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Re: Security



On 12 Aug 2008, at 10:31 AM, Simon Josefsson wrote:

I have no seen adequate support for MUSTs here.


Nor have I, but I don't believe MUST is required.  PLAIN contains:

  By default, implementations SHOULD advertise and make use of the
  PLAIN mechanism only when adequate data security services are in
  place.

It continues with:

  Specifications for IETF protocols that indicate that this
mechanism is an applicable authentication mechanism MUST mandate that implementations support an strong data security service, such as TLS. 

That places restrictions on specifications, not implementations, which
is somewhat weird, but CRAM-MD5 could do the same.  That is what I
propose to do.
I personally think such a change would be good. I feel that TLS recommendations to protect CRAM-MD5 ought to be the same as those we made for the TLS protection of PLAIN. 





None of the arguments made in the
document would still stand against that construct (I think). What is 
puzzling is that the document already appear to strongly suggest use
of
TLS and UTF-8 and SASLprep, so I think we have already solved the
security and interoperability problem inherent in the old CRAM-MD5
specification.


I don't believe the SHOULDs are adequate to ensure independently
developed interoperability.


SHOULD has worked fine for PLAIN, so I disagree.
It works fine because of PLAIN's design. The party, the server, is preparing both the presented and stored strings. In CRAM-MD5, two parties need to agree on the preparation on what preparation to use for things to work properly. 




/Simon