draft-ietf-avtcore-srtp-aes-gcm-10.txt   draft-ietf-avtcore-srtp-aes-gcm-11.txt 
Network Working Group D. McGrew Network Working Group D. McGrew
Internet Draft Cisco Systems, Inc. Internet Draft Cisco Systems, Inc.
Intended Status: Standards Track K. Igoe Intended Status: Standards Track K. Igoe
Expires: March 27, 2014 National Security Agency Expires: October 03, 2014 National Security Agency
September 23, 2013 April 01, 2014
AES-GCM and AES-CCM Authenticated Encryption in Secure RTP (SRTP) AES-GCM and AES-CCM Authenticated Encryption in Secure RTP (SRTP)
draft-ietf-avtcore-srtp-aes-gcm-10 draft-ietf-avtcore-srtp-aes-gcm-11
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current. Drafts is at http://datatracker.ietf.org/drafts/current.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 27, 2014. This Internet-Draft will expire on October 03, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 15 skipping to change at page 2, line 15
Abstract Abstract
This document defines how AES-GCM and AES-CCM Authenticated This document defines how AES-GCM and AES-CCM Authenticated
Encryption with Associated Data algorithms can be used to provide Encryption with Associated Data algorithms can be used to provide
confidentiality and data authentication in the SRTP protocol. confidentiality and data authentication in the SRTP protocol.
Table of Contents Table of Contents
1. Introduction.....................................................3 1. Introduction.....................................................3
2. Conventions Used In This Document................................4 2. Conventions Used In This Document................................4
3. Overview of the SRTP/SRTCP Security Architecture.................4 3. Overview of the SRTP/SRTCP AEAD security Architecture............4
4. Terminology......................................................4 4. Terminology......................................................5
5. Generic AEAD Processing..........................................5 5. Generic AEAD Processing..........................................5
5.1. Types of Input Data.........................................5 5.1. Types of Input Data.........................................5
5.2. AEAD Invocation Inputs and Outputs..........................6 5.2. AEAD Invocation Inputs and Outputs..........................5
5.2.1. Encrypt Mode...........................................6 5.2.1. Encrypt Mode...........................................6
5.2.2. Decrypt Mode...........................................6 5.2.2. Decrypt Mode...........................................6
5.3. Handling of AEAD Authentication.............................7 5.3. Handling of AEAD Authentication.............................7
6. Counter Mode Encryption..........................................7 6. Counter Mode Encryption..........................................7
7. AEAD_AES_128_CCM_12 and AEAD_AES_256_CCM_12......................8 7. AEAD_AES_128_CCM_12 and AEAD_AES_256_CCM_12......................8
8. Unneeded SRTP/SRTCP Fields.......................................8 8. Unneeded SRTP/SRTCP Fields.......................................8
8.1. SRTP/SRTCP Authentication Field.............................9 8.1. SRTP/SRTCP Authentication Field.............................9
8.2. RTP Padding.................................................9 8.2. RTP Padding.................................................9
9. AES-GCM/CCM processing for SRTP..................................9 9. AES-GCM/CCM processing for SRTP..................................9
9.1. SRTP IV formation for AES-GCM and AES-CCM...................9 9.1. SRTP IV formation for AES-GCM and AES-CCM...................9
9.2. Data Types in SRTP Packets.................................10 9.2. Data Types in SRTP Packets.................................10
9.3. Handling Header Extensions.................................11 9.3. Handling Header Extensions.................................12
9.4. Prevention of SRTP IV Reuse................................12 9.4. Prevention of SRTP IV Reuse................................13
10. AES-GCM/CCM Processing of SRTCP Compound Packets...............12 10. AES-GCM/CCM Processing of SRTCP Compound Packets...............14
10.1. SRTCP IV formation for AES-GCM and AES-CCM................12 10.1. SRTCP IV formation for AES-GCM and AES-CCM................14
10.2. Data Types in Encrypted SRTCP Compound Packets............13 10.2. Data Types in Encrypted SRTCP Compound Packets............14
10.3. Data Types in Unencrypted SRTCP Compound Packets..........14 10.3. Data Types in Unencrypted SRTCP Compound Packets..........16
10.4. Prevention of SRTCP IV Reuse..............................15 10.4. Prevention of SRTCP IV Reuse..............................17
11. Constraints on AEAD for SRTP and SRTCP.........................15 11. Constraints on AEAD for SRTP and SRTCP.........................17
12. Key Derivation Functions.......................................16 12. Key Derivation Functions.......................................18
13. Summary of Algorithm Characteristics...........................16 13. Summary of Algorithm Characteristics...........................19
13.1. AES-GCM for SRTP/SRTCP....................................17 13.1. AES-GCM for SRTP/SRTCP....................................19
13.2. AES-CCM for SRTP/SRTCP....................................19 13.2. AES-CCM for SRTP/SRTCP....................................21
14. Security Considerations........................................22 14. Security Considerations........................................24
14.1. Handling of Security Critical Parameters..................22 14.1. Handling of Security Critical Parameters..................24
14.2. Size of the Authentication Tag............................22 14.2. Size of the Authentication Tag............................25
15. IANA Considerations............................................23 15. IANA Considerations............................................26
15.1. SDES......................................................23 15.1. SDES......................................................26
15.2. DTLS......................................................24 15.2. DTLS......................................................27
15.3. MIKEY.....................................................27 15.3. MIKEY.....................................................30
15.4. AEAD registry.............................................28 15.4. AEAD registry.............................................31
16. Parameters for use with MIKEY..................................28 16. Parameters for use with MIKEY..................................31
17. Acknowledgements...............................................29 17. Acknowledgements...............................................32
18. References.....................................................30 18. References.....................................................33
18.1. Normative References......................................30 18.1. Normative References......................................33
18.2. Informative References....................................32 18.2. Informative References....................................35
1. Introduction 1. Introduction
The Secure Real-time Transport Protocol (SRTP) [RFC3711] is a profile The Secure Real-time Transport Protocol (SRTP) [RFC3711] is a profile
of the Real-time Transport Protocol (RTP) [RFC3550], which can of the Real-time Transport Protocol (RTP) [RFC3550], which can
provide confidentiality, message authentication, and replay provide confidentiality, message authentication, and replay
protection to the RTP traffic and to the control traffic for RTP, the protection to the RTP traffic and to the control traffic for RTP, the
Real-time Transport Control Protocol (RTCP). It is important to note Real-time Transport Control Protocol (RTCP). It is important to note
that the outgoing SRTP packets from a single endpoint may be that the outgoing SRTP packets from a single endpoint may be
originating from several independent data sources. originating from several independent data sources.
skipping to change at page 3, line 39 skipping to change at page 3, line 39
upon AES. This specification makes use of the AES versions that use upon AES. This specification makes use of the AES versions that use
128-bit and 256-bit keys, which we call AES-128 and AES-256, 128-bit and 256-bit keys, which we call AES-128 and AES-256,
respectively. respectively.
Any AEAD algorithm provides an intrinsic authentication tag. In many Any AEAD algorithm provides an intrinsic authentication tag. In many
applications the authentication tag is truncated to less than full applications the authentication tag is truncated to less than full
length. This document only allows three values for the length of the length. This document only allows three values for the length of the
authentication tag: the length of the authentication tags MUST be authentication tag: the length of the authentication tags MUST be
either 8 octets, 12 octets, or 16 octets in length. As with the size either 8 octets, 12 octets, or 16 octets in length. As with the size
of the key, the length of the authentication tag size is set when the of the key, the length of the authentication tag size is set when the
session is initiated and SHOULD NOT be altered. Thus each AEAD will session is initiated and SHOULD NOT be altered. Thus each algorithm
have a total of six configurations, reflecting the two choices for AEAD will have a total of six configurations, reflecting the two
key size (either 128 or 256 bits) and the three choices for the choices for key size (either 128 or 256 bits) and the three choices
length of the authentication tag (either 8, 12 or 16 octets). for the length of the authentication tag (either 8, 12 or 16
octets).
The Galois/Counter Mode of operation (GCM) and the Counter with The Galois/Counter Mode of operation (GCM) and the Counter with
Cipher Block Chaining-Message Authentication Code mode of operation Cipher Block Chaining-Message Authentication Code mode of operation
(CCM) are both AEAD modes of operation for block ciphers. Both use (CCM) are both AEAD modes of operation for block ciphers. Both use
counter mode to encrypt the data, an operation that can be counter mode to encrypt the data, an operation that can be
efficiently pipelined. Further, GCM authentication uses operations efficiently pipelined. Further, GCM authentication uses operations
that are particularly well suited to efficient implementation in that are particularly well suited to efficient implementation in
hardware, making it especially appealing for high-speed hardware, making it especially appealing for high-speed
implementations, or for implementations in an efficient and compact implementations, or for implementations in an efficient and compact
circuit. CCM is well suited for use in compact software circuit. CCM is well suited for use in compact software
skipping to change at page 4, line 16 skipping to change at page 4, line 16
particularly AES-GCM and AES-CCM, to provide confidentiality and particularly AES-GCM and AES-CCM, to provide confidentiality and
message authentication within SRTP and SRTCP packets. message authentication within SRTP and SRTCP packets.
2. Conventions Used In This Document 2. Conventions Used In This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
3. Overview of the SRTP/SRTCP Security Architecture 3. Overview of the SRTP/SRTCP AEAD security Architecture
SRTP/SRTCP security is based upon the following principles: SRTP/SRTCP AEAD security is based upon the following principles:
a) Both privacy and authentication are based upon the use of a) Both privacy and authentication are based upon the use of
symmetric algorithms. An AEAD algorithm such as AES-CCM or symmetric algorithms. An AEAD algorithm such as AES-CCM or
AES-GCM combines privacy and authentication into a single AES-GCM combines privacy and authentication into a single
process. process.
b) A secret master key is shared by all participating endpoints, b) A secret master key is shared by all participating endpoints,
both those originating SRTP/SRTCP packets and those receiving both those originating SRTP/SRTCP packets and those receiving
these packets. Any given master key MAY be used these packets. Any given master key MAY be used
simultaneously by several endpoints to originate SRTP/SRTCP simultaneously by several endpoints to originate SRTP/SRTCP
packets (as well one or more endpoints using this master key packets (as well one or more endpoints using this master key
to process inbound data). to process inbound data).
c) A Key Derivation Function is applied to the shared master key c) A Key Derivation Function is applied to the shared master key
value to form separate encryption keys, authentication keys value to form separate encryption keys, authentication keys
and salting keys for SRTP and for SRTCP (a total of six and salting keys for SRTP and for SRTCP (a total of six
keys). This process is described in sections 4.3.1 and 4.3.3 keys). This process is described in section 4.3 of
of [RFC3711]. Since AEAD algorithms such as AES-CCM and [RFC3711]. Since AEAD algorithms such as AES-CCM and AES-GCM
AES-GCM combine encryption and authentication into a single combine encryption and authentication into a single process,
process, AEAD algorithms do not make use of the AEAD algorithms do not make use of the authentication keys.
authentication keys. The master key MUST be at least as The master key MUST be at least as large as the encryption
large as the encryption key derived from it. key derived from it.
d) Each time an instantiation of AES-GCM or AES-CCM is invoked d) Aside from making modifications to IANA registries to allow
AES-GCM and AES-CCM to work with SDES, DTLS and MIKEY, the
details of how the master key is established and shared
between the participants are outside the scope of this
document. Similarly any mechanism for rekeying an existing
session is outside the scope of the document.
e) Each time an instantiation of AES-GCM or AES-CCM is invoked
to encrypt and authenticate an SRTP or SRTCP data packet a to encrypt and authenticate an SRTP or SRTCP data packet a
new IV is used. SRTP combines the 4-octet synchronization new IV is used. SRTP combines the 4-octet synchronization
source (SSRC) identifier, the 4-octet rollover counter (ROC), source (SSRC) identifier, the 4-octet rollover counter (ROC),
and the 2-octet sequence number(SEQ) with the 12-octet and the 2-octet sequence number (SEQ) with the 12-octet
encryption salt to form a 12-octet IV (see section 9.1). encryption salt to form a 12-octet IV (see section 9.1).
SRTCP combines the SSRC and 31-bit SRTCP index with the SRTCP combines the SSRC and 31-bit SRTCP index with the
encryption salt to form a 12-octet IV (see section 10.1). encryption salt to form a 12-octet IV (see section 10.1).
4. Terminology 4. Terminology
The following terms have very specific meanings in the context of The following terms have very specific meanings in the context of
this RFC: this RFC:
Crypto Context: For the purposes of this document, a crypto
context is the outcome of any process which
results in authentication of each endpoint in the
SRTP session and possession by each endpoint of a
shared secret master key. Various encryption
keys, authentication keys and salts are derived
from the master key. Aside from making
modifications to IANA registries to allow AES-GCM
and AES-CCM to work with SDES, DTLS and MIKEY,
the details of how the master key is established
are outside the scope of this document.
Similarly any mechanism for rekeying an existing
Cipher Context is outside the scope of the
document.
Instantiation: In AEAD, an instantiation is an (Encryption_key, Instantiation: In AEAD, an instantiation is an (Encryption_key,
salt) pair together with all of the data salt) pair together with all of the data
structures (for example, counters) needed for it structures (for example, counters) needed for it
to function properly. In SRTP/SRTCP, each to function properly. In SRTP/SRTCP, each
endpoint will need two instantiations of the AEAD endpoint will need two instantiations of the AEAD
algorithm for each master key in its possession, algorithm for each master key in its possession,
one instantiation for SRTP traffic and one one instantiation for SRTP traffic and one
instantiation for SRTCP traffic. instantiation for SRTCP traffic.
Invocation: SRTP/SRTCP data streams are broken into packets. Invocation: SRTP/SRTCP data streams are broken into packets.
skipping to change at page 6, line 8 skipping to change at page 6, line 4
Raw Data: Data that is to be neither encrypted nor Raw Data: Data that is to be neither encrypted nor
authenticated. authenticated.
Which portions of SRTP/SRTCP packets that are to be treated as Which portions of SRTP/SRTCP packets that are to be treated as
associated data, which are to be treated as plaintext, and which are associated data, which are to be treated as plaintext, and which are
to be treated as raw data are covered in sections 9.2, 10.2 and to be treated as raw data are covered in sections 9.2, 10.2 and
10.3. 10.3.
5.2. AEAD Invocation Inputs and Outputs 5.2. AEAD Invocation Inputs and Outputs
5.2.1. Encrypt Mode 5.2.1. Encrypt Mode
Inputs: Inputs:
Encryption_key Octet string, either 16 or 32 Encryption_key Octet string, either 16 or 32
octets long octets long
Initialization_Vector Octet string, 12 octets long Initialization_Vector Octet string, 12 octets long
Associated_Data Bit string of variable length Associated_Data Octet string of variable length
Plaintext Bit string of variable length Plaintext Octet string of variable length
Tag_Size_Flag (CCM only*) One Octet Tag_Size_Flag (CCM only*) One Octet
Outputs Outputs
Ciphertext Bit string, length = Ciphertext Octet string, length =
length(Plaintext)+tag_length length(Plaintext)+tag_length
(*) For GCM, the algorithm choice determines the tag size. (*) CCM mode requires tag length to be explicitly input to
the algorithm, whereas with GCM, the tag is simply truncated.
For GCM, the algorithm choice determines the tag size.
As defined in [RFC3610], AES-CCM authentication uses a Tag_Size_Flag In both CCM and GCM, the algorithm negotiation selects what tag size
to specify the length of the intrinsic authentication tag provided by is to be used. In GCM, the authentication tag is simply truncated to
AES-CCM authentication. For the three tag lengths allowed in this the appropriate length, but CCM requires that the tag length be an
document the corresponding Tag_Size_Flag values are as follows: explicitly input to the algorithm as the Tag_Size_Field. For the
three tag lengths allowed in this document the corresponding
Tag_Size_Flag values are as follows:
Tag Length | Tag_Size_Flag (hex) Tag Length | Tag_Size_Flag (hex)
---------------------------------- -----------------------------------
8 bytes | 5A 8 octets | 5A
12 bytes | 6A 12 octets | 6A
16 bytes | 7A 16 octets | 7A
Once an SRTP/SRTCP session has been initiated the length of the tag Once an SRTP/SRTCP session has been initiated the length of the tag
is a fixed value and cannot be altered. is a fixed value and MUST NOT be altered.
5.2.2. Decrypt Mode 5.2.2. Decrypt Mode
Inputs: Inputs:
Encryption_key Octet string, either 16 or 32 Encryption_key Octet string, either 16 or 32
Octets long octets long
Initialization_Vector Octet string, 12 octets long Initialization_Vector Octet string, 12 octets long
Associated_Data Octet string of variable length Associated_Data Octet string of variable length
Ciphertext Octet string of variable length Ciphertext Octet string of variable length
Tag_Size_Flag (CCM only*) One octet Tag_Size_Flag (CCM only*) One octet
Outputs Outputs
Plaintext Bit string, length = Plaintext Octet string, length =
length(Ciphertext)-tag_length length(Ciphertext)-tag_length
Validity_Flag Boolean, TRUE if valid, Validity_Flag Boolean, TRUE if valid,
FALSE otherwise FALSE otherwise
(*) For GCM, the algorithm choice determines the tag size. (*) For GCM, the algorithm choice determines the tag size.
As mentioned in section 5.2.1, only three tag lengths are supported As mentioned in section 5.2.1, only three tag lengths are supported
for use in SRTP/SRTCP, namely 8 octets, 12 octets and 16 octets. for use in SRTP/SRTCP, namely 8 octets, 12 octets and 16 octets.
5.3. Handling of AEAD Authentication 5.3. Handling of AEAD Authentication
skipping to change at page 7, line 18 skipping to change at page 7, line 15
(*) For GCM, the algorithm choice determines the tag size. (*) For GCM, the algorithm choice determines the tag size.
As mentioned in section 5.2.1, only three tag lengths are supported As mentioned in section 5.2.1, only three tag lengths are supported
for use in SRTP/SRTCP, namely 8 octets, 12 octets and 16 octets. for use in SRTP/SRTCP, namely 8 octets, 12 octets and 16 octets.
5.3. Handling of AEAD Authentication 5.3. Handling of AEAD Authentication
AEAD requires that all incoming packets MUST pass AEAD authentication AEAD requires that all incoming packets MUST pass AEAD authentication
before any other action takes place. Plaintext and associated data before any other action takes place. Plaintext and associated data
MUST NOT be released until the AEAD authentication tag has been MUST NOT be released until the AEAD authentication tag has been
validated. Further, when GCM is being used, the ciphertext MUST NOT validated. Further the ciphertext MUST NOT be decrypted until the
be decrypted until the AEAD tag has been validated. AEAD tag has been validated.
Should the AEAD tag prove to be invalid, the packet in question is to Should the AEAD tag prove to be invalid, the packet in question is to
be discarded and a Validation Error flag raised. Local policy be discarded and a Validation Error flag raised. Local policy
determines how this flag is to be handled and is outside the scope of determines how this flag is to be handled and is outside the scope of
this document. this document.
6. Counter Mode Encryption 6. Counter Mode Encryption
In both GCM and CCM, each outbound packet uses a 12-octet IV and an In both GCM and CCM, each outbound packet uses a 12-octet IV and an
encryption key to form two outputs, a 16-octet first_key_block which encryption key to form two outputs, a 16-octet first_key_block which
is used in forming the authentication tag and a keystream of octets is used in forming the authentication tag and a keystream of octets
which is XORed to the plaintext to form cipher. which is XORed to the plaintext to form cipher.
When GCM is used, the concatenation of a 12-octet IV (see sections When GCM is used, the concatenation of a 12-octet IV (see sections
9.1 and 10.1)with a 4-octet block counter forms the input to AES. 9.1 and 10.1) with a 4-octet block counter forms the input to AES.
This is used to build a key_stream as follows: This is used to build a key_stream as follows:
def GCM_keystream( Plaintext, IV, Encryption_key ): def GCM_keystream( Plaintext_len, IV, Encryption_key ):
assert len(plaintext) <= (2**36) - 32 ## measured in octets assert Plaintext_len <= (2**36) - 32 ## measured in octets
key_stream = "" key_stream = ""
block_counter = 1 block_counter = 1
first_key_block = AES_ENC( data=IV||block_counter, first_key_block = AES_ENC( data=IV||block_counter,
key=Encryption_key ) key=Encryption_key )
while len(key_stream) < len(Plaintext): while len(key_stream) < Plaintext_len:
block_counter = block_counter + 1 block_counter = block_counter + 1
key_block = AES_ENC( data=IV||block_counter, key_block = AES_ENC( data=IV||block_counter,
key=Encryption_key ) key=Encryption_key )
key_stream = key_stream || key_block key_stream = key_stream || key_block
key_stream = truncate( key_stream, len(Plaintext) ) key_stream = truncate( key_stream, Plaintext_len )
return (first_key_block, key_stream ) return (first_key_block, key_stream )
In AES-CCM counter mode encryption, the AES data input consists of In AES-CCM counter mode encryption, the AES data input consists of
the concatenation of a 1-octet flag, a 12-octet IV, and a 3-octet the concatenation of a 1-octet flag, a 12-octet IV, and a 3-octet
block counter. Note that in this application the flag octet will block counter. Note that in this application the flag octet will
always have the value 0x02 (see section 2.3 of [RFC3610]). A always have the value 0x02 (see section 2.3 of [RFC3610]). A
(first_key_block, key_stream) pair is formed as follows: (first_key_block, key_stream) pair is formed as follows:
def CCM_keystream( Plaintext, IV, Encryption_key ): def CCM_keystream( Plaintext_len, IV, Encryption_key ):
assert len(Plaintext) <= (2**28)-16 ## measured in octets assert Plaintext_len <= (2**28)-16 ## measured in octets
key_stream = "" key_stream = ""
block_counter = 0 block_counter = 0
first_key_block = AES_ENC( data=0x02||IV||block_counter, first_key_block = AES_ENC( data=0x02||IV||block_counter,
key=Encryption_key ) key=Encryption_key )
while len(key_stream)<len(Plaintext): while len(key_stream)<Plaintext_len:
block_counter = block_counter + 1 block_counter = block_counter + 1
key_block = AES_ENC( data=0x02||IV||block_counter, key_block = AES_ENC( data=0x02||IV||block_counter,
key=Encryption_key ) key=Encryption_key )
key_stream = key_stream || key_block key_stream = key_stream || key_block
key_stream = truncate( key_stream, len(Plaintext) ) key_stream = truncate( key_stream, Plaintext_len )
return (first_key_block, key_stream ) return (first_key_block, key_stream )
These keystream generation processes allow for a keystream of length These keystream generation processes allow for a keystream of length
up to (2^28)-16 octets for AES-CCM and up to (2^36)-32 octets for up to (2^28)-16 octets for AES-CCM and up to (2^36)-32 octets for
AES-GCM. AES-GCM.
With any counter mode, if the same (IV, Encryption_key) pair is used With any counter mode, if the same (IV, Encryption_key) pair is used
twice, precisely the same keystream is formed. As explained in twice, precisely the same keystream is formed. As explained in
section 9.1 of RFC 3711, this is a cryptographic disaster. section 9.1 of RFC 3711, this is a cryptographic disaster. For GCM
the consequences are even worse as also the integrity is compromised,
and not only for the current packet stream, but for all future use of
encryption_key.
7. AEAD_AES_128_CCM_12 and AEAD_AES_256_CCM_12 7. AEAD_AES_128_CCM_12 and AEAD_AES_256_CCM_12
AEAD_AES_128_CCM and AEAD_AES_256_CCM are defined in [RFC5116] with AEAD_AES_128_CCM and AEAD_AES_256_CCM are defined in [RFC5116] with
an authentication tag length of 16-octets. AEAD_AES_128_CCM_8 and an authentication tag length of 16-octets. AEAD_AES_128_CCM_8 and
AEAD_AES_256_CCM_8 are defined in [RFC6655] with an authentication AEAD_AES_256_CCM_8 are defined in [RFC6655] with an authentication
tag length of 8-octets. We require two new variants, tag length of 8-octets. We require two new variants,
AEAD_AES_128_CCM_12 and AEAD_AES_256_CCM_12, with 12-octet AEAD_AES_128_CCM_12 and AEAD_AES_256_CCM_12, with 12-octet
authentication tags. In each case the authentication tag is formed authentication tags. In each case the authentication tag is formed
by taking the 12 most significant octets (in network order) of the by taking the 12 most significant octets (in network order) of the
skipping to change at page 9, line 36 skipping to change at page 9, line 36
provided by RTP. It is RECOMMENDED that the RTP padding mechanism provided by RTP. It is RECOMMENDED that the RTP padding mechanism
not be used unless it is necessary to disguise the length of the not be used unless it is necessary to disguise the length of the
underlying plaintext. underlying plaintext.
9. AES-GCM/CCM processing for SRTP 9. AES-GCM/CCM processing for SRTP
9.1. SRTP IV formation for AES-GCM and AES-CCM 9.1. SRTP IV formation for AES-GCM and AES-CCM
The 12 octet initialization vector used by both AES-GCM and AES-CCM The 12 octet initialization vector used by both AES-GCM and AES-CCM
SRTP is formed by first concatenating 2-octets of zeroes, the 4-octet SRTP is formed by first concatenating 2-octets of zeroes, the 4-octet
SSRC, the 4-octer Rollover Counter (ROC) and the two octet sequence SSRC, the 4-octet Rollover Counter (ROC) and the two octet sequence
number SEQ. The resulting 12-octet value is then XORed to the number SEQ. The resulting 12-octet value is then XORed to the
12-octet salt to form the 12-octet IV. 12-octet salt to form the 12-octet IV.
0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 1 1
0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1
+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+
|00|00| SSRC | ROC | SEQ |---+ |00|00| SSRC | ROC | SEQ |---+
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
skipping to change at page 10, line 26 skipping to change at page 10, line 26
| Initialization Vector |<--+ | Initialization Vector |<--+
+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+
Figure 1: AES-GCM and AES-CCM SRTP Figure 1: AES-GCM and AES-CCM SRTP
Initialization Vector formation. Initialization Vector formation.
9.2. Data Types in SRTP Packets 9.2. Data Types in SRTP Packets
All SRTP packets MUST be both authenticated and encrypted. The data All SRTP packets MUST be both authenticated and encrypted. The data
fields within the SRTP packets are broken into Associated Data, fields within the SRTP packets are broken into Associated Data,
Plaintext and Raw Data as follows (see figure 2): Plaintext and Raw Data as follows (see Figure 2):
Associated Data: The version (2 bits), padding flag (1 bit), Associated Data: The version V (2 bits), padding flag P (1 bit),
extension flag (1 bit), CSRC count (4 bits), extension flag X (1 bit), CSRC count CC (4 bits),
sequence number (16 bits), timestamp (32 bits), marker M (1 bit), the Payload Type PT (8 bits),
SSRC (32 bits), optional contributing source the sequence number (16 bits), timestamp (32
identifiers (CSRCs, 32 bits each), and optional bits), SSRC (32 bits), optional contributing
RTP extension (variable length). source identifiers (CSRCs, 32 bits each), and
optional RTP extension (variable length).
Plaintext: The RTP payload (variable length), RTP padding Plaintext: The RTP payload (variable length), RTP padding
(if used, variable length), and RTP pad count ( (if used, variable length), and RTP pad count (
if used, 1 octet). if used, 1 octet).
Raw Data: The optional 32-bit SRTP MKI and the 32-bit SRTP Raw Data: The optional variable length SRTP MKI and SRTP
authentication tag (whose use is NOT authentication tag (whose use is NOT
RECOMMENDED). RECOMMENDED). These fields are appended after
encryption has been performed.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A |V=2|P|X| CC |M| Packet Type | sequence number | A |V=2|P|X| CC |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | timestamp | A | timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | synchronization source (SSRC) identifier | A | synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
A | contributing source (CSRC) identifiers (optional) | A | contributing source (CSRC) identifiers (optional) |
A | .... | A | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | RTP extension (OPTIONAL) | A | RTP extension (OPTIONAL) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P | payload ... | P | payload ... |
P | +-------------------------------+ P | +-------------------------------+
P | | RTP padding | RTP pad count | P | | RTP padding | RTP pad count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R : SRTP MKI (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R : authentication tag (NOT RECOMMENDED) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P = Plaintext (to be encrypted and authenticated) P = Plaintext (to be encrypted and authenticated)
A = Associated Data (to be authenticated only) A = Associated Data (to be authenticated only)
R = neither encrypted nor authenticated
Note: The RTP padding and RTP padding count fields are optional Figure 2: Structure of an SRTP packet before Authenticated
and are not recommended Encryption
Figure 2: AEAD inputs from an SRTP packet 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A |V=2|P|X| CC |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
A | contributing source (CSRC) identifiers (optional) |
A | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | RTP extension (OPTIONAL) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
C | cipher |
C | ... |
C | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R : SRTP MKI (OPTIONAL) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R : SRTP authentication tag (NOT RECOMMENDED) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Since the AEAD cipher is larger than the plaintext by exactly the C = Cipertext (encrypted and authenticated)
A = Associated Data (authenticated only)
R = neither encrypted nor authenticated, added
after authenticated encryption completed
Figure 3: Structure of an SRTP packet after Authenticated
Encryption
Since the AEAD ciphertext is larger than the plaintext by exactly the
length of the AEAD authentication tag, the corresponding SRTP length of the AEAD authentication tag, the corresponding SRTP
encrypted packet replaces the plaintext field by a slightly larger encrypted packet replaces the plaintext field by a slightly larger
field containing the cipher. Even if the plaintext field is empty, field containing the cipher. Even if the plaintext field is empty,
AEAD encryption must still be performed, with the resulting cipher AEAD encryption must still be performed, with the resulting cipher
consisting solely of the authentication tag. This tag is to be consisting solely of the authentication tag. This tag is to be
placed immediately before the optional SRTP MKI and SRTP placed immediately before the optional SRTP MKI and SRTP
authentication tag fields. authentication tag fields.
9.3. Handling Header Extensions 9.3. Handling Header Extensions
skipping to change at page 12, line 12 skipping to change at page 13, line 12
selected RTP header extension elements. For the AEAD_AES_128_GCM and selected RTP header extension elements. For the AEAD_AES_128_GCM and
the AEAD_AES_128_CCM algorithms, this keystream MUST be generated in the AEAD_AES_128_CCM algorithms, this keystream MUST be generated in
the manner defined in [RFC6904] using the AES_128_CM transform. For the manner defined in [RFC6904] using the AES_128_CM transform. For
the AEAD_AES_256_GCM and the AEAD_AES_256_CCM algorithms, the the AEAD_AES_256_GCM and the AEAD_AES_256_CCM algorithms, the
keystream MUST be generated in the manner defined for the AES_256_CM keystream MUST be generated in the manner defined for the AES_256_CM
transform. The originator must perform any required header extension transform. The originator must perform any required header extension
encryption before the AEAD algorithm is invoked. encryption before the AEAD algorithm is invoked.
As with the other fields contained within the RTP header, both As with the other fields contained within the RTP header, both
encrypted and unencrypted header extensions are to be treated by the encrypted and unencrypted header extensions are to be treated by the
AEAD algorithm as Additional Authenticated Data (AAD). Thus the AEAD AEAD algorithm as Associated Data (AD). Thus the AEAD algorithm does
algorithm does not provide any additional privacy for the header not provide any additional privacy for the header extensions, but
extensions, but does provide integrity and authentication. does provide integrity and authentication.
9.4. Prevention of SRTP IV Reuse 9.4. Prevention of SRTP IV Reuse
In order to prevent IV reuse, we must ensure that the (ROC,SEQ,SSRC) In order to prevent IV reuse, we must ensure that the (ROC,SEQ,SSRC)
triple is never used twice with the same master key. There are two triple is never used twice with the same master key. There are two
phases to this issue. phases to this issue.
Counter Management: A rekey MUST be performed to establish a new Counter Management: A rekey MUST be performed to establish a new
master key before the (ROC,SEQ) pair cycles master key before the (ROC,SEQ) pair cycles
back to its original value. back to its original value. Note that
implicitly assumes that either the outgoing RTP
process is trusted to not attempt to repeat a
SEQ value, or that the encryption process
ensures that the SEQ number of the packets
presented to it are always incremented in the
proper fashion. This is particularly important
for GCM since using the same SEQ value twice
compromises the authentication mechanism. For
GCM, the SEQ and SSRC values used MUST either
be generated or checked by the SRTP
implementation, or by a module (e.g. the RTP
application) that can be considered equally
trusted as the SRTP implementation. While
[RFC3711] allows detecting SSRC collisions
after they happen, SRTP using GCM with shared
master keys MUST prevent SSRC collision from
happening even once.
SSRC Management: For a given master key, the set of all SSRC SSRC Management: For a given master key, the set of all SSRC
values used with that master key must be values used with that master key must be
partitioned into disjoint pools, one pool for partitioned into disjoint pools, one pool for
each endpoint using that master key to each endpoint using that master key to
originate outbound data. Each such originating originate outbound data. Each such originating
endpoint MUST only issue SSRC values from the endpoint MUST only issue SSRC values from the
pool it has been assigned. Further, each pool it has been assigned. Further, each
originating endpoint MUST maintain a history of originating endpoint MUST maintain a history of
outbound SSRC identifiers that it has issued outbound SSRC identifiers that it has issued
within the lifetime of the current master key, within the lifetime of the current master key,
and when a new synchronization source requests and when a new synchronization source requests
an SSRC identifier it MUST NOT be given an an SSRC identifier it MUST NOT be given an
identifier that has been previously issued. A identifier that has been previously issued. A
rekey MUST be performed before any of the rekey MUST be performed before any of the
originating endpoints using that master key originating endpoints using that master key
exhausts its pool of SSRC values. exhausts its pool of SSRC values. Further, the
identity of the entity giving out SSRC values
MUST be verified, and the SSRC signaling MUST
be integrity protected.
10. AES-GCM/CCM Processing of SRTCP Compound Packets 10. AES-GCM/CCM Processing of SRTCP Compound Packets
All SRTCP compound packets MUST be authenticated, but unlike SRTP, All SRTCP compound packets MUST be authenticated, but unlike SRTP,
SRTCP packet encryption is optional. A sender can select which SRTCP packet encryption is optional. A sender can select which
packets to encrypt, and indicates this choice with a 1-bit encryption packets to encrypt, and indicates this choice with a 1-bit encryption
flag (located just before the 31-bit SRTCP index) flag (located just before the 31-bit SRTCP index)
10.1. SRTCP IV formation for AES-GCM and AES-CCM 10.1. SRTCP IV formation for AES-GCM and AES-CCM
The 12 octet initialization vector used by both AES-GCM and AES-CCM The 12-octet initialization vector used by both AES-GCM and AES-CCM
SRTCP is formed by first concatenating 2-octets of zeroes, the SRTCP is formed by first concatenating 2-octets of zeroes, the
4-octet Synchronization Source identifier (SSRC), 2-octets of zeroes, 4-octet Synchronization Source identifier (SSRC), 2-octets of zeroes,
a single zero bit, and the 31-bit SRTCP Index. The resulting a single zero bit, and the 31-bit SRTCP Index. The resulting
12-octet value is then XORed to the 12-octet salt to form the 12-octet value is then XORed to the 12-octet salt to form the
12-octet IV. 12-octet IV.
0 1 2 3 4 5 6 7 8 9 10 11 0 1 2 3 4 5 6 7 8 9 10 11
+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+
|00|00| SSRC |00|00|0+SRTCP Idx|---+ |00|00| SSRC |00|00|0+SRTCP Idx|---+
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
| Encryption Salt |->(+) | Encryption Salt |->(+)
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
| Initialization Vector |<--+ | Initialization Vector |<--+
+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+
Figure 3: SRTCP Initialization Vector formation Figure 4: SRTCP Initialization Vector formation
10.2. Data Types in Encrypted SRTCP Compound Packets 10.2. Data Types in Encrypted SRTCP Compound Packets
When the encryption flag is set to 1, the SRTCP packet is broken into When the encryption flag is set to 1, the SRTCP packet is broken into
plaintext, associated data, and raw (untouched) data as listed below plaintext, associated data, and raw (untouched) data as listed below
(see figure 4): (see figure 5):
Associated Data: The packet version (2 bits), padding flag (1 Associated Data: The packet version V (2 bits), padding flag P (1
bit), reception report count (5 bits), packet bit), reception report count RC (5 bits), packet
type (8 bits), length (2 octets), SSRC (4 type (8 bits), length (2 octets), SSRC (4
octets), encryption flag (1 bit) and SRTCP index octets), encryption flag (1 bit) and SRTCP index
(31 bits). (31 bits).
Raw Data: The 32-bit optional SRTCP MKI index and 32-bit Raw Data: The 32-bit optional SRTCP MKI index and 32-bit
SRTCP authentication tag (whose use is NOT SRTCP authentication tag (whose use is NOT
RECOMMENDED). RECOMMENDED).
Plaintext: All other data. Plaintext: All other data.
skipping to change at page 14, line 12 skipping to change at page 16, line 12
of the authentication tag. This tag is to be placed immediately of the authentication tag. This tag is to be placed immediately
before the encryption flag and SRTCP index. before the encryption flag and SRTCP index.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A |V=2|P| RC | Packet Type | length | A |V=2|P| RC | Packet Type | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | synchronization source (SSRC) of Sender | A | synchronization source (SSRC) of Sender |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P | sender info | P | sender info :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P | report block 1 | P | report block 1 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P | report block 2 | P | report block 2 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P | ... | P | ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P |V=2|P| SC | Packet Type | length | P |V=2|P| SC | Packet Type | length |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
P | SSRC/CSRC_1 | P | SSRC/CSRC_1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P | SDES items | P | SDES items :
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
P | ... | P | ... :
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
A |1| SRTCP index | A |1| SRTCP index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R | SRTCP MKI (optional) index | R | SRTCP MKI (optional) index :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R : authentication tag (NOT RECOMMENDED) : R : SRTCP authentication tag (NOT RECOMMENDED) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
P = Plaintext (to be encrypted and authenticated) P = Plaintext (to be encrypted and authenticated)
A = Associated Data (to be authenticated only) A = Associated Data (to be authenticated only)
R = neither encrypted nor authenticated R = neither encrypted nor authenticated, added after
encryption
Figure 4: AEAD SRTCP inputs when encryption flag = 1. Figure 5: AEAD SRTCP inputs when encryption flag = 1.
10.3. Data Types in Unencrypted SRTCP Compound Packets 10.3. Data Types in Unencrypted SRTCP Compound Packets
When the encryption flag is set to 0, the SRTCP compound packet is When the encryption flag is set to 0, the SRTCP compound packet is
broken into plaintext, associated data, and raw (untouched) data as broken into plaintext, associated data, and raw (untouched) data as
follows (see figure 5): follows (see figure 6):
Plaintext: None. Plaintext: None.
Raw Data: The 32-bit optional SRTCP MKI index and 32-bit Raw Data: The variable length optional SRTCP MKI index and
SRTCP authentication tag (whose use is NOT SRTCP authentication tag (whose use is NOT
RECOMMENDED). RECOMMENDED).
Associated Data: All other data. Associated Data: All other data.
Even though there is no plaintext in this RTCP packet, AEAD Even though there is no plaintext in this RTCP packet, AEAD
encryption returns a cipher field which is precisely the length of encryption returns a cipher field which is precisely the length of
the AEAD authentication tag. This cipher is to be placed before the the AEAD authentication tag. This cipher is to be placed before the
Encryption flag and the SRTCP index in the authenticated SRTCP Encryption flag and the SRTCP index in the authenticated SRTCP
packet. packet.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A |V=2|P| RC | Packet Type | length | A |V=2|P| RC | Packet Type | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | synchronization source (SSRC) of Sender | A | synchronization source (SSRC) of Sender |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | sender info | A | sender info :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | report block 1 | A | report block 1 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | report block 2 | A | report block 2 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | ... | A | ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A |V=2|P| SC | Packet Type | length | A |V=2|P| SC | Packet Type | length |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
A | SSRC/CSRC_1 | A | SSRC/CSRC_1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | SDES items | A | SDES items :
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
A | ... | A | ... :
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
A |0| SRTCP index | A |0| SRTCP index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R | SRTCP MKI (optional)index | R | SRTCP MKI (optional)index :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R : authentication tag (NOT RECOMMENDED) : R : authentication tag (NOT RECOMMENDED) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A = Associated Data (to be authenticated only) A = Associated Data (to be authenticated only)
R = neither encrypted nor authenticated R = neither encrypted nor authenticated, added after
encryption
Figure 5: AEAD SRTCP inputs when encryption flag = 0 Figure 6: AEAD SRTCP inputs when encryption flag = 0
10.4. Prevention of SRTCP IV Reuse 10.4. Prevention of SRTCP IV Reuse
A new master key MUST be established before the 31-bit SRTCP index A new master key MUST be established before the 31-bit SRTCP index
cycles back to its original value. Ideally, a rekey performed should cycles back to its original value. Ideally, a rekey should be
be performed and a new master key put in place well before the SRTCP performed and a new master key put in place well before the SRTCP
index overflows. cycles back to the starting value.
The comments on SSRC management in section 9.4 also apply. The comments on SSRC management in section 9.4 also apply.
11. Constraints on AEAD for SRTP and SRTCP 11. Constraints on AEAD for SRTP and SRTCP
In general, any AEAD algorithm can accept inputs with varying In general, any AEAD algorithm can accept inputs with varying
lengths, but each algorithm can accept only a limited range of lengths, but each algorithm can accept only a limited range of
lengths for a specific parameter. In this section, we describe the lengths for a specific parameter. In this section, we describe the
constraints on the parameter lengths that any AEAD algorithm must constraints on the parameter lengths that any AEAD algorithm must
support to be used in AEAD-SRTP. Additionally, we specify a complete support to be used in AEAD-SRTP. Additionally, we specify a complete
parameter set for two specific AEAD algorithms, namely AES-GCM and parameter set for two specific AEAD algorithms, namely AES-GCM and
AES-CCM. AES-CCM.
All AEAD algorithms used with SRTP/SRTCP MUST satisfy the three All AEAD algorithms used with SRTP/SRTCP MUST satisfy the three
constraints listed below: constraints listed below:
skipping to change at page 16, line 16 skipping to change at page 18, line 17
constraints on the parameter lengths that any AEAD algorithm must constraints on the parameter lengths that any AEAD algorithm must
support to be used in AEAD-SRTP. Additionally, we specify a complete support to be used in AEAD-SRTP. Additionally, we specify a complete
parameter set for two specific AEAD algorithms, namely AES-GCM and parameter set for two specific AEAD algorithms, namely AES-GCM and
AES-CCM. AES-CCM.
All AEAD algorithms used with SRTP/SRTCP MUST satisfy the three All AEAD algorithms used with SRTP/SRTCP MUST satisfy the three
constraints listed below: constraints listed below:
PARAMETER Meaning Value PARAMETER Meaning Value
A_MAX maximum additional MUST be at least 12 octets. A_MAX maximum associated MUST be at least 12 octets.
authenticated data data length
length
N_MIN minimum nonce (IV) MUST be 12 octets. N_MIN minimum nonce (IV) MUST be 12 octets.
length length
N_MAX maximum nonce (IV) MUST be 12 octets. N_MAX maximum nonce (IV) MUST be 12 octets.
length length
C_MAX maximum ciphertext GCM: MUST be <= 2^36-16 octets. C_MAX maximum ciphertext GCM: MUST be <= 2^36-16 octets.
length per invocation CCM: MUST be <= 2^28-16 octets. length per invocation CCM: MUST be <= 2^28 octets.
The values for C_MAX are based on purely cryptographic The values for C_MAX are based on purely cryptographic
considerations. considerations.
For sake of clarity we specify two additional parameters: For sake of clarity we specify two additional parameters:
AEAD Authentication Tag Length MUST be either 8, 12, or 16 AEAD Authentication Tag Length MUST be either 8, 12, or 16
octets octets
Maximum number of invocations MUST be at most 2^48 for SRTP Maximum number of invocations MUST be at most 2^48 for SRTP
for a given instantiation MUST be at most 2^31 for SRTCP for a given instantiation MUST be at most 2^31 for SRTCP
skipping to change at page 17, line 17 skipping to change at page 19, line 20
13.1. AES-GCM for SRTP/SRTCP 13.1. AES-GCM for SRTP/SRTCP
AES-GCM is a family of AEAD algorithms built around the AES block AES-GCM is a family of AEAD algorithms built around the AES block
cipher algorithm. AES-GCM uses AES counter mode for encryption and cipher algorithm. AES-GCM uses AES counter mode for encryption and
Galois Message Authentication Code (GMAC) for authentication. A Galois Message Authentication Code (GMAC) for authentication. A
detailed description of the AES-GCM family can be found in detailed description of the AES-GCM family can be found in
[RFC5116]. The following members of the AES-GCM family may be used [RFC5116]. The following members of the AES-GCM family may be used
with SRTP/SRTCP: with SRTP/SRTCP:
Table 1: AES-GCM algorithms for SRTP/SRTCP
Name Key Size AEAD Tag Size Reference Name Key Size AEAD Tag Size Reference
================================================================ ================================================================
AEAD_AES_128_GCM 16 octets 16 octets [RFC5116] AEAD_AES_128_GCM 16 octets 16 octets [RFC5116]
AEAD_AES_256_GCM 32 octets 16 octets [RFC5116] AEAD_AES_256_GCM 32 octets 16 octets [RFC5116]
AEAD_AES_128_GCM_8 16 octets 8 octets [RFC5282] AEAD_AES_128_GCM_8 16 octets 8 octets [RFC5282]
AEAD_AES_256_GCM_8 32 octets 8 octets [RFC5282] AEAD_AES_256_GCM_8 32 octets 8 octets [RFC5282]
AEAD_AES_128_GCM_12 16 octets 12 octets [RFC5282] AEAD_AES_128_GCM_12 16 octets 12 octets [RFC5282]
AEAD_AES_256_GCM_12 32 octets 12 octets [RFC5282] AEAD_AES_256_GCM_12 32 octets 12 octets [RFC5282]
Any implementation of AES-GCM SRTP SHOULD support both Table 1: AES-GCM algorithms for SRTP/SRTCP
AEAD_AES_128_GCM_8 and AEAD_AES_256_GCM_8, and it MAY support the
four other variants shown in table 1. Below we summarize parameters Any implementation of AES-GCM SRTP MUST support both AEAD_AES_128_GCM
associated with these six GCM algorithms: and AEAD_AES_256_GCM (the versions with 16 octet AEAD authentication
tags), and it MAY support the four other variants shown in table 1.
Below we summarize parameters associated with these six GCM
algorithms:
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 128 bits | | Master key length | 128 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_CM_PRF [RFC3711] | | Key Derivation Function | AES_CM_PRF [RFC3711] |
| Default key lifetime (SRTP) | 2^48 packets | | Default key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Default key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_GCM_8 | | Cipher (for SRTP and SRTCP) | AEAD_AES_128_GCM_8 |
| AEAD authentication tag length | 64 bits | | AEAD authentication tag length | 64 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 2: The AEAD_AES_128_GCM_8 Crypto Suite Table 2: The AEAD_AES_128_GCM_8 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 128 bits | | Master key length | 128 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_CM_PRF [RFC3711] | | Key Derivation Function | AES_CM_PRF [RFC3711] |
| Default key lifetime (SRTP) | 2^48 packets | | Default key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Default key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_GCM_12 | | Cipher (for SRTP and SRTCP) | AEAD_AES_128_GCM_12 |
| AEAD authentication tag length | 96 bits | | AEAD authentication tag length | 96 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 3: The AEAD_AES_128_GCM_12 Crypto Suite Table 3: The AEAD_AES_128_GCM_12 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 128 bits | | Master key length | 128 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_CM_PRF [RFC3711] | | Key Derivation Function | AES_CM_PRF [RFC3711] |
| Default key lifetime (SRTP) | 2^48 packets | | Default key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Default key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_GCM | | Cipher (for SRTP and SRTCP) | AEAD_AES_128_GCM |
| AEAD authentication tag length | 128 bits | | AEAD authentication tag length | 128 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 4: The AEAD_AES_128_GCM Crypto Suite Table 4: The AEAD_AES_128_GCM Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 256 bits | | Master key length | 256 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_256_CM_PRF [RFC6188] | | Key Derivation Function | AES_256_CM_PRF [RFC6188] |
| Default key lifetime (SRTP) | 2^48 packets | | Default key lifetime (SRTP) | 2^17 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Default key lifetime (SRTCP) | 2^17 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_GCM_8 | | Cipher (for SRTP and SRTCP) | AEAD_AES_256_GCM_8 |
| AEAD authentication tag length | 64 bits | | AEAD authentication tag length | 64 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 5: The AEAD_AES_256_GCM_8 Crypto Suite Table 5: The AEAD_AES_256_GCM_8 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 256 bits | | Master key length | 256 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_256_CM_PRF [RFC6188] | | Key Derivation Function | AES_256_CM_PRF [RFC6188] |
| Default key lifetime (SRTP) | 2^48 packets | | Default key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Default key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_GCM_12 | | Cipher (for SRTP and SRTCP) | AEAD_AES_256_GCM_12 |
| AEAD authentication tag length | 96 bits | | AEAD authentication tag length | 96 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 6: The AEAD_AES_256_GCM_12 Crypto Suite Table 6: The AEAD_AES_256_GCM_12 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 256 bits | | Master key length | 256 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_256_CM_PRF [RFC6188] | | Key Derivation Function | AES_256_CM_PRF [RFC6188] |
| Default key lifetime (SRTP) | 2^48 packets | | Default key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Default key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_GCM | | Cipher (for SRTP and SRTCP) | AEAD_AES_256_GCM |
| AEAD authentication tag length | 128 bits | | AEAD authentication tag length | 128 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 7: The AEAD_AES_256_GCM Crypto Suite Table 7: The AEAD_AES_256_GCM Crypto Suite
13.2. AES-CCM for SRTP/SRTCP 13.2. AES-CCM for SRTP/SRTCP
AES-CCM is another family of AEAD algorithms built around the AES AES-CCM is another family of AEAD algorithms built around the AES
block cipher algorithm. AES-CCM uses AES counter mode for encryption block cipher algorithm. AES-CCM uses AES counter mode for encryption
and AES Cipher Block Chaining Message Authentication Code (CBC MAC) and AES Cipher Block Chaining Message Authentication Code (CBC-MAC)
for authentication. A detailed description of the AES-CCM family can for authentication. A detailed description of the AES-CCM family can
be found in [RFC5116]. Four of the six CCM algorithms used in this be found in [RFC5116]. Four of the six CCM algorithms used in this
document are defined in previous RFCs, while two, AEAD_AES_128_CCM_12 document are defined in previous RFCs, while two, AEAD_AES_128_CCM_12
and AEAD_AES_256_CCM_12, are defined in section 7 of this document. and AEAD_AES_256_CCM_12, are defined in section 7 of this document.
Table 8: AES-CCM algorithms for SRTP/SRTCP
Name Key Size AEAD Tag Size Reference Name Key Size AEAD Tag Size Reference
================================================================ ================================================================
AEAD_AES_128_CCM 128 bits 16 octets [RFC5116] AEAD_AES_128_CCM 128 bits 16 octets [RFC5116]
AEAD_AES_256_CCM 256 bits 16 octets [RFC5116] AEAD_AES_256_CCM 256 bits 16 octets [RFC5116]
AEAD_AES_128_CCM_12 128 bits 12 octets see section 7 AEAD_AES_128_CCM_12 128 bits 12 octets see section 7
AEAD_AES_256_CCM_12 256 bits 12 octets see section 7 AEAD_AES_256_CCM_12 256 bits 12 octets see section 7
AEAD_AES_128_CCM_8 128 bits 8 octets [RFC6655] AEAD_AES_128_CCM_8 128 bits 8 octets [RFC6655]
AEAD_AES_256_CCM_8 256 bits 8 octets [RFC6655] AEAD_AES_256_CCM_8 256 bits 8 octets [RFC6655]
Table 8: AES-CCM algorithms for SRTP/SRTCP
Any implementation of AES-CCM SRTP/SRTCP SHOULD support both Any implementation of AES-CCM SRTP/SRTCP MUST support both
AEAD_AES_128_CCM_8 and AEAD_AES_256_CCM_8, and MAY support the other AEAD_AES_128_CCM and AEAD_AES_256_CCM (the versions with 16 octet
four variants. AEAD authentication tags), and MAY support the other four variants.
In addition to the flag octet used in counter mode encryption, In addition to the flag octet used in counter mode encryption,
AES-CCM authentications also uses a flag octet that conveys AES-CCM authentications also uses a flag octet that conveys
information about the length of the authentication tag, length of the information about the length of the authentication tag, length of the
block counter, and presence of additional authenticated data (see block counter, and presence of additional authenticated data (see
section 2.2 of [RFC3610]). For AES-CCM in SRTP/SRTCP, the flag octet section 2.2 of [RFC3610]). For AES-CCM in SRTP/SRTCP, the flag octet
has the hex value 5A if an 8-octet AEAD authentication tag is used, has the hex value 5A if an 8-octet AEAD authentication tag is used,
6A if a 12-octet AEAD authentication tag is used, and 7A if a 6A if a 12-octet AEAD authentication tag is used, and 7A if a
16-octet AEAD authentication tag is used. The flag octet is one of 16-octet AEAD authentication tag is used. The flag octet is one of
the inputs to AES during the counter mode encryption of the the inputs to AES during the counter mode encryption of the
plaintext. plaintext.
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 128 bits | | Master key length | 128 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_CM_PRF [RFC3711] | | Key Derivation Function | AES_CM_PRF [RFC3711] |
| Default key lifetime (SRTP) | 2^48 packets | | Maximum key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Maximum key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_CCM_8 | | Cipher (for SRTP and SRTCP) | AEAD_AES_128_CCM_8 |
| AEAD authentication tag length | 64 bits | | AEAD authentication tag length | 64 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 9: The AEAD_AES_128_CCM_8 Crypto Suite Table 9: The AEAD_AES_128_CCM_8 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 128 bits | | Master key length | 128 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_CM_PRF [RFC3711] | | Key Derivation Function | AES_CM_PRF [RFC3711] |
| Default key lifetime (SRTP) | 2^48 packets | | Maximum key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Maximum key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_CCM_12 | | Cipher (for SRTP and SRTCP) | AEAD_AES_128_CCM_12 |
| AEAD authentication tag length | 96 bits | | AEAD authentication tag length | 96 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 10: The AEAD_AES_128_CCM_12 Crypto Suite Table 10: The AEAD_AES_128_CCM_12 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 128 bits | | Master key length | 128 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_CM_PRF [RFC3711] | | Key Derivation Function | AES_CM_PRF [RFC3711] |
| Default key lifetime (SRTP) | 2^48 packets | | Maximum key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Maximum key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_CCM | | Cipher (for SRTP and SRTCP) | AEAD_AES_128_CCM |
| AEAD authentication tag length | 128 bits | | AEAD authentication tag length | 128 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 11: The AEAD_AES_128_CCM Crypto Suite Table 11: The AEAD_AES_128_CCM Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 256 bits | | Master key length | 256 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_256_CM_PRF [RFC6188] | | Key Derivation Function | AES_256_CM_PRF [RFC6188] |
| Default key lifetime (SRTP) | 2^48 packets | | Maximum key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Maximum key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_CCM_8 | | Cipher (for SRTP and SRTCP) | AEAD_AES_256_CCM_8 |
| AEAD authentication tag length | 64 bits | | AEAD authentication tag length | 64 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 12: The AEAD_AES_256_CCM_8 Crypto Suite Table 12: The AEAD_AES_256_CCM_8 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 256 bits | | Master key length | 256 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_256_CM_PRF [RFC6188] | | Key Derivation Function | AES_256_CM_PRF [RFC6188] |
| Default key lifetime (SRTP) | 2^48 packets | | Maximum key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Maximum key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_CCM_12 | | Cipher (for SRTP and SRTCP) | AEAD_AES_256_CCM_12 |
| AEAD authentication tag length | 96 bits | | AEAD authentication tag length | 96 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 13: The AEAD_AES_256_CCM_12 Crypto Suite Table 13: The AEAD_AES_256_CCM_12 Crypto Suite
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Parameter | Value | | Parameter | Value |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
| Master key length | 256 bits | | Master key length | 256 bits |
| Master salt length | 96 bits | | Master salt length | 96 bits |
| Key Derivation Function | AES_256_CM_PRF [RFC6188] | | Key Derivation Function | AES_256_CM_PRF [RFC6188] |
| Default key lifetime (SRTP) | 2^48 packets | | Maximum key lifetime (SRTP) | 2^48 packets |
| Default key lifetime (SRTCP) | 2^31 packets | | Maximum key lifetime (SRTCP) | 2^31 packets |
| Cipher (for SRTP and SRTCP) | AEAD_AES_CCM | | Cipher (for SRTP and SRTCP) | AEAD_AES_256_CCM |
| AEAD authentication tag length | 128 bits | | AEAD authentication tag length | 128 bits |
+--------------------------------+------------------------------+ +--------------------------------+------------------------------+
Table 14: The AEAD_AES_256_CCM Crypto Suite Table 14: The AEAD_AES_256_CCM Crypto Suite
14. Security Considerations 14. Security Considerations
14.1. Handling of Security Critical Parameters 14.1. Handling of Security Critical Parameters
As with any security process, the implementer must take care to As with any security process, the implementer must take care to
skipping to change at page 22, line 36 skipping to change at page 24, line 36
algorithms, but we include them here to emphasize their importance. algorithms, but we include them here to emphasize their importance.
- If the master salt is to be kept secret, it MUST be properly - If the master salt is to be kept secret, it MUST be properly
erased when no longer needed. erased when no longer needed.
- The secret master key and all keys derived from it MUST be kept - The secret master key and all keys derived from it MUST be kept
secret. All keys MUST be properly erased when no longer secret. All keys MUST be properly erased when no longer
needed. needed.
- At the start of each packet, the block counter MUST be reset (to - At the start of each packet, the block counter MUST be reset (to
0 for CCM, to 1 for GCM). The block counter is incremented 0 for CCM, to 1 for GCM). The block counter is incremented
after each block key has been produced, but it MUST NOT be after each block key has been produced, but it MUST NOT be
allowed to exceed 2^32 for GCM and 2^24 for CCM. allowed to exceed 2^32-1 for GCM and 2^24-1 for CCM. Note that
even though the block counter is reset at the start of each
packet, IV uniqueness is ensured by the inclusion of
SSRC/ROC/SEQ or SRTCP Index in the IV. (The reader is reminded
that in both GCM and CCM the first block of key produced is
reserved for use in authenticating the packet and is not used to
encrypt plaintext.)
- Each time a rekey occurs, the initial values of the SRTCP index - Each time a rekey occurs, the initial values of the SRTCP index
and the values of all the SEQ counters MUST be saved. and the SRTP packet indices MUST be saved in order to prevent IV
- Processing MUST cease if the 48-bit Packet Counter or the 31-bit reuse.
SRTCP index cycles back to its initial value. Processing MUST - Processing MUST cease if the 31-bit SRTCP index or any of the
NOT resume until a new SRTP/SRTCP session has been established 48-bit packet indices cycle back their initial values .
using a new SRTP master key. Ideally, a rekey should be done Processing MUST NOT resume until a new SRTP/SRTCP session has
well before either of these counters cycle. been established using a new SRTP master key. Ideally, a rekey
should be done well before any of these counters cycle.
14.2. Size of the Authentication Tag 14.2. Size of the Authentication Tag
We require that the AEAD authentication tag must be at least 8 We require that the AEAD authentication tag must be at least 8
octets, significantly reducing the probability of an adversary octets, significantly reducing the probability of an adversary
successfully introducing fraudulent data. The goal of an successfully introducing fraudulent data. The goal of an
authentication tag is to minimize the probability of a successful authentication tag is to reduce the probability of a successful
forgery occurring anywhere in the network we are attempting to forgery occurring anywhere in the network we are attempting to
defend. There are three relevant factors: how low we wish the defend. There are three relevant factors: how low we wish the
probability of successful forgery to be (prob_success), how many probability of successful forgery to be (prob_success), how many
attempts the adversary can make (N_tries) and the size of the attempts the adversary can make (N_tries) and the size of the
authentication tag in bits (N_tag_bits). Then authentication tag in bits (N_tag_bits). Then
prob_success < expected number of successes prob_success <= expected number of successes
= N_tries * 2^-N_tag_bits. = N_tries * 2^-N_tag_bits.
When the expected number of successes is much less than one, the
probability of success is well approximated by the expected number of
successes.
Suppose an adversary wishes to introduce a forged or altered packet Suppose an adversary wishes to introduce a forged or altered packet
into a target network by randomly selecting an authentication value into a target network by randomly selecting an authentication value
until by chance they hit a valid authentication tag. The table below until by chance they hit a valid authentication tag. The table below
summarizes the relationship between the number of forged packets the summarizes the relationship between the number of forged packets the
adversary has tried, the size of the authentication tag, and the adversary has tried, the size of the authentication tag, and the
probability of a compromise occurring (i.e. at least one of the probability of a compromise occurring (i.e. at least one of the
attempted forgeries having a valid authentication tag). The reader attempted forgeries having a valid authentication tag). The reader
is reminded that the forgery attempts can be made over the entire is reminded that the forgery attempts can be made over the entire
network, not just a single link, and that frequently changing the key network, not just a single link, and that frequently changing the key
does not decrease the probability of a compromise occurring. does not decrease the probability of a compromise occurring.
+==================+========================================+ It should be noted that the cryptographic properties of the GHASH
| Authentication | Probability of a Compromise Occurring | algorithm used in GCM reduces the effective authentication tag size
| Tag | for a given number of forgery attempts | (in bits) by the log base 2 of the of blocks of encrypted and/or
| Size |------------+-------------+-------------| authenticated data in a packet. In practice an SRTP payload will be
| (octets) | prob=2^-30 | prob=2^-20 | prob=2^-10 | less than 2^16 bytes, because of the 16-bit IPv4 and UDP length
|==================+=============+=============+============| fields. The exception to this case is IPv6 jumbograms [RFC2675],
| 4 | 2^2 tries | 2^12 tries | 2^22 tries | which is unlikely to be used for RTP-based multimedia traffic
|==================+============+=============+=============| [RFC3711]. This corresponds to 2^12 blocks of data, so the effective
| 8 | 2^34 tries | 2^44 tries | 2^54 tries | GCM authentication tag size is reduced by at most 12 bits.
|==================+============+=============+=============|
| 12 | 2^66 tries | 2^76 tries | 2^86 tries |
|==================+============+=============+=============|
| 16 | 2^98 tries | 2^108 tries | 2^118 tries |
+=================+============+=============+==============+
Table 15: Probability of a compromise occurring for a given +===========+=============+========================================+
number of forgery attempts and tag size. | Auth. Tag | Eff. Tag | Number of Forgery Attempts |
| Size | Tag Size | Needed to Achieve a Given |
| (bytes) | (bits) | Probability of Success |
|-----------+-------------+------------+-------------+-------------|
| | prob=2^-30 | prob=2^-20 | prob=2^-10 |
|===========+=============+=============+============+=============|
| | 32 (CCM) | 2^2 tries | 2^12 tries | 2^22 tries |
| 4 +-------------+------------+-------------+-------------|
| | 20 (GCM) | 1 try | 1 try | 2^10 tries |
|===========+=============+============+=============+=============|
| | 64 (CCM) | 2^34 tries | 2^44 tries | 2^54 tries |
| 8 +-------------+------------+-------------+-------------|
| | 52 (GCM) | 2^22 tries | 2^32 tries | 2^42 tries |
|===========+=============+============+=============+=============|
| | 96 (CCM) | 2^66 tries | 2^76 tries | 2^86 tries |
| 12 +-------------+------------+-------------+-------------|
| | 84 (GCM) | 2^54 tries | 2^64 tries | 2^74 tries |
|===========+=============+============+=============+=============|
| | 128 (CCM) | 2^86 tries | 2^96 tries | 2^106 tries |
| 16 +-------------+------------+-------------+-------------|
| | 116 (GCM) | 2^98 tries | 2^108 tries | 2^118 tries |
|===========+=============+============+=============+=============|
Table 15: Number of forgery attempts needed to achieve a given
probability of success for various tag sizes.
15. IANA Considerations 15. IANA Considerations
15.1. SDES 15.1. SDES
SDP Security Descriptions [RFC4568] defines SRTP "crypto suites". A SDP Security Descriptions [RFC4568] defines SRTP "crypto suites". A
crypto suite corresponds to a particular AEAD algorithm in SRTP. In crypto suite corresponds to a particular AEAD algorithm in SRTP. In
order to allow SDP to signal the use of the algorithms defined in order to allow Security Descriptions to signal the use of the
this document, IANA will register the following crypto suites into algorithms defined in this document, IANA will register the following
the "SRTP Crypto Suite Registrations" subregistry of the "Session crypto suites into the "SRTP Crypto Suite Registrations" subregistry
Description Protocol (SDP) Parameters" registry. of the "Session Description Protocol (SDP) Security Descriptions"
registry.
srtp-crypto-suite-ext = "AEAD_AES_128_GCM" / srtp-crypto-suite-ext = "AEAD_AES_128_GCM" /
"AEAD_AES_256_GCM" / "AEAD_AES_256_GCM" /
"AEAD_AES_128_GCM_8" / "AEAD_AES_128_GCM_8" /
"AEAD_AES_256_GCM_8" / "AEAD_AES_256_GCM_8" /
"AEAD_AES_128_GCM_12" / "AEAD_AES_128_GCM_12" /
"AEAD_AES_256_GCM_12" / "AEAD_AES_256_GCM_12" /
"AEAD_AES_128_CCM" / "AEAD_AES_128_CCM" /
"AEAD_AES_256_CCM" / "AEAD_AES_256_CCM" /
"AEAD_AES_128_CCM_8" / "AEAD_AES_128_CCM_8" /
skipping to change at page 24, line 43 skipping to change at page 27, line 32
AEAD_AES_128_CCM = {TBD, TBD } AEAD_AES_128_CCM = {TBD, TBD }
AEAD_AES_256_CCM = {TBD, TBD } AEAD_AES_256_CCM = {TBD, TBD }
AEAD_AES_128_CCM_8 = {TBD, TBD } AEAD_AES_128_CCM_8 = {TBD, TBD }
AEAD_AES_256_CCM_8 = {TBD, TBD } AEAD_AES_256_CCM_8 = {TBD, TBD }
AEAD_AES_128_CCM_12 = {TBD, TBD } AEAD_AES_128_CCM_12 = {TBD, TBD }
AEAD_AES_256_CCM_12 = {TBD, TBD } AEAD_AES_256_CCM_12 = {TBD, TBD }
Below we list the SRTP transform parameters for each of these Below we list the SRTP transform parameters for each of these
protection profile. Unless separate parameters for SRTCP and SRTCP protection profile. Unless separate parameters for SRTCP and SRTCP
are explicitly listed, these parameters apply to both SRTP and are explicitly listed, these parameters apply to both SRTP and
SRTCP. SRTCP. Note that GCM with an 8 octet auth_tag_length has a smaller
than anticipated maximum lifetime due to the constraints imposed by
NIST SP 800-38D appendix C.
AEAD_AES_128_CCM AEAD_AES_128_CCM
cipher: AES_128_CCM cipher: AES_128_CCM
cipher_key_length: 128 bits cipher_key_length: 128 bits
cipher_salt_length: 96 bits cipher_salt_length: 96 bits
aead_auth_tag_length: 16 octets aead_auth_tag_length: 16 octets
auth_function: NULL auth_function: NULL
auth_key_length: N/A auth_key_length: N/A
auth_tag_length: N/A auth_tag_length: N/A
maximum lifetime: at most 2^31 SRTCP packets and maximum lifetime: at most 2^31 SRTCP packets and
skipping to change at page 26, line 38 skipping to change at page 29, line 30
at most 2^48 SRTP packets at most 2^48 SRTP packets
AEAD_AES_128_GCM_8 AEAD_AES_128_GCM_8
cipher: AES_128_GCM cipher: AES_128_GCM
cipher_key_length: 128 bits cipher_key_length: 128 bits
cipher_salt_length: 96 bits cipher_salt_length: 96 bits
aead_auth_tag_length: 8 octets aead_auth_tag_length: 8 octets
auth_function: NULL auth_function: NULL
auth_key_length: N/A auth_key_length: N/A
auth_tag_length: N/A auth_tag_length: N/A
maximum lifetime: at most 2^31 SRTCP packets and maximum lifetime: at most 2^17 SRTCP packets and
at most 2^48 SRTP packets at most 2^17 SRTP packets
AEAD_AES_256_GCM_8 AEAD_AES_256_GCM_8
cipher: AES_256_GCM cipher: AES_256_GCM
cipher_key_length: 256 bits cipher_key_length: 256 bits
cipher_salt_length: 96 bits cipher_salt_length: 96 bits
aead_auth_tag_length: 8 octets aead_auth_tag_length: 8 octets
auth_function: NULL auth_function: NULL
auth_key_length: N/A auth_key_length: N/A
auth_tag_length: N/A auth_tag_length: N/A
maximum lifetime: at most 2^31 SRTCP packets and maximum lifetime: at most 2^17 SRTCP packets and
at most 2^48 SRTP packets at most 2^17 SRTP packets
AEAD_AES_128_GCM_12 AEAD_AES_128_GCM_12
cipher: AES_128_GCM cipher: AES_128_GCM
cipher_key_length: 128 bits cipher_key_length: 128 bits
cipher_salt_length: 96 bits cipher_salt_length: 96 bits
aead_auth_tag_length: 12 octets aead_auth_tag_length: 12 octets
auth_function: NULL auth_function: NULL
auth_key_length: N/A auth_key_length: N/A
auth_tag_length: N/A auth_tag_length: N/A
maximum lifetime: at most 2^31 SRTCP packets and maximum lifetime: at most 2^31 SRTCP packets and
skipping to change at page 27, line 35 skipping to change at page 30, line 27
auth_function, auth_key, or auth_tag. The term aead_auth_tag_length auth_function, auth_key, or auth_tag. The term aead_auth_tag_length
is used to emphasize that this refers to the authentication tag is used to emphasize that this refers to the authentication tag
provided by the AEAD algorithm and that this tag is not located in provided by the AEAD algorithm and that this tag is not located in
the authentication tag field provided by SRTP/SRTCP. the authentication tag field provided by SRTP/SRTCP.
15.3. MIKEY 15.3. MIKEY
In accordance with "MIKEY: Multimedia Internet KEYing" [RFC3830], In accordance with "MIKEY: Multimedia Internet KEYing" [RFC3830],
IANA maintains several subregitries under "Multimedia Internet KEYing IANA maintains several subregitries under "Multimedia Internet KEYing
(MIKEY) Payload Name Spaces". This document requires additions to (MIKEY) Payload Name Spaces". This document requires additions to
two of the MIKEY subregistries. lists maintained under "MIKEY two of the MIKEY subregistries.
Security Protocol Parameters".
In the "MIKEY Security Protocol Parameters" subregistry we request In the "MIKEY Security Protocol Parameters" subregistry we request
the following addition: the following addition:
Type | Meaning | Possible values Type | Meaning | Possible values
---------------------------------------------------------------- ----------------------------------------------------------------
TBD | AEAD authentication tag length | 8, 12, or 16 (in octets) TBD | AEAD authentication tag length | 8, 12, or 16 (in octets)
This list is, of course, intended for use with CM and GCM. It is
conceivable that new AEAD algorithms introduced at some point in the
future may require a different set of Authentication tag lengths.
In the "Encryption Algorithm" subregistry (derived from Table In the "Encryption Algorithm" subregistry (derived from Table
6.10.1.b of [RFC3830]) we request the following additions: 6.10.1.b of [RFC3830]) we request the following additions:
SRTP encr alg. | Value | Default Session Encr. Key Length SRTP encr | Value | Default Session | Default Auth.
Algorithm | | Encr. Key Length | Tag Length
----------------------------------------------------------- -----------------------------------------------------------
AES-CCM | TBD | 16 octets AES-CCM | TBD | 16 octets | 16 octets
AES-GCM | TBD | 16 octets AES-GCM | TBD | 16 octets | 16 octets
The SRTP encryption algorithm, session encryption key length, and The SRTP encryption algorithm, session encryption key length, and
AEAD authentication tag values received from MIKEY fully determine AEAD authentication tag values received from MIKEY fully determine
the AEAD algorithm (e.g., AEAD_AES_256_GCM_8). The exact mapping is the AEAD algorithm (e.g., AEAD_AES_256_GCM_8). The exact mapping is
described in section 16. described in section 16.
15.4. AEAD registry 15.4. AEAD registry
We request that IANA make the following additions to the IANA We request that IANA make the following additions to the IANA
"Authenticated Encryption with Associated Data (AEAD) Parameters" "Authenticated Encryption with Associated Data (AEAD) Parameters"
page's registry for "AEAD Algorithms": page's registry for "AEAD Algorithms":
AEAD_AES_128_CCM_12 = TBD AEAD_AES_128_CCM_12 = TBD
AEAD_AES_256_CCM_12 = TBD AEAD_AES_256_CCM_12 = TBD
16. Parameters for use with MIKEY 16. Parameters for use with MIKEY
MIKEY specifies the algorithm family separately from the key length MIKEY specifies the algorithm family separately from the key length
(which is specified by the Session Encryption key length ) and the (which is specified by the Session Encryption key length) and the
authentication tag length (specified by AEAD Auth. tag length). authentication tag length (specified by AEAD Auth. tag length).
+------------+-------------+-------------+ +------------+-------------+-------------+
| Encryption | Encryption | AEAD Auth. | | Encryption | Encryption | AEAD Auth. |
| Algorithm | Key Length | Tag Length | | Algorithm | Key Length | Tag Length |
+============+=============+=============+ +============+=============+=============+
AEAD_AES_128_GCM | AES-GCM | 16 octets | 16 octets | AEAD_AES_128_GCM | AES-GCM | 16 octets | 16 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_128_CCM | AES-CCM | 16 octets | 16 octets | AEAD_AES_128_CCM | AES-CCM | 16 octets | 16 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_128_GCM_12 | AES-GCM | 16 octets | 12 octets | AEAD_AES_128_GCM_12 | AES-GCM | 16 octets | 12 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_128_CCM_12 | AES-CCM | 16 octets | 12 octets | AEAD_AES_128_CCM_12 | AES-CCM | 16 octets | 12 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_128_GCM_8 | AES-GCM | 16 octets | 8 octets | AEAD_AES_128_GCM_8 | AES-GCM | 16 octets | 8 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_128_CCM_8 | AES-CCM | 16 octets | 8 octets | AEAD_AES_128_CCM_8 | AES-CCM | 16 octets | 8 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_256_GCM | AES-GCM | 32 octets | 16 octets | AEAD_AES_256_GCM | AES-GCM | 32 octets | 16 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_256_CCM | AES-CCM | 32 octets | 16 octets | AEAD_AES_256_CCM | AES-CCM | 32 octets | 16 octets |
skipping to change at page 29, line 40 skipping to change at page 32, line 6
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_256_CCM_8 | AES-CCM | 32 octets | 8 octets | AEAD_AES_256_CCM_8 | AES-CCM | 32 octets | 8 octets |
+============+=============+=============+ +============+=============+=============+
Table 16: Mapping MIKEY parameters to AEAD algorithm Table 16: Mapping MIKEY parameters to AEAD algorithm
Section 12 in this document restricts the choice of Key Derivation Section 12 in this document restricts the choice of Key Derivation
Function for AEAD algorithms. To enforce this restriction in MIKEY, Function for AEAD algorithms. To enforce this restriction in MIKEY,
we require that the SRTP PRF has value AES-CM whenever an AEAD we require that the SRTP PRF has value AES-CM whenever an AEAD
algorithm is used. Note that, according to Section 6.10.1 in algorithm is used. Note that, according to Section 6.10.1 in
[RFC3830], the key length of the Key Derivation Function (i.e. the [RFC3830], the input key length of the Key Derivation Function (i.e.
SRTP master key length) is always equal to the session encryption key the SRTP master key length) is always equal to the session encryption
length. This means, for example, that AEAD_AES_256_GCM will use key length. This means, for example, that AEAD_AES_256_GCM will use
AES_256_CM_PRF as the Key Derivation Function. AES_256_CM_PRF as the Key Derivation Function.
17. Acknowledgements 17. Acknowledgements
The authors would like to thank Michael Peck, Michael Torla, Qin Wu, The authors would like to thank Michael Peck, Michael Torla, Qin Wu,
Magnus Westerland, Oscar Ohllson, Woo-Hwan Kim and many other Magnus Westerland, Oscar Ohllson, Woo-Hwan Kim, John Mattsson,
reviewers who provided valuable comments on earlier drafts of this Richard Barnes and many other reviewers who provided valuable
document. comments on earlier drafts of this document.
18. References 18. References
18.1. Normative References 18.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Casner, S., Frederick, R., and V. Jacobson, "RTP: A [RFC3550] Casner, S., Frederick, R., and V. Jacobson, "RTP: A
Transport Protocol for Real-Time Applications", RFC 3550, Transport Protocol for Real-Time Applications", RFC 3550,
 End of changes. 113 change blocks. 
234 lines changed or deleted 317 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/