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Versions: (draft-lha-des-die-die-die) 00 01 02 03 04 RFC 6649

Network Working Group                               L. Hornquist Astrand
Internet-Draft                                                Apple, Inc
Updates: 1510, 1964, 3961, 4120, 4121                              T. Yu
(if approved)                                    MIT Kerberos Consortium
Intended status: Standards Track                        February 3, 2012
Expires: August 6, 2012


                   Deprecate DES support for Kerberos
                  draft-ietf-krb-wg-des-die-die-die-00

Abstract

   The Kerberos 5 network authentication protocol originally used the
   Data Encryption Standard (DES) for encryption.  Almost 30 years it
   introduced the first DES standard, the National Institute of
   Standards and Technology (NIST) finally withdrew the DES standard in
   2005, reflecting a long-established consensus that DES no longer
   provides adequate security.  In 2006, it cost less than EUR 10,000 to
   build a machine to brute force DES keys in an average of 8.7 days.
   By 2008, it was possible to buy commercial hardware that breaks DES
   keys in less than a day on average.  DES is long past its sell-by
   date.  Accordingly, this document updates RFC1964, RFC4120, and
   RFC4121 to deprecate the use of DES in Kerberos.  Because the
   original Kerberos 5 specification, RFC1510 (obsoleted by RFC 4120),
   supports only DES, this document also reclassifies RFC1510 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 August 6, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   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
   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.








































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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.  Introduction

   The original specification of the Kerberos 5 network authentication
   protocol [RFC1510] supports only the Data Encryption Standard (DES)
   for encryption.  For many years, cryptographic community has regarded
   DES as providing inadequate security.  This document reclassifies
   [RFC1510] as Historic, and updates current Kerberos-related
   specifications [RFC1964], [RFC4120], and [RFC4121] to deprecate the
   use of DES in Kerberos.










































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3.  Affected specifications

   The initial IETF specification of the Kerberos 5 network
   authentication protocol [RFC1510] supports only the Data Encryption
   Standard (DES) for encryption.  [RFC4120] updates the Kerberos
   specification to include additional cryptographic algorithms.
   [RFC3961] describes the Kerberos cryptographic system and includes
   support for Data Encryption Standard (DES) encryption types.

   DES no longer provides adequate cryptographic protection.  This
   document updates [RFC1964], [RFC4120], and [RFC4121] to deprecate the
   use of DES in Kerberos.  Because the version of Kerberos specified in
   [RFC1510] supports only DES, and [RFC4120] supersedes it, this
   document reclassifies [RFC1510] as Historic.

   The specification of the Kerberos Generic Security Services
   Application Programming Interface (GSS-API) mechanism [RFC1964] and
   its updated version [RFC4121] define checksum and encryption
   mechanisms based on DES.  With the existence of newer encryption
   types for Kerberos GSS-API defined in [RFC4121], Microsoft's ARCFOUR-
   HMAC based GSS-API mechanism, and MIT's DES3, there is no need to
   support the old DES based integrity (SGN) and confidentiality (SEAL)
   types.




























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4.  DES insecurity

   The insecurity of DES has been evident for many years.  The National
   Institute of Standards and Technology (NIST) officially withdrew DES
   in 2005 [DES-Withdrawal], and also announced a transition period that
   ended on May 19, 2007 [DES-Transition-Plan].  The IETF has also
   published its position in [RFC4772], in which the recommendation
   summary is very clear: "don't use DES".

   In 2006, researchers demonstrated the ability to brute force a DES
   key in an average of less than 9 days using less than EUR 10,000
   worth of hardware [Break-DES].  By 2008, a company was offering
   hardware capable of breaking a DES key in less than a day on average
   [DES-1day].  Brute force key searches of DES will only get faster and
   cheaper.  (The aforementioned company markets its device for one-
   click recovery of lost DES keys.)  It is clear that it is well past
   time to retire the use of DES in Kerberos.


































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5.  Recommendations

   This document removes the following 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 types: 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 used with non-DES encryption types, for
   example, when doing a TGS-REQ with ARCFOUR-HMAC-MD5, some clients use
   RSA-MD5 for the checksum that is stored inside the encrypted part of
   the authenticator.  This use of RSA-MD5 is to be considered safe, so
   Kerberos implementations MAY allow this usage when used with legacy
   systems 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].

   This document hereby reclassifies [RFC1510] as Historic.

















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6.  Other old enctypes

   The following older encryption types and checksum types should not be
   deployed and can be disabled by default by implementations:

   XXX add list here













































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7.  Acknowledgements

   Jeffrey Hutzelman, Simon Josefsson, Mattias Amnefelt, Leif Johansson,
   and Ran Atkinson have read the document and provided suggestions for
   improvements.  Sam Hartman proposed moving [RFC1510] to Historic.














































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8.  Security Considerations

   Removing support for single DES improves security since DES is
   considered to be insecure.

   Kerberos defines some encryption types that are either underspecified
   or that were only allocated a number in the specifications.
   Implementations should make sure that they only implement and enable
   secure encryption types.

   RC4, used in ARCFOUR-HMAC, is considered weak; however, the use in
   Kerberos is vetted and considered secure for now.  The main reason to
   not actively discourage the use of ARCFOUR-HMAC is that it is the
   only encryption type that interoperates with older versions of
   Microsoft Windows once DES is removed.




































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9.  IANA Considerations

   There are no IANA Considerations for this document
















































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10.  References

10.1.  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.

10.2.  Informative References

   [Break-DES]
              Kumar, S., Paar, C., Pelzl, J., Pfeiffer, G., Rupp, A.,
              and M. Schimmler, "How to break DES for EUR 8,980 - SHARCS
              workshop 2006", April 2006.

   [DES-1day]
              SciEngines GmbH, "Break DES in less than a single day", <h
              ttp://www.sciengines.com/company/news-a-events/
              74-des-in-1-day.html>.

   [DES-Transition-Plan]
              National Institute of Standards and Technology, "DES
              Transition Plan", May 2005, <http://csrc.nist.gov/groups/
              STM/common_documents/DESTranPlan.pdf>.

   [DES-Withdrawal]
              National Institute of Standards and Technology,
              "Announcing Approval of the Withdrawal of Federal
              Information Processing Standard (FIPS) 46-3, Data
              Encryption Standard (DES); FIPS 74, Guidelines for
              Implementing and Using the NBS Data Encryption Standard;
              and FIPS 81, DES Modes of Operation - Federal Register
              Document 05-9945, 70 FR 28907-28908", May 2005, <http://
              www.gpo.gov/fdsys/pkg/FR-2005-05-19/pdf/05-9945.pdf>.



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   [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.














































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Authors' Addresses

   Love Hornquist Astrand
   Apple, Inc
   Cupertino
   USA

   Email: lha@apple.com


   Tom Yu
   MIT Kerberos Consortium

   Email: tlyu@mit.edu





































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