AVT Working Group S. Yoon Internet Draft J. Kim Expires: August 2008 H. Kim H. Jeong Y. Won Korea Information Security Agency February 19, 2008 The SEED Cipher Algorithm and Its Use with the Secure Real-time Transport Protocol (SRTP) draft-ietf-avt-seed-srtp-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on August 25, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document describes the use of SEED block cipher algorithm in the Secure Real-time Transport Protocol (SRTP) for confidentiality to the Yoon, et al. Expires August 25, 2008 [Page 1] Internet-Draft SEED-SRTP October 24, 2007 RTP traffic and to the control traffic for RTP, the Real-time Transport Control Protocol (RTCP). Table of Contents 1. Introduction..................................................3 1.1. SEED.....................................................3 2. SEED encryption...............................................3 3. SEED-CM PRF...................................................3 4. Crypto Suites.................................................4 5. Security Considerations.......................................5 6. References....................................................5 6.1. Normative References.....................................5 6.2. Informative References...................................5 Author's Addresses...............................................6 Yoon, et al. Expires August 25, 2008 [Page 2] Internet-Draft SEED-SRTP October 24, 2007 1. Introduction 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 had 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 generated from the key scheduling. 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. 2. SEED encryption 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. SEED-CM use a 112-bit salt as an input, as does AES-CM. 3. SEED-CM PRF Section 4.3.3 of [RFC3711] defines AES counter mode key derivation function, which it refers to as "AES-CM PRF". The SEED PRF is defined in a similar manner, and is denoted as SEED-CM PRF. The only difference in the processing is that SEED-CM PRF uses SEED. SEED-CM PRF uses a 112-bit salt as an input, as done the AES-CM PRF. Yoon, et al. Expires August 25, 2008 [Page 3] Internet-Draft SEED-SRTP October 24, 2007 4. Crypto Suites The table below defines SRTP crypto suites that use the ciphers and key derivation functions defined in this document. +----------------------------------+-------------------------------+ | Parameter | Value | +----------------------------------+-------------------------------+ | SRTP and SRTCP encr transf. | SEED-CM | | | | | SRTP and SRTCP auth transf. | HMAC-SHA1 | | | | | SRTP and SRTCP auth tag length | 80 bits | | | | | Key derivation PRF | SEED-CM | | | | | Key material params | | | (for each master key) : | | | master key length | 128 bits | | n_e (encr session key length) | 128 bits | | n_a (auth session key length) | 160 bits | | master salt key length | 112 bits | | n_s (session salt key length) | 112 bits | | | | | key lifetime | | | SRTP-packets-max-lifetime | 2^48 | | SRTCP-packets-max-lifetime | 2^31 | +----------------------------------+-------------------------------+ Yoon, et al. Expires August 25, 2008 [Page 4] Internet-Draft SEED-SRTP October 24, 2007 5. 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 [CRYPTREC] and [SEED-EVAL]. 6. References 6.1. Normative References [SEED] Park, J., Lee, S., Kim, J., and J. Lee, "The SEED Encryption Algorithm", RFC 4009, February 2005 [RFC3711] M. Baugher, D. McGrew, M. Naslund, E.Carrara, K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. 6.2. Informative References [CRYPTREC] Information-technology Promotion Agency (IPA), Japan, CRYPTREC. "SEED Evaluation Report", February, 2002 http://www.kisa.or.kr/kisa/seed/data/Document_pdf/SEED_Ev aluation_Report_by_CRYPTREC.pdf [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 Yoon, et al. Expires August 25, 2008 [Page 5] Internet-Draft SEED-SRTP October 24, 2007 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 Yoon, et al. Expires August 25, 2008 [Page 6] Internet-Draft SEED-SRTP October 24, 2007 Copyright Statement Copyright (C) The IETF Trust (2008). 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