The RFC Archive
 The RFC Archive   RFC 4615   « Jump to any RFC number directly 
 RFC Home
Full RFC Index
Recent RFCs
RFC Standards
Best Current Practice
RFC Errata
1 April RFC



IETF RFC 4615

The Advanced Encryption Standard-Cipher-based Message Authentication Code-Pseudo-Random Function-128 (AES-CMAC-PRF-128) Algorithm for the Internet Key Exchange Protocol (IKE)

Last modified on Tuesday, August 8th, 2006

Permanent link to RFC 4615
Search GitHub Wiki for RFC 4615
Show other RFCs mentioning RFC 4615







Network Working Group                                            J. Song
Request for Comments: 4615                                 R. Poovendran
Category: Standards Track                     University of Washington
                                                                  J. Lee
                                                     Samsung Electronics
                                                                T. Iwata
                                                       Nagoya University
                                                             August 2006


             The Advanced Encryption Standard-Cipher-based
        Message Authentication Code-Pseudo-Random Function-128
                 (AES-CMAC-PRF-128) Algorithm for the
                  Internet Key Exchange Protocol (IKE)

 Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

 Copyright Notice

   Copyright © The Internet Society (2006).

 Abstract

   Some implementations of IP Security (IPsec) may want to use a
   pseudo-random function (PRF) based on the Advanced Encryption
   Standard (AES).  This memo describes such an algorithm, called
   AES-CMAC-PRF-128.  It supports fixed and variable key sizes.

 Table of Contents

   1. Introduction ....................................................2
   2. Basic Definitions ...............................................2
   3. The AES-CMAC-PRF-128 Algorithm ..................................2
   4. Test Vectors ....................................................4
   5. Security Considerations .........................................4
   6. IANA Considerations .............................................5
   7. Acknowledgements ................................................5
   8. References ......................................................5
      8.1. Normative References .......................................5
      8.2. Informative References .....................................5





Song, et al.                Standards Track                  PAGE 1 top


RFC 4615 AES-CMAC-PRF-128 for IKE August 2006 1. Introduction [RFC 4493] describes a method to use the Advanced Encryption Standard (AES) as a Message Authentication Code (MAC) that has a 128-bit output length. The 128-bit output is useful as a long-lived pseudo- random function (PRF). This document specifies a PRF that supports fixed and variable key sizes for IKEv2 [RFC 4306] Key Derivation Function (KDF) and authentication. 2. Basic Definitions VK Variable-length key for AES-CMAC-PRF-128, denoted by VK. 0^128 The string that consists of 128 zero-bits, which is equivalent to 0x00000000000000000000000000000000 in hexadecimal notation. AES-CMAC The AES-CMAC algorithm with a 128-bit long key described in section 2.4 of [RFC 4493]. 3. The AES-CMAC-PRF-128 Algorithm The AES-CMAC-PRF-128 algorithm is identical to AES-CMAC defined in [RFC 4493] except that the 128-bit key length restriction is removed. IKEv2 [RFC 4306] uses PRFs for multiple purposes, most notably for generating keying material and authentication of the IKE_SA. The IKEv2 specification differentiates between PRFs with fixed key sizes and those with variable key sizes. When using AES-CMAC-PRF-128 as the PRF described in IKEv2, AES-CMAC- PRF-128 is considered to take fixed size (16 octets) keys for generating keying material but it takes variable key sizes for authentication. That is, when generating keying material, "half the bits must come from Ni and half from Nr, taking the first bits of each" as described in IKEv2, section 2.14; but for authenticating with shared secrets (IKEv2, section 2.16), the shared secret does not have to be 16 octets and the length may vary. Song, et al. Standards Track PAGE 2 top

RFC 4615 AES-CMAC-PRF-128 for IKE August 2006 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + AES-CMAC-PRF-128 + +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + + + Input : VK (Variable-length key) + + : M (Message, i.e., the input data of the PRF) + + : VKlen (length of VK in octets) + + : len (length of M in octets) + + Output : PRV (128-bit Pseudo-Random Variable) + + + +-------------------------------------------------------------------+ + Variable: K (128-bit key for AES-CMAC) + + + + Step 1. If VKlen is equal to 16 + + Step 1a. then + + K := VK; + + Step 1b. else + + K := AES-CMAC(0^128, VK, VKlen); + + Step 2. PRV := AES-CMAC(K, M, len); + + return PRV; + + + +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Figure 1. The AES-CMAC-PRF-128 Algorithm In step 1, the 128-bit key, K, for AES-CMAC is derived as follows: o If the key, VK, is exactly 128 bits, then we use it as-is. o If it is longer or shorter than 128 bits, then we derive the key, K, by applying the AES-CMAC algorithm using the 128-bit all-zero string as the key and VK as the input message. This step is described in step 1b. In step 2, we apply the AES-CMAC algorithm using K as the key and M as the input message. The output of this algorithm is returned. Song, et al. Standards Track PAGE 3 top

RFC 4615 AES-CMAC-PRF-128 for IKE August 2006 4. Test Vectors ------------------------------------------------------------ Test Case AES-CMAC-PRF-128 with 20-octet input Key : 00010203 04050607 08090a0b 0c0d0e0f edcb Key Length : 18 Message : 00010203 04050607 08090a0b 0c0d0e0f 10111213 PRF Output : 84a348a4 a45d235b abfffc0d 2b4da09a Test Case AES-CMAC-PRF-128 with 20-octet input Key : 00010203 04050607 08090a0b 0c0d0e0f Key Length : 16 Message : 00010203 04050607 08090a0b 0c0d0e0f 10111213 PRF Output : 980ae87b 5f4c9c52 14f5b6a8 455e4c2d Test Case AES-CMAC-PRF-128 with 20-octet input Key : 00010203 04050607 0809 Key Length : 10 Message : 00010203 04050607 08090a0b 0c0d0e0f 10111213 PRF Output : 290d9e11 2edb09ee 141fcf64 c0b72f3d ------------------------------------------------------------ 5. Security Considerations The security provided by AES-CMAC-PRF-128 is based upon the strength of AES and AES-CMAC. At the time of this writing, there are no known practical cryptographic attacks against AES or AES-CMAC. However, as is true with any cryptographic algorithm, part of its strength lies in the secret key, VK, and the correctness of the implementation in all of the participating systems. The key, VK, needs to be chosen independently and randomly based on RFC 4086 [RFC 4086], and both keys, VK and K, should be kept safe and periodically refreshed. Section 4 presents test vectors that assist in verifying the correctness of the AES-CMAC-PRF-128 code. If VK is longer than 128 bits and it is shortened to meet the AES-128 key size, then some entropy might be lost. However, as long as VK is longer than 128 bits, then the new key, K, preserves sufficient entropy, i.e., the entropy of K is about 128 bits. Therefore, we recommend the use of VK that is longer than or equal to 128 bits, and we discourage the use of VK that is shorter than or equal to 64 bits, because of the small entropy. Song, et al. Standards Track PAGE 4 top

RFC 4615 AES-CMAC-PRF-128 for IKE August 2006 6. IANA Considerations IANA has allocated a value of 8 for IKEv2 Transform Type 2 (Pseudo- Random Function) to the PRF_AES128_CMAC algorithm. 7. Acknowledgements Portions of this text were borrowed from [RFC 3664] and [RFC 4434]. Many thanks to Russ Housley and Paul Hoffman for suggestions and guidance. We also thank Alfred Hoenes for many useful comments. We acknowledge support from the following grants: Collaborative Technology Alliance (CTA) from US Army Research Laboratory, DAAD19-01-2-0011; Presidential Award from Army Research Office,- W911NF-05-1-0491; ONR YIP N00014-04-1-0479. Results do not reflect any position of the funding agencies. 8. References 8.1. Normative References [RFC 4493] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The AES-CMAC Algorithm", RFC 4493, June 2006. [RFC 4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. [RFC 4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. 8.2. Informative References [RFC 3664] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the Internet Key Exchange Protocol (IKE)", RFC 3664, January 2004. [RFC 4434] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the Internet Key Exchange Protocol (IKE)", RFC 4434, February 2006. Song, et al. Standards Track PAGE 5 top

RFC 4615 AES-CMAC-PRF-128 for IKE August 2006 Authors' Addresses JunHyuk Song Samsung Electronics University of Washington Phone: (206) 853-5843 EMail: junhyuk.song@samsung.com, junhyuk.song@gmail.com Radha Poovendran Network Security Lab University of Washington Phone: (206) 221-6512 EMail: radha@ee.washington.edu Jicheol Lee Samsung Electronics Phone: +82-31-279-3605 EMail: jicheol.lee@samsung.com Tetsu Iwata Nagoya University EMail: iwata@cse.nagoya-u.ac.jp Song, et al. Standards Track PAGE 6 top

RFC 4615 AES-CMAC-PRF-128 for IKE August 2006 Full Copyright Statement Copyright © The Internet Society (2006). 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. 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. Intellectual Property 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. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Song, et al. Standards Track PAGE 7 top

The Advanced Encryption Standard-Cipher-based Message Authentication Code-Pseudo-Random Function-128 (AES-CMAC-PRF-128) Algorithm for the Internet Key Exchange Protocol (IKE) RFC TOTAL SIZE: 13312 bytes PUBLICATION DATE: Tuesday, August 8th, 2006 LEGAL RIGHTS: The IETF Trust (see BCP 78)


RFC-ARCHIVE.ORG

© RFC 4615: The IETF Trust, Tuesday, August 8th, 2006
© the RFC Archive, 2024, RFC-Archive.org
Maintainer: J. Tunnissen

Privacy Statement