Re: [secdir] SecDir Review of draft-ietf-httpauth-scram-auth-11

Russ Housley <housley@vigilsec.com> Tue, 01 December 2015 19:14 UTC

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From: Russ Housley <housley@vigilsec.com>
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To: Alexey Melnikov <alexey.melnikov@isode.com>
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Cc: IETF SecDir <secdir@ietf.org>, draft-ietf-httpauth-scram-auth.all@ietf.org
Subject: Re: [secdir] SecDir Review of draft-ietf-httpauth-scram-auth-11
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Alexey:

Continuing the discussion on two of my major concerns.

>> Section 5 says: "The "server-first-message" contains the user's
>> iteration count i, the user's salt, and the nonce with a
>> concatenation of the client-specified one with a server nonce."
>> It needs to be more clear that the nonce is a concatenation of the
>> client nonce from the client-first-message and a freshly generated
>> nonce by the server.
> This is described in RFC 5802, which is a normative reference.

I looked before sending this comment, and I did not find anything about freshness.
Can you point me to the text I missed?

>> Section 5.1 says: "[[CREF1: Should some counter be added to make
>> "sr" unique for each reauth?]]".  This needs to be specified.  In my
>> opinion, something needs to be done to make the AuthMessage different
>> for each invocation.  One possibility is to include a counter in
>> AuthMessage as follows:
>> 
>>       AuthMessage := client-first-message-bare + "," +
>>                      server-first-message + "," + counter + "," +
>>                      client-final-message-without-proof
> This was fixed in -12.

I just looked at the text in -12, and I think it needs to be more clear about the
number of octets that are used to represent nonce-count.  Perhaps you can
use INT().  If you use INT(), please define it as a bullet of its own in Section
1.2.

Russ