Deprecate DES, RC4-HMAC-EXP, and Other Weak Cryptographic Algorithms in Kerberos
RFC 6649

[Ballot comment]
I cleared my Discuss after a conversation with the AD and WG chair on the understanding that they will close the loop with the WG on whether the code points in any IANA registries should be deprecated.

[Ballot discuss]
I'm wondering about code points that identify the use of "DES, RC4-HMAC-EXP, and other weak cryptographic algorithms" in various protocols.

Are there any? Should they be deprecated? Has someone already worried about this so I don't need to?

[Ballot discuss]
[Thanks for addressing my other DISCUSS comments]

I do want to make sure that we send the right announcement for both this document *and* the moving of 1510 to Historic. I'm just leaving this DISCUSS point as a placeholder until we figure out how to do that.

[Ballot comment]
I am not entirely clear why this is a BCP and not part of the standards track specification of Kerberos. This is a change to a protocol and therefore part of a technical specification, not a policy or operational guideline.

[Ballot discuss]
[Thanks for addressing my other DISCUSS comments]

- I do want to make sure that we send the right announcement for both this document *and* the moving of 1510 to Historic. I'm just leaving this DISCUSS point as a placeholder until we figure out how to do that.

- I am not entirely clear why this is a BCP and not part of the standards track specification of Kerberos. This is a change to a protocol and therefore part of a technical specification, not a policy or operational guideline.

[Ballot comment]
This draft does not update RFC 1510 but aims to obsolete it , i.e. the header of the draft is not correct:
"Updates: 1510, 1964, 4120, 4121, 4757"

However, Pete's discuss covers this already.

[Ballot comment]
This draft does not update RFC 1510 but aims to obsolete it it, i.e. the header of the draft is not correct:
"Updates: 1510, 1964, 4120, 4121, 4757"

However, Pete's discuss covers this already.

[Ballot discuss]
This is all procedural cruft that the authors can ignore.

- We never seem to follow the procedure set out in our IESG Statement :

  If a document (whatever its intended status) moves another document
  to "Historic" status, the Last Call should go out saying, "Last Call:
  to Informational and RFC XXXX to Historic", the document should be
  handled as a Protocol Action on the IESG agenda using IESG Protocol
  Action procedures, and a "Protocol Action" announcement should be
  sent out when the document is approved.

The proper Last Call didn't happen. A suggestion: Instead of re-Last Calling this document and delaying it, if we make the following changes (which would make me happier anyway) we can simply approve this document and then separately Last Call the move of 1510 to Historic:

Abstract
OLD
  this document reclassifies RFC1510 as Historic.
NEW
  this document recommends the reclassification of RFC1510 as Historic.

Section 2
OLD
  Accordingly, this document reclassifies [RFC1510]
  (obsoleted by [RFC4120]) as Historic
NEW
  Accordingly, this document recommends the reclassification of
  [RFC1510] (obsoleted by [RFC4120]) as Historic


Section 5
OLD
  This document hereby reclassifies [RFC1510] as Historic.
NEW
  This document recommends the reclassification of [RFC1510] as
  Historic.

- The header of this document says that it "Updates: 1510", not "Obsoletes: 1510". Making 1510 Historic and Updating it seem to be incompatible operations. Even obsoleting it seems weird, since it's already absolete, but I could live with that.

- I am not entirely clear why this is a BCP and not part of the standards track specification of Kerberos. This is a change to a protocol and therefore part of a technical specification, not a policy or operational guideline.

[Ballot comment]
I am glad to see this draft and it is well-written.

I am curious as to why the recommendation is limited to SHOULD NOTs and not MUSTs.  Are there reasons to allow this wiggle room?  If so, it would be good to give an example in the draft.

State changed to In Last Call from Last Call Requested

The following Last Call Announcement was sent out:

From: The IESG

To: IETF-Announce

CC:

Reply-To: ietf@ietf.org

Subject: Last Call:  (Deprecate DES, RC4-HMAC-EXP, and other weak cryptographic algorithms in Kerberos) to Best Current Practice



This is a repeat last call, just to include the downref (omitted by a careless AD:-)



The IESG has received a request from the Kerberos WG (krb-wg) to consider

the following document:

- 'Deprecate DES, RC4-HMAC-EXP, and other weak cryptographic algorithms

  in Kerberos'

  as a Best Current Practice



The IESG plans to make a decision in the next few weeks, and solicits

final comments on this action. Please send substantive comments to the

ietf@ietf.org mailing lists by 2012-04-08. Exceptionally, comments may be

sent to iesg@ietf.org instead. In either case, please retain the

beginning of the Subject line to allow automated sorting.



Abstract





  The Kerberos 5 network authentication protocol, originally specified

  in RFC1510, can use the Data Encryption Standard (DES) for

  encryption.  Almost 30 years after first publishing DES, the National

  Institute of Standards and Technology (NIST) finally withdrew the

  standard in 2005, reflecting a long-established consensus that DES is

  insufficiently secure.  By 2008, commercial hardware costing less

  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

  updates RFC1964, RFC4120, RFC4121, and RFC4757 to deprecate the use

  of DES, RC4-HMAC-EXP, and other weak cryptographic algorithms in

  Kerberos.  Because RFC1510 (obsoleted by RFC4120) supports only DES,

  this document reclassifies RFC1510 as Historic.



The file can be obtained via

http://datatracker.ietf.org/doc/draft-ietf-krb-wg-des-die-die-die/



IESG discussion can be tracked via

http://datatracker.ietf.org/doc/draft-ietf-krb-wg-des-die-die-die/ballot/





No IPR declarations have been submitted directly on this I-D.



  There is

  a downward reference to RFC 4757 in order to deprecate an algorithm

  specified in that RFC; this downward reference is appropriate

  because reclassifying RFC 4757 as standards track is not desired.

The IANA Considerations section states that this document doesn't have
any actions, but it also appears to deprecate several registrations in
http://www.iana.org/assignments/kerberos-parameters. Should this be
reflected in the registry? If so, the IANA Considerations section needs
to list each registration we need to mark "(DEPRECATED)" or "(OBSOLETED)."

State changed to In Last Call from Last Call Requested

The following Last Call Announcement was sent out:

From: The IESG

To: IETF-Announce

CC:

Reply-To: ietf@ietf.org

Subject: Last Call:  (Deprecate DES, RC4-HMAC-EXP, and other weak cryptographic algorithms in Kerberos) to Best Current Practice





The IESG has received a request from the Kerberos WG (krb-wg) to consider

the following document:

- 'Deprecate DES, RC4-HMAC-EXP, and other weak cryptographic algorithms

  in Kerberos'

  as a Best Current Practice



The IESG plans to make a decision in the next few weeks, and solicits

final comments on this action. Please send substantive comments to the

ietf@ietf.org mailing lists by 2012-04-05. Exceptionally, comments may be

sent to iesg@ietf.org instead. In either case, please retain the

beginning of the Subject line to allow automated sorting.



Abstract





  The Kerberos 5 network authentication protocol, originally specified

  in RFC1510, can use the Data Encryption Standard (DES) for

  encryption.  Almost 30 years after first publishing DES, the National

  Institute of Standards and Technology (NIST) finally withdrew the

  standard in 2005, reflecting a long-established consensus that DES is

  insufficiently secure.  By 2008, commercial hardware costing less

  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

  updates RFC1964, RFC4120, RFC4121, and RFC4757 to deprecate the use

  of DES, RC4-HMAC-EXP, and other weak cryptographic algorithms in

  Kerberos.  Because RFC1510 (obsoleted by RFC4120) supports only DES,

  this document reclassifies RFC1510 as Historic.









The file can be obtained via

http://datatracker.ietf.org/doc/draft-ietf-krb-wg-des-die-die-die/



IESG discussion can be tracked via

http://datatracker.ietf.org/doc/draft-ietf-krb-wg-des-die-die-die/ballot/





No IPR declarations have been submitted directly on this I-D.

(1.a) Who is the Document Shepherd for this document? Has the
Document Shepherd personally reviewed this version of the
document and, in particular, does he or she believe this
version is ready for forwarding to the IESG for publication?

>> The Document Shepherd for this document is Sam Hartman,
>> . I have reviewed this document, and I believe
>> it is ready for IETF-wide review and publication as a
>> BCP.

(1.b) Has the document had adequate review both from key WG members
and from key non-WG members? Does the Document Shepherd have
any concerns about the depth or breadth of the reviews that
have been performed?

>> This document has received substantial review within the
>> working group. As its purpose is to deprecate support for
>> specific cryptographic algorithms in the Kerberos protocol,
>> no particular review from non-WG members was needed.

(1.c) Does the Document Shepherd have concerns that the document
needs more review from a particular or broader perspective,
e.g., security, operational complexity, someone familiar with
AAA, internationalization or XML?

>> I don't believe any particular outside review is required.
>> Of course, more review is always welcome.

(1.d) Does the Document Shepherd have any specific concerns or
issues with this document that the Responsible Area Director
and/or the IESG should be aware of? For example, perhaps he
or she is uncomfortable with certain parts of the document, or
has concerns whether there really is a need for it. In any
event, if the WG has discussed those issues and has indicated
that it still wishes to advance the document, detail those
concerns here. Has an IPR disclosure related to this document
been filed? If so, please include a reference to the
disclosure and summarize the WG discussion and conclusion on
this issue.

>> I have no concerns.
>> No IPR disclosures related to this document have been filed; the key editors indicate any required disclosures have been filed; we do not anticipate IPR related to how not to use DES.

(1.e) How solid is the WG consensus behind this document? Does it
represent the strong concurrence of a few individuals, with
others being silent, or does the WG as a whole understand and
agree with it?

>> There is solid concensus within the working group to
>> publish this document.

(1.f) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise the areas of conflict in
separate email messages to the Responsible Area Director. (It
should be in a separate email because this questionnaire is
entered into the ID Tracker.)

>> There have been no expressions of discontent.

(1.g) Has the Document Shepherd personally verified that the
document satisfies all ID nits? (See
http://www.ietf.org/ID-Checklist.html and
http://tools.ietf.org/tools/idnits/). Boilerplate checks are
not enough; this check needs to be thorough. Has the document
met all formal review criteria it needs to, such as the MIB
Doctor, media type and URI type reviews?

>> This document has been run through the idnits tool. No additional formal review criteria
>> apply to this document.

(1.h) Has the document split its references into normative and
informative? Are there normative references to documents that
are not ready for advancement or are otherwise in an unclear
state? If such normative references exist, what is the
strategy for their completion? Are there normative references
that are downward references, as described in [RFC3967]? If
so, list these downward references to support the Area
Director in the Last Call procedure for them [RFC3967].

>> References have been split appropriately. There is a normative downward reference to RFC 4757 which is informational in order to deprecate an algorithm specified by that document. This down-ref needs to be called out in the last call. There is,
>> deliberately, an informative reference to RFC1510, which
>> defined the original Kerberos V specification and has been
>> replaced by RFC3961 and RFC4120.

(1.i) Has the Document Shepherd verified that the document IANA
consideration section exists and is consistent with the body
of the document? If the document specifies protocol
extensions, are reservations requested in appropriate IANA
registries? Are the IANA registries clearly identified? If
the document creates a new registry, does it define the
proposed initial contents of the registry and an allocation
procedure for future registrations? Does it suggest a
reasonable name for the new registry? See [RFC2434]. If the
document describes an Expert Review process has Shepherd
conferred with the Responsible Area Director so that the IESG
can appoint the needed Expert during the IESG Evaluation?

>> This document requires no IANA actions.

(1.j) Has the Document Shepherd verified that sections of the
document that are written in a formal language, such as XML
code, BNF rules, MIB definitions, etc., validate correctly in
an automated checker?

>> No part of this document is written in a formal language
>> requiring such verification.

(1.k) The IESG approval announcement includes a Document
Announcement Write-Up. Please provide such a Document
Announcement Write-Up? Recent examples can be found in the
"Action" announcements for approved documents. The approval
announcement contains the following sections:


Technical Summary

A long long time ago Data Encryption Standard (DES) was
standardized. Some 30 years later (2005) IT was withdrawn as a
standard by National Institute of Standards and Technology (NIST),
today 7 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. This document updates RFC1964, RFC4120, RFC4121 and RFC 4757
to deprecate the use of DES in Kerberos. Because the version of
Kerberos specified in RFC1510 only supports DES and has been
replaced by RFC4120, RFC1510 is reclassified as historic. There is
a downward reference to RFC 4757 in order to deprecate an algorithm
specified in that RFC; this downward reference is appropriate
because reclassifying RFC 4757 as standards track is not desired.


Working Group Summary

This document represents the consensus of the Kerberos Working Group.


Document Quality

At least three major Kerberos implementations have already either
implemented the recommendations of this document by removing DES
support entirely, or changed their default configuration such that
DES and related algorithms deprecated by this document must be
explicitly enabled by an administrator before they can be used.


Personnel

The Document Shepherd for this document is Sam Hartman; Jeffrey Hutzelman acted as shepherd for much of the life of this document.
The responsible Area Director is Stephen Farrell.