Network Working Group L. Hornquist Astrand
Internet-Draft Apple, Inc
Updates: 1964, 1510, 3961, 4120, July 10, 2010
4121 (if approved)
Intended status: Standards Track
Expires: January 11, 2011
Deprecate DES support for Kerberos
draft-lha-des-die-die-die-05
Abstract
A long long time ago Data Encryption Standard (DES) was standardized.
Some 30 years later (2003) is was withdrawn as a standard by National
Institute of Standards and Technology (NIST), today 6 years later,
its time for DES to finally die. By 2008 it was possible to brute
force DES keys in 6.4 days using less than USD 10k worth of hardware.
So by 2008 DES had passed its sell-by date. This document updates
RFC1964, RFC4120, and RFC4121 to deprecate the use of DES in
Kerberos. Because the version of Kerberos specified in RFC1510 only
supports DES and has been replaced by RFC4120, RFC1510 is
reclassified as historic.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on January 11, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
Hornquist Astrand Expires January 11, 2011 [Page 1]
Internet-Draft Deprecate DES support for Kerberos July 2010
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Hornquist Astrand Expires January 11, 2011 [Page 2]
Internet-Draft Deprecate DES support for Kerberos July 2010
1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Hornquist Astrand Expires January 11, 2011 [Page 3]
Internet-Draft Deprecate DES support for Kerberos July 2010
2. Background
Kerberos 5 was defined in [RFC1510] and updated in [RFC4120], the
Kerberos crypto system is defined by [RFC3961] and includes support
for DES encryption types. This document updates [RFC1964],
[RFC4120], and [RFC4121] to deprecate the use of DES in Kerberos.
Because the version of Kerberos specified in [RFC1510] only supports
DES and has been replaced by [RFC4120], [RFC1510] is reclassified as
historic.
DES was withdrawn in [DES-Transition-Plan] by National Institute of
Standards and Technology (NIST). IETF have also published its the
position in [RFC4772], which in the recommendation summery is made
very clear: "don't use DES".
In Kerberos Generic Security Services Application Programming
Interface (GSS-API) mechanism [RFC1964] and the updated version
[RFC4121] the following checksum and encryption mechanism is defined:
three SGN ALG: 0000 - DES MAC MD5, 0100 - MD2.5 0200 - DES MAC and
one SEAL ALG 0000 - DES. With newer encryption types for Kerberos
defined in [RFC4121], Microsofts ARCFOUR4-HMAC based GSS-API mech,
and MITs DES3 , there is no need to support the old DES based SGN/
SEAL types.
Hornquist Astrand Expires January 11, 2011 [Page 4]
Internet-Draft Deprecate DES support for Kerberos July 2010
3. Recommendations
This document removes the RECOMMENDED types from [RFC4120]:
Encryption: DES-CBC-MD5(3)
Checksums: DES-MD5 (8, RSA-MD5-DES from [RFC3961]).
Kerberos implementation and deployments SHOULD NOT implement the
single DES encryption types: DES-CBC-CRC(1), DES-CBC-MD4(2), DES-CBC-
MD5(3).
Kerberos implementation and deployments SHOULD NOT implement the
checksum type: CRC32(1), RSA-MD4(2), RSA-MD4-DES(3), DES-MAC(4), DES-
MAC-K(5), RSA-MD4-MAC-K(6), DES-MD5(7), RSA-MD5-DES(8).
Note that RSA-MD5 might be with non-DES encryption types, for
example, when doing a TGS-REQ with a ARCFOUR-HMAC-MD5 some client
uses RSA-MD5 for the checksum that is stored inside the encrypted
part of the authenticator. This use of RSA-MD5 should probably be
considered safe, so the Kerberos implementation should make sure this
usage is not disabled when used with legacy system that can't handle
newer checksum types.
Kerberos GSS mechanism implementation and deployments SHOULD NOT
implement the SGN ALG: DES MAC MD5(0000), MD2.5(0100), DES MAC(0200)
(updates [RFC1964]).
Kerberos GSS mechanism implementation and deployments SHOULD NOT
implement the SEAL ALG: DES(0000) (updates [RFC1964]).
The effect of the two last sentences is that this document deprecates
section 1.2 in [RFC1964].
Hornquist Astrand Expires January 11, 2011 [Page 5]
Internet-Draft Deprecate DES support for Kerberos July 2010
4. Acknowledgements
Jeffrey Hutzelman, Simon Josefsson, Mattias Amnefelt and Leif
Johansson have read the document and provided suggestions for
improvements. Sam hartman proposed moving [RFC1510] to historic.
Hornquist Astrand Expires January 11, 2011 [Page 6]
Internet-Draft Deprecate DES support for Kerberos July 2010
5. Security Considerations
Removing support for single DES improves security since DES is
considered to be insecure.
Hornquist Astrand Expires January 11, 2011 [Page 7]
Internet-Draft Deprecate DES support for Kerberos July 2010
6. IANA Considerations
There are no IANA Considerations for this document
Hornquist Astrand Expires January 11, 2011 [Page 8]
Internet-Draft Deprecate DES support for Kerberos July 2010
7. References
7.1. Normative References
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5", RFC 3961, February 2005.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", RFC 4121,
July 2005.
7.2. Informative References
[DES-Transition-Plan]
National Institute of Standards and Technology, "DES
Transition Plan - Federal Register / Vol. 70, No. 96",
May 2006.
[RFC1510] Kohl, J. and B. Neuman, "The Kerberos Network
Authentication Service (V5)", RFC 1510, September 1993.
[RFC4772] Kelly, S., "Security Implications of Using the Data
Encryption Standard (DES)", RFC 4772, December 2006.
Hornquist Astrand Expires January 11, 2011 [Page 9]
Internet-Draft Deprecate DES support for Kerberos July 2010
Author's Address
Love Hornquist Astrand
Apple, Inc
Cupertino
USA
Email: lha@apple.com
Hornquist Astrand Expires January 11, 2011 [Page 10]