Network Working Group L. Hornquist Astrand
Internet-Draft Apple, Inc
Updates: 3961, 4120 August 2, 2009
(if approved)
Intended status: Standards Track
Expires: February 3, 2010
Deprecate DES support for Kerberos
draft-lha-des-die-die-die-01
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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(2003) is was withdrawn as a standard by NIST, today 6 years later,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.
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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DES was withdrawn in [DES-Transition-Plan] by NIST.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".
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3. Recommendations
This document removes the mandatory-to-implement types from
[RFC4120]: Encryption: DES-CBC-MD5
This document removes the mandatory-to-implement types from [RFC4120]
when used in conjunction with DES-CBC-MD5: Checksums: DES-MD5
Kerberos implementation and deployments SHOULD NOT implement the
single DES encryption types: DES-CBC-MD5, DES-CBC-MD4, DES-CBC-CRC.
Kerberos implementation and deployments SHOULD NOT implement the
checksum type: CRC, RSA-MD4, RSA-MD4-DES, RSA-MAC, RSA-MAC-K, RSA-
MD5, RSA-MD5-DES.
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.
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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 by most parties.
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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
[RFC1510] Kohl, J. and B. Neuman, "The Kerberos Network
Authentication Service (V5)", RFC 1510, September 1993.
[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.
[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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