Network Working Group L. Hornquist Astrand
Internet-Draft Apple, Inc
Updates: 1964, 3961, 4120, 4121 March 25, 2010
(if approved)
Intended status: Standards Track
Expires: September 26, 2010
Deprecate DES support for Kerberos
draft-lha-des-die-die-die-03
Abstract
A long long time ago DES was standardized. Some 30 years later
(2003) is was withdrawn as a standard by NIST, today 6 years later,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. Use in Kerberos should
therefore stop.
Status of this Memo
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This Internet-Draft will expire on September 26, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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described in the BSD License.
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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].
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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 move all of the DES
encryption and related checksum types to historic.
DES was withdrawn in [DES-Transition-Plan] by NIST.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 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.
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3. Recommendations
This document removes the mandatory-to-implement types from
[RFC4120]: Encryption: DES-CBC-MD5(3)
This document removes the mandatory-to-implement types from [RFC4120]
when used in conjunction with DES-CBC-MD5: Checksums: DES-MD5(7)
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).
Kerberos GSS mechanism implementation and deployments SHOULD NOT
implement the SEAL ALG: DES(0000).
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4. Acknowledgements
Jeffery Hutzelman, Simon Josefsson, Mattias Amnefelt and Leif
Johansson have read the document and provided suggestions for
improvements.
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5. Security Considerations
Removing support for single DES improves security since DES is
considered to be insecure.
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6. IANA Considerations
There are no IANA Considerations for this document
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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.
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.
[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.
[RFC4772] Kelly, S., "Security Implications of Using the Data
Encryption Standard (DES)", RFC 4772, December 2006.
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Author's Address
Love Hornquist Astrand
Apple, Inc
Cupertino
USA
Email: lha@apple.com
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