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RE: [saag] [Cfrg] Re: TCP-AO MAC algorithms

Sean Shuo Shen <sshen@huawei.com> Fri, 04 January 2008 03:36 UTC

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Date: Fri, 04 Jan 2008 11:35:17 +0800
From: Sean Shuo Shen <sshen@huawei.com>
Subject: RE: [saag] [Cfrg] Re: TCP-AO MAC algorithms
In-reply-to: <20080104030507.7297e280@cs.columbia.edu>
To: "'Steven M. Bellovin'" <smb@cs.columbia.edu>
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Thank you Steven.

>>Sean Shuo Shen <sshen@huawei.com> wrote:
>> Hi Stephen,
>> Can you talk more details about the FIPS evaluation problem?
 
>The issue is what the assurance boundary is.  If the TCP sequence
>number is cryptographically significant, the entire process by which
>it's set (including original generation and anything else in the stack
>or kernel that could touch it) has to be part of the evaluation, too.

The isn generation of some windows versions and linux is not random enough
and is vulnerable (like RST attack). So the seq num can not be a source for
randomness. But if a seq num is used just as an index instead of a random
seed, it is not cryptographically significant and I don't think it will
affect the cryptographic strength. What do you think, Steven?

Regards

Sean



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