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

Tony Arcieri <bascule@gmail.com> Thu, 13 August 2015 22:17 UTC

Return-Path: <bascule@gmail.com>
X-Original-To: acme@ietfa.amsl.com
Delivered-To: acme@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id C1AEE1B3B82 for <acme@ietfa.amsl.com>; Thu, 13 Aug 2015 15:17:29 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.999
X-Spam-Level:
X-Spam-Status: No, score=-1.999 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_PASS=-0.001] autolearn=ham
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 3s1QaAulCCAV for <acme@ietfa.amsl.com>; Thu, 13 Aug 2015 15:17:28 -0700 (PDT)
Received: from mail-ob0-x236.google.com (mail-ob0-x236.google.com [IPv6:2607:f8b0:4003:c01::236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 4F0E31B3B81 for <acme@ietf.org>; Thu, 13 Aug 2015 15:17:28 -0700 (PDT)
Received: by obbop1 with SMTP id op1so48631763obb.2 for <acme@ietf.org>; Thu, 13 Aug 2015 15:17:27 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; bh=vFzA1jVpVytMNmKaojpryBiQ3QDZl2NYTw/AjARJhd0=; b=dJ25NS42dwyeq7gD2aNI56aIOg66PAl602BwSrS4yzQDny5IzVPkWqSRSTxdTXGShd M/SW01bPNAkww0kmZg7R5k46EYdrpxDjfHH9RIv2bbHpVQaZCzlkhvIy1JMIiLIpFlKg CuDWZje7nwif/ko4f68DzCfzrrIo4xNIZ3NUHL/Tlt2WOEnsWssmZoRrC+8oTwmAyrmI FvgAUhVAm/1cq9jitZh4yVb97HYHkVk8gnTMrYFnb6Rd+zlA0liv+zCoX2MqTlZuUgQj ATDk6LXR+6Jz03UvuVbn1uam69m3Gx5q+QWQp/ogAsw0LiODtFE5N6lXdLc0kpoFzg99 xLzg==
X-Received: by 10.60.141.3 with SMTP id rk3mr36724550oeb.3.1439504247802; Thu, 13 Aug 2015 15:17:27 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.76.159.227 with HTTP; Thu, 13 Aug 2015 15:17:08 -0700 (PDT)
In-Reply-To: <CAMm+LwhF8odJ77Jh9WXAfffcYBDAwrx8jr5Y5TQ9-P=ZKeRk9g@mail.gmail.com>
References: <20150811085205.bbcd37b3b0bb0482f6522b1a@andrewayer.name> <CAL02cgRf2M0Gkqymif-=rmNG0v9hhaMC2SBiXf-n5aYiRKBnmQ@mail.gmail.com> <20150812160405.b824b673ad9b139a4fd9446f@andrewayer.name> <CAL02cgReCTMZ+ECiZVtv2=sNDng3mvEmGv4w6V_REbZ6xf75dw@mail.gmail.com> <55CC6BEC.6050706@cs.tcd.ie> <CAMm+Lwi4Y5J2w2TB=n78KQnRvS7f171k8rUjcD3RRu5PMNPPMQ@mail.gmail.com> <20150813145155.GA7501@LK-Perkele-VII> <CAMm+LwgfD6bJYsNOKgwAG368zHU3b2_WLej0--5QCfCjW6NVAw@mail.gmail.com> <87si7n8abu.fsf@latte.josefsson.org> <CAHOTMVJiySnM1_st0vW2RE9XJ+Ejn0KNDD0o8BFJwJfhamU3JA@mail.gmail.com> <CAMm+LwhF8odJ77Jh9WXAfffcYBDAwrx8jr5Y5TQ9-P=ZKeRk9g@mail.gmail.com>
From: Tony Arcieri <bascule@gmail.com>
Date: Thu, 13 Aug 2015 15:17:08 -0700
Message-ID: <CAHOTMVJF5NgF7Lm53jRk1CX8iwEUfU1Mgw8vKu9hWDAwSOOSUw@mail.gmail.com>
To: Phillip Hallam-Baker <phill@hallambaker.com>
Content-Type: multipart/alternative; boundary=047d7b339faf57d3d3051d38b3a2
Archived-At: <http://mailarchive.ietf.org/arch/msg/acme/RzpWCBQlg3L2_hahPJ9CL9MJn3I>
Cc: Simon Josefsson <simon@josefsson.org>, Richard Barnes <rlb@ipv.sx>, "acme@ietf.org" <acme@ietf.org>, Ilari Liusvaara <ilari.liusvaara@elisanet.fi>, Andrew Ayer <agwa@andrewayer.name>, Stephen Farrell <stephen.farrell@cs.tcd.ie>
Subject: Re: [Acme] Signature misuse vulnerability in draft-barnes-acme-04
X-BeenThere: acme@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: Automated Certificate Management Environment <acme.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/acme>, <mailto:acme-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/acme/>
List-Post: <mailto:acme@ietf.org>
List-Help: <mailto:acme-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/acme>, <mailto:acme-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 13 Aug 2015 22:17:29 -0000

On Thu, Aug 13, 2015 at 3:11 PM, Phillip Hallam-Baker <phill@hallambaker.com
> wrote:

> I'd agree, this is a conceptual misuse of digital signatures. While
>> creating a signature algorithm resistant to this is a "neat trick" much
>> like nonce reuse resistant AEAD schemes, you shouldn't design protocols
>> that rely on that resistance in either case.
>>
>
>
[...] People need to change their attitudes. We are designing building
> blocks that are going to be used by pin heads as well as geniuses. And on
> occasion the genius is going to build something on a bad day. The harder it
> is to screw up, the better.
>

In case I was unclear, I support the creation of schemes that take the
sharp edges off, hence the hat tip to nonce reuse-resistant AEAD. In fact I
have participated in the development of and tried to popularize libraries
that try to remove as many sharp edges as possible, such as libsodium.

The caveat I gave was that protocol designers shouldn't assume those sharp
edges aren't present. I think you'll find most digital signature algorithms
break under the assumption that two keys can't produce the same digital
signature.

-- 
Tony Arcieri