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

Shawn M Emery <shawn.emery@oracle.com> Wed, 24 August 2016 05:18 UTC

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To: Greg Hudson <ghudson@mit.edu>, kitten@ietf.org
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From: Shawn M Emery <shawn.emery@oracle.com>
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Date: Tue, 23 Aug 2016 23:20:56 -0600
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Subject: Re: [kitten] I-D Action: draft-ietf-kitten-rfc6112bis-01.txt
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On 08/17/16 09:58 AM, Greg Hudson wrote:
> 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."

I don't think "channels" is the right word in the updated sentence. I 
interpreted the original text to indicate that an active attacker can 
not snoop key exchanges between the client and KDC in order to 
compromise a subsequent secure channel.

>>> "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...".

Sorry, was focused on the entire sentence.  Done.

Shawn.
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