RFC 4494
The AES-CMAC-96 Algorithm and Its Use with IPsec
RFC 4494: The AES-CMAC-96 Algorithm and Its Use with IPsec 🎀
Okay bestie, this one is a Standards Track doc from the Network Working Group, dated June 2006 📅. It was written by JH. Song (Junhyuk Song), R. Poovendran (Radha Poovendran) and J. Lee (Jicheol Lee) 💅. Song and Poovendran are from the University of Washington, and Song and Lee are from Samsung Electronics. Its title block doesn't list anything it obsoletes or updates, so it's a fresh standard 🌸.
Status of This Memo ✨
This doc specifies an Internet standards track protocol for the Internet community, and it wants discussion and suggestions for improvements 💬. Check the current edition of the "Internet Official Protocol Standards" (STD 1) for where this protocol stands. Distribution of this memo is unlimited 🦋.
Copyright Notice 🔖
Copyright (C) The Internet Society (2006).
Abstract 💖
Okay so NIST just specified the Cipher-based Message Authentication Code (CMAC) 🔐. It's the same thing as OMAC1, which Iwata and Kurosawa submitted, and OMAC1 is a glow-up of XCBC that shrinks the key size 💅. This memo says how to use CMAC for authentication in IPsec's Encapsulating Security Payload (ESP) and Authentication Header (AH) protocols 🎀. The new algorithm is called AES-CMAC-96 and it is literally iconic 👑.
1. Introduction ✨
NIST has recently specified CMAC 🌈. CMAC [NIST-CMAC] is a message authentication code built on a symmetric key block cipher like the Advanced Encryption Standard [NIST-AES]. It's equivalent to the One-Key CBC MAC1 (OMAC1) that Iwata and Kurosawa submitted [OMAC1a, OMAC1b]. OMAC1 improves on the eXtended Cipher Block Chaining mode (XCBC) that Black and Rogaway submitted [XCBCa, XCBCb], and XCBC was itself an upgrade on the basic CBC-MAC 📈. XCBC fixes the security problems of CBC-MAC, and OMAC1 cuts down the key size of XCBC. Literally a whole arc 🫶.
This memo describes how to use CMAC for authentication in the IPsec Encapsulating Security Payload [ESP] and Authentication Header [AH] protocols 🧚. The new algorithm is called AES-CMAC-96. For more on AH and ESP, check [AH] and [ROADMAP] 📚.
2. Basic Definitions 🍓
Here's the glossary, bestie. Everything is in the table below 💜.
CBC Cipher Block Chaining mode of operation for message
authentication code.
MAC Message Authentication Code.
A bit string of a fixed length, computed by the MAC
generation algorithm, that is used to establish the
authority and, hence, the integrity of a message.
CMAC Cipher-based MAC based on an approved symmetric key
block cipher, such as the Advanced Encryption
Standard.
Key (K) 128-bit (16-octet) key for AES-128 cipher block.
Denoted by K.
Message (M) Message to be authenticated.
Denoted by M.
Length (len) The length of message M in octets.
Denoted by len.
The minimum value is 0. The maximum value is not
specified in this document.
truncate(T,l) Truncate T (MAC) in most-significant-bit-first
(MSB-first) order to a length of l octets.
T The output of AES-CMAC.
Truncated T The truncated output of AES-CMAC-128 in MSB-first
order.
AES-CMAC CMAC generation function based on AES block cipher
with 128-bit key.
AES-CMAC-96 IPsec AH and ESP MAC generation function based on
AES-CMAC, which truncates the 96 most significant
bits of the 128-bit output.3. AES-CMAC 🦋
AES-CMAC-96 runs on the AES-CMAC [AES-CMAC] core 🌸. Under the hood, AES-CMAC uses the Advanced Encryption Standard cipher block [NIST-AES] and the newish CMAC mode of operation [NIST-CMAC]. It gives you way stronger data integrity than a checksum or an error detecting code, which only catch accidental changes to your data 😭. CMAC is built to catch intentional, unauthorized changes too, not just accidental ones 🛡️. The AES-CMAC output can validate the input message, and that gives you assurance of integrity and authenticity from the source 💅. According to [NIST-CMAC], at least 64 bits should be used against guessing attacks 🙈. AES-CMAC hits a similar security goal to HMAC [RFC-HMAC]. The difference is that AES-CMAC is built on a symmetric key block cipher (AES), while HMAC is built on a hash function (like SHA-1). So AES-CMAC is a great fit for systems where AES is easier to get than a hash function 🔥. More details are in [AES-CMAC] and [NIST-CMAC] 📖.
4. AES-CMAC-96 👑
For IPsec message authentication on AH and ESP, AES-CMAC-96 should be used 💖. It's AES-CMAC with the output truncated to 96 bits in MSB-first order. The result is a 96-bit MAC that meets the default authenticator length in [AH], and the truncation keeps the most significant bits first. For more on AES-CMAC, refer to [AES-CMAC] and [NIST-CMAC] 🧚.
Figure 1 shows the AES-CMAC-96 algorithm 🎀:
In step 1, AES-CMAC is applied to the message M of length len with key K ✨.
In step 2, the output block T is truncated to 12 octets in MSB-first order, and the result, Truncated T (TT), is returned 💅.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Algorithm AES-CMAC-96 +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ +
+ Input : K (128-bit Key described in Section 4.1) +
+ : M (message to be authenticated) +
+ : len (length of message in octets) +
+ Output : Truncated T (truncated output to length 12 octets) +
+ +
+-------------------------------------------------------------------+
+ +
+ Step 1. T := AES-CMAC (K,M,len); +
+ Step 2. TT := truncate (T, 12); +
+ return TT; +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Figure 1: Algorithm AES-CMAC-965. Test Vectors 🧪
These test cases match the ones in [NIST-CMAC], except that the output is truncated to 96 bits 🌈.
--------------------------------------------------
K 2b7e1516 28aed2a6 abf71588 09cf4f3c
Subkey Generation
AES_128(key,0) 7df76b0c 1ab899b3 3e42f047 b91b546f
K1 fbeed618 35713366 7c85e08f 7236a8de
K2 f7ddac30 6ae266cc f90bc11e e46d513b
Test Case 1: len = 0
M <empty string>
AES_CMAC_96 bb1d6929 e9593728 7fa37d12
Test Case 2: len = 16
M 6bc1bee2 2e409f96 e93d7e11 7393172a
AES_CMAC_96 070a16b4 6b4d4144 f79bdd9d
Test Case 3: len = 40
M 6bc1bee2 2e409f96 e93d7e11 7393172a
ae2d8a57 1e03ac9c 9eb76fac 45af8e51
30c81c46 a35ce411
AES_CMAC_96 dfa66747 de9ae630 30ca3261
Test Case 4: len = 64
M 6bc1bee2 2e409f96 e93d7e11 7393172a
ae2d8a57 1e03ac9c 9eb76fac 45af8e51
30c81c46 a35ce411 e5fbc119 1a0a52ef
f69f2445 df4f9b17 ad2b417b e66c3710
AES_CMAC_96 51f0bebf 7e3b9d92 fc497417
--------------------------------------------------6. Interaction with the ESP Cipher Mechanism 🔐
As of this writing, there are no known issues that stop AES-CMAC-96 from being used with any specific cipher algorithm 💖.
7. Security Considerations 🚨
This is serious, bestie 😭🚨. For the security considerations, you have to read the security considerations section of [AES-CMAC]. Don't skip it!!
8. IANA Considerations 📋
IANA has allocated value 8 for IKEv2 Transform Type 3 (Integrity Algorithm) to the AUTH_AES_CMAC_96 algorithm 🎟️.
9. Acknowledgements 🫶
Parts of this text were borrowed from [NIST-CMAC] and [XCBCa] 🌷. The authors want to thank Russ Housley for his helpful comments 💜.
The authors also acknowledge support from these grants: the Collaborative Technology Alliance (CTA) from the US Army Research Laboratory, DAAD19-01-2-0011; the Presidential Award from the Army Research Office, W911NF-05-1-0491; and NSF CAREER, ANI-0093187. The results don't reflect the position of any of the funding agencies 🌈.
10. References 📚
10.1. Normative References 💅
[AES-CMAC] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
AES-CMAC Algorithm", RFC 4493, June 2006.
[AH] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
[ESP] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.
[NIST-AES] NIST, FIPS 197, "Advanced Encryption Standard (AES)",
November 2001, http://csrc.nist.gov/publications/fips/
fips197/fips-197.pdf.
[NIST-CMAC] NIST, Special Publication 800-38B Draft, "Recommendation
for Block Cipher Modes of Operation: The CMAC Method for
Authentication", March 9, 2005.10.2. Informative References 🦋
[OMAC1a] Tetsu Iwata and Kaoru Kurosawa, "OMAC: One-Key CBC MAC",
Fast Software Encryption, FSE 2003, LNCS 2887, pp. 129-
153, Springer-Verlag, 2003.
[OMAC1b] Tetsu Iwata and Kaoru Kurosawa, "OMAC: One-Key CBC MAC",
Submission to NIST, December 2002. Available from
http://csrc.nist.gov/CryptoToolkit/modes/proposedmodes/
omac/omac-spec.pdf.
[RFC-HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[ROADMAP] Thayer, R., Doraswamy, N., and R. Glenn, "IP Security
Document Roadmap", RFC 2411, November 1998.
[XCBCa] John Black and Phillip Rogaway, "A Suggestion for
Handling Arbitrary-Length Messages with the CBC MAC",
NIST Second Modes of Operation Workshop, August 2001.
Available from http://csrc.nist.gov/CryptoToolkit/modes/
proposedmodes/xcbc-mac/xcbc-mac-spec.pdf.
[XCBCb] John Black and Phillip Rogaway, "CBC MACs for Arbitrary-
Length Messages: The Three-Key Constructions", Journal of
Cryptology, Vol. 18, No. 2, pp. 111-132, Springer-Verlag,
Spring 2005.Authors' Addresses 💌
Junhyuk Song
University of Washington
Samsung Electronics
Phone: (206) 853-5843
EMail: songlee@ee.washington.edu, junhyuk.song@samsung.com
Jicheol Lee
Samsung Electronics
Phone: +82-31-279-3605
EMail: jicheol.lee@samsung.com
Radha Poovendran
Network Security Lab (NSL)
Dept. of Electrical Engineering
University of Washington
Phone: (206) 221-6512
EMail: radha@ee.washington.eduFull Copyright Statement ✨
Okay, bestie, the legal bit 💅 Copyright (C) The Internet Society (2006). 💖
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📦 where this page comes from
- ietf: rfc4494 2006-06
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