JunHyuk Song
Radha Poovendran
University of Washington
Jicheol Lee
INTERNET DRAFT Samsung Electronics
Expires: April 26, 2006 October 25 2005
The AES-CMAC-PRF-128 Algorithm for
the Internet Key Exchange Protocol (IKE)
draft-songlee-aes-cmac-prf-128-01.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
Some implementations of IP Security (IPsec) may want to use a
pseudo-random function derived from the Advanced Encryption Standard
(AES). This memo describes such an algorithm, called AES-CMAC-
PRF-128.
Song et al. Expires April 2006 [Page 1]
Internet Draft October 2005
1. Introduction
[AES-CMAC] describes a method to use the Advanced Encryption
Standard (AES) as a message authentication code (MAC) whose output
is 128 bits long. 128 bits output is useful as a long-lived pseudo-
random function (PRF) in either IKE version 1 or version 2. This
document specifies PRF that support fixed and variable key sizes for
IKEv2 [IKEv2] Key Derivation Function (KDF) and authentication.
2. Basic definitions
Key (K) Variable length key for AES-CMAC-PRF-128, Denoted
by K.
truncate(K,16) Truncate K(key) in msb-first order with 16 bytes.
Padding (K,16) Padding 0 in lsb-first order with 16 bytes.
3. The AES-CMAC-PRF-128 Algorithm
The AES-CMAC-PRF-128 algorithm is identical to AES-CMAC defined
in [AES-CMAC] except that the 128 bits key length restriction is
removed.
IKEv2 [IKEv2] uses PRFs for multiple purposes, most notably for
generating keying material and authentication of the the IKE_SA.
The IKEv2 specification differentiates between PRFs with fixed key
sizes and those with variable key sizes
When using the PRF described in this document with IKEv2, the PRF is
considered to be fixed-length for generating keying material but
variable-length for authentication.
The key for AES-CMAC-PRF-128 is created as follows:
- If the key is exactly 128 bits long, use is as-is
- If the key has fewer than 128 bits, lengthen it to exactly 128
bits by padding it on the right with zero bits.
- If the key is 129 bits or longer, shorten it to exactly 128 bits
by truncating msb-first order with 128 bits.
Song et al. Expires April 2006 [Page 2]
Internet Draft October 2005
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Algorithm AES-CMAC-PRF-128 +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ +
+ Input : VK ( Variable length key ) +
+ : M ( Message to be authenticated ) +
+ : len ( length of message in bytes ) +
+ : K ( 128-bits (16bytes) fixed key ) +
+ Output : PRV ( 128 bits Pseudo Random Variable) +
+ +
+-------------------------------------------------------------------+
+ +
+ Step 1. If length of VK > 16 bytes +
+ then K:= truncate (VK, 16); +
+ Else if length of VK < 16 bytes +
+ then K:= padding (VK, 16); +
+ Step 2. PRV := AES-CMAC-PRF-128 (K,M,len); +
+ +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Figure 1 Algorithm AES-CMAC-PRF-128
4. Test Vectors
Test Case AES-CMAC-PRF-128 with 20-byte input
Test Case AES-CMAC-PRF-128 with 20-byte 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-byte input
Key : 00010203 04050607 0809
Key Length : 10
Message : 00010203 04050607 08090a0b 0c0d0e0f 10111213
PRF Output : 81a33ea4 0fc1a5a9 64c504b0 206b6d5c
Test Case AES-CMAC-PRF-128 with 20-byte input
Key : 00010203 04050607 08090a0b 0c0d0e0f edcb
Key Length : 18
Message : 00010203 04050607 08090a0b 0c0d0e0f 10111213
PRF Output : 980ae87b 5f4c9c52 14f5b6a8 455e4c2d
Song et al. Expires April 2006 [Page 3]
Internet Draft October 2005
5. Security Considerations
The security provided by AES-CMAC-PRF-128 is based upon the strength
of AES. At the time of this writing, there are no known practical
cryptographic attacks against AES or AES-CMAC-PRF-128.
As is true with any cryptographic algorithm, part of its strength
lies in the security of the key management mechanism, the strength of
the associated secret key, and upon the correctness of the
implementations in all of the participating systems.
6. IANA Consideration
IPsec IKEv2 algorithms needs to be updated to refer this document
when it is published.
7. Acknowledgement
Portions of this text were borrowed from [AES-XCBC-MAC] and
[AES-XCBC-MAC_bis]
8. Normative References
[AES-CMAC] JunHyuk Song and Jicheol Lee, "The AES-CMAC
Algorithm," draft-songlee-aes-cmac-02.txt,
(work in progress) October 2005.
[AES-XCBC-MAC] P. Hoffman, "The AES-XCBC-PRF-128 Algorithm for
the Internet Key Exchange Protocol (IKE),"
RFC3664, Jan 2004.
[AES-XCBC-MAC_bis] P. Hoffman, "The AES-XCBC-PRF-128 Algorithm for
the Internet Key Exchange Protocol (IKE),"
draft-hoffman-rfc3664bis-05.txt
(work in progress), October 2005.
[IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
Protocol", draft-ietf-ipsec-ikev2-17
(work in progress), September 2004.
Song et al. Expires April 2006 [Page 4]
Internet Draft October 2005
Author's Address
Junhyuk Song
Samsung Electronics
University of Washington
(206) 853-5843
songlee@u.washington.edu
junhyuk.song@samsung.com
Jicheol Lee
Samsung Electronics
+82-31-279-3605
jicheol.lee@samsung.com
Radha Poovendran
Network Security Lab
University of Washington
(206) 221-6512
radha@ee.washington.edu
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 et al. Expires April 2006 [Page 5]
Internet Draft October 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 et al. Expires April 2006 [Page 6]
