Re: [kitten] I-D Action: draft-ietf-kitten-rfc6112bis-01.txt

Greg Hudson <ghudson@mit.edu> Wed, 17 August 2016 15:58 UTC

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To: Shawn M Emery <shawn.emery@oracle.com>, kitten@ietf.org
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From: Greg Hudson <ghudson@mit.edu>
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Date: Wed, 17 Aug 2016 11:58:15 -0400
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Subject: Re: [kitten] I-D Action: draft-ietf-kitten-rfc6112bis-01.txt
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On 08/16/2016 12:12 AM, Shawn M Emery wrote:
>> In section 7, "To ensure that an attacker cannot create a channel with a
>> given name" was changed to "To ensure that an attacker cannot create a
>> channel by observing exchanges."  The original wording may have used
>> "name" in a non-intuitive way, but I think the new wording is more
>> wrong.  The threat is that a MITM attacker might create two channels
>> with the same ticket session key (known to the attacker); the new
>> wording suggests that the threat comes from a passive attacker.
> 
> Yes, the key word "observing" indicates a passive state.  How about?:
> 
> To ensure that an attacker cannot create a channel by obtaining key
> exchanges between the client and KDC, it is desirable that neither the
> KDC nor the client unilaterally determine the ticket session key.

That still suggests a passive attacker to me.  I suggest:

"To ensure that an active attacker cannot create separate channels to
the client and KDC with the same known key, it is desirable that neither
the KDC nor the client unilaterally determine the ticket session key."

>> "By requiring the session key in a way that..." is not grammatical.
>>
> 
> How about?:
> 
> This protocol binds the ticket to the DH exchange and prevents the MITM
> attack by requiring the session key in a way that can be verified by the
> client.

I believe that change just reverses the two main clauses of the sentence
without eliminating the grammar error.  You could say "requiring the
session key to be created in a way...".