Re: [secdir] Secdir review of draft-murchison-nntp-compress-05

Ken Murchison <murch@andrew.cmu.edu> Tue, 25 October 2016 12:04 UTC

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From: Ken Murchison <murch@andrew.cmu.edu>
Organization: Carnegie Mellon University
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Date: Tue, 25 Oct 2016 07:55:15 -0400
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Subject: Re: [secdir] Secdir review of draft-murchison-nntp-compress-05
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I'm fine with the changes.


On 10/24/2016 04:20 PM, Julien ÉLIE wrote:
> Hi Barry,
>
> Thanks again for your valuable comments on the document.  They were very
> much appreciated, and permitted to fix a few issues.
>
> I've just finalized a revised draft, taking into account all the comments
> received during Last Call.
> I just want to highlight the following change in wording.
> Ken and Michael, as respectively co-author and document shepherd, please
> tell if you think the new wording is not the right thing to do.
>
> Personally, I think this document (draft-murchison-nntp-compress) should
> only focus on standardizing the COMPRESS command and not try to fix
> how authentication works in another kind of compression (TLS-level
> compression).  It would otherwise be an update to RFC 4643.
>
> Updating TLS usage with NNTP is the aim of a second, separate document
> (draft-elie-nntp-tls-recommendations) that updates RFC 4643 with
> best current practices.  That one discourages the use of TLS-level
> compression, thus dealing with authentication layered with a TLS-level
> compression method.
>
>
>>>    In order to help mitigate leaking authentication credentials via for
>>>    instance a CRIME attack [CRIME], authentication SHOULD NOT be
>>>    attempted when a compression layer is active.  Consequently, a server
>>>    SHOULD NOT return any arguments with the AUTHINFO capability label
>>>    (or SHOULD NOT advertise it at all) in response to a CAPABILITIES
>>>    command received from an unauthenticated client after a compression
>>>    layer is active, and such a client SHOULD NOT attempt to utilize any
>>>    AUTHINFO [RFC4643] commands.  It implies that a server SHOULD reply
>>>    with a 502 response code if a syntactically valid AUTHINFO command is
>>>    received while a compression layer is already active.
>>>
>>> Why are these SHOULD, and not MUST?  Under what conditions would it be
>>> necessary or reasonable for an implementation not to abide by these,
>>> and what considerations need to be considered when making that
>>> determination?  (And this is also directly referred to in Section 6.)
> [...]
>> OK.  I've adopted your suggestion.
> [...]
>> Hmm...  I think I should now do a pass on the document and explicitly
>> say when "compression layer" only means the one negotiated with COMPRESS.
>> As a matter of fact, I do not think it's a good idea to say in this
>> draft that authentication MUST NOT be attempted when TLS-level
>> compression is active!  It would otherwise be a change in how
>> authentication works (RFC 4643 heavily mentions the preferred use of
>> AUTHINFO along with TLS, and RFC 4642 allows TLS-level compression).
>> This document would otherwise be an update to RFC 4643, by no longer
>> allowing AUTHINFO when TLS-level compression is active.
> Pass done.  I updated the wording in a few parts of the document.
> The above quoted paragraph becomes:
>
>     In order to help mitigate leaking authentication credentials via for
>     instance a CRIME attack [CRIME], authentication MUST NOT be attempted
>     after a successful use of the COMPRESS command.  Consequently, a
>     server MUST either list the AUTHINFO capability with no arguments or
>     not advertise it at all, in response to a CAPABILITIES command
>     received from an unauthenticated client after a successful use of the
>     COMPRESS command, and such a client MUST NOT attempt to utilize any
>     AUTHINFO [RFC4643] commands.  It implies that a server MUST reply
>     with a 502 response code if a syntactically valid AUTHINFO command is
>     received after a successful use of the COMPRESS command.  (Note that
>     this specification does not change the behaviour of AUTHINFO as
>     described in [RFC4643] independently of TLS-level compression.
>     Authentication is therefore still allowed, even though TLS-level
>     compression is active.)
>
>
> I hope you're all fine with that.
> Have a nice day,
>

-- 
Kenneth Murchison
Principal Systems Software Engineer
Carnegie Mellon University