Re: [Cfrg] Help with the use of contexts

Yaron Sheffer <yaronf.ietf@gmail.com> Tue, 17 January 2017 11:31 UTC

Return-Path: <yaronf.ietf@gmail.com>
X-Original-To: cfrg@ietfa.amsl.com
Delivered-To: cfrg@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 553BB129418 for <cfrg@ietfa.amsl.com>; Tue, 17 Jan 2017 03:31:17 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.7
X-Spam-Level:
X-Spam-Status: No, score=-2.7 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, RCVD_IN_DNSWL_LOW=-0.7, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
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 U4-b597WyesD for <cfrg@ietfa.amsl.com>; Tue, 17 Jan 2017 03:31:15 -0800 (PST)
Received: from mail-wm0-x234.google.com (mail-wm0-x234.google.com [IPv6:2a00:1450:400c:c09::234]) (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 A13AD12945F for <cfrg@irtf.org>; Tue, 17 Jan 2017 03:31:15 -0800 (PST)
Received: by mail-wm0-x234.google.com with SMTP id c206so218152295wme.0 for <cfrg@irtf.org>; Tue, 17 Jan 2017 03:31:15 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding; bh=xX1hGPTHEQVsmA4IVt5ycoA4y96LIQaqEIuMiLO/3JI=; b=kBQEeDwr2RaSe5xW39vN2EUbphS9vPtX5wzQwqnHtPILiuTTe2+1lTdWd+UUfODfho dowuBbFjhewmLMzhBPdPbyho42vF1mV6A5o6QawlfUaysxeSUwimtRatls0EquXdoce+ 7wYfmitTg+dg2Qrphm31Y/bSes/41evLYnx3zTjPSZ97nR5SasRNFpeEffxugCn05wY0 4apEuVSEY0+CoTJvTubA3mljj0/3xEpEkcOkbxawLmrwVyzI0IW5T06ZVIbyeZ1U2n7e Kib5MlJOnHNLTMC1SmPwMBjHyaLM8XEdCFvSNonmIj9oUIRKSHCMo7yjcM5DRfhQXw34 EqMA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=xX1hGPTHEQVsmA4IVt5ycoA4y96LIQaqEIuMiLO/3JI=; b=SkCcikVB7e46DfsYjaCDeD8vGWs3ukMT8V7bBKBr46962eZWkNev12+ZmaSuzcYOah YHQAQksOgmIa4RXkRV1x6ClpLAx8X74EJjrFZmsC87cB/NTO6IIu3uDJGeYPhcld7bXW fIs3oCXcKClPiVwktzieaXSsXQNWOv4E35B9mts2uqqS7/QddqnqRrNItRsHCMzkTnDm IxghA0wC3v/lwA/nORE5o+pcqqcGWh3KxhKdaSgFbNHo8fXMSLBt2ruquXk7evxHVT9J ImPmbeSC+REV2NCGr09mo5GesmwnCBvlQMUvTcACaKF3ZJoNLC5mDNudeCx2AEbLutW+ hC+g==
X-Gm-Message-State: AIkVDXIzudxoRrIxBvq/BM4VckeHtp1TFFPrHLXj6vUmse9jy7eo6fJi19FI1hPsDPQ9TQ==
X-Received: by 10.223.175.36 with SMTP id z33mr26575833wrc.25.1484652673597; Tue, 17 Jan 2017 03:31:13 -0800 (PST)
Received: from [172.18.133.122] (cowboy3.intuit.com. [65.204.229.13]) by smtp.gmail.com with ESMTPSA id d29sm36384363wmi.19.2017.01.17.03.31.11 for <cfrg@irtf.org> (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Jan 2017 03:31:12 -0800 (PST)
To: cfrg@irtf.org
References: <mailman.133.1484592340.4842.cfrg@irtf.org>
From: Yaron Sheffer <yaronf.ietf@gmail.com>
Message-ID: <235ec588-9358-eeb1-9fa2-202409854afc@gmail.com>
Date: Tue, 17 Jan 2017 13:31:07 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1
MIME-Version: 1.0
In-Reply-To: <mailman.133.1484592340.4842.cfrg@irtf.org>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/cfrg/GdiY6aM2M0eJ5_w2mDnMGJ0AI3k>
Subject: Re: [Cfrg] Help with the use of contexts
X-BeenThere: cfrg@irtf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Crypto Forum Research Group <cfrg.irtf.org>
List-Unsubscribe: <https://www.irtf.org/mailman/options/cfrg>, <mailto:cfrg-request@irtf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/cfrg/>
List-Post: <mailto:cfrg@irtf.org>
List-Help: <mailto:cfrg-request@irtf.org?subject=help>
List-Subscribe: <https://www.irtf.org/mailman/listinfo/cfrg>, <mailto:cfrg-request@irtf.org?subject=subscribe>
X-List-Received-Date: Tue, 17 Jan 2017 11:31:17 -0000

> Domain separation for signed values is important and TLS already defines
> context strings for signature operations:
> https://tools.ietf.org/html/draft-ietf-tls-tls13-18#section-4.4.2
>
> The way that this is constructed (due to me) is generic for any signature
> scheme. (Basically just have the context string be NUL-terminated at the
> beginning of the signed message.)
>
> So for TLS I believe that the issue is already taken care of. It would also
> probably just add pain for implementers if the context string were to be
> duplicated as an input to the signature scheme where signature schemes
> support it.
>
>
> Cheers
>
> AGL

Hi Adam,

Wide industry adoption of TLS 1.2 took around 10 years. So IMO saying 
"this is solved in TLS 1.3" is not a good enough answer, if in the 
meantime we will continue to see cross-protocol and cross-TLS-version 
attacks.

Please note that the original post refers to "TLS 1.2 (and earlier)."

Thanks,
	Yaron