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

Michael Bäuerle <michael.baeuerle@stz-e.de> Tue, 25 October 2016 16:41 UTC

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Date: Tue, 25 Oct 2016 18:41:26 +0200
From: Michael =?ISO-8859-1?B?QuR1ZXJsZQ==?= <michael.baeuerle@stz-e.de>
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Cc: draft-murchison-nntp-compress.all@ietf.org, Barry Leiba <barryleiba@computer.org>, IESG <iesg@ietf.org>, "secdir@ietf.org" <secdir@ietf.org>
Subject: Re: [secdir] Secdir review of draft-murchison-nntp-compress-05
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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.

I'm fine with it.


Regards,

Michael Bäuerle