JunHyuk Song Jicheol Lee INTERNET DRAFT Samsung Electronics Expires: November 24, 2005 May 25 2005 The AES-CMAC-96 Algorithm and its use with IPsec draft-songlee-aes-cmac-96-01.txt 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. Copyright Notice Copyright (C) The Internet Society (2005). Abstract National Institute of Standards and Technology (NIST) has newly specified the Cipher based MAC (CMAC) which is equivalent to the One-Key CBC-MAC1 (OMAC1) algorithm submitted by Iwata and Kurosawa. OMAC1 efficiently reduces the key size of Extended Cipher Block Chaining mode (XCBC). This memo specifies the use of CMAC mode on authentication mechanism of IPsec Encapsulating Security Payload (ESP) and the Authentication Header (AH) protocols. This new algorithm is named AES-CMAC-96. Song and Lee. Expires November 2005 [Page 1] Internet Draft May 2005 1. Introduction National Institute of Standards and Technology (NIST) has newly specified the Cipher based MAC (CMAC). CMAC [NIST-CMAC] is a keyed hashed function that is based on a symmetric key block cipher such as Advanced Encryption Standard [AES]. CMAC is equivalent to the One-Key CBC-MAC1 (OMAC1) algorithm submitted by Iwata and Kurosawa [OMAC1]. Although the OMAC1 algorithm is based on the eXtended Cipher Block Chaining mode (XCBC) algorithm submitted by Rogaway and Black [XCBC], OMAC1 efficiently reduces the key size of XCBC. This memo specifies the usage of CMAC on authentication mechanism of IPsec Encapsulating Security Payload (ESP) and the Authentication Header (AH) protocols. This new algorithm is named AES-CMAC-96. For further information on AH and ESP, refer to [AH] and [ROADMAP]. 2. Specification of Language The keywords "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 [3]. In addition, the following words are used to signify the requirements of the specification. 3. Basic definitions CBC Cipher Block Chaining mode of operation for message authentication code. MAC Message Authentication Code. A bitstring of a fixed length, computed by MAC generation algorithm, that is used to established 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-bits (16bytes) long key for AES-128 cipher block. Denoted by K. Message (M) Message to be authenticated. Denoted by M. The total message M is denoted by sequence of M_i where M_i is the i'th block with size 128-bit. Message can be null message which means that the length of M is 0. Song and Lee. Expires November 2005 [Page 3] Internet Draft May 2005 Length (len) The length of message M in bytes. Denoted by len. Minimum value of the length can be 0. The maximum value of the length is not specified in this document. truncate(T,l) Truncate T (MAC) in msb-first order with l bytes. T The output of AES-CMAC-128. 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-bits key AES-CMAC-96 IPsec AH and ESP MAC generation function based on CMAC-AES-128 which truncates MSB 96 bits of 128 bits output 4. AES-CMAC-96 The underlying algorithm for AES-CMAC-96 are Advanced Encryption Standard cipher block [AES] and recently defined CMAC mode of operation [NIST-CMAC]. The output of AES-CMAC can validate the input message. Validating the message provide assurance of the integrity and authenticity over the message from the source. According to [NIST-CMAC] at least 64-bits should be used for against guessing attack. For use in IPsec message authentication on AH and ESP, AES-CMAC-96 should be used. AES-CMAC-96 is a AES-CMAC with 96-bit-long truncated output in most significant bit first order. The output of 96 bits MAC that will meet the default authenticator length as specified in [AH]. The result of truncation should be taken in most significant bits first order. For further information on AES-CMAC, refer to [AES-CMAC] and [NIST-CMAC]. Figure 1 describes AES-CMAC-96 algorithm: In step 1, AES-CMAC is applied to the message 'M' in length 'len' with key 'K' In step 2, Truncate output block, T with 12 byte in msb-first-order and return TT. Song and Lee. Expires November 2005 [Page 4] Internet Draft May 2005 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + Algorithm AES-CMAC-96 + +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + + + Input : K (128-bit Key described in section 4.1) + + : M ( message to be authenticated ) + + : len ( length of message in bytes ) + + Output : Truncated T (Truncated output with length 12 bytes) + + + +-------------------------------------------------------------------+ + + + Step 1. T := AES-CMAC-128 (K,M,len); + + Step 2. TT := truncate (T, 12); + + return TT; + +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Figure 1 Algorithm AES-CMAC-96 5. Test Vectors These test cases same as defined in [NIST-CMAC] with one exception of 96 bits truncation -------------------------------------------------- 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 Example 1: len = 0 M AES_CMAC_96 bb1d6929 e9593728 7fa37d12 Example 2: len = 16 M 6bc1bee2 2e409f96 e93d7e11 7393172a AES_CMAC_96 070a16b4 6b4d4144 f79bdd9d Example 3: len = 40 M 6bc1bee2 2e409f96 e93d7e11 7393172a ae2d8a57 1e03ac9c 9eb76fac 45af8e51 30c81c46 a35ce411 AES_CMAC_96 dfa66747 de9ae630 30ca3261 Example 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 -------------------------------------------------- Song and Lee. Expires November 2005 [Page 5] Internet Draft May 2005 6. Interaction with the ESP Cipher Mechanism As of this writing, there are no known issues which preclude the use of AES-CMAC-96 with any specific cipher algorithm. 7. Security Considerations The security provided by AES-CMAC-96 is based upon the strength of AES. At the time of this writing there are no practical cryptographic attacks against AES or AES-CMAC-96. As is true with any cryptographic algorithm, part of its strength lies in the correctness of the algorithm implementation, the security of the key management mechanism and its implementation, the strength of the associated secret key, and upon the correctness of the implementation in all of the participating systems. This document contains test vectors to assist in verifying the correctness of AES-CMAC-96 code. 8. IANA Consideration TBD 9. Acknowledgement Portions of this text were borrowed from [NIST-CMAC] and [AES-XCBC-MAC]. We would like to thank to OMAC1 author Tetsu Iwata and Kaoru Kurosawa, and CMAC author Morris Dworkin. 10. References [NIST-CMAC] NIST, Special Publication 800-38B Draft,"Recommendation for Block Cipher Modes of Operation: The CMAC Method for Authentication," March 9, 2005 [AES] NIST, FIPS 197, "Advanced Encryption Standard (AES)," November 2001. http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf [OMAC1] "OMAC: One-Key CBC MAC," Tetsu Iwata and Kaoru Kurosawa, Department of Computer and Information Sciences, Ilbaraki University, March 10, 2003. [AH] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, November 1998. [ROADMAP] Thayer, R., N. Doraswamy, and R. Glenn, "IP Security Document Roadmap", RFC 2411, November 1998. Song and Lee. Expires November 2005 [Page 6] Internet Draft May 2005 [XCBC] Black, J. and P. Rogaway, "A Suggestion for Handling Arbitrary-Length Messages with the CBC MAC," NIST Second Modes of Operation Workshop, August 2001. http://csrc.nist.gov/CryptoToolkit/modes/proposedmodes/ xcbc-mac/xcbc-mac-spec.pdf [AES-CMAC] JunHyuk Song and Jicheol Lee, "The AES-CMAC Algorithm" draft-songlee-aes-cmac-00.txt, May 2005 11. Author's Address Junhyuk Song Samsung Electronics +82-31-279-3639 santajunman@hanafos.com Jicheol Lee Samsung Electronics +82-31-279-3605 jicheol.lee@samsung.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Song and Lee. Expires November 2005 [Page 7] Internet Draft May 2005 Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Song and Lee. Expires November 2005 [Page 8]