RFC 5669
The SEED Cipher Algorithm and Its Use with the Secure Real-Time Transport Protocol (SRTP)
RFC 5669: The SEED Cipher Algorithm and Its Use with the Secure Real-Time Transport Protocol (SRTP) 💖
Okay, title block first, because it's all the vital stats 🎀
- Series: Internet Engineering Task Force (IETF)
- Number: Request for Comments 5669 🦋
- Authors: S. Yoon, J. Kim, H. Park, H. Jeong, Y. Won
- Organization: Korea Internet & Security Agency
- Category: Standards Track
- ISSN: 2070-1721
- Date: August 2010
- Obsoletes / Updates: the title block doesn't list anything it obsoletes or updates 🌸
Abstract
Okay so this doc is all about using the SEED block cipher inside SRTP ✨ It's how you get confidentiality for RTP traffic (the real-time media stream) and for RTCP, the control traffic that goes along with it 🔐
Status of This Memo
This is an Internet Standards Track document. 💅
It's a product of the IETF, so it represents the consensus of the IETF community. It went through public review and got approved for publication by the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check Section 2 of RFC 5741 📚
For the current status, any errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc5669 🧚
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. 🎀
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they're in effect on the date of publication. Please read these carefully, bestie, because they explain your rights and restrictions for this document 🫶 Code Components pulled out of this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty, as the Simplified BSD License describes.
This document may contain material from IETF Documents or IETF Contributions that were published or made publicly available before November 10, 2008. The people who control the copyright in some of that older material may not have given the IETF Trust permission to allow modifications outside the IETF Standards Process. So unless you get an adequate license from those copyright holders, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process. The one exceptions are formatting it for publication as an RFC or translating it into languages other than English 🌈
Table of Contents
1. Introduction ....................................................3
1.1. SEED .......................................................3
1.2. Terminology ................................................3
1.3. Definitions ................................................3
2. Cryptographic Transforms ........................................4
2.1. Counter ....................................................4
2.1.1. Message Authentication/Integrity: HMAC-SHA1 .........4
2.2. Counter with CBC-MAC (CCM) .................................4
2.3. Galois/Counter Mode (GCM) ..................................6
3. Nonce Format for CCM and GCM ....................................6
3.1. Nonce for SRTP .............................................6
3.2. Nonce for SRTCP ............................................6
4. Key Derivation: SEED-CTR PRF ....................................7
5. Mandatory-to-Implement Transforms ...............................7
6. Security Considerations .........................................7
7. IANA Considerations .............................................8
8. Acknowledgements ................................................8
9. References ......................................................8
9.1. Normative References .......................................8
9.2. Informative References .....................................9
Appendix A. Test Vectors ..........................................10
A.1. SEED-CTR Test Vectors .....................................10
A.2. SEED-CCM Test Vectors .....................................11
A.3. SEED-GCM Test Vectors .....................................121. Introduction ✨
This doc explains how to use the SEED [RFC4269] block cipher inside the Secure Real-time Transport Protocol (SRTP) [RFC3711]. The goal is confidentiality for Real-time Transport Protocol (RTP) [RFC3550] traffic, and for the control traffic for RTP, which is the Real-time Transport Control Protocol (RTCP) [RFC3550] 🦋
1.1. SEED 🌸
SEED is a symmetric encryption algorithm. The Korea Information Security Agency (KISA) and a group of experts developed it, starting in 1998 🇰🇷
Its input/output block size is 128-bit, and its key length is also 128-bit. SEED has a 16-round Feistel structure. A 128-bit input gets split into two 64-bit blocks, and the right 64-bit block goes into the round function along with a 64-bit subkey that comes from the key scheduling. It's giving precision 🔥
SEED is easy to implement in lots of software and hardware, because it's designed to be efficient with memory storage and simple when generating keys, all without hurting the security of the algorithm. It can be used really effectively in computing environments with restricted resources, like mobile devices, smart cards, and so on 📱
SEED is a national industrial association standard [TTASSEED], and it's widely used in South Korea for electronic commerce and financial services that run on wired and wireless PKI 💜
The algorithm specification and object identifiers are described in [RFC4269]. The SEED homepage, http://seed.kisa.or.kr/eng/main.jsp, has tons of info about SEED, including the detailed specification, evaluation reports, test vectors, and more 🧚
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]. Those are the official BCP 14 key words, so read them carefully 🫶
1.3. Definitions 🎀
|| concatenation
XOR exclusive or2. Cryptographic Transforms 🔐
All symmetric block cipher algorithms share some common characteristics, including mode, key size, weak keys, and block size. The next sections describe the relevant characteristics of SEED 💖
SEED doesn't have any restrictions on the modes of operation used with this block cipher. We define three ways of running SEED: (1) SEED in counter mode, (2) SEED in counter mode with CBC-MAC (CCM), and (3) SEED in Galois/Counter Mode (GCM) ✨
2.1. Counter 🦋
Section 4.1.1 of [RFC3711] defines AES counter mode encryption, which that document calls AES-CM. SEED counter mode works in a similar way, and it's called SEED-CTR. The plaintext inputs to the block cipher are formed just like in AES-CM, and the block cipher outputs get processed just like in AES-CM. The only difference is that SEED-CTR uses SEED as the underlying encryption primitive 🌈
When SEED-CTR is used, it MUST be used only in conjunction with an authentication function. This is a non-negotiable, bestie 🚨
2.1.1. Message Authentication/Integrity: HMAC-SHA1 🌸
HMAC-SHA1 [RFC2104], as defined in Section 4.2.1 of [RFC3711], SHALL be the default message-authentication code used with SEED-CTR. 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, but only after careful consideration of the issues discussed in Sections 7.5 and 9.5 of [RFC3711]. So think it through first 💀
2.2. Counter with CBC-MAC (CCM) 💜
CCM [RFC3610] is a generic authenticate-and-encrypt block cipher mode. In this spec, CCM used with the SEED block cipher is called SEED-CCM 🎀
Section 3.3 of [RFC3711] defines the procedures to construct, or to authenticate and decrypt, SRTP packets. For SEED-CCM, though, the sender does Step 7 before Step 5, and the receiver does the second half of Step 5 (verification) after Step 6. That means authentication happens on the plaintext instead of the ciphertext. This applies equally to SRTCP 🔥
All SRTP packets MUST be authenticated and encrypted. No exceptions, periodt 💅 SRTCP is different though, since SRTCP packet encryption is optional (but authentication is mandatory). A sender can pick which packets to encrypt, and it signals that choice with a 1-bit encryption flag, which sits in the leftmost bit of the 32-bit word containing 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 SHOULD be used, and implementations 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, which means L is 3 ✨
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 a key size of 128 bits 🔑
- Nonce: The size of the nonce depends on the value selected for the parameter L. It's 15-L octets. L equals 3, so the nonce size equals 12 octets 🧁
- Plaintext: For SRTP, the plaintext is the payload of the RTP packet, the RTP padding, and the RTP pad count field (if the latter two fields are present). For 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): For SRTP, the header of the RTP packet, including the contributing source (CSRC) identifier (if present) and the RTP header extension (if present), counts as AAD. For 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, the encryption 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 that provides both confidentiality and data origin authentication [GCM]. GCM used with the SEED block cipher is called SEED-GCM 🌈
SEED-GCM has four inputs: a key, a plaintext, a nonce, and the additional authenticated data (AAD), all described in 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 🦋
(Part 2 picks up right here, so stay tuned 🫶)
3.1. Nonce for SRTP 💖
okay so the nonce for SRTP SHALL be built like this, no cap 🎀
Nonce = (16 bits of zeroes || SSRC || ROC || SEQ) XOR Saltthe 4-octet SSRC and the 2-octet SEQ SHALL be grabbed from the RTP header 🦋 the 4-octet ROC comes from the cryptographic context 🌸 and the 12-octet Salt SHALL be produced by the SRTP key derivation function ✨
3.2. Nonce for SRTCP 🧚
the nonce for SRTCP SHALL be formed like this, and it's giving tidy 💅
Nonce = (16 bits of zeroes || SSRC || 16 bits of zeroes ||
SRTCP index) XOR Saltthe 4-octet SSRC SHALL be taken from the RTCP header 🫶 and the 31-bit SRTCP index (packed zero-filled and right-justified into a 4-octet field) comes from each packet 💜 the 12-octet Salt SHALL be produced by the SRTP key derivation function, same as before, iykyk 🌈
4. Key Derivation: SEED-CTR PRF ✨
okay this part is so iconic 👑 Section 4.3.3 of [RFC3711] defines the AES-128 counter mode key derivation function, which it calls "AES-CM PRF" 🎀 the SEED-CTR PRF is built the same way, except every AES invocation gets swapped out for a SEED invocation 🔁
the currently defined PRF is keyed by the 128-bit master key 🔑 it 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, as described in Section 2.1 ✨ it SHALL be applied to key k_master, have IV equal to (x*2^16), and have the output keystream truncated to the first n (leftmost) bits 🦋
5. Mandatory-to-Implement Transforms 💅
"mandatory-to-implement" means conformance to this specification 🫶 and Table 1 in this document does not supercede a similar table in Section 5 of [RFC3711] 🌸 an RTP implementation that supports SEED MUST implement the modes listed in Table 1 of this document 🔥 the table, bestie:
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
SRTCP6. Security Considerations 💀
⚠️ this section is SERIOUS, so read it slowly and don't skip anything 😭
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] 📚
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 🔒 that one is a big deal, periodt 💜
7. IANA Considerations 🌸
[RFC4568] defines SRTP "crypto suites" ✨ so the Session Description Protocol (SDP) can signal the algorithms defined in this document, IANA registered the following crypto suites into the subregistry for SRTP crypto suites under the Media Stream Transports of the SDP Security Descriptions 🎀 the new suites are:
SEED_CTR_128_HMAC_SHA1_80
SEED_128_CCM_80
SEED_128_GCM_968. 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 🧚💖 they really showed up for this one 👑
9. References 📚
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
- [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: 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., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003.
- [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-MAC (CCM)", RFC 3610, September 2003.
- [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
- [RFC4269] Lee, H., Lee, S., Yoon, J., Cheon, D., and J. Lee, "The SEED Encryption Algorithm", RFC 4269, December 2005.
- [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session Description Protocol (SDP) Security Descriptions for Media Streams", RFC 4568, July 2006.
- [TTASSEED] Telecommunications Technology Association (TTA), South Korea, "128-bit Symmetric Block Cipher (SEED)", TTAS.KO-12.0004/R1, December 2005, (In Korean) http://www.tta.or.kr/English/index.jsp.
9.2. Informative References 🦋
- [SEED-EVAL] KISA, "Self Evaluation Report", http://seed.kisa.or.kr/eng/main.jsp
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
Authentication Key: f93563311b354748c978913795530631
Session Salt: cd3a7c42c671e0067a2a2639b43a
Initialization Vector: cd3a7c42e69915ed7a2a263985640000
RTP Payload: f57af5fd4ae19562976ec57a5a7ad55a
5af5c5e5c5fdf5c55ad57a4a7272d572
62e9729566ed66e97ac54a4a5a7ad5e1
5ae5fdd5fd5ac5d56ae56ad5c572d54a
e54ac55a956afd6aed5a4ac562957a95
16991691d572fd14e97ae962ed7a9f4a
955af572e162f57a956666e17ae1f54a
95f566d54a66e16e4afd6a9f7ae1c5c5
5ae5d56afde916c5e94a6ec56695e14a
fde1148416e94ad57ac5146ed59d1cc5
Encrypted RTP Payload: df5a89291e7e383e9beff765e691a737
49c9e33139ad3001cd8da73ad07f69a2
805a70358b5c7c8c60ed359f95cf5e08
f713c53ff7b808250d79a19ccb8d1073
4e3cb72ed1f0a4e85b002b248049ab07
63dbe571bec52cf9153fdf2019e421ef
779cd6f4bd1c8211da8c272e2fce4393
4b9eabb87362510f254149f992599036
f5e43102327db1ac5e78adc4f66546ed
7abfb5a4db320fb7b9c52a61bc554e44
Authentication Tag: a5cdaa4d9edc53763855A.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: 486843a881df215a8574650ddabf5dbb
2650f06f51252bccaeb4012899d6d71e
30c64dad5ead5d8ba65ffe9d79aaf30d
c9e6334490c07e7533d704114a9006ec
b3b3bff59ecf585485bc0bd286ed434c
fd684d19a1ad514ca5f37b71d93288c0
7cf4d5e9b83db8becc8c692a7279b6a9
ac62ba970fc54f46dcc926d434c0b5ad
8678fbf0e7a03037924dae342ef64fa6
5b8eaea260fecb477a57e3919c5dab82
Authentication Tag: b0a8274cf6a8bb6cc466A.3. SEED-GCM Test Vectors 🦋
Key: e91e5e75da65554a48181f3846349562
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: 8a5363682c6b1bbf13c0b09cf747a551
2543cb2f129b8bd0e92dfadf735cda8f
88c4bbf90288f5e58d20c4f1bb0d5844
6ea009103ee57ba99cdeabaaa18d4a9a
05ddb46e7e5290a5a2284fe50b1f6fe9
ad3f1348c354181e85b24f1a552a1193
cf0e13eed5ab95ae854fb4f5b0edb2d3
ee5eb238c8f4bfb136b2eb6cd7876042
0680ce1879100014f140a15e07e70133
ed9cbb6d57b75d574acb0087eefbac99
Authentication Tag: 36cd9ae602be3ee2cd8d5d9dAuthors' Addresses 🌸
Seokung Yoon
Korea Internet & Security Agency
IT Venture Tower, Jungdaero 135
Songpa-gu, Seoul, Korea 138-950
EMail: seokung@kisa.or.kr
Joongman Kim
Korea Internet & Security Agency
IT Venture Tower, Jungdaero 135
Songpa-gu, Seoul, Korea 138-950
EMail: seopo@kisa.or.kr
Haeryong Park
Korea Internet & Security Agency
IT Venture Tower, Jungdaero 135
Songpa-gu, Seoul, Korea 138-950
EMail: hrpark@kisa.or.kr
Hyuncheol Jeong
Korea Internet & Security Agency
IT Venture Tower, Jungdaero 135
Songpa-gu, Seoul, Korea 138-950
EMail: hcjung@kisa.or.kr
Yoojae Won
Korea Internet & Security Agency
IT Venture Tower, Jungdaero 135
Songpa-gu, Seoul, Korea 138-950
EMail: yjwon@kisa.or.kr📦 where this page comes from
- ietf: rfc5669 2010-08
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms