Re: [Hash] Charter discussion, round 1

Ben Laurie <ben@algroup.co.uk> Tue, 28 June 2005 16:34 UTC

Received: from localhost.localdomain ([127.0.0.1] helo=megatron.ietf.org) by megatron.ietf.org with esmtp (Exim 4.32) id 1DnJ2F-00037F-OI; Tue, 28 Jun 2005 12:34:07 -0400
Received: from odin.ietf.org ([132.151.1.176] helo=ietf.org) by megatron.ietf.org with esmtp (Exim 4.32) id 1DnJ2F-000375-1N for hash@megatron.ietf.org; Tue, 28 Jun 2005 12:34:07 -0400
Received: from ietf-mx.ietf.org (ietf-mx [132.151.6.1]) by ietf.org (8.9.1a/8.9.1a) with ESMTP id MAA29305 for <hash@ietf.org>; Tue, 28 Jun 2005 12:34:03 -0400 (EDT)
Received: from mail.links.org ([217.155.92.109]) by ietf-mx.ietf.org with esmtp (Exim 4.33) id 1DnJRb-0001W2-Fb for hash@ietf.org; Tue, 28 Jun 2005 13:00:20 -0400
Received: from [193.133.15.218] (localhost [127.0.0.1]) by mail.links.org (Postfix) with ESMTP id D920733C1B; Tue, 28 Jun 2005 17:34:09 +0100 (BST)
Message-ID: <42C17BFD.1000402@algroup.co.uk>
Date: Tue, 28 Jun 2005 17:34:05 +0100
From: Ben Laurie <ben@algroup.co.uk>
User-Agent: Mozilla Thunderbird 1.0 (Windows/20041206)
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: Paul Hoffman <paul.hoffman@vpnc.org>
Subject: Re: [Hash] Charter discussion, round 1
References: <6.2.1.2.2.20050609152413.078e8ac0@mail.binhost.com> <p06210245bece4ebbbea1@[10.20.30.249]> <20050616081143.GC32581@raktajino.does-not-exist.org> <p0621023abed742623640@[10.20.30.249]> <20050617084345.GJ32581@raktajino.does-not-exist.org> <6.2.1.2.2.20050617114209.0640e0d0@mail.binhost.com> <42BFEA9E.6080603@algroup.co.uk> <p06230977bee71c108c83@[10.20.30.249]> <42C172A7.8080807@algroup.co.uk> <p06230979bee7272458a8@[10.20.30.249]>
In-Reply-To: <p06230979bee7272458a8@[10.20.30.249]>
X-Enigmail-Version: 0.89.6.0
X-Enigmail-Supports: pgp-inline, pgp-mime
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Spam-Score: 0.0 (/)
X-Scan-Signature: 7baded97d9887f7a0c7e8a33c2e3ea1b
Content-Transfer-Encoding: 7bit
Cc: w3t-archive@w3.org, hash@ietf.org
X-BeenThere: hash@lists.ietf.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: hash.lists.ietf.org
List-Unsubscribe: <https://www1.ietf.org/mailman/listinfo/hash>, <mailto:hash-request@lists.ietf.org?subject=unsubscribe>
List-Archive: <http://www1.ietf.org/pipermail/hash>
List-Post: <mailto:hash@lists.ietf.org>
List-Help: <mailto:hash-request@lists.ietf.org?subject=help>
List-Subscribe: <https://www1.ietf.org/mailman/listinfo/hash>, <mailto:hash-request@lists.ietf.org?subject=subscribe>
Sender: hash-bounces@lists.ietf.org
Errors-To: hash-bounces@lists.ietf.org

Paul Hoffman wrote:
> At 4:54 PM +0100 6/28/05, Ben Laurie wrote:
>>> Do you have different wording that would help, for example, TLS use 
>>> these kinds of functions if we define them?
>>
>> 'Including a random value in the hash function computation.  The 
>> random block used is transferred at appropriate points in the protocol 
>> (ideally once for each use of the hash function).  This approach is 
>> sometimes called a "salted" or "randomized" hash function.'
> 
> I prefer "value" to "block" in the second sentence, but the rest seems 
> fine to me.

Fair enough - I took that word from the existing wording.

> Do others have an opinion on this wording?
> 
>> And now I'm thinking harder about this, we also should say that care 
>> needs to be taken that the right party chooses the random value (or it 
>> may be that both (all?) parties should choose it in some cases) - 
>> since allowing the attacker to choose it would be bad.
> 
> The whole purpose here is to allow the signing party to add randomness 
> to the message they are signing.

It is? Isn't the purpose to try to mitigate _all_ the problems caused by 
weak hashes?

> If the attacker is signing, don't they 
> already have all the control they need for the collision attacks?

Not if the relying party chooses the random value.

-- 
 >>>ApacheCon Europe<<<                   http://www.apachecon.com/

http://www.apache-ssl.org/ben.html       http://www.thebunker.net/

"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff

_______________________________________________
Hash mailing list
Hash@lists.ietf.org
https://www1.ietf.org/mailman/listinfo/hash