draft-ietf-krb-wg-des-die-die-die-00.txt   draft-ietf-krb-wg-des-die-die-die-01.txt 
Network Working Group L. Hornquist Astrand Network Working Group L. Hornquist Astrand
Internet-Draft Apple, Inc Internet-Draft Apple, Inc
Updates: 1510, 1964, 3961, 4120, 4121 T. Yu Updates: 1510, 1964, 4120, 4121 T. Yu
(if approved) MIT Kerberos Consortium (if approved) MIT Kerberos Consortium
Intended status: Standards Track February 3, 2012 Intended status: Standards Track February 8, 2012
Expires: August 6, 2012 Expires: August 11, 2012
Deprecate DES support for Kerberos Deprecate DES support for Kerberos
draft-ietf-krb-wg-des-die-die-die-00 draft-ietf-krb-wg-des-die-die-die-01
Abstract Abstract
The Kerberos 5 network authentication protocol originally used the The Kerberos 5 network authentication protocol, originally specified
Data Encryption Standard (DES) for encryption. Almost 30 years it in RFC1510, can use the Data Encryption Standard (DES) for
introduced the first DES standard, the National Institute of encryption. Almost 30 years after first publishing DES, the National
Standards and Technology (NIST) finally withdrew the DES standard in Institute of Standards and Technology (NIST) finally withdrew the
2005, reflecting a long-established consensus that DES no longer standard in 2005, reflecting a long-established consensus that DES is
provides adequate security. In 2006, it cost less than EUR 10,000 to insufficiently secure. By 2008, commercial hardware costing less
build a machine to brute force DES keys in an average of 8.7 days. than USD 15,000 could break DES keys in less than a day on average.
By 2008, it was possible to buy commercial hardware that breaks DES DES is long past its sell-by date. Accordingly, this document
keys in less than a day on average. DES is long past its sell-by updates RFC1964, RFC4120, and RFC4121 to deprecate the use of DES in
date. Accordingly, this document updates RFC1964, RFC4120, and Kerberos. Because RFC1510 (obsoleted by RFC4120) supports only DES,
RFC4121 to deprecate the use of DES in Kerberos. Because the this document also reclassifies RFC1510 as Historic.
original Kerberos 5 specification, RFC1510 (obsoleted by RFC 4120),
supports only DES, this document also reclassifies RFC1510 as
Historic.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 6, 2012. This Internet-Draft will expire on August 11, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 4, line 9 skipping to change at page 2, line 23
1. Requirements Notation 1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Introduction 2. Introduction
The original specification of the Kerberos 5 network authentication The original specification of the Kerberos 5 network authentication
protocol [RFC1510] supports only the Data Encryption Standard (DES) protocol [RFC1510] supports only the Data Encryption Standard (DES)
for encryption. For many years, cryptographic community has regarded for encryption. For many years, the cryptographic community has
DES as providing inadequate security. This document reclassifies regarded DES as providing inadequate security. Accordingly, this
[RFC1510] as Historic, and updates current Kerberos-related document reclassifies [RFC1510] (obsoleted by [RFC4120]) as Historic,
specifications [RFC1964], [RFC4120], and [RFC4121] to deprecate the and updates current Kerberos-related specifications [RFC1964],
use of DES in Kerberos. [RFC4120], and [RFC4121] to deprecate the use of DES in Kerberos.
3. Affected specifications 3. Affected specifications
The initial IETF specification of the Kerberos 5 network The original IETF specification of Kerberos 5 [RFC1510] only supports
authentication protocol [RFC1510] supports only the Data Encryption DES for encryption. [RFC4120] obsoletes [RFC1510] and updates the
Standard (DES) for encryption. [RFC4120] updates the Kerberos Kerberos specification to include additional cryptographic
specification to include additional cryptographic algorithms. algorithms, but still permits the use of DES.
[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 The specification of the Kerberos Generic Security Services
Application Programming Interface (GSS-API) mechanism [RFC1964] and Application Programming Interface (GSS-API) mechanism [RFC1964] and
its updated version [RFC4121] define checksum and encryption its updated version [RFC4121] define checksum and encryption
mechanisms based on DES. With the existence of newer encryption mechanisms based on DES. With the existence of newer encryption
types for Kerberos GSS-API defined in [RFC4121], Microsoft's ARCFOUR- 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 HMAC based GSS-API mechanism, and MIT's DES3, there is no need to
support the old DES based integrity (SGN) and confidentiality (SEAL) support the old DES based integrity (SGN) and confidentiality (SEAL)
types. types.
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Institute of Standards and Technology (NIST) officially withdrew DES Institute of Standards and Technology (NIST) officially withdrew DES
in 2005 [DES-Withdrawal], and also announced a transition period that in 2005 [DES-Withdrawal], and also announced a transition period that
ended on May 19, 2007 [DES-Transition-Plan]. The IETF has also ended on May 19, 2007 [DES-Transition-Plan]. The IETF has also
published its position in [RFC4772], in which the recommendation published its position in [RFC4772], in which the recommendation
summary is very clear: "don't use DES". summary is very clear: "don't use DES".
In 2006, researchers demonstrated the ability to brute force a 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 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 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 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 [DES-1day] that cost less than USD 15,000 [DES-crack]. Brute force
cheaper. (The aforementioned company markets its device for one- key searches of DES will only get faster and cheaper. (The
click recovery of lost DES keys.) It is clear that it is well past aforementioned company markets its device for one-click recovery of
time to retire the use of DES in Kerberos. lost DES keys.) It is clear that it is well past time to retire the
use of DES in Kerberos.
5. Recommendations 5. Recommendations
This document removes the following RECOMMENDED types from [RFC4120]: This document hereby removes the following RECOMMENDED types from
[RFC4120]:
Encryption: DES-CBC-MD5(3) Encryption: DES-CBC-MD5(3)
Checksums: DES-MD5 (8, named RSA-MD5-DES in [RFC3961]).
Checksums: DES-MD5 (8, RSA-MD5-DES from [RFC3961]). Kerberos implementations and deployments SHOULD NOT implement the
Kerberos implementation and deployments SHOULD NOT implement the
single DES encryption types: DES-CBC-CRC(1), DES-CBC-MD4(2), DES-CBC- single DES encryption types: DES-CBC-CRC(1), DES-CBC-MD4(2), DES-CBC-
MD5(3). MD5(3).
Kerberos implementation and deployments SHOULD NOT implement the Kerberos implementations and deployments SHOULD NOT implement the
checksum types: CRC32(1), RSA-MD4(2), RSA-MD4-DES(3), DES-MAC(4), 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). DES-MAC-K(5), RSA-MD4-MAC-K(6), RSA-MD5-DES(8).
Note that RSA-MD5 might be used with non-DES encryption types, for It is possible to safely use the RSA-MD5(7) checksum type, but only
example, when doing a TGS-REQ with ARCFOUR-HMAC-MD5, some clients use with additional protection, such as the protection that an encrypted
RSA-MD5 for the checksum that is stored inside the encrypted part of Authenticator provides. Implementations MAY use RSA-MD5 inside an
the authenticator. This use of RSA-MD5 is to be considered safe, so encrypted Authenticator for backward compatibility with systems that
Kerberos implementations MAY allow this usage when used with legacy do not support newer checksum types. One example is that some legacy
systems that can't handle newer checksum types. systems only support ARCFOUR-HMAC-MD5 for encryption when DES is not
available; these systems use RSA-MD5 checksums inside Authenticators
encrypted with ARCFOUR-HMAC-MD5.
Kerberos GSS mechanism implementation and deployments SHOULD NOT Kerberos GSS mechanism implementations and deployments SHOULD NOT
implement the SGN ALG: DES MAC MD5(0000), MD2.5(0100), DES MAC(0200) implement the SGN ALG: DES MAC MD5(0000), MD2.5(0100), DES MAC(0200)
(updates [RFC1964]). (updates [RFC1964]).
Kerberos GSS mechanism implementation and deployments SHOULD NOT Kerberos GSS mechanism implementations and deployments SHOULD NOT
implement the SEAL ALG: DES(0000) (updates [RFC1964]). implement the SEAL ALG: DES(0000) (updates [RFC1964]).
The effect of the two last sentences is that this document deprecates The effect of the two last sentences is that this document deprecates
section 1.2 in [RFC1964]. section 1.2 in [RFC1964].
This document hereby reclassifies [RFC1510] as Historic. This document hereby reclassifies [RFC1510] as Historic.
6. Other old enctypes 6. Acknowledgements
The following older encryption types and checksum types should not be
deployed and can be disabled by default by implementations:
XXX add list here
7. Acknowledgements
Jeffrey Hutzelman, Simon Josefsson, Mattias Amnefelt, Leif Johansson, Jeffrey Hutzelman, Simon Josefsson, Mattias Amnefelt, Leif Johansson,
and Ran Atkinson have read the document and provided suggestions for and Ran Atkinson have read the document and provided suggestions for
improvements. Sam Hartman proposed moving [RFC1510] to Historic. improvements. Sam Hartman proposed moving [RFC1510] to Historic.
8. Security Considerations 7. Security Considerations
Removing support for single DES improves security since DES is Removing support for single DES improves security, because DES is
considered to be insecure. considered to be insecure.
Kerberos defines some encryption types that are either underspecified Kerberos defines some encryption types that are either underspecified
or that were only allocated a number in the specifications. or that only have number assignments but no specifications.
Implementations should make sure that they only implement and enable Implementations should make sure that they only implement and enable
secure encryption types. secure encryption types.
RC4, used in ARCFOUR-HMAC, is considered weak; however, the use in RC4, used in ARCFOUR-HMAC, is considered weak; however, the use in
Kerberos is vetted and considered secure for now. The main reason to 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 not actively discourage the use of ARCFOUR-HMAC is that it is the
only encryption type that interoperates with older versions of only encryption type that interoperates with older versions of
Microsoft Windows once DES is removed. Microsoft Windows once DES is removed.
9. IANA Considerations 8. IANA Considerations
There are no IANA Considerations for this document There are no IANA Considerations for this document.
10. References 9. References
10.1. Normative References 9.1. Normative References
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996. RFC 1964, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. 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 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120, Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005. July 2005.
[RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", RFC 4121, Interface (GSS-API) Mechanism: Version 2", RFC 4121,
July 2005. July 2005.
10.2. Informative References 9.2. Informative References
[Break-DES] [Break-DES]
Kumar, S., Paar, C., Pelzl, J., Pfeiffer, G., Rupp, A., Kumar, S., Paar, C., Pelzl, J., Pfeiffer, G., Rupp, A.,
and M. Schimmler, "How to break DES for EUR 8,980 - SHARCS and M. Schimmler, "How to break DES for EUR 8,980 -
workshop 2006", April 2006. SHARCS'06 - Special-purpose Hardware for Attacking
Cryptographic Systems", April 2006, <http://
www.copacobana.org/paper/copacobana_SHARCS2006.pdf>.
[DES-1day] [DES-1day]
SciEngines GmbH, "Break DES in less than a single day", <h SciEngines GmbH, "Break DES in less than a single day", <h
ttp://www.sciengines.com/company/news-a-events/ ttp://www.sciengines.com/company/news-a-events/
74-des-in-1-day.html>. 74-des-in-1-day.html>.
[DES-Transition-Plan] [DES-Transition-Plan]
National Institute of Standards and Technology, "DES National Institute of Standards and Technology, "DES
Transition Plan", May 2005, <http://csrc.nist.gov/groups/ Transition Plan", May 2005, <http://csrc.nist.gov/groups/
STM/common_documents/DESTranPlan.pdf>. STM/common_documents/DESTranPlan.pdf>.
[DES-Withdrawal] [DES-Withdrawal]
National Institute of Standards and Technology, National Institute of Standards and Technology,
"Announcing Approval of the Withdrawal of Federal "Announcing Approval of the Withdrawal of Federal
Information Processing Standard (FIPS) 46-3, Data Information Processing Standard (FIPS) 46-3, Data
Encryption Standard (DES); FIPS 74, Guidelines for Encryption Standard (DES); FIPS 74, Guidelines for
Implementing and Using the NBS Data Encryption Standard; Implementing and Using the NBS Data Encryption Standard;
and FIPS 81, DES Modes of Operation - Federal Register and FIPS 81, DES Modes of Operation - Federal Register
Document 05-9945, 70 FR 28907-28908", May 2005, <http:// Document 05-9945", 70 FR 28907-28908, May 2005, <http://
www.gpo.gov/fdsys/pkg/FR-2005-05-19/pdf/05-9945.pdf>. www.gpo.gov/fdsys/pkg/FR-2005-05-19/pdf/05-9945.pdf>.
[DES-crack]
Scott, T., "DES Brute Force Cracking Efforts 1977 to
2010", 2010, <http://www.tjscott.net/security.extras/
des.crack.efforts.pdf>.
[RFC1510] Kohl, J. and B. Neuman, "The Kerberos Network [RFC1510] Kohl, J. and B. Neuman, "The Kerberos Network
Authentication Service (V5)", RFC 1510, September 1993. Authentication Service (V5)", RFC 1510, September 1993.
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5", RFC 3961, February 2005.
[RFC4772] Kelly, S., "Security Implications of Using the Data [RFC4772] Kelly, S., "Security Implications of Using the Data
Encryption Standard (DES)", RFC 4772, December 2006. Encryption Standard (DES)", RFC 4772, December 2006.
Authors' Addresses Authors' Addresses
Love Hornquist Astrand Love Hornquist Astrand
Apple, Inc Apple, Inc
Cupertino Cupertino
USA USA
Email: lha@apple.com Email: lha@apple.com
Tom Yu Tom Yu
MIT Kerberos Consortium MIT Kerberos Consortium
77 Massachusetts Ave
Cambridge, Massachusetts
USA
Email: tlyu@mit.edu Email: tlyu@mit.edu
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