wdiff rfc5669.alt-original rfc5669.txt

AVT Working Group
Internet Engineering Task Force (IETF) S. Yoon
Internet Draft
Request for Comments: 5669 J. Kim
Expires: December 15, 2009
Category: Informational H. Park
ISSN: 2070-1721 H. Jeong
Y. Won
Korea Information Internet & Security Agency
June 15, 2009
January 2010

The SEED Cipher Algorithm and Its Use
with the Secure Real-time Real-Time Transport Protocol (SRTP)
draft-ietf-avt-seed-srtp-14

Abstract

This document describes the use of the SEED block cipher algorithm in
the Secure Real-time Transport Protocol (SRTP) for providing
confidentiality for the Real-time Transport Protocol (RTP) traffic and
for the control traffic for RTP, the Real-time Transport Control
Protocol (RTCP).

Status of this This Memo

This Internet-Draft document is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents not an Internet Standards Track specification; it is
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The list level of Internet
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This Internet-Draft will expire on December 15, 2009.
http://www.rfc-editor.org/info/rfc5669.

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Table of Contents

1. Introduction..................................................3 Introduction ....................................................2
1.1. SEED.....................................................3 SEED .......................................................2
1.2. Terminology..............................................3 Terminology ................................................3
1.3. Definitions..............................................3 Definitions ................................................3
2. Cryptographic Transforms......................................4 Transforms ........................................3
2.1. Counter..................................................4 Counter ....................................................3
2.1.1. Message Authentication/Integrity: HMAC-SHA1.........4 HMAC-SHA1 .........3
2.2. Counter with CBC-MAC (CCM)...............................4 (CCM) .................................4
2.3. Galois/Counter Mode (GCM)................................6 (GCM) ..................................5
3. Nonce Format for CCM and GCM..................................6 GCM ....................................5
3.1. Nonce for SRTP...........................................6 SRTP .............................................5
3.2. Nonce for SRTCP..........................................6 SRTCP ............................................6
4. Key Derivation: SEED-CTR PRF..................................7 PRF ....................................6
5. Mandatory-to-implement Transforms.............................7 Mandatory-to-Implement Transforms ...............................6
6. Security Considerations.......................................7 Considerations .........................................7
7. IANA Considerations...........................................8 Considerations .............................................7
8. References....................................................8
8.1. Acknowledgements ................................................7
9. References ......................................................7
9.1. Normative References.....................................8
8.2. References .......................................7
9.2. Informative References...................................9
APPENDIX A: References .....................................8
Appendix A. Test Vectors........................................10 Vectors ...........................................9
A.1. SEED-CTR Test Vectors...................................10 Vectors ......................................9
A.2. SEED-CCM Test Vectors...................................11 Vectors .....................................10
A.3. SEED-GCM Test Vectors...................................12
Author's Addresses..............................................13 Vectors .....................................11

1. Introduction

This document describes the use of the SEED [RFC4269] block cipher
algorithm in the Secure Real-time Transport Protocol (SRTP) [RFC3711]
for providing confidentiality for the Real-time Transport Protocol (RTP)
[RFC3550] traffic and for the control traffic for RTP, the Real-time
Transport Control Protocol (RTCP) [RFC3550].

1.1. SEED

SEED is a Korean National Industrial Association standard 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 128-bit, symmetric-key block cipher that has been developed
by KISA (Korea
Information Security Agency) and a group of experts have been
developing since 1998. The input/output block size of SEED is 128-bit 128
bits and the key length is also 128-bit. 128 bits. SEED has a 16-round
Feistel structure.

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 [RFC2119].

1.3. Definitions

|| concatenation
XOR exclusive or

2. Cryptographic Transforms

All symmetric block cipher algorithms share common characteristics characteristics,
including mode, key size, weak keys, and block size. The following
sections contain descriptions of the relevant characteristics of
SEED.

SEED does not have any restrictions for modes of operation that are
used with this block cipher. We define three modes of running SEED, SEED:
(1) SEED in Counter Mode, counter mode, (2) SEED in Counter counter mode with CBC-MAC (CCM) Mode
(CCM), and (3) SEED in Galois/Counter Mode (GCM) Mode. (GCM).

2.1. Counter

Section 4.1.1 of [RFC3711] defines AES counter mode encryption, which
it
that document refers to as AES-CM. SEED counter mode is defined in a
similar
manner, manner and is denoted as SEED-CTR. 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-CTR uses SEED as the underlying encryption
primitive. When SEED-
CTR SEED-CTR is used, it MUST be used only in
conjunction with an authentication function.

2.1.1. Message Authentication/Integrity: HMAC-SHA1

HMAC-SHA1 [RFC2104], as defined in section Section 4.2.1 of [RFC3711], SHALL
be the default message authentication message-authentication code to be used with SEED-CTR.
The default session authentication key-length 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, RECOMMENDED but MAY be used after careful
consideration of the issues discussed in section Sections 7.5 and 9.5 of
[RFC3711].

2.2. Counter with CBC-MAC (CCM)

CCM [RFC3610] is a generic authenticate-and-encrypt block cipher mode
[RFC3610].
mode. In this specification, CCM used with the SEED block cipher is
denoted as SEED-CCM.

Section 3.3 of [RFC3711] defines procedures to construct or to
authenticate and decrypt SRTP packets. For SEED-CCM SEED-CCM, however, the
sender performs Step 7 before Step 5 and the receiver performs the
second half of Step 5 (performs verification) (verification) after Step 6. This means that
authentication is performed on the plaintext rather than the
ciphertext. This applies equally to SRTCP.

All SRTP packets MUST be authenticated and encrypted. Unlike SRTP,
SRTCP
Secure Real-time Transport Control Protocol (SRTCP) packet encryption
is optional (but authentication is mandatory). A sender can select
which packets to encrypt, encrypt and indicates this choice with a 1-bit
encryption flag (located in the leftmost bit of the 32-bit word that
contains the SRTCP index).

SEED-CCM has two parameters:

M M indicates the size of the authentication tag. In SRTP, a
full 80-bit authentication-tag authentication tag SHOULD be used and
implementation of this specification MUST support M values of
10 octets.

L L indicates the size of the length field in octets. The
number of octets in the nonce MUST be 12, i.e., L is 3.

SEED-CCM has four inputs:

Key

A single key is used to calculate the authentication tag using
CBC-MAC
(using CBC-MAC) and to perform payload encryption using
counter mode. SEED only supports a key size of 128 bits.

Nonce

The size of the nonce depends on the value selected for the
parameter L. It is 15-L octets. L equals 3 3, and hence the
nonce size equals 12 octets.

Plaintext

In the case of SRTP, the payload of the RTP packet and packet, the RTP
padding
padding, and the RTP pad count field (if the latter two fields
are
present). present) are treated as plaintext.

In the case of SRTCP, when the encryption flag is set to 1,
the Encrypted Portion described in Fig.2 of [RFC3711] is
treated as plaintext. When the encryption flag is set to 0,
the plaintext is zero-length.

Additional Authentication Data (AAD)

In the case of SRTP, the header of the RTP packet packet, including
the contributing source (CSRC) identifier (if present) and the
RTP header extension (if present). present), is considered AAD.

In the case of SRTCP, when the encryption flag is set to 0,
the Authentication Portion described in Fig.2 of [RFC3711] is
treated as AAD. When the encryption flag is set to 1, the
first
8-octets, 8 octets, the encryption flag flag, and the SRTCP index are
treated as AAD.

SEED-CCM accepts these four inputs and returns a ciphertext field.

2.3. Galois/Counter Mode (GCM)

GCM is a block cipher mode of operation providing both
confidentiality and data origin authentication [GCM]. GCM used with
the SEED block cipher is denoted as SEED-GCM.

SEED-GCM has four inputs: a key, a plaintext, a nonce nonce, and the
additional authenticated data (AAD) (AAD), all described in section Section 2.2.

The bit length of the tag, denoted t, is 12, and an authentication
tag with a length of 12 octets (96 bits) is used.

3. Nonce Format for CCM and GCM

3.1. Nonce for SRTP

The nonce for SRTP SHALL be formed in the following way:

Nonce = (16 bits of zeroes || SSRC || ROC || SEQ) XOR Salt

The 4-octet SSRC and the 2-octet SEQ SHALL be taken from the RTP
header. The 4-octet ROC is from the cryptographic context. The 12-
octet Salt SHALL be produced by the SRTP Key Derivation Function. key derivation function.

3.2. Nonce for SRTCP

The nonce for SRTCP SHALL be formed in the following way:

Nonce = (16 bits of zeroes || SSRC || 16 bits of zeroes ||
SRTCP index) XOR Salt

The 4-octet SSRC SHALL be taken from the RTCP header and The the 31-bit
SRTCP index (packed zero-filled, right justified zero-filled and right-justified into a 4-octet
field) is from each packet. The 12-octet Salt SHALL be produced by
the SRTP Key Derivation Function. key derivation function.

4. Key Derivation: SEED-CTR PRF

Section 4.3.3 of [RFC3711] defines the AES-128 counter mode key
derivation function, which it refers to as "AES-CM PRF". The SEED-CTR SEED-
CTR PRF is defined in a similar manner, but with each invocation of
AES replaced with an invocation of SEED.

The currently defined PRF, keyed by the 128-bit master key, has input
block size m = 128 and can produce n-bit outputs for n up to 2^23.
SEED-PRF_n(k_master, x) SHALL be SEED in Counter Mode counter mode, as described
in
section 2.1, Section 2.1; it SHALL be applied to key k_master, and have IV equal to
(x*2^16), and
with have the output keystream truncated to the n first (left-most) n
(leftmost) bits.

5. Mandatory-to-implement Mandatory-to-Implement Transforms

"Mandatory-to-implement" means that conformance to the specification, and
that specification
is required. Table 1 does not supersede a similar table in Section 5
of [RFC3711]. An RTP implementation that supports SEED MUST
implement the modes listed in Table 1.

mandatory-to-implement optional

encryption SEED-CTR SEED-CCM,SEED-GCM
message integrity HMAC-SHA1 SEED-CCM,SEED-GCM
key derivation (PRF) SEED-CTR -

Table 1: Mandatory-to-implement and optional transforms in SRTP and
SRTCP.
SRTCP

6. Security Considerations

No security problem has been found on SEED. SEED is secure against
all known attacks attacks, including Differential 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].

See [RFC3610] and [GCM] for security considerations regarding the CCM
and GCM Modes of Operation, respectively. In the context of SRTP,
the procedures in [RFC3711] ensure the critical property of non-reuse
of counter values.

7. IANA Considerations

[RFC4568] defines SRTP "crypto suites". In order to allow SDP the
Session Description Protocol (SDP) to signal the use of the
algorithms defined in this document, IANA will
register has registered the
following crypto suites into the subregistry for SRTP crypto suites
under the SRTP transport Media Stream Transports of the SDP Security Descriptions:

srtp-crypto-suite-ext = "SEED_CTR_128_HMAC_SHA1_80"/
"SEED_128_CCM_80"/
"SEED_128_GCM_96"/
srtp-crypto-suite-ext

SEED_CTR_128_HMAC_SHA1_80
SEED_128_CCM_80
SEED_128_GCM_96

8. Acknowledgements

The authors would like to thank David McGrew, Eric Rescorla, Alexey
Melnikov, Alfred Hoenes, Colin Perkins, Young-Chan Shin, the AVT WG
(in particular, the chairmen Roni Even and Tom Taylor), and the
Real-time Applications and Infrastructure Area Directors for their
reviews and support.

9. References

8.1.

9.1. Normative References

[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
http://csrc.nist.gov/publications/nistpubs/800-38D/
SP-800-38D.pdf

[RFC2104] Krawczyk, H.,Bellare, M. H., Bellare, M., and R. Canetti, "HMAC: keyed- Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3550] Schulzrinne, H., Casner, S., Frederick, R. R., and V.
Jacobson, "RTP: A Transport Protocol for Real-time Real-Time
Applications", RFC3550, STD 64, RFC 3550, July 2003 2003.

[RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with
CBC-MAC (CCM)", RFC 3610, September 2003.

[RFC3711] M. Baugher, D. M., McGrew, M. D., Naslund, E.Carrara, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol
(SRTP)", RFC 3711, March 2004.

[RFC4269] H. Lee, S. H., Lee, J. S., Yoon, D. J., Cheon, D., and J. Lee, "The
SEED Encryption Algorithm", RFC 4269, December 2005.

[RFC4568] F. Andreasen, M. F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for
Media Streams", RFC 4568, July 2006.

8.2.

9.2. Informative References

[SEED-EVAL] KISA, "Self Evaluation Report",
http://www.kisa.or.kr/kisa/seed/down/SEED_Evaluation_Repo
rt_by_CRYPTREC.pdf

APPENDIX A: http://www.kisa.or.kr/
kisa/seed/down/SEED_Evaluation_Report_by_CRYPTREC.pdf

Appendix A. Test Vectors

All values are in hexadecimal.

A.1. SEED-CTR Test Vectors

Session Key: 0c5ffd37a11edc42c325287fc0604f2e

Rollover Counter: 00000000

Sequence Number: 315e

SSRC: 20e8f5eb

Session Salt: cd3a7c42c671e0067a2a2639b43a

Initialization 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

A.2. SEED-CCM Test Vectors

Key: 974bee725d44fc3992267b284c3c6750

Rollover Counter: 00000000

Sequence Number: 315e

SSRC: 20e8f5eb

Nonce: 000020e8f5eb00000000315e

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: 1eb0e7008c838b19c8fc

A.3. SEED-GCM Test Vectors

Key: e91e5e75da65554a48181f3846349562

Rollover Counter: 00000000

Sequence Number: 315e

SSRC: 20e8f5eb

Nonce: 000020e8f5eb00000000315e

AAD: 8008315ebf2e6fe020e8f5eb

Encrypted RTP Payload: 8a5363682c6b1bbf13c0b09cf747a551
2543cb2f129b8bd0e92dfadf735cda8f
88c4bbf90288f5e58d20c4f1bb0d5844
6ea009103ee57ba99cdeabaaa18d4a9a
05ddb46e7e5290a5a2284fe50b1f6fe9
ad3f1348c354181e85b24f1a552a1193
cf0e13eed5ab95ae854fb4f5b0edb2d3
ee5eb238c8f4bfb136b2eb6cd7876042
0680ce1879100014f140a15e07e70133
ed9cbb6d57b75d574acb0087eefbac99

Authentication Tag: 36cd9ae602be3ee2cd8d5d9d

Author's

Authors' Addresses

Seokung Yoon
Korea Information Internet & Security Agency
IT Venture Tower, Jungdaero 135, 135
Songpa-gu, Seoul, Korea 138-950
Email:
EMail: seokung@kisa.or.kr

Joongman Kim
Korea Information Internet & Security Agency
IT Venture Tower, Jungdaero 135, 135
Songpa-gu, Seoul, Korea 138-950
Email:
EMail: seopo@kisa.or.kr

Haeryong Park
Korea Information Internet & Security Agency
IT Venture Tower, Jungdaero 135, 135
Songpa-gu, Seoul, Korea 138-950
Email:
EMail: hrpark@kisa.or.kr

Hyuncheol Jeong
Korea Information Internet & Security Agency
IT Venture Tower, Jungdaero 135, 135
Songpa-gu, Seoul, Korea 138-950
Email:
EMail: hcjung@kisa.or.kr

Yoojae Won
Korea Information Internet & Security Agency
IT Venture Tower, Jungdaero 135, 135
Songpa-gu, Seoul, Korea 138-950
Email:
EMail: yjwon@kisa.or.kr