporation ericm@lne.com
cox@ibeam.jf.intel.com
Cheri Dowell Avi Rubin
Sun Microsystems Bellcore
cheri@eng.sun.com rubin@bellcore.com
Stuart Haber Don Stephenson
Bellcore Sun Microsystems
stuart@bellcore.com don.stephenson@eng.sun.com
Burt Kaliski Joe Tardo
RSA Data Security, Inc. General Magic
burt@rsa.com tardo@genmagic.com
Comments Comments
] Comments on this draft should be sent to the editors, Tim Dierks and ] Comments on this draft should be sent to the editors, Tim Dierks and
] Christopher Allen at the address <ietf-tls-editors@consensus.com>, ] Christopher Allen at the address <ietf-tls-editors@consensus.com>,
] or to the IETF Transport Layer Security (TLS) Working Group. ] or to the IETF Transport Layer Security (TLS) Working Group.
] The discussion list for the IETF TLS working group is located at the ] The discussion list for the IETF TLS working group is located at the
] e-mail address <ietf-tls@consensus.com>. Information on the group ] e-mail address <ietf-tls@consensus.com>. Information on the group
] and information on how to subscribe to the list is at ] and information on how to subscribe to the list is at
 End of changes. 

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