draft-ietf-avtcore-srtp-aes-gcm-15.txt   draft-ietf-avtcore-srtp-aes-gcm-16.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: October 16, 2015 National Security Agency Expires: December 07, 2015 National Security Agency
April 14, 2015 June 05, 2015
AES-GCM Authenticated Encryption in Secure RTP (SRTP) AES-GCM Authenticated Encryption in Secure RTP (SRTP)
draft-ietf-avtcore-srtp-aes-gcm-15 draft-ietf-avtcore-srtp-aes-gcm-16
Status of this Memo Status of this Memo
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Abstract Abstract
This document defines how the AES-GCM Authenticated Encryption with This document defines how the AES-GCM Authenticated Encryption with
Associated Data family of algorithms can be used to provide Associated Data family of algorithms can be used to provide
confidentiality and data authentication in the SRTP protocol. Note: confidentiality and data authentication in the SRTP protocol.
this is an intermediate draft, awaiting the inclusion of test
vectors. Care is being taken to ensure these test vectors will be
correct, always a desirable property.
Table of Contents Table of Contents
1. Introduction.....................................................3 1. Introduction.....................................................4
2. Conventions Used In This Document................................4 2. Conventions Used In This Document................................5
3. Overview of the SRTP/SRTCP AEAD security Architecture............4 3. Overview of the SRTP/SRTCP AEAD security Architecture............5
4. Terminology......................................................5 4. Terminology......................................................6
5. Generic AEAD Processing..........................................5 5. Generic AEAD Processing..........................................6
5.1. Types of Input Data.........................................5 5.1. Types of Input Data.........................................6
5.2. AEAD Invocation Inputs and Outputs..........................5 5.2. AEAD Invocation Inputs and Outputs..........................6
5.2.1. Encrypt Mode...........................................5 5.2.1. Encrypt Mode...........................................6
5.2.2. Decrypt Mode...........................................6 5.2.2. Decrypt Mode...........................................7
5.3. Handling of AEAD Authentication.............................6 5.3. Handling of AEAD Authentication.............................7
6. Counter Mode Encryption..........................................6 6. Counter Mode Encryption..........................................7
7. Unneeded SRTP/SRTCP Fields.......................................7 7. Unneeded SRTP/SRTCP Fields.......................................8
7.1. SRTP/SRTCP Authentication Field.............................7 7.1. SRTP/SRTCP Authentication Field.............................8
7.2. RTP Padding.................................................8 7.2. RTP Padding.................................................9
8. AES-GCM processing for SRTP......................................8 8. AES-GCM processing for SRTP......................................9
8.1. SRTP IV formation for AES-GCM...............................8 8.1. SRTP IV formation for AES-GCM...............................9
8.2. Data Types in SRTP Packets..................................8 8.2. Data Types in SRTP Packets..................................9
8.3. Handling Header Extensions.................................10 8.3. Handling Header Extensions.................................11
8.4. Prevention of SRTP IV Reuse................................11 8.4. Prevention of SRTP IV Reuse................................12
9. AES-GCM Processing of SRTCP Compound Packets....................12 9. AES-GCM Processing of SRTCP Compound Packets....................13
9.1. SRTCP IV formation for AES-GCM.............................12 9.1. SRTCP IV formation for AES-GCM.............................13
9.2. Data Types in Encrypted SRTCP Compound Packets.............13 9.2. Data Types in Encrypted SRTCP Compound Packets.............14
9.3. Data Types in Unencrypted SRTCP Compound Packets...........14 9.3. Data Types in Unencrypted SRTCP Compound Packets...........15
9.4. Prevention of SRTCP IV Reuse...............................15 9.4. Prevention of SRTCP IV Reuse...............................16
10. Constraints on AEAD for SRTP and SRTCP.........................15 10. Constraints on AEAD for SRTP and SRTCP.........................16
11. Key Derivation Functions.......................................16 11. Key Derivation Functions.......................................17
12. Summary of AES-GCM in SRTP/SRTCP...............................16 12. Summary of AES-GCM in SRTP/SRTCP...............................17
13. Security Considerations........................................17 13. Security Considerations........................................18
13.1. Handling of Security Critical Parameters..................18 13.1. Handling of Security Critical Parameters..................19
13.2. Size of the Authentication Tag............................18 13.2. Size of the Authentication Tag............................19
14. IANA Considerations............................................19 14. IANA Considerations............................................21
14.1. SDES......................................................19 14.1. SDES......................................................21
14.2. DTLS-SRTP.................................................20 14.2. DTLS-SRTP.................................................21
14.3. MIKEY.....................................................21 14.3. MIKEY.....................................................22
15. Parameters for use with MIKEY..................................21 15. Parameters for use with MIKEY..................................23
16. Acknowledgements...............................................22 16. Some RTP Test Vectors..........................................23
17. References.....................................................23 16.1. AEAD_AES_128_GCM_8........................................24
17.1. Normative References......................................23 16.1.1. AEAD_AES_128_GCM_8 Encryption........................24
17.2. Informative References....................................24 16.1.2. AEAD_AES_128_GCM_8 Decryption........................26
16.1.3. AEAD_AES_128_GCM_8 Authentication Tagging............27
16.1.4. AEAD_AES_128_GCM_8 Tag Verification..................28
16.2. AEAD_AES_128_GCM..........................................29
16.2.1. AEAD_AES_128_GCM Encryption..........................29
16.2.2. AEAD_AES_128_GCM Decryption..........................31
16.2.3. AEAD_AES_128_GCM Authentication Tagging..............32
16.2.4. AEAD_AES_128_GCM Tag Verification....................33
16.3. AEAD_AES_256_GCM..........................................34
16.3.1. AEAD_AES_256_GCM Encryption..........................34
16.3.2. AEAD_AES_256_GCM Decryption..........................36
16.3.3. AEAD_AES_256_GCM Authentication Tagging..............37
16.3.4. AEAD_AES_256_GCM Tag Verification....................38
17. RTCP Test Vectors..............................................39
17.1. AEAD_AES_128_GCM_8 Encrypt and Tag........................40
17.2. AEAD_AES_256_GCM Verify and Decryption....................42
17.3. AEAD_AES_128_GCM Tag Only.................................44
17.4. AEAD_AES_256_GCM Tag Verification.........................45
18. Acknowledgements...............................................46
19. References.....................................................47
19.1. Normative References......................................47
19.2. Informative References....................................47
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 45 skipping to change at page 4, line 45
can only be used with AES-128. Thus when used in SRTP, GCM will have can only be used with AES-128. Thus when used in SRTP, GCM will have
three configurations: three configurations:
AEAD_AES_128_GCM_8 AES-128 with an 8 byte authentication tag AEAD_AES_128_GCM_8 AES-128 with an 8 byte authentication tag
AEAD_AES_128_GCM AES-128 with a 16 byte authentication tag AEAD_AES_128_GCM AES-128 with a 16 byte authentication tag
AEAD_AES_256_GCM AES-256 with a 16 byte authentication tag AEAD_AES_256_GCM AES-256 with a 16 byte authentication tag
The key size and the length of the authentication tag are set when The key size and the length of the authentication tag are set when
the session is initiated and SHOULD NOT be altered. the session is initiated and SHOULD NOT be altered.
The Galois/Counter Mode of operation (GCM) ia an AEAD mode of The Galois/Counter Mode of operation (GCM) is an AEAD mode of
operation for block ciphers. GCM use counter mode to encrypt the operation for block ciphers. GCM use counter mode to encrypt the
data, an operation that can be efficiently pipelined. Further, GCM data, an operation that can be efficiently pipelined. Further, GCM
authentication uses operations that are particularly well suited to authentication uses operations that are particularly well suited to
efficient implementation in hardware, making it especially appealing efficient implementation in hardware, making it especially appealing
for high-speed implementations, or for implementations in an for high-speed implementations, or for implementations in an
efficient and compact circuit. efficient and compact circuit.
In summary, this document defines how to use an AEAD algorithm, In summary, this document defines how to use an AEAD algorithm,
particularly AES-GCM, to provide confidentiality and message particularly AES-GCM, to provide confidentiality and message
authentication within SRTP and SRTCP packets. authentication within SRTP and SRTCP packets.
skipping to change at page 6, line 51 skipping to change at page 7, line 51
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
Each outbound packet uses a 12-octet IV and an encryption key to form Each outbound packet uses a 12-octet IV and an encryption key to form
two outputs, a 16-octet first_key_block which is used in forming the two outputs, a 16-octet first_key_block which is used in forming the
authentication tag and a key stream of octets, formed in blocks of authentication tag and a key stream of octets, formed in blocks of
16-octets each. The first 16-octet block of key is saved for use in 16-octets each. The first 16-octet block of key is saved for use in
forming the authentication tag, and the of remainder of the key forming the authentication tag, and the remainder of the key stream
stream is XORed to the plaintext to form cipher. This key stream is is XORed to the plaintext to form cipher. This key stream is formed
formed one block at a time by inputting the concatenation of a one block at a time by inputting the concatenation of a 12-octet IV
12-octet IV (see sections 8.1 and 9.1) with a 4-octet block to AES. (see sections 8.1 and 9.1) with a 4-octet block to AES. The
The pseudo-code below illustrates this process: pseudo-code below illustrates this process:
def GCM_keystream( Plaintext_len, IV, Encryption_key ): def GCM_keystream( Plaintext_len, IV, Encryption_key ):
assert Plaintext_len <= (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) < Plaintext_len: 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,
skipping to change at page 8, line 37 skipping to change at page 9, line 37
| Encryption Salt |->(+) | Encryption Salt |->(+)
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+ |
| Initialization Vector |<--+ | Initialization Vector |<--+
+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+
Figure 1: AES-GCM SRTP Initialization Figure 1: AES-GCM SRTP Initialization
Vector formation. Vector formation.
The 12 octet initialization vector used by AES-GCM SRTP is formed by The 12 octet initialization vector used by AES-GCM SRTP is formed by
first concatenating 2-octets of zeroes, the 4-octet SSRC, the 4-octet first concatenating 2 octets of zeroes, the 4-octet SSRC, the 4-octet
Rollover Counter (ROC) and the two octet sequence number SEQ. The Rollover Counter (ROC) and the 2-octet sequence number SEQ. The
resulting 12-octet value is then XORed to the 12-octet salt to form resulting 12-octet value is then XORed to the 12-octet salt to form
the 12-octet IV. the 12-octet IV.
8.2. Data Types in SRTP Packets 8.2. 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 RTP 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 V (2 bits), padding flag P (1 bit), Associated Data: The version V (2 bits), padding flag P (1 bit),
extension flag X (1 bit), CSRC count CC (4 bits), extension flag X (1 bit), CSRC count CC (4 bits),
marker M (1 bit), the Payload Type PT (7 bits), marker M (1 bit), the Payload Type PT (7 bits),
the sequence number (16 bits), timestamp (32 the sequence number (16 bits), timestamp (32
bits), SSRC (32 bits), optional contributing bits), SSRC (32 bits), optional contributing
source identifiers (CSRCs, 32 bits each), and source identifiers (CSRCs, 32 bits each), and
optional RTP extension (variable length). optional RTP extension (variable length).
skipping to change at page 9, line 39 skipping to change at page 10, line 39
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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)
Figure 2: Structure of an SRTP packet before Authenticated Figure 2: Structure of an RTP packet before Authenticated
Encryption Encryption
Since the AEAD ciphertext is larger than the plaintext by exactly the 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 variable length SRTP MKI and placed immediately before the optional variable length SRTP MKI and
SRTP authentication tag fields. SRTP authentication tag fields.
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8.3. Handling Header Extensions 8.3. Handling Header Extensions
RTP header extensions were first defined in RFC 3550. RFC 6904 RTP header extensions were first defined in RFC 3550. RFC 6904
[RFC6904] describes how these header extensions are to be encrypted [RFC6904] describes how these header extensions are to be encrypted
in SRTP. in SRTP.
When RFC 6904 is in use, a separate keystream is generated to encrypt When RFC 6904 is in use, a separate keystream is generated to encrypt
selected RTP header extension elements. For the AEAD_AES_128_GCM and selected RTP header extension elements. For the AEAD_AES_128_GCM and
AEAD_AES_128_GCM_8 algorithms, this keystream MUST be generated in AEAD_AES_128_GCM_8 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-CM transform. For the
the AEAD_AES_256_GCM algorithm, the keystream MUST be generated in AEAD_AES_256_GCM algorithm, the keystream MUST be generated in the
the manner defined for the AES_256_CM transform. The originator must manner defined for the AES_256_CM transform. The originator must
perform any required header extension encryption before the AEAD perform any required header extension encryption before the AEAD
algorithm is invoked. 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 Associated Data (AD). Thus the AEAD algorithm does AEAD algorithm as Associated Data (AD). Thus the AEAD algorithm does
not provide any additional privacy for the header extensions, but not provide any additional privacy for the header extensions, but
does provide integrity and authentication. does provide integrity and authentication.
8.4. Prevention of SRTP IV Reuse 8.4. Prevention of SRTP IV Reuse
skipping to change at page 15, line 39 skipping to change at page 16, line 39
The comments on SSRC management in section 8.4 also apply. The comments on SSRC management in section 8.4 also apply.
10. Constraints on AEAD for SRTP and SRTCP 10. 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 one specific fasmily of AEAD algorithms, namely parameter set for one specific family of AEAD algorithms, namely
AES-GCM. AES-GCM.
All AEAD algorithms used with SRTP/SRTCP MUST satisfy the five All AEAD algorithms used with SRTP/SRTCP MUST satisfy the five
constraints listed below: constraints listed below:
PARAMETER Meaning Value PARAMETER Meaning Value
A_MAX maximum associated MUST be at least 12 octets. A_MAX maximum associated MUST be at least 12 octets.
data length data length
N_MIN minimum nonce (IV) MUST be 12 octets. N_MIN minimum nonce (IV) MUST be 12 octets.
skipping to change at page 16, line 33 skipping to change at page 17, line 33
MUST use the (128-bit) AES_CM_PRF Key Derivation Function described MUST use the (128-bit) AES_CM_PRF Key Derivation Function described
in [RFC3711]. AEAD_AES_256_GCM MUST use the AES_256_CM_PRF Key in [RFC3711]. AEAD_AES_256_GCM MUST use the AES_256_CM_PRF Key
Derivation Function described in [RFC6188]. Derivation Function described in [RFC6188].
12. Summary of AES-GCM in SRTP/SRTCP 12. Summary of AES-GCM in SRTP/SRTCP
For convenience, much of the information about the use of AES-GCM For convenience, much of the information about the use of AES-GCM
family of algorithms in SRTP is collected in the tables contained in family of algorithms in SRTP is collected in the tables contained in
this section. this section.
The AES-GCM family of AEAD algorithms built around the AES block The AES-GCM family of AEAD algorithms is 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:
Name Key Size AEAD Tag Size Reference Name Key Size AEAD Tag Size Reference
================================================================ ================================================================
AEAD_AES_128_GCM_8 16 octets 8 octets [RFC5282] AEAD_AES_128_GCM_8 16 octets 8 octets [RFC5282]
AEAD_AES_128_GCM 16 octets 16 octets [RFC5116] AEAD_AES_128_GCM 16 octets 16 octets [RFC5116]
skipping to change at page 18, line 29 skipping to change at page 19, line 29
GCM. Note that even though the block counter is reset at the GCM. Note that even though the block counter is reset at the
start of each packet, IV uniqueness is ensured by the inclusion start of each packet, IV uniqueness is ensured by the inclusion
of SSRC/ROC/SEQ or SRTCP Index in the IV. (The reader is of SSRC/ROC/SEQ or SRTCP Index in the IV. (The reader is
reminded that the first block of key produced is reserved for reminded that the first block of key produced is reserved for
use in authenticating the packet and is not used to encrypt use in authenticating the packet and is not used to encrypt
plaintext.) plaintext.)
- Each time a rekey occurs, the initial values of both the 31-bit - Each time a rekey occurs, the initial values of both the 31-bit
SRTCP index and the 48-bit SRTP packet index (ROC||SEQ) MUST be SRTCP index and the 48-bit SRTP packet index (ROC||SEQ) MUST be
saved in order to prevent IV reuse. saved in order to prevent IV reuse.
- Processing MUST cease if either the 31-bit SRTCP index or the - Processing MUST cease if either the 31-bit SRTCP index or the
48-bit packet index ROC||SEQ cycles back their initial values . 48-bit packet index ROC||SEQ cycles back to its initial value.
Processing MUST NOT resume until a new SRTP/SRTCP session has Processing MUST NOT resume until a new SRTP/SRTCP session has
been established using a new SRTP master key. Ideally, a rekey been established using a new SRTP master key. Ideally, a rekey
should be done well before any of these counters cycle. should be done well before any of these counters cycle.
13.2. Size of the Authentication Tag 13.2. 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 reduce 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 to consider:
probability of successful forgery to be (prob_success), how many
attempts the adversary can make (N_tries) and the size of the
authentication tag in bits (N_tag_bits). Then
prob_success <= expected number of successes - How low should one make the probability that an adversary can
= N_tries * 2^-N_tag_bits. succeed in introducing a forgery into the network we are trying
to protect?
- How many packets can an adversary hijack in an attempt to
introduce a forgery?
- What is the size of the authentication tag that will be used?
When the expected number of successes is much less than one, the Neither of the attacks considered below is viable with a 16-octet tag
probability of success is well approximated by the expected number of because the amount of data required to run the attack is prohibitive
successes. in the 16-octet case. In the following discussions we shall assume
that the tag size is 8 octets = 64 bits.
Suppose an adversary wishes to introduce a forged or altered packet Niels Ferguson of Microsoft discovered an attack which allows the
into a target network by randomly selecting an authentication value recovery of the secret hash subkey H, whose compromise would allow an
until by chance they hit a valid authentication tag. The table below adversary to modify packets in transit and have the recipient accept
summarizes the relationship between the number of forged packets the these modified packets as being valid (see [FERG]. This attack
adversary has tried, the size of the authentication tag, and the requires the careful modification of a large number of packets while
probability of a compromise occurring (i.e. at least one of the in transit, using the recipient as an oracle as to whether or not the
attempted forgeries having a valid authentication tag). The reader recipient has accepted a given packet as being valid. Note that
is reminded that the forgery attempts can be made over the entire silently discarding invalid packets blocks this attack.
network, not just a single link, and that frequently changing the key
does not decrease the probability of a compromise occurring.
It should be noted that the cryptographic properties of the GHASH NIST recommends mitigating this attack by limiting the number of
algorithm used in GCM reduces the effective authentication tag size packets sent to at most 2^37 before the keys must be changed. This
(in bits) by the log base 2 of the of blocks of encrypted and/or reduces the probability of the attacker having enough data to
authenticated data in a packet. In practice an SRTP payload will be successfully run the Ferguson attack to about 2^-26.
less than 2^16 bytes, because of the 16-bit IPv4 and UDP length
fields. The exception to this case is IPv6 jumbograms [RFC2675],
which is unlikely to be used for RTP-based multimedia traffic
[RFC3711]. This corresponds to 2^12 blocks of data, so the effective
GCM authentication tag size is reduced by at most 12 bits.
+===========+=============+========================================+ Note that because GCM encrypts plain text by XORing it to a
| Auth. Tag | Effective | Number of Forgery Attempts | keystream, flipping a bit of cipher will flip the corresponding bit
| Size | Tag Size | Needed to Achieve a Given | of plain text. But any change to either the cipher or the additional
| (bytes) | (bits) | Probability of Success | authenticated data will change the authentication tag in a way that
|-----------+-------------+------------+-------------+-------------| depends upon the secret hash subkey H.
| | prob=2^-30 | prob=2^-20 | prob=2^-10 |
|===========+=============+=============+============+=============|
| 4 | 20 (GCM) | 1 try | 1 try | 2^10 tries |
|===========+=============+============+=============+=============|
| 8 | 52 (GCM) | 2^22 tries | 2^32 tries | 2^42 tries |
|===========+=============+============+=============+=============|
| 12 | 84 (GCM) | 2^54 tries | 2^64 tries | 2^74 tries |
|===========+=============+============+=============+=============|
| 16 | 116 (GCM) | 2^86 tries | 2^96 tries | 2^106 tries |
|===========+=============+============+=============+=============|
Table 5: Number of forgery attempts needed to achieve a given The second type of attack is a brute force attack. There is nothing
probability of success for various tag sizes. clever about this attack; we merely keep bombarding the recipient
with modified packets until by chance we find one that has a valid
GMAC. A priori there is a probability p=2^-64 that a given modified
packet being accepted as valid. Ferguson has a technique to reduce
this to a mere p=2^-52, albeit at the cost of severely reducing the
types of modifications that can be made.
If we use p=2^-52, a mere N=2^26 forgeries are needed until the
probability of success approaches the 2^-26 value achieved by the
Ferguson attack. Using the more realistic value of p=2^-64 raises
this to N=2^38 forgery attempts.
Sadly frequently changing the key has no effect on the brute force
attack. However the damage done by this attack is far less than in
the Ferguson attack. The brute force attack only results in a single
forged packet being accepted while the Ferguson attack allows the
attacker to easily manufacture as many authentically tagged forged
messages as they want once H has been recovered.
The above discussions lead to the following requirements:
- This document follows the NIST SP 800-38D and requires that when
an 8-octet authentication tag is being used the key must be
changed before 2^37 packets have been sent. Since SRTCP already
imposes a limit of 2^31 packets, the 2^37 limit only affects
SRTP.
- In applications where the successful introduction even a of
single forged packet into the network being protected could have
serious consequences, 8-octet tags SHOULD NOT be used.
14. IANA Considerations 14. IANA Considerations
14.1. SDES 14.1. 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 Security Descriptions to signal the use of the order to allow Security Descriptions to signal the use of the
algorithms defined in this document, IANA will register the following algorithms defined in this document, IANA will register the following
crypto suites into the "SRTP Crypto Suite Registrations" subregistry crypto suites into the "SRTP Crypto Suite Registrations" subregistry
skipping to change at page 20, line 19 skipping to change at page 21, line 30
srtp-crypto-suite-ext srtp-crypto-suite-ext
14.2. DTLS-SRTP 14.2. DTLS-SRTP
DTLS-SRTP [RFC5764] defines a DTLS-SRTP "SRTP Protection Profile". DTLS-SRTP [RFC5764] defines a DTLS-SRTP "SRTP Protection Profile".
These also correspond to the use of an AEAD algorithm in SRTP. In These also correspond to the use of an AEAD algorithm in SRTP. In
order to allow the use of the algorithms defined in this document in order to allow the use of the algorithms defined in this document in
DTLS-SRTP, we request IANA register the following SRTP Protection DTLS-SRTP, we request IANA register the following SRTP Protection
Profiles: Profiles:
AEAD_AES_128_GCM = {TBD, TBD } SRTP_AEAD_AES_128_GCM = {TBD, TBD }
AEAD_AES_128_GCM_8 = {TBD, TBD } SRTP_AEAD_AES_128_GCM_8 = {TBD, TBD }
AEAD_AES_256_GCM = {TBD, TBD } SRTP_AEAD_AES_256_GCM = {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.
AEAD_AES_128_GCM SRTP_AEAD_AES_128_GCM
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: 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
at most 2^48 SRTP packets at most 2^48 SRTP packets
AEAD_AES_128_GCM_8 SRTP_AEAD_AES_128_GCM_64
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 2^31 SRTCP packets and
at most 2^48 SRTP packets at most 2^37 SRTP packets
AEAD_AES_256_GCM SRTP_AEAD_AES_256_GCM
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: 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
at most 2^48 SRTP packets at most 2^48 SRTP packets
skipping to change at page 21, line 46 skipping to change at page 23, line 10
future may require a different set of Authentication tag lengths. 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 addition: 6.10.1.b of [RFC3830]) we request the following addition:
SRTP encr | Value | Default Session | Default Auth. SRTP encr | Value | Default Session | Default Auth.
Algorithm | | Encr. Key Length | Tag Length Algorithm | | Encr. Key Length | Tag Length
----------------------------------------------------------- -----------------------------------------------------------
AES-GCM | TBD | 16 octets | 16 octets AES-GCM | TBD | 16 octets | 16 octets
The SRTP encryption algorithm, session encryption key length, and The encryption algorithm, session encryption key length, and AEAD
AEAD authentication tag values received from MIKEY fully determine authentication tag sizes received from MIKEY fully determine the AEAD
the AEAD algorithm (e.g., AEAD_AES_256_GCM_8). The exact mapping is algorithm to be used. The exact mapping is described in section 15.
described in section 16.
15. Parameters for use with MIKEY 15. 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_8 | AES-GCM | 16 octets | 8 octets | AEAD_AES_128_GCM_8 | AES-GCM | 16 octets | 8 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_128_GCM | AES-GCM | 16 octets | 16 octets | AEAD_AES_128_GCM | AES-GCM | 16 octets | 16 octets |
+------------+-------------+-------------+ +------------+-------------+-------------+
AEAD_AES_256_GCM | AES-GCM | 32 octets | 16 octets | AEAD_AES_256_GCM | AES-GCM | 32 octets | 16 octets |
+============+=============+=============+ +============+=============+=============+
Table 6: Mapping MIKEY parameters to AEAD algorithm Table 6: Mapping MIKEY parameters to AEAD algorithm
Section 11 in this document restricts the choice of Key Derivation Section 11 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 input key length of the Key Derivation Function (i.e. [RFC3830], the input key length of the Key Derivation Function (i.e.
the SRTP master key length) is always equal to the session encryption the SRTP master key length) is always equal to the session encryption
key 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.
16. Acknowledgements 16. Some RTP Test Vectors
The examples in this section are all based upon the same RTP packet
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
consisting of a 12 octet header (8040f17b 8041f8d3 5501a0b2) and a 38
octet payload (47616c6c 69612065 7374206f 6d6e6973 20646976 69736120
696e2070 61727465 73207472 6573) which is just the ASCII string
"Gallia est omnis divisa in partes tres". The salt used (51756964
2070726f 2071756f) comes from the ASCII string "Quid pro quo". The
16 octet (128 bit) key is 00 01 02 ... 0f and the 32 octet (256 bit)
key is 00 01 02 ... 1f. The RTP payload type (1000000 binary = 64
decimal) was at the time this document was written an unassigned
value.
As shown in section 8.1, the IV is formed XORing two 12-octet
values. The first 12-octet value is formed by concatenating two zero
octets, the 4-octet SSRC (found in the 9th thru 12th octets of the
packet), the 4-octet rollover counter ROC maintained at each end of
the link, and the 2-octet sequence number SEQ (found in the 3rd and
4th octets of the packet). The second 12-octet value is the salt, a
value that is held constant at least until the key is changed.
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt 51 75 69 64 20 70 72 6f 20 71 75 6f
------------------------------------
IV 51 75 3c 65 80 c2 72 6f 20 71 84 14
All of the RTP examples use this IV.
16.1. AEAD_AES_128_GCM_8
16.1.1. AEAD_AES_128_GCM_8 Encryption
Encrypting the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2
PT: 47616c6c 69612065 7374206f 6d6e6973
20646976 69736120 696e2070 61727465
73207472 6573
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Encrypt plaintext
block # 0
IV||blk_cntr: 51753c6580c2726f2071841400000002
key_block: b5 2c 8f cf 92 55 fe 09 df ce a6 73 f0 10 22 b9
plain_block: 47 61 6c 6c 69 61 20 65 73 74 20 6f 6d 6e 69 73
cipher_block: f2 4d e3 a3 fb 34 de 6c ac ba 86 1c 9d 7e 4b ca
block # 1
IV||blk_cntr: 51753c6580c2726f2071841400000003
key_block: 9e 07 52 a3 64 5a 2f 4f 2b cb d4 0a 30 b5 a5 fe
plain_block: 20 64 69 76 69 73 61 20 69 6e 20 70 61 72 74 65
cipher_block: be 63 3b d5 0d 29 4e 6f 42 a5 f4 7a 51 c7 d1 9b
block # 2
IV||blk_cntr: 51753c6580c2726f2071841400000004
key_block: 45 fe 4e ad ed 40 0a 5d 1a f3 63 f9 0c e1 49 3b
plain_block: 73 20 74 72 65 73
cipher_block: 36 de 3a df 88 33
Cipher before tag appended
f24de3a3 fb34de6c acba861c 9d7e4bca
be633bd5 0d294e6f 42a5f47a 51c7d19b
36de3adf 8833
Compute GMAC tag
Process AAD
AAD word: 8040f17b8041f8d35501a0b200000000
partial hash: bcfb3d1d0e6e3e78ba45403377dba11b
Process Cipher
Cipher word: f24de3a3fb34de6cacba861c9d7e4bca
partial hash: 0ebc0abe1b15b32fedd2b07888c1ef61
Cipher word: be633bd50d294e6f42a5f47a51c7d19b
partial hash: 438e5797011ea860585709a2899f4685
Cipher word: 36de3adf883300000000000000000000
partial hash: 336fb643310d7bac2aeaa76247f6036d
Proceess Length Word
Length word: 00000000000000600000000000000130
partial hash: 1b964067078c408c4e442a8f015e5264
Turn GHASH into GMAC
GHASH: 1b 96 40 67 07 8c 40 8c 4e 44 2a 8f 01 5e 52 64
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 89 9d 7f 27 be b1 6a 91 52 cf 76 5e e4 39 0c ce
truncated GMAC: 89 9d 7f 27 be b1 6a 91
Cipher with tag
f24de3a3 fb34de6c acba861c 9d7e4bca
be633bd5 0d294e6f 42a5f47a 51c7d19b
36de3adf 8833899d 7f27beb1 6a91
Encrypted and Tagged packet:
8040f17b 8041f8d3 5501a0b2 f24de3a3
fb34de6c acba861c 9d7e4bca be633bd5
0d294e6f 42a5f47a 51c7d19b 36de3adf
8833899d 7f27beb1 6a91
16.1.2. AEAD_AES_128_GCM_8 Decryption
Decrypting the following packet:
8040f17b 8041f8d3 5501a0b2 f24de3a3
fb34de6c acba861c 9d7e4bca be633bd5
0d294e6f 42a5f47a 51c7d19b 36de3adf
8833899d 7f27beb1 6a91
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2
CT: f24de3a3 fb34de6c acba861c 9d7e4bca
be633bd5 0d294e6f 42a5f47a 51c7d19b
36de3adf 8833899d 7f27beb1 6a91
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Verify received tag 89 9d 7f 27 be b1 6a 91
Process AAD
AAD word: 8040f17b8041f8d35501a0b200000000
partial hash: bcfb3d1d0e6e3e78ba45403377dba11b
Process Cipher
Cipher word: f24de3a3fb34de6cacba861c9d7e4bca
partial hash: 0ebc0abe1b15b32fedd2b07888c1ef61
Cipher word: be633bd50d294e6f42a5f47a51c7d19b
partial hash: 438e5797011ea860585709a2899f4685
Cipher word: 36de3adf883300000000000000000000
partial hash: 336fb643310d7bac2aeaa76247f6036d
Proceess Length Word
Length word: 00000000000000600000000000000130
partial hash: 1b964067078c408c4e442a8f015e5264
Turn GHASH into GMAC
GHASH: 1b 96 40 67 07 8c 40 8c 4e 44 2a 8f 01 5e 52 64
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 89 9d 7f 27 be b1 6a 91 52 cf 76 5e e4 39 0c ce
truncated GMAC: 89 9d 7f 27 be b1 6a 91
Received tag = 899d7f27 beb16a91
Computed tag = 899d7f27 beb16a91
Received tag verified.
Decrypt cipher
block # 0
IV||blk_cntr: 51753c6580c2726f2071841400000002
key_block: b5 2c 8f cf 92 55 fe 09 df ce a6 73 f0 10 22 b9
cipher_block: f2 4d e3 a3 fb 34 de 6c ac ba 86 1c 9d 7e 4b ca
plain_block: 47 61 6c 6c 69 61 20 65 73 74 20 6f 6d 6e 69 73
block # 1
IV||blk_cntr: 51753c6580c2726f2071841400000003
key_block: 9e 07 52 a3 64 5a 2f 4f 2b cb d4 0a 30 b5 a5 fe
cipher_block: be 63 3b d5 0d 29 4e 6f 42 a5 f4 7a 51 c7 d1 9b
plain_block: 20 64 69 76 69 73 61 20 69 6e 20 70 61 72 74 65
block # 2
IV||blk_cntr: 51753c6580c2726f2071841400000004
key_block: 45 fe 4e ad ed 40 0a 5d 1a f3 63 f9 0c e1 49 3b
cipher_block: 36 de 3a df 88 33
plain_block: 73 20 74 72 65 73
Verified and Taged packet:
47616c6c 69612065 7374206f 6d6e6973
20646976 69736120 696e2070 61727465
73207472 6573
16.1.3. AEAD_AES_128_GCM_8 Authentication Tagging
Tagging the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Encrypt plaintext
Compute GMAC tag
Process AAD
AAD word: 8040f17b8041f8d35501a0b247616c6c
partial hash: 79f41fea34a474a77609d8925e9f2b22
AAD word: 696120657374206f6d6e697320646976
partial hash: 84093a2f85abf17ab37d3ce2f706138f
AAD word: 69736120696e20706172746573207472
partial hash: ab2760fee24e6dec754739d8059cd144
AAD word: 65730000000000000000000000000000
partial hash: e84f3c55d287fc561c41d09a8aada4be
Proceess Length Word
Length word: 00000000000001900000000000000000
partial hash: b04200c26b81c98af55cc2eafccd1cbc
Turn GHASH into GMAC
GHASH: b0 42 00 c2 6b 81 c9 8a f5 5c c2 ea fc cd 1c bc
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 22 49 3f 82 d2 bc e3 97 e9 d7 9e 3b 19 aa 42 16
truncated GMAC: 22 49 3f 82 d2 bc e3 97
Cipher with tag
22493f82 d2bce397
Tagged Packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
65732249 3f82d2bc e397
16.1.4. AEAD_AES_128_GCM_8 Tag Verification
Verifying the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
65732249 3f82d2bc e397
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
CT: 22493f82 d2bce397
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Verify received tag 22 49 3f 82 d2 bc e3 97
Process AAD
AAD word: 8040f17b8041f8d35501a0b247616c6c
partial hash: 79f41fea34a474a77609d8925e9f2b22
AAD word: 696120657374206f6d6e697320646976
partial hash: 84093a2f85abf17ab37d3ce2f706138f
AAD word: 69736120696e20706172746573207472
partial hash: ab2760fee24e6dec754739d8059cd144
AAD word: 65730000000000000000000000000000
partial hash: e84f3c55d287fc561c41d09a8aada4be
Proceess Length Word
Length word: 00000000000001900000000000000000
partial hash: b04200c26b81c98af55cc2eafccd1cbc
Turn GHASH into GMAC
GHASH: b0 42 00 c2 6b 81 c9 8a f5 5c c2 ea fc cd 1c bc
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 22 49 3f 82 d2 bc e3 97 e9 d7 9e 3b 19 aa 42 16
truncated GMAC: 22 49 3f 82 d2 bc e3 97
Received tag = 22493f82 d2bce397
Computed tag = 22493f82 d2bce397
Received tag verified.
16.2. AEAD_AES_128_GCM
16.2.1. AEAD_AES_128_GCM Encryption
Encrypting the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2
PT: 47616c6c 69612065 7374206f 6d6e6973
20646976 69736120 696e2070 61727465
73207472 6573
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Encrypt plaintext
block # 0
IV||blk_cntr: 51753c6580c2726f2071841400000002
key_block: b5 2c 8f cf 92 55 fe 09 df ce a6 73 f0 10 22 b9
plain_block: 47 61 6c 6c 69 61 20 65 73 74 20 6f 6d 6e 69 73
cipher_block: f2 4d e3 a3 fb 34 de 6c ac ba 86 1c 9d 7e 4b ca
block # 1
IV||blk_cntr: 51753c6580c2726f2071841400000003
key_block: 9e 07 52 a3 64 5a 2f 4f 2b cb d4 0a 30 b5 a5 fe
plain_block: 20 64 69 76 69 73 61 20 69 6e 20 70 61 72 74 65
cipher_block: be 63 3b d5 0d 29 4e 6f 42 a5 f4 7a 51 c7 d1 9b
block # 2
IV||blk_cntr: 51753c6580c2726f2071841400000004
key_block: 45 fe 4e ad ed 40 0a 5d 1a f3 63 f9 0c e1 49 3b
plain_block: 73 20 74 72 65 73
cipher_block: 36 de 3a df 88 33
Cipher before tag appended
f24de3a3 fb34de6c acba861c 9d7e4bca
be633bd5 0d294e6f 42a5f47a 51c7d19b
36de3adf 8833
Compute GMAC tag
Process AAD
AAD word: 8040f17b8041f8d35501a0b200000000
partial hash: bcfb3d1d0e6e3e78ba45403377dba11b
Process Cipher
Cipher word: f24de3a3fb34de6cacba861c9d7e4bca
partial hash: 0ebc0abe1b15b32fedd2b07888c1ef61
Cipher word: be633bd50d294e6f42a5f47a51c7d19b
partial hash: 438e5797011ea860585709a2899f4685
Cipher word: 36de3adf883300000000000000000000
partial hash: 336fb643310d7bac2aeaa76247f6036d
Proceess Length Word
Length word: 00000000000000600000000000000130
partial hash: 1b964067078c408c4e442a8f015e5264
Turn GHASH into GMAC
GHASH: 1b 96 40 67 07 8c 40 8c 4e 44 2a 8f 01 5e 52 64
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 89 9d 7f 27 be b1 6a 91 52 cf 76 5e e4 39 0c ce
Cipher with tag
f24de3a3 fb34de6c acba861c 9d7e4bca
be633bd5 0d294e6f 42a5f47a 51c7d19b
36de3adf 8833899d 7f27beb1 6a9152cf
765ee439 0cce
Encrypted and Tagged packet:
8040f17b 8041f8d3 5501a0b2 f24de3a3
fb34de6c acba861c 9d7e4bca be633bd5
0d294e6f 42a5f47a 51c7d19b 36de3adf
8833899d 7f27beb1 6a9152cf 765ee439
0cce
16.2.2. AEAD_AES_128_GCM Decryption
Decrypting the following packet:
8040f17b 8041f8d3 5501a0b2 f24de3a3
fb34de6c acba861c 9d7e4bca be633bd5
0d294e6f 42a5f47a 51c7d19b 36de3adf
8833899d 7f27beb1 6a9152cf 765ee439
0cce
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2
CT: f24de3a3 fb34de6c acba861c 9d7e4bca
be633bd5 0d294e6f 42a5f47a 51c7d19b
36de3adf 8833899d 7f27beb1 6a9152cf
765ee439 0cce
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Verify received tag 89 9d 7f 27 be b1 6a 91 52 cf 76 5e e4 39 0c ce
Process AAD
AAD word: 8040f17b8041f8d35501a0b200000000
partial hash: bcfb3d1d0e6e3e78ba45403377dba11b
Process Cipher
Cipher word: f24de3a3fb34de6cacba861c9d7e4bca
partial hash: 0ebc0abe1b15b32fedd2b07888c1ef61
Cipher word: be633bd50d294e6f42a5f47a51c7d19b
partial hash: 438e5797011ea860585709a2899f4685
Cipher word: 36de3adf883300000000000000000000
partial hash: 336fb643310d7bac2aeaa76247f6036d
Proceess Length Word
Length word: 00000000000000600000000000000130
partial hash: 1b964067078c408c4e442a8f015e5264
Turn GHASH into GMAC
GHASH: 1b 96 40 67 07 8c 40 8c 4e 44 2a 8f 01 5e 52 64
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 89 9d 7f 27 be b1 6a 91 52 cf 76 5e e4 39 0c ce
Received tag = 899d7f27 beb16a91 52cf765e e4390cce
Computed tag = 899d7f27 beb16a91 52cf765e e4390cce
Received tag verified.
Decrypt cipher
block # 0
IV||blk_cntr: 51753c6580c2726f2071841400000002
key_block: b5 2c 8f cf 92 55 fe 09 df ce a6 73 f0 10 22 b9
cipher_block: f2 4d e3 a3 fb 34 de 6c ac ba 86 1c 9d 7e 4b ca
plain_block: 47 61 6c 6c 69 61 20 65 73 74 20 6f 6d 6e 69 73
block # 1
IV||blk_cntr: 51753c6580c2726f2071841400000003
key_block: 9e 07 52 a3 64 5a 2f 4f 2b cb d4 0a 30 b5 a5 fe
cipher_block: be 63 3b d5 0d 29 4e 6f 42 a5 f4 7a 51 c7 d1 9b
plain_block: 20 64 69 76 69 73 61 20 69 6e 20 70 61 72 74 65
block # 2
IV||blk_cntr: 51753c6580c2726f2071841400000004
key_block: 45 fe 4e ad ed 40 0a 5d 1a f3 63 f9 0c e1 49 3b
cipher_block: 36 de 3a df 88 33
plain_block: 73 20 74 72 65 73
Verified and Taged packet:
47616c6c 69612065 7374206f 6d6e6973
20646976 69736120 696e2070 61727465
73207472 6573
16.2.3. AEAD_AES_128_GCM Authentication Tagging
Tagging the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Encrypt plaintext
Compute GMAC tag
Process AAD
AAD word: 8040f17b8041f8d35501a0b247616c6c
partial hash: 79f41fea34a474a77609d8925e9f2b22
AAD word: 696120657374206f6d6e697320646976
partial hash: 84093a2f85abf17ab37d3ce2f706138f
AAD word: 69736120696e20706172746573207472
partial hash: ab2760fee24e6dec754739d8059cd144
AAD word: 65730000000000000000000000000000
partial hash: e84f3c55d287fc561c41d09a8aada4be
Proceess Length Word
Length word: 00000000000001900000000000000000
partial hash: b04200c26b81c98af55cc2eafccd1cbc
Turn GHASH into GMAC
GHASH: b0 42 00 c2 6b 81 c9 8a f5 5c c2 ea fc cd 1c bc
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 22 49 3f 82 d2 bc e3 97 e9 d7 9e 3b 19 aa 42 16
Cipher with tag
22493f82 d2bce397 e9d79e3b 19aa4216
Tagged Packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
65732249 3f82d2bc e397e9d7 9e3b19aa
4216
16.2.4. AEAD_AES_128_GCM Tag Verification
Verifying the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
65732249 3f82d2bc e397e9d7 9e3b19aa
4216
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
CT: 22493f82 d2bce397 e9d79e3b 19aa4216
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: c6a13b37878f5b826f4f8162a1c8d879
Verify received tag 22 49 3f 82 d2 bc e3 97 e9 d7 9e 3b 19 aa 42 16
Process AAD
AAD word: 8040f17b8041f8d35501a0b247616c6c
partial hash: 79f41fea34a474a77609d8925e9f2b22
AAD word: 696120657374206f6d6e697320646976
partial hash: 84093a2f85abf17ab37d3ce2f706138f
AAD word: 69736120696e20706172746573207472
partial hash: ab2760fee24e6dec754739d8059cd144
AAD word: 65730000000000000000000000000000
partial hash: e84f3c55d287fc561c41d09a8aada4be
Proceess Length Word
Length word: 00000000000001900000000000000000
partial hash: b04200c26b81c98af55cc2eafccd1cbc
Turn GHASH into GMAC
GHASH: b0 42 00 c2 6b 81 c9 8a f5 5c c2 ea fc cd 1c bc
K0: 92 0b 3f 40 b9 3d 2a 1d 1c 8b 5c d1 e5 67 5e aa
full GMAC: 22 49 3f 82 d2 bc e3 97 e9 d7 9e 3b 19 aa 42 16
Received tag = 22493f82 d2bce397 e9d79e3b 19aa4216
Computed tag = 22493f82 d2bce397 e9d79e3b 19aa4216
Received tag verified.
16.3. AEAD_AES_256_GCM
16.3.1. AEAD_AES_256_GCM Encryption
Encrypting the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
AAD: 8040f17b 8041f8d3 5501a0b2
PT: 47616c6c 69612065 7374206f 6d6e6973
20646976 69736120 696e2070 61727465
73207472 6573
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: f29000b62a499fd0a9f39a6add2e7780
Encrypt plaintext
block # 0
IV||blk_cntr: 51753c6580c2726f2071841400000002
key_block: 75 d0 b2 14 c1 43 de 77 9c eb 58 95 5e 40 5a d9
plain_block: 47 61 6c 6c 69 61 20 65 73 74 20 6f 6d 6e 69 73
cipher_block: 32 b1 de 78 a8 22 fe 12 ef 9f 78 fa 33 2e 33 aa
block # 1
IV||blk_cntr: 51753c6580c2726f2071841400000003
key_block: 91 e4 7b 4e f3 2b 83 d3 dc 65 0a 72 17 8d da 6a
plain_block: 20 64 69 76 69 73 61 20 69 6e 20 70 61 72 74 65
cipher_block: b1 80 12 38 9a 58 e2 f3 b5 0b 2a 02 76 ff ae 0f
block # 2
IV||blk_cntr: 51753c6580c2726f2071841400000004
key_block: 68 86 43 eb dd 08 07 98 16 3a 16 d5 e5 04 f6 3a
plain_block: 73 20 74 72 65 73
cipher_block: 1b a6 37 99 b8 7b
Cipher before tag appended
32b1de78 a822fe12 ef9f78fa 332e33aa
b1801238 9a58e2f3 b50b2a02 76ffae0f
1ba63799 b87b
Compute GMAC tag
Process AAD
AAD word: 8040f17b8041f8d35501a0b200000000
partial hash: 0154dcb75485b71880e1957c877351bd
Process Cipher
Cipher word: 32b1de78a822fe12ef9f78fa332e33aa
partial hash: c3f07db9a8b9cb4345eb07f793d322d2
Cipher word: b18012389a58e2f3b50b2a0276ffae0f
partial hash: 6d1e66fe32eb32ecd8906ceab09db996
Cipher word: 1ba63799b87b00000000000000000000
partial hash: b3d1d2f1fa3b366619bc42cd2eedafee
Proceess Length Word
Length word: 00000000000000600000000000000130
partial hash: 7debf5fa1fac3bd318d5e1a7ee401091
Turn GHASH into GMAC
GHASH: 7d eb f5 fa 1f ac 3b d3 18 d5 e1 a7 ee 40 10 91
K0: 07 48 2e cc c0 53 ed 63 e1 6e 99 df 39 e7 7c 82
full GMAC: 7a a3 db 36 df ff d6 b0 f9 bb 78 78 d7 a7 6c 13
Cipher with tag
32b1de78 a822fe12 ef9f78fa 332e33aa
b1801238 9a58e2f3 b50b2a02 76ffae0f
1ba63799 b87b7aa3 db36dfff d6b0f9bb
7878d7a7 6c13
Encrypted and Tagged packet:
8040f17b 8041f8d3 5501a0b2 32b1de78
a822fe12 ef9f78fa 332e33aa b1801238
9a58e2f3 b50b2a02 76ffae0f 1ba63799
b87b7aa3 db36dfff d6b0f9bb 7878d7a7
6c13
16.3.2. AEAD_AES_256_GCM Decryption
Decrypting the following packet:
8040f17b 8041f8d3 5501a0b2 32b1de78
a822fe12 ef9f78fa 332e33aa b1801238
9a58e2f3 b50b2a02 76ffae0f 1ba63799
b87b7aa3 db36dfff d6b0f9bb 7878d7a7
6c13
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
AAD: 8040f17b 8041f8d3 5501a0b2
CT: 32b1de78 a822fe12 ef9f78fa 332e33aa
b1801238 9a58e2f3 b50b2a02 76ffae0f
1ba63799 b87b7aa3 db36dfff d6b0f9bb
7878d7a7 6c13
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: f29000b62a499fd0a9f39a6add2e7780
Verify received tag 7a a3 db 36 df ff d6 b0 f9 bb 78 78 d7 a7 6c 13
Process AAD
AAD word: 8040f17b8041f8d35501a0b200000000
partial hash: 0154dcb75485b71880e1957c877351bd
Process Cipher
Cipher word: 32b1de78a822fe12ef9f78fa332e33aa
partial hash: c3f07db9a8b9cb4345eb07f793d322d2
Cipher word: b18012389a58e2f3b50b2a0276ffae0f
partial hash: 6d1e66fe32eb32ecd8906ceab09db996
Cipher word: 1ba63799b87b00000000000000000000
partial hash: b3d1d2f1fa3b366619bc42cd2eedafee
Proceess Length Word
Length word: 00000000000000600000000000000130
partial hash: 7debf5fa1fac3bd318d5e1a7ee401091
Turn GHASH into GMAC
GHASH: 7d eb f5 fa 1f ac 3b d3 18 d5 e1 a7 ee 40 10 91
K0: 07 48 2e cc c0 53 ed 63 e1 6e 99 df 39 e7 7c 82
full GMAC: 7a a3 db 36 df ff d6 b0 f9 bb 78 78 d7 a7 6c 13
Received tag = 7aa3db36 dfffd6b0 f9bb7878 d7a76c13
Computed tag = 7aa3db36 dfffd6b0 f9bb7878 d7a76c13
Received tag verified.
Decrypt cipher
block # 0
IV||blk_cntr: 51753c6580c2726f2071841400000002
key_block: 75 d0 b2 14 c1 43 de 77 9c eb 58 95 5e 40 5a d9
cipher_block: 32 b1 de 78 a8 22 fe 12 ef 9f 78 fa 33 2e 33 aa
plain_block: 47 61 6c 6c 69 61 20 65 73 74 20 6f 6d 6e 69 73
block # 1
IV||blk_cntr: 51753c6580c2726f2071841400000003
key_block: 91 e4 7b 4e f3 2b 83 d3 dc 65 0a 72 17 8d da 6a
cipher_block: b1 80 12 38 9a 58 e2 f3 b5 0b 2a 02 76 ff ae 0f
plain_block: 20 64 69 76 69 73 61 20 69 6e 20 70 61 72 74 65
block # 2
IV||blk_cntr: 51753c6580c2726f2071841400000004
key_block: 68 86 43 eb dd 08 07 98 16 3a 16 d5 e5 04 f6 3a
cipher_block: 1b a6 37 99 b8 7b
plain_block: 73 20 74 72 65 73
Verified and Taged packet:
47616c6c 69612065 7374206f 6d6e6973
20646976 69736120 696e2070 61727465
73207472 6573
16.3.3. AEAD_AES_256_GCM Authentication Tagging
Tagging the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
AAD: 8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: f29000b62a499fd0a9f39a6add2e7780
Encrypt plaintext
Compute GMAC tag
Process AAD
AAD word: 8040f17b8041f8d35501a0b247616c6c
partial hash: c059753e6763791762ca630d8ef97714
AAD word: 696120657374206f6d6e697320646976
partial hash: a4e3401e712900dc4f1d2303bc4b2675
AAD word: 69736120696e20706172746573207472
partial hash: 1c8c1af883de0d67878f379a19c65987
AAD word: 65730000000000000000000000000000
partial hash: 958462781aa8e8feacce6d93b54472ac
Proceess Length Word
Length word: 00000000000001900000000000000000
partial hash: af2efb5dcfdb9900e7127721fdb56956
Turn GHASH into GMAC
GHASH: af 2e fb 5d cf db 99 00 e7 12 77 21 fd b5 69 56
K0: 07 48 2e cc c0 53 ed 63 e1 6e 99 df 39 e7 7c 82
full GMAC: a8 66 d5 91 0f 88 74 63 06 7c ee fe c4 52 15 d4
Cipher with tag
a866d591 0f887463 067ceefe c45215d4
Tagged Packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573a866 d5910f88 7463067c eefec452
15d4
16.3.4. AEAD_AES_256_GCM Tag Verification
Verifying the following packet:
8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573a866 d5910f88 7463067c eefec452
15d4
Form the IV
| Pad | SSRC | ROC | SEQ |
00 00 55 01 a0 b2 00 00 00 00 f1 7b
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
AAD: 8040f17b 8041f8d3 5501a0b2 47616c6c
69612065 7374206f 6d6e6973 20646976
69736120 696e2070 61727465 73207472
6573
CT: a866d591 0f887463 067ceefe c45215d4
IV: 51 75 3c 65 80 c2 72 6f 20 71 84 14
H: f29000b62a499fd0a9f39a6add2e7780
Verify received tag a8 66 d5 91 0f 88 74 63 06 7c ee fe c4 52 15 d4
Process AAD
AAD word: 8040f17b8041f8d35501a0b247616c6c
partial hash: c059753e6763791762ca630d8ef97714
AAD word: 696120657374206f6d6e697320646976
partial hash: a4e3401e712900dc4f1d2303bc4b2675
AAD word: 69736120696e20706172746573207472
partial hash: 1c8c1af883de0d67878f379a19c65987
AAD word: 65730000000000000000000000000000
partial hash: 958462781aa8e8feacce6d93b54472ac
Proceess Length Word
Length word: 00000000000001900000000000000000
partial hash: af2efb5dcfdb9900e7127721fdb56956
Turn GHASH into GMAC
GHASH: af 2e fb 5d cf db 99 00 e7 12 77 21 fd b5 69 56
K0: 07 48 2e cc c0 53 ed 63 e1 6e 99 df 39 e7 7c 82
full GMAC: a8 66 d5 91 0f 88 74 63 06 7c ee fe c4 52 15 d4
Received tag = a866d591 0f887463 067ceefe c45215d4
Computed tag = a866d591 0f887463 067ceefe c45215d4
Received tag verified.
17. RTCP Test Vectors
The examples in this section are all based upon the same RTCP packet:
81c8000e 4d617273 4e545031 4e545031
52545020 0000042a 0000eb98 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef
with 32-bit SRTCP index 000005d4.
As shown in section 9.1, the IV is formed by XORing two 12-octet
values. The first 12-octet value is formed by concatenating two zero
octets, the 4-octet SSRC (found in the 5th thru 8th octets of the RTP
packet), another 2 padding octets and the 31-bit SRTCP index, right
justified in a 32-bit = 4-octet field with a single "0" bit
pre-pended as padding. An example of SRTCP IV formation is shown
below:
| Pad | SSRC | Pad | 0+SRTCP |
00 00 4d 61 72 73 00 00 00 00 05 d4
salt 51 75 69 64 20 70 72 6f 20 71 75 6f
------------------------------------
IV 51 75 24 05 52 03 72 6f 20 71 70 bb
In an SRTCP packet a 1-bit encryption flag is pre-pended to the
31-bit SRTCP index to form a 32-bit value we shall call the ESRTCP
word. The E flag is one if the SRTCP packet has been encrypted and
zero if it has been tagged but not encrypted. Note that the ESRTCP
field is only present in an SRTCP packet, not in an RTCP packet. The
full ESRTCP word is part of the AAD.
When encrypting and tagging an RTCP packet (E flag = 1), the SRTCP
packet consists of the following fields in the following order:
- The first 8 octets of the RTCP packet (part of the AAD).
- The cipher.
- The ESRTCP word (the final part of the AAD).
- Any raw data that might have been appended to the end of the
original RTCP packet.
Recall that AEAD treats the authentication tag as an integral part of
the cipher, and in fact the authentication tag is the last 8 or 16
octets of the cipher.
The reader is reminded that when the RTCP packet is to be tagged but
not encrypted (E flag = 0), GCM will produce cipher that consists
solely of the 8 or 16 byte authentication tag. The tagged SRTCP
consists of the following fields in the order listed below:
- All of the AAD save for the ECSRTP word.
- The cipher (= the authentication tag).
- The ESRTCP word (the final part of the AAD).
- Any raw data that might have been appended to the end of the
original RTCP packet.
17.1. AEAD_AES_128_GCM_8 Encrypt and Tag
Encrypting the following packet:
81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef
Key size = 128 bits
Tag size = 8 octets
Form the IV
| Pad | SSRC | Pad | SRTCP |
00 00 4d 61 72 73 00 00 00 00 05 d4
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 81c8000d 4d617273 800005d4
PT: 4e545031 4e545032 52545020 0000042a
0000e930 4c756e61 deadbeef deadbeef
deadbeef deadbeef deadbeef
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
H: c6a13b37878f5b826f4f8162a1c8d879
Encrypt plaintext
block # 0
IV||blk_cntr: 517524055203726f207170bb00000002
key_block: 2d bd 18 b4 92 8e e6 4e f5 73 87 46 2f 6b 7a b3
plain_block: 4e 54 50 31 4e 54 50 32 52 54 50 20 00 00 04 2a
cipher_block: 63 e9 48 85 dc da b6 7c a7 27 d7 66 2f 6b 7e 99
block # 1
IV||blk_cntr: 517524055203726f207170bb00000003
key_block: 7f f5 29 c7 20 73 9d 4c 18 db 1b 1e ad a0 d1 35
plain_block: 00 00 e9 30 4c 75 6e 61 de ad be ef de ad be ef
cipher_block: 7f f5 c0 f7 6c 06 f3 2d c6 76 a5 f1 73 0d 6f da
block # 2
IV||blk_cntr: 517524055203726f207170bb00000004
key_block: 92 4d 25 a9 58 9d 83 02 d5 14 99 b4 e0 14 78 15
plain_block: de ad be ef de ad be ef de ad be ef
cipher_block: 4c e0 9b 46 86 30 3d ed 0b b9 27 5b
Cipher before tag appended
63e94885 dcdab67c a727d766 2f6b7e99
7ff5c0f7 6c06f32d c676a5f1 730d6fda
4ce09b46 86303ded 0bb9275b
Compute GMAC tag
Process AAD
AAD word: 81c8000d4d617273800005d400000000
partial hash: 085d6eb166c555aa62982f630430ec6e
Process Cipher
Cipher word: 63e94885dcdab67ca727d7662f6b7e99
partial hash: 8c9221be93466d68bbb16fa0d42b0187
Cipher word: 7ff5c0f76c06f32dc676a5f1730d6fda
partial hash: 221ebb044ec9fd0bf116d7780f198792
Cipher word: 4ce09b4686303ded0bb9275b00000000
partial hash: 50f70b9ca110ab312dce212657328dae
Proceess Length Word
Length word: 00000000000000600000000000000160
partial hash: 7296107c9716534371dfc1a30c5ffeb5
Turn GHASH into GMAC
GHASH: 72 96 10 7c 97 16 53 43 71 df c1 a3 0c 5f fe b5
K0: ba dc b4 24 01 d9 1e 6c b4 74 39 d1 49 86 14 6b
full GMAC: c8 4a a4 58 96 cf 4d 2f c5 ab f8 72 45 d9 ea de
truncated GMAC: c8 4a a4 58 96 cf 4d 2f
Cipher with tag
63e94885 dcdab67c a727d766 2f6b7e99
7ff5c0f7 6c06f32d c676a5f1 730d6fda
4ce09b46 86303ded 0bb9275b c84aa458
96cf4d2f
Add SRTCP with Eflag set.
Cext:63e94885 dcdab67c a727d766 2f6b7e99
7ff5c0f7 6c06f32d c676a5f1 730d6fda
4ce09b46 86303ded 0bb9275b c84aa458
96cf4d2f 800005d4
Encrypted and Tagged packet:
81c8000d 4d617273 63e94885 dcdab67c
a727d766 2f6b7e99 7ff5c0f7 6c06f32d
c676a5f1 730d6fda 4ce09b46 86303ded
0bb9275b c84aa458 96cf4d2f 800005d4
17.2. AEAD_AES_256_GCM Verify and Decryption
Key size = 256 bits
Tag size = 16 octets
Proceess Length Word
Decrypting the following packet:
81c8000d 4d617273 d50ae4d1 f5ce5d30
4ba297e4 7d470c28 2c3ece5d bffe0a50
a2eaa5c1 110555be 8415f658 c61de047
6f1b6fad 1d1eb30c 4446839f 57ff6f6c
b26ac3be 800005d4
Key size = 256 bits
Key size = 16 octets
Form the IV
| Pad | SSRC | Pad | SRTCP |
00 00 4d 61 72 73 00 00 00 00 05 d4
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
AAD: 81c8000d 4d617273 800005d4
CT: d50ae4d1 f5ce5d30 4ba297e4 7d470c28
2c3ece5d bffe0a50 a2eaa5c1 110555be
8415f658 c61de047 6f1b6fad 1d1eb30c
4446839f 57ff6f6c b26ac3be
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
H: f29000b62a499fd0a9f39a6add2e7780
Verify received tag 1d 1e b3 0c 44 46 83 9f 57 ff 6f 6c b2 6a c3 be
Process AAD
AAD word: 81c8000d4d617273800005d400000000
partial hash: 3ae5afd36dead5280b18950400176b5b
Process Cipher
Cipher word: d50ae4d1f5ce5d304ba297e47d470c28
partial hash: e90fab7546f6940781227227ac926ebe
Cipher word: 2c3ece5dbffe0a50a2eaa5c1110555be
partial hash: 9b236807d8b2dab07583adce367aa88f
Cipher word: 8415f658c61de0476f1b6fad00000000
partial hash: e69313f423a75e3e0b7eb93321700e86
Proceess Length Word
Length word: 00000000000000600000000000000160
partial hash: 3a284af2616fdf505faf37eec39fbc8b
Turn GHASH into GMAC
GHASH: 3a 28 4a f2 61 6f df 50 5f af 37 ee c3 9f bc 8b
K0: 27 36 f9 fe 25 29 5c cf 08 50 58 82 71 f5 7f 35
full GMAC: 1d 1e b3 0c 44 46 83 9f 57 ff 6f 6c b2 6a c3 be
Received tag = 1d1eb30c 4446839f 57ff6f6c b26ac3be
Computed tag = 1d1eb30c 4446839f 57ff6f6c b26ac3be
Received tag verified.
Decrypt cipher
block # 0
IV||blk_cntr: 517524055203726f207170bb00000002
key_block: 9b 5e b4 e0 bb 9a 0d 02 19 f6 c7 c4 7d 47 08 02
cipher_block: d5 0a e4 d1 f5 ce 5d 30 4b a2 97 e4 7d 47 0c 28
plain_block: 4e 54 50 31 4e 54 50 32 52 54 50 20 00 00 04 2a
block # 1
IV||blk_cntr: 517524055203726f207170bb00000003
key_block: 2c 3e 27 6d f3 8b 64 31 7c 47 1b 2e cf a8 eb 51
cipher_block: 2c 3e ce 5d bf fe 0a 50 a2 ea a5 c1 11 05 55 be
plain_block: 00 00 e9 30 4c 75 6e 61 de ad be ef de ad be ef
block # 2
IV||blk_cntr: 517524055203726f207170bb00000004
key_block: 5a b8 48 b7 18 b0 5e a8 b1 b6 d1 42 3b 74 39 55
cipher_block: 84 15 f6 58 c6 1d e0 47 6f 1b 6f ad
plain_block: de ad be ef de ad be ef de ad be ef
Verified and Decrypted packet:
81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef
17.3. AEAD_AES_128_GCM Tag Only
Tagging the following packet:
81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef
Key size = 128 bits
Tag size = 16 octets
Form the IV
| Pad | SSRC | Pad | SRTCP |
00 00 4d 61 72 73 00 00 00 00 05 d4
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
AAD: 81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef 000005d4
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
H: c6a13b37878f5b826f4f8162a1c8d879
Compute GMAC tag
Process AAD
AAD word: 81c8000d4d6172734e5450314e545032
partial hash: f8dbbe278e06afe17fb4fb2e67f0a22e
AAD word: 525450200000042a0000e9304c756e61
partial hash: 6ccd900dfd0eb292f68f8a410d0648ec
AAD word: deadbeefdeadbeefdeadbeefdeadbeef
partial hash: 6a14be0ea384c6b746235ba955a57ff5
AAD word: deadbeef000005d40000000000000000
partial hash: cc81f14905670a1e37f8bc81a91997cd
Proceess Length Word
Length word: 00000000000001c00000000000000000
partial hash: 3ec16d4c3c0e90a59e91be415bd976d8
Turn GHASH into GMAC
GHASH: 3e c1 6d 4c 3c 0e 90 a5 9e 91 be 41 5b d9 76 d8
K0: ba dc b4 24 01 d9 1e 6c b4 74 39 d1 49 86 14 6b
full GMAC: 84 1d d9 68 3d d7 8e c9 2a e5 87 90 12 5f 62 b3
Cipher with tag
841dd968 3dd78ec9 2ae58790 125f62b3
Tagged Packet:
81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef 841dd968 3dd78ec9 2ae58790
125f62b3 000005d4
17.4. AEAD_AES_256_GCM Tag Verification
Key size = 256 bits
Tag size = 16 octets
Proceess Length Word
Verifying the following packet:
81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef 91db4afb feee5a97 8fab4393
ed2615fe 000005d4
Key size = 256 bits
Key size = 16 octets
Form the IV
| Pad | SSRC | Pad | SRTCP |
00 00 4d 61 72 73 00 00 00 00 05 d4
salt: 51 75 69 64 20 70 72 6f 20 71 75 6f
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
Key: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
AAD: 81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef 000005d4
CT: 91db4afb feee5a97 8fab4393 ed2615fe
IV: 51 75 24 05 52 03 72 6f 20 71 70 bb
H: f29000b62a499fd0a9f39a6add2e7780
Verify received tag 91 db 4a fb fe ee 5a 97 8f ab 43 93 ed 26 15 fe
Process AAD
AAD word: 81c8000d4d6172734e5450314e545032
partial hash: 7bc665c71676a5a5f663b3229af4b85c
AAD word: 525450200000042a0000e9304c756e61
partial hash: 34ed77752703ab7d69f44237910e3bc0
AAD word: deadbeefdeadbeefdeadbeefdeadbeef
partial hash: 74a59f1a99282344d64ab1c8a2be6cf8
AAD word: deadbeef000005d40000000000000000
partial hash: 126335c0baa7ab1b79416ceeb9f7a518
Proceess Length Word
Length word: 00000000000001c00000000000000000
partial hash: b6edb305dbc7065887fb1b119cd36acb
Turn GHASH into GMAC
GHASH: b6 ed b3 05 db c7 06 58 87 fb 1b 11 9c d3 6a cb
K0: 27 36 f9 fe 25 29 5c cf 08 50 58 82 71 f5 7f 35
full GMAC: 91 db 4a fb fe ee 5a 97 8f ab 43 93 ed 26 15 fe
Received tag = 91db4afb feee5a97 8fab4393 ed2615fe
Computed tag = 91db4afb feee5a97 8fab4393 ed2615fe
Received tag verified.
Verified Packet:
81c8000d 4d617273 4e545031 4e545032
52545020 0000042a 0000e930 4c756e61
deadbeef deadbeef deadbeef deadbeef
deadbeef
18. 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, John Mattsson, Magnus Westerlund, Oscar Ohllson, Woo-Hwan Kim, John Mattsson,
Richard Barnes, John Mattisson, Morris Dworkin, Stehen Farrell and Richard Barnes, John Mattisson, Morris Dworkin, Stehen Farrell and
many other reviewers who provided valuable comments on earlier drafts many other reviewers who provided valuable comments on earlier drafts
of this document. of this document.
17. References 19. References
17.1. Normative References 19.1. 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] Schulzrinne, H., Casner, S., Frederick, R., and V.
Transport Protocol for Real-Time Applications", RFC 3550, Jacobson, "RTP: A Transport Protocol for Real-Time
July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and
K. Norrman, "The Secure Real-time Transport Protocol K. Norrman, "The Secure Real-time Transport Protocol
(SRTP)", RFC 3711, September 2003. (SRTP)", RFC 3711, September 2003.
[RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M.,and [RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M.,and
Norrman, K, "MIKEY: Multimedia Internet KEYing", RFC 3830, Norrman, K, "MIKEY: Multimedia Internet KEYing", RFC 3830,
August 2004. August 2004.
[RFC4568] Andreasen, F., Baugher, M., and D.Wing, "Session [RFC4568] Andreasen, F., Baugher, M., and D.Wing, "Session
skipping to change at page 23, line 47 skipping to change at page 47, line 47
[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for the Secure Security (DTLS) Extension to Establish Keys for the Secure
Real-time Transport Protocol (SRTP)", RFC 5764, May 2010. Real-time Transport Protocol (SRTP)", RFC 5764, May 2010.
[RFC6188] D. McGrew, "The Use of AES-192 and AES-256 in Secure [RFC6188] D. McGrew, "The Use of AES-192 and AES-256 in Secure
RTP", RFC 6188, March 2011. RTP", RFC 6188, March 2011.
[RFC6904] J. Lennox, "Encryption of Header Extensions in the Secure [RFC6904] J. Lennox, "Encryption of Header Extensions in the Secure
Real-Time Transport Protocol (SRTP)", January 2013. Real-Time Transport Protocol (SRTP)", January 2013.
, January 2013. 19.2. Informative References
[RFC6904] J. Lennox, "Encryption of Header Extensions in the Secure
Real-Time Transport Protocol (SRTP)", January 2013.
17.2. Informative References
[BN00] Bellare, M. and C. Namprempre, "Authenticated encryption: [BN00] Bellare, M. and C. Namprempre, "Authenticated encryption:
Relations among notions and analysis of the generic Relations among notions and analysis of the generic
composition paradigm", Proceedings of ASIACRYPT 2000, composition paradigm", Proceedings of ASIACRYPT 2000,
Springer-Verlag, LNCS 1976, pp. 531-545 http:// Springer-Verlag, LNCS 1976, pp. 531-545 http://
www-cse.ucsd.edu/users/mihir/papers/oem.html. www-cse.ucsd.edu/users/mihir/papers/oem.html.
[Ferg] Ferguson, N., "Authentication weaknesses in GCM", http://
csrc.nist.gov/groups/ST/toolkit/BCM/documents/comments/
CWC-GCM/Ferguson2.pdf. May 2005.
[GCM] Dworkin, M., "NIST Special Publication 800-38D: [GCM] Dworkin, M., "NIST Special Publication 800-38D:
Recommendation for Block Cipher Modes of Operation: Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC.", U.S. National Galois/Counter Mode (GCM) and GMAC.", U.S. National
Institute of Standards and Technology http:// Institute of Standards and Technology http://
csrc.nist.gov/publications/nistpubs/800-38D/SP800-38D.pdf. csrc.nist.gov/publications/nistpubs/800-38D/SP800-38D.pdf.
[R02] Rogaway, P., "Authenticated encryption with Associated- [R02] Rogaway, P., "Authenticated encryption with Associated-
Data", ACM Conference on Computer and Communication Data", ACM Conference on Computer and Communication
Security (CCS'02), pp. 98-107, ACM Press, Security (CCS'02), pp. 98-107, ACM Press,
2002. http://www.cs.ucdavis.edu/~rogaway/papers/ad.html. 2002. http://www.cs.ucdavis.edu/~rogaway/papers/ad.html.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4771] Lehtovirta, V., Naslund, M., and K. Norrman, "Integrity [RFC4771] Lehtovirta, V., Naslund, M., and K. Norrman, "Integrity
Transform Carrying Roll-Over Counter for the Secure Real- Transform Carrying Roll-Over Counter for the Secure Real-
time Transport Protocol (SRTP)", RFC 4771, January 2007. time Transport Protocol (SRTP)", RFC 4771, January 2007.
Author's Address Author's Address
David A. McGrew David A. McGrew
Cisco Systems, Inc. Cisco Systems, Inc.
510 McCarthy Blvd. 510 McCarthy Blvd.
Milpitas, CA 95035 Milpitas, CA 95035
 End of changes. 39 change blocks. 
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