Re: [Acme] Signature misuse vulnerability in draft-barnes-acme-04

Simon Josefsson <simon@josefsson.org> Thu, 13 August 2015 15:42 UTC

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From: Simon Josefsson <simon@josefsson.org>
To: Phillip Hallam-Baker <phill@hallambaker.com>
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Date: Thu, 13 Aug 2015 17:41:41 +0200
In-Reply-To: <CAMm+LwgfD6bJYsNOKgwAG368zHU3b2_WLej0--5QCfCjW6NVAw@mail.gmail.com> (Phillip Hallam-Baker's message of "Thu, 13 Aug 2015 11:00:31 -0400")
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Cc: Richard Barnes <rlb@ipv.sx>, Stephen Farrell <stephen.farrell@cs.tcd.ie>, "acme@ietf.org" <acme@ietf.org>, Ilari Liusvaara <ilari.liusvaara@elisanet.fi>, Andrew Ayer <agwa@andrewayer.name>
Subject: Re: [Acme] Signature misuse vulnerability in draft-barnes-acme-04
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Phillip Hallam-Baker <phill@hallambaker.com>; writes:

> On Thu, Aug 13, 2015 at 10:51 AM, Ilari Liusvaara <
> ilari.liusvaara@elisanet.fi>; wrote:
>
>> On Thu, Aug 13, 2015 at 10:27:09AM -0400, Phillip Hallam-Baker wrote:
>> > +1
>> >
>> > I would much rather block the entire class of attacks rather than spend
>> any
>> > time working out if there is a way to do this with ECC based keys.
>>
>> FYI, one of the five proposals for CFRG signatures:
>> - One is definitely vulernable (and key-checking won't help).
>> - Two are definitely not vulernable.
>> - Two I don't know.
>>
>> So good idea to just block the attack.
>
> I hadn't actually thought of using this as a discrimination function on the
> CFRG algorithms. It is as good as anything else.

This is not a good discriminator of the CFRG options -- this problem is
a weakness in this protocol, and should be addressed here.

/Simon