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

Julien ÉLIE <julien@trigofacile.com> Mon, 24 October 2016 20:28 UTC

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To: Barry Leiba <barryleiba@computer.org>, draft-murchison-nntp-compress.all@ietf.org, =?UTF-8?Q?Michael_B=c3=a4uerle?= <michael.baeuerle@stz-e.de>
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Subject: Re: [secdir] Secdir review of draft-murchison-nntp-compress-05
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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,

-- 
Julien ÉLIE

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