draft-ietf-krb-wg-des-die-die-die-03.txt   draft-ietf-krb-wg-des-die-die-die-04.txt 
Network Working Group L. Hornquist Astrand Network Working Group L. Hornquist Astrand
Internet-Draft Apple, Inc Internet-Draft Apple, Inc
Updates: 1510, 1964, 4120, 4121, 4757 T. Yu Updates: 1510, 1964, 4120, 4121, 4757 T. Yu
(if approved) MIT Kerberos Consortium (if approved) MIT Kerberos Consortium
Intended status: BCP February 16, 2012 Intended status: BCP February 27, 2012
Expires: August 19, 2012 Expires: August 30, 2012
Deprecate DES, "export strength" RC4, and other weak cryptographic Deprecate DES, RC4-HMAC-EXP, and other weak cryptographic algorithms in
algorithms in Kerberos Kerberos
draft-ietf-krb-wg-des-die-die-die-03 draft-ietf-krb-wg-des-die-die-die-04
Abstract Abstract
The Kerberos 5 network authentication protocol, originally specified The Kerberos 5 network authentication protocol, originally specified
in RFC1510, can use the Data Encryption Standard (DES) for in RFC1510, can use the Data Encryption Standard (DES) for
encryption. Almost 30 years after first publishing DES, the National encryption. Almost 30 years after first publishing DES, the National
Institute of Standards and Technology (NIST) finally withdrew the Institute of Standards and Technology (NIST) finally withdrew the
standard in 2005, reflecting a long-established consensus that DES is standard in 2005, reflecting a long-established consensus that DES is
insufficiently secure. By 2008, commercial hardware costing less insufficiently secure. By 2008, commercial hardware costing less
than USD 15,000 could break DES keys in less than a day on average. than USD 15,000 could break DES keys in less than a day on average.
DES is long past its sell-by date. Accordingly, this document DES is long past its sell-by date. Accordingly, this document
updates RFC1964, RFC4120, RFC4121, and RFC4757 to deprecate the use updates RFC1964, RFC4120, RFC4121, and RFC4757 to deprecate the use
of DES, "export strength" RC4, and other weak cryptographic of DES, RC4-HMAC-EXP, and other weak cryptographic algorithms in
algorithms in Kerberos. Because RFC1510 (obsoleted by RFC4120) Kerberos. Because RFC1510 (obsoleted by RFC4120) supports only DES,
supports only DES, this document reclassifies RFC1510 as Historic. this document 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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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 19, 2012. This Internet-Draft will expire on August 30, 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
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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, the cryptographic community has for encryption. For many years, the cryptographic community has
regarded DES as providing inadequate security, mostly because of its regarded DES as providing inadequate security, mostly because of its
small key size. Accordingly, this document reclassifies [RFC1510] small key size. Accordingly, this document reclassifies [RFC1510]
(obsoleted by [RFC4120]) as Historic, and updates current Kerberos- (obsoleted by [RFC4120]) as Historic, and updates current Kerberos-
related specifications [RFC1964], [RFC4120], and [RFC4121] to related specifications [RFC1964], [RFC4120], and [RFC4121] to
deprecate the use of DES and other weak cryptographic algorithms in deprecate the use of DES and other weak cryptographic algorithms in
Kerberos, including some unkeyed checksums and hashes, along with the Kerberos, including some unkeyed checksums and hashes, along with the
weak "export strength" RC4 enctype of [RFC4757]. weak 56-bit "export strength" RC4 variant enctype of [RFC4757].
3. Affected specifications 3. Affected specifications
The original IETF specification of Kerberos 5 [RFC1510] only supports The original IETF specification of Kerberos 5 [RFC1510] only supports
DES for encryption. [RFC4120] obsoletes [RFC1510] and updates the DES for encryption. [RFC4120] obsoletes [RFC1510] and updates the
Kerberos specification to include additional cryptographic Kerberos specification to include additional cryptographic
algorithms, but still permits the use of DES. [RFC3961] describes algorithms, but still permits the use of DES. [RFC3961] describes
the Kerberos cryptographic system and includes support for DES the Kerberos cryptographic system and includes support for DES
encryption types, but it does not specify requirement levels for encryption types, but it does not specify requirement levels for
them. them.
skipping to change at page 3, line 40 skipping to change at page 3, line 40
lost DES keys.) It is clear that it is well past time to retire the lost DES keys.) It is clear that it is well past time to retire the
use of DES in Kerberos. use of DES in Kerberos.
5. Recommendations 5. Recommendations
This document hereby removes the following RECOMMENDED types from This document hereby removes the following RECOMMENDED types from
[RFC4120]: [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, named RSA-MD5-DES in [RFC3961]).
Kerberos implementations and deployments SHOULD NOT provide the Kerberos implementations and deployments SHOULD NOT implement or
following single DES encryption types: DES-CBC-CRC(1), DES-CBC- deploy the following single DES encryption types: DES-CBC-CRC(1),
MD4(2), DES-CBC-MD5(3) (updates [RFC4120]). DES-CBC-MD4(2), DES-CBC-MD5(3) (updates [RFC4120]).
Kerberos implementations and deployments SHOULD NOT provide the Kerberos implementations and deployments SHOULD NOT implement or
following "export strength" RC4 encryption type: RC4-HMAC-EXP(24) deploy the following "export strength" RC4 variant encryption type:
(updates [RFC4757]). This document does not add any sort of RC4-HMAC-EXP(24) (updates [RFC4757]). This document does not add any
requirement for conforming implementations to provide RC4-HMAC(23). sort of requirement for conforming implementations to implement RC4-
HMAC(23).
Kerberos implementations and deployments SHOULD NOT provide the Kerberos implementations and deployments SHOULD NOT implement or
following checksum types: CRC32(1), RSA-MD4(2), RSA-MD4-DES(3), DES- deploy the following checksum types: CRC32(1), RSA-MD4(2), RSA-MD4-
MAC(4), DES-MAC-K(5), RSA-MD4-DES-K(6), RSA-MD5-DES(8) (updates DES(3), DES-MAC(4), DES-MAC-K(5), RSA-MD4-DES-K(6), RSA-MD5-DES(8)
[RFC4120]). (updates [RFC4120]).
It is possible to safely use the RSA-MD5(7) checksum type, but only It is possible to safely use the RSA-MD5(7) checksum type, but only
with additional protection, such as the protection that an encrypted with additional protection, such as the protection that an encrypted
Authenticator provides. Implementations MAY use RSA-MD5 inside an Authenticator provides. Implementations MAY use RSA-MD5 inside an
encrypted Authenticator for backward compatibility with systems that encrypted Authenticator for backward compatibility with systems that
do not support newer checksum types (updates [RFC4120]). One example do not support newer checksum types (updates [RFC4120]). One example
is that some legacy systems only support RC4-HMAC(23) [RFC4757] for is that some legacy systems only support RC4-HMAC(23) [RFC4757] for
encryption when DES is not available; these systems use RSA-MD5 encryption when DES is not available; these systems use RSA-MD5
checksums inside Authenticators encrypted with RC4-HMAC. checksums inside Authenticators encrypted with RC4-HMAC.
Kerberos GSS mechanism implementations and deployments SHOULD NOT Kerberos GSS mechanism implementations and deployments SHOULD NOT
provide the following SGN ALG: DES MAC MD5(0000), MD2.5(0100), DES implement or deploy the following SGN ALG: DES MAC MD5(0000),
MAC(0200) (updates [RFC1964]). MD2.5(0100), DES MAC(0200) (updates [RFC1964]).
Kerberos GSS mechanism implementations and deployments SHOULD NOT Kerberos GSS mechanism implementations and deployments SHOULD NOT
provide the following SEAL ALG: DES(0000) (updates [RFC1964]). implement or deploy the following 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. Acknowledgements 6. Acknowledgements
Mattias Amnefelt, Ran Atkinson, Henry Hotz, Jeffrey Hutzelman, Leif Mattias Amnefelt, Ran Atkinson, Henry Hotz, Jeffrey Hutzelman, Leif
Johansson, and Simon Josefsson have read the document and provided Johansson, Simon Josefsson, and Martin Rex have read the document and
suggestions for improvements. Sam Hartman proposed moving [RFC1510] provided suggestions for improvements. Sam Hartman proposed moving
to Historic. Michiko Short provided information about the dates of [RFC1510] to Historic. Michiko Short provided information about the
end of support for Windows releases. dates of end of support for Windows releases.
7. Security Considerations 7. Security Considerations
Removing support for single DES improves security, because DES is Removing support for single DES improves security, because DES is
considered to be insecure. RC4-HMAC-EXP has a similarly inadequate considered to be insecure. RC4-HMAC-EXP has a similarly inadequate
key size, so removing support for it also improves security. key size, so removing support for it also improves security.
Kerberos defines some encryption types that are either underspecified Kerberos defines some encryption types that are either underspecified
or that only have number assignments but no 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
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