AVT Working Group S. Yoon
Internet Draft J. Kim
Expires: March 2009 H. Kim
H. Jeong
Y. Won
Korea Information Security Agency
September 4, 2008
The SEED Cipher Algorithm and Its Use with the Secure Real-time
Transport Protocol (SRTP)
draft-ietf-avt-seed-srtp-04
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document describes the use of the SEED block cipher algorithm in
the Secure Real-time Transport Protocol (SRTP) for providing
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confidentiality for the RTP traffic and for the control traffic for
RTP, the Real-time Transport Control Protocol (RTCP).
Table of Contents
1. Introduction.................................................3
1.1. SEED....................................................3
1.2. Terminology.............................................3
2. Cipher Suite Definitions.....................................3
2.1. Mode....................................................4
2.1.1. Counter............................................4
2.1.2. Counter with CBC-MAC (CCM).........................4
2.1.3. Galois/Counter Mode (GCM)..........................5
2.2. Key Size and Number of Rounds...........................5
2.3. Block Size..............................................6
2.4. Performance.............................................6
3. Security Considerations......................................6
4. References...................................................7
4.1. Normative References....................................7
4.2. Informative References..................................7
APPENDIX A: Test Vectors........................................8
A.1. SEED-CM Test Vectors....................................8
A.2. SEED-CCM Test Vectors...................................9
A.3. SEED-GCM Test Vectors..................................10
Author's Addresses.............................................11
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1. Introduction
This document describes the use of SEED block cipher algorithm in the
Secure Real-time Transport Protocol (SRTP) for confidentiality to the
RTP traffic and to the control traffic for RTP, the Real-time
Transport Control Protocol (RTCP)
1.1. SEED
SEED is a national industrial association standard [TTASSEED] and is
widely used in South Korea for electronic commerce and financial
services that are operated on wired and wireless communications.
SEED is a 128-bit symmetric key block cipher that has been developed
by KISA (Korea Information Security Agency) and a group of experts
since 1998. The input/output block size of SEED is 128-bit and the
key length is also 128-bit. SEED has the 16-round Feistel structure.
A 128-bit input is divided into two 64-bit blocks, and the right 64-
bit block is an input to the round function with a 64-bit subkey that
is generated from the key scheduling.
SEED is robust against known attacks including DC (Differential
cryptanalysis), LC (Linear cryptanalysis), and related key attacks.
SEED has gone through wide public scrutinizing procedures. It has
been evaluated and is considered cryptographically secure by credible
organizations such as ISO/IEC JTC 1/SC 27.
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC-2119].
2. Cipher Suite Definitions
All symmetric block cipher algorithms share common characteristics
and valuables, including mode, key size, weak keys, block size, and
rounds. The following sections contain description of the relevant
characteristics of SEED.
The algorithm specification and object identifiers are described in
[ISOSEED] [SEED]. The SEED homepage, http://www.kisa.or.kr, contains
a wealth of information about SEED, including detailed specification,
evaluation report, test vectors, and so on.
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2.1. Mode
The SEED does not have any restriction for modes of operation that
are used in block ciphers. We define 3 modes of running SEED and an
implementation may choose to operate in a single mode of operation.
2.1.1. Counter
Section 4.1.1 of [RFC3711] defines AES counter mode encryption, which
it refers to as AES-CM. SEED counter mode is defined in a similar
manner, and is denoted as SEED_CM respectively. The plaintext inputs
to the block cipher are formed as in AES-CM, and the block cipher
outputs are processed as in AES-CM. The only difference in the
processing is that SEED-CM use SEED. Implementations MUST use SEED-CM
in conjunction with an authentication function. The pre-defined
authentication transform for SRTP is HMAC-SHA1 [RFC 2104]. SEED-CM
uses a 112-bit salt as an input, as does AES-CM. The default session
authentication key-length SHALL be 160 bits, the default
authentication tag length SHALL be 80 bits, and the
SRTP_PREFIX_LENGTH SHALL be zero for HMAC-SHA1. For SRTP, smaller
values are NOT RECOMMENDED, but MAY be used after careful
consideration of the issues in section 7.5 and 9.5 of [RFC3711].
2.1.2. Counter with CBC-MAC (CCM)
CCM is a generic authenticate-and-encrypt block cipher mode [CCM]. In
this specification, CCM is used with the SEED block cipher.
SEED CCM has two parameters:
M M indicates the size of the authentication tag. In SRTP, a
full 80-bit authentication-tag SHOULD be used, but a shorter
tag or even a zero-length tag MAY be used under certain
conditions to support either of the following two application
environment described in section 7.5 of [RFC3711].
Implementation MUST support M values of 10 octets, and
implementation MAY support M values of less than 10 octets.
L L indicates the size of the length field in octets. In SRTP,
the size of length field is 16 bits. Implementations MUST
support an L value of 2 octets.
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SEED CCM has four inputs:
Key
A single key is used to calculate the authentication tag using
CBC-MAC and to perform payload encryption using counter mode.
SEED only supports key size of 128 bits. Implementation MUST
support this key size.
Nonce
The size of the nonce depends on the value selected for the
parameter L. It is 15-L octets. Implementations MUST support a
nonce of 13 octets. SEED-CCM nonce is defined as the most
significant bit of the initialization vector (IV) defined in
section 4.1.1 of [RFC3711].
Payload
The payload of the RTP packet.
Additional Authentication Data
The header of the RTP packet.
SEED-CCM generates one output : The final result c consists of the
encrypted RTP payload followed by the authentication tag.
2.1.3. Galois/Counter Mode (GCM)
GCM is a block cipher mode of operation providing both
confidentiality and data origin authentication [GCM].GCM is used with
the SEED block cipher.
SEED-GCM has four inputs: a key, an initialization vector (IV), a
payload, and an additional authenticated data (AAD). Four inputs
except IV are described in section 2.1.2.
SEED-GCM defines an IV. The size of the IV is 12 octets.
Implementations MUST support this octet size. SEED-GCM IV is defined
as the most significant bit of the initialization vector (IV) defined
in section 4.1.1 of [RFC3711].
2.2. Key Size and Number of Rounds
SEED supports 128-bit key and has the 16-round Feistel structure.
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2.3. Block Size
SEED uses a block size of 16 octets (128 bits).
2.4. Performance
Performance figures of SEED are available at
http://www.kisa.or.kr/seed/seed_eng.html.
3. Security Considerations
No security problem has been found on SEED. SEED is secure against
all known attacks including Differential cryptanalysis, linear
cryptanalysis, and related key attacks. The best known attack is only
an exhaustive search for the key. For further security considerations,
the reader is encouraged to read [SEED-EVAL].
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4. References
4.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[SEED] Park, J., Lee, S., Kim, J., and J. Lee, "The SEED
Encryption Algorithm", RFC 4009, February 2005.
[CCM] Whiting, D., Housley, R., and N. Ferguson, "Counter with
CBC-MAC (CCM), RFC 3610, September 2003.
[GCM] Dworkin, M., "NIST Special Publication 800-38D:
Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC.", U.S. National
Institute of Standards and Technology
http://csrc.nist.gov/Publications/nistpubs/800-38D/SP-
800-38D.pdf
[RFC3711] M. Baugher, D. McGrew, M. Naslund, E.Carrara, K. Norrman,
"The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC2104] Krawczyk, H.,Bellare, M. and R. Canetti, "HMAC: keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
4.2. Informative References
[ISOSEED] ISO/IEC JTC 1/SC 27, "National Body contributions on NP
18033 "Encryption Algorithms" in Response to SC 27 N2563
(ATT.3 Korea Contribution)", ISO/IEC JTC 1/SC 27 N2656r1
(n2656_3.zip), October, 2000.
[SEED-EVAL] KISA, "Self Evaluation Report",
http://www.kisa.or.kr/kisa/seed/data/Document_pdf/SEED_Ev
aluation_Report_by_CRYPTREC.pdf
[TTASSEED] Telecommunications Technology Association (TTA), South
Korea, "128-bit Symmetric Block Cipher (SEED)", TTAS.KO-
12.0004, September, 1998 (In Korean)
http://www.tta.or.kr/English/new/main/index.htm
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APPENDIX A: Test Vectors
All values are in hexadecimal.
A.1. SEED-CM Test Vectors
Session Key: 0c5ffd37a11edc42c325287fc0604f2e
Rollover Counter: 00000000
Sequence Number: 315e
SSRC: 20e8f5eb
Session Salt: cd3a7c42c671e0067a2a2639b43a
Initial Vector: cd3a7c42e69915ed7a2a263985640000
RTP Payload: f57af5fd4ae19562976ec57a5a7ad55a
5af5c5e5c5fdf5c55ad57a4a7272d572
62e9729566ed66e97ac54a4a5a7ad5e1
5ae5fdd5fd5ac5d56ae56ad5c572d54a
e54ac55a956afd6aed5a4ac562957a95
16991691d572fd14e97ae962ed7a9f4a
955af572e162f57a956666e17ae1f54a
95f566d54a66e16e4afd6a9f7ae1c5c5
5ae5d56afde916c5e94a6ec56695e14a
fde1148416e94ad57ac5146ed59d1cc5
Encrypted RTP Payload: df5a89291e7e383e9beff765e691a737
70d5b9319162589956544855ce99a71f
48c90e413272cbb576447855e691a78c
70c58101a9c56889666458ca7999a727
cf6ab98ec1f55036e1db78dade7e08f8
3cb96a4581ed5048e5fbdb7d5191ed27
bf7a89a6b5fd582699e754fec60a8727
bfd51a011ef94c32467c5880c60ab7a8
70c5a9bea976bb99e5cb5cdada7e9327
d7c168504276e7897644267169766ea8
Authentication Tag: 28b7a194b1e3df3c573d
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A.2. SEED-CCM Test Vectors
Key: 974bee725d44fc3992267b284c3c6750
Rollover Counter: 00000000
Sequence Number: 315e
SSRC: 20e8f5eb
Nonce: b446cb282d9c7cf8d620670d72
Payload: f57af5fd4ae19562976ec57a5a7ad55a
5af5c5e5c5fdf5c55ad57a4a7272d572
62e9729566ed66e97ac54a4a5a7ad5e1
5ae5fdd5fd5ac5d56ae56ad5c572d54a
e54ac55a956afd6aed5a4ac562957a95
16991691d572fd14e97ae962ed7a9f4a
955af572e162f57a956666e17ae1f54a
95f566d54a66e16e4afd6a9f7ae1c5c5
5ae5d56afde916c5e94a6ec56695e14a
fde1148416e94ad57ac5146ed59d1cc5
AAD: 8008315ebf2e6fe020e8f5eb
Encrypted RTP Payload: 39b63931862d59ae5ba209b696b61996
96390929093139099619b686bebe19be
ae25be59aa21aa25b609868696b6192d
9629311931960919a629a61909be1986
2986099659a631a621968609ae59b659
da55da5d19be31d825b625ae21b65386
599639be2dae39b659aaaa2db62d3986
5939aa1986aa2da28631a653b62d0909
962919a63125da092586a209aa592d86
312dd848da258619b609d8a21951d009
Authentication Tag: 1ea5f4dabf178ebf8cec
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A.3. SEED-GCM Test Vectors
Key: e91e5e75da65554a48181f3846349562
Rollover Counter: 00000000
Sequence Number: 315e
SSRC: 20e8f5eb
Initial Vector: a679885189eb9982113f7152
Payload: f57af5fd4ae19562976ec57a5a7ad55a
5af5c5e5c5fdf5c55ad57a4a7272d572
62e9729566ed66e97ac54a4a5a7ad5e1
5ae5fdd5fd5ac5d56ae56ad5c572d54a
e54ac55a956afd6aed5a4ac562957a95
16991691d572fd14e97ae962ed7a9f4a
955af572e162f57a956666e17ae1f54a
95f566d54a66e16e4afd6a9f7ae1c5c5
5ae5d56afde916c5e94a6ec56695e14a
fde1148416e94ad57ac5146ed59d1cc5
AAD: 8008315ebf2e6fe020e8f5eb
Encrypted RTP Payload: 05863f37b87ac8ac5977b2bb66c22d70
bc5e4240c7d175adc56273aaafe63a3d
3b28292f2484056e14cc3b1bdd59bffa
8e8f3ad87d92657a1f673a9a8b69e1d7
feeab9c0b0892892cad0e544473970b8
ed8c4ea0482be1a2275089198f336a31
343b6be5ac00065a7d8ed54b92d65d07
a14a243948b327d391fe4405bd3bbbe3
3dcb6d42cc8d9e71d4e181f7ef146438
e2793f7a7cecd803eabe1ce4f2dd62ac
Authentication Tag: d35f789b1ee2ff180c1d
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Author's Addresses
Seokung Yoon
Korea Information Security Agency
78, Karak-dong, Songpa-Gu, Seoul 138-160, KOREA
Phone: +82-2-405-5361
Email: seokung@kisa.or.kr
Joongman Kim
Korea Information Security Agency
78, Karak-dong, Songpa-Gu, Seoul 138-160, KOREA
Phone: +82-2-405-5314
Email: seopo@kisa.or.kr
Hyun Kim
Korea Information Security Agency
78, Karak-dong, Songpa-Gu, Seoul 138-160, KOREA
Phone: +82-2-405-5355
Email: hkim@kisa.or.kr
Hyuncheol Jeong
Korea Information Security Agency
78, Karak-dong, Songpa-Gu, Seoul 138-160, KOREA
Phone: +82-2-405-5360
Email: hcjung@kisa.or.kr
Yoojae Won
Korea Information Security Agency
78, Karak-dong, Songpa-Gu, Seoul 138-160, KOREA
Phone: +82-2-405-5300
Email: yjwon@kisa.or.kr
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