INTERNET DRAFT K. Raeburn Kerberos Working Group MIT Document: draft-ietf-krb-wg-sha1-00.txt October 18, 2004 expires April 18, 2005 Unkeyed SHA-1 Checksum Specification for Kerberos 5 Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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 a "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract The Kerberos cryptosystem specification requires a profile detailing several operations for a new checksum type for ensuring the integrity of data in Kerberos and related protocol exchanges. This document specifies the use of a simple unkeyed checksum type based on SHA-1. Raeburn [Page 1]
INTERNET DRAFT October 2004 1. Introduction The Kerberos cryptosystem specification requires a profile detailing several operations for a new checksum type for ensuring the integrity of data in Kerberos and related protocol exchanges. This document specifies the use of a simple unkeyed checksum type based on SHA-1. (...to be expanded on a bit, describe PKINIT use...) 2. Checksum Definition The SHA-1 Kerberos checksum type calculates a checksum using the SHA-1 hash algorithm. This algorithm takes as input a message of arbitrary length, and produces as output a 160-bit (20 octet) hash value. Any general specification of a Kerberos checksum value to be computed must include the encryption key and a key usage value [KCRYPTO]. Both of these values are ignored for the SHA-1 checksum type, thus this checksum algorithm may be used with any encryption key type. The parameters for the Kerberos checksum profile for this type are thus: sha1 ---------------------------------------------- associated cryptosystem any get_mic sha1(msg) verify_mic get_mic and compare The sha1 checksum algorithm is assigned a checksum type number of 14. 3. Security Considerations Unkeyed checksum types should be used with caution, in limited circumstances where the lack of a key does not provide an avenue for an attacker to compromise the integrity of the data being conveyed. Even when encrypted, the use of unkeyed checksums may allow some forms of attack; this is discussed in the Security Considerations section of [KCRYPTO]. The use of unkeyed checksums for integrity protection should be done with great care. Raeburn [Page 2]
INTERNET DRAFT October 2004 4. IANA Considerations The Kerberos checksum type values 10 and 14 have both been reserved for "sha1 (unkeyed)" per [KCRYPTO], the latter with intent to use it with this specification, and the former on the basis of speculation that some implementation might have used that value for the same purpose. XXX...mention PKINIT above as the intended use? IANA is directed to assign the Kerberos checksum type value 14 to "sha1" with a reference to this document. As no supporting information has been found regarding any existing experimental use of or specification for Kerberos checksum type 10, IANA is directed to delete that registry entry, leaving the value available for future assignment. Normative References [KCRYPTO] Raeburn, K., "Encryption and Checksum Specifications for Kerberos 5", draft-ietf-krb-wg-crypto-07.txt, February 2004. [SHA1] NIST, "Secure Hash Standard", FIPS PUB 180-1, April 1995. Informative References [KRB] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The Kerberos Network Authentication Service (V5)", draft-ietf-krb-wg-kerberos- clarifications-07.txt, September 2004. [PKINIT] Tung, B., Neuman, C., Hur, M., Medvinsky, A., Medvinsky, S., Wray, J., and J. Trostle, "Public Key Cryptography for Initial Authentication in Kerberos", draft-ietf-cat-kerberos-pk- init-20.txt, July 2004. Author's Address Kenneth Raeburn Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge, MA 02139 raeburn@mit.edu Raeburn [Page 3]
INTERNET DRAFT October 2004 Full Copyright Statement Copyright (C) The Internet Society 2004. 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. Disclaimer 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. Raeburn [Page 4]
