Re: [TLS] Semi-Static Diffie-Hellman Key Establishment for TLS 1.3

Eric Rescorla <ekr@rtfm.com> Thu, 08 March 2018 23:25 UTC

Return-Path: <ekr@rtfm.com>
X-Original-To: tls@ietfa.amsl.com
Delivered-To: tls@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id C29581205D3 for <tls@ietfa.amsl.com>; Thu, 8 Mar 2018 15:25:37 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.599
X-Spam-Level:
X-Spam-Status: No, score=-2.599 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=rtfm-com.20150623.gappssmtp.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 NcKoL87Wk2JE for <tls@ietfa.amsl.com>; Thu, 8 Mar 2018 15:25:35 -0800 (PST)
Received: from mail-qk0-x233.google.com (mail-qk0-x233.google.com [IPv6:2607:f8b0:400d:c09::233]) (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 28C8E1204DA for <tls@ietf.org>; Thu, 8 Mar 2018 15:25:35 -0800 (PST)
Received: by mail-qk0-x233.google.com with SMTP id z197so1708177qkb.6 for <tls@ietf.org>; Thu, 08 Mar 2018 15:25:35 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rtfm-com.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=XEISwmf/dICwIrWeQVjDUiU7IkBKqvR704D6Nb+0FiA=; b=fEnSy6iMaxL/z3e9LDRDDP6DwXQMTWQinzSDFRka5aKn6ytqiLac8S1wGKq8VNexff Wdve5yuC6vHh4UMs/W2gsPNdKsRiJmgWQ8oAbHuVX4RtpJletdbndVE+Q0/FwmWdA/fE j2ehfxM/bx/H4RdBEYzjspJdaeQEupK0+VaBlJE4Xn5lpZJsRdlQvQkie1IMGDB3FT4n sjejW2yYSBuVSXo+mcRaWp96SHCcEOADHH4hN3XnL4EnvxmJY23DyvNZIaIfz/qfL/TN 5CFSrSowpnbwddVswYtO4OU54/sVkJcRztnmFBM4GxiPKQEaxw5z/Z+6p5fKl4YyCEge ECOw==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=XEISwmf/dICwIrWeQVjDUiU7IkBKqvR704D6Nb+0FiA=; b=C59Q1qVR44CWVBYAuw6EPXC7ufWkt0vuS/ZomV5C7gha4Zr7qXRvluSQ5xcw4fksY5 dKQcg9GivOxg9rJjVNaOOhIWVJ6OIsK7KwiZYrafX+Cj+oMEG1J0riAW2BOzuCbS3EPw nnBb9iYlmFD1IeQZeylaPrgZZRdnRS+nsLIiDK6p8LRPDLhz6LM4YtPHLr9rZQJblc1x RswRf9+FwPUZOgmtwGMWKw0z9ex1CIwiNndk7fs0FiFkNXwK2Q8NO2kyWcrvzkNW+QeO rUW0khn9UjaOk20X6A3EpaWfGgAili/Quq/ArVnbJTVgm6zw/mCx/PCy8Zzv3oEd5aAI inBw==
X-Gm-Message-State: AElRT7HQZAyB+zDayS77hwEAchHIc8XYsdXvOsKg2prQ8ifkLgOSelRw PmhXW0EE4Xp5DvYeLQVsh0tiH6Aha4CP4TD0EDJPxYMt
X-Google-Smtp-Source: AG47ELtytbNaKS6CN7yvp1ZP+Dy5/QF9EjifpVF7S3q+zCUJVSuwRSGsTb1zMxwF+MdChpsJbppQc1DEert2mr6gcKw=
X-Received: by 10.55.137.132 with SMTP id l126mr42792445qkd.15.1520551534110; Thu, 08 Mar 2018 15:25:34 -0800 (PST)
MIME-Version: 1.0
Received: by 10.200.37.176 with HTTP; Thu, 8 Mar 2018 15:24:53 -0800 (PST)
In-Reply-To: <140080C241BAA1419B58F093108F9EDC1678CD1A@UK-MAL-MBOX-02.dyson.global.corp>
References: <CABcZeBON1KiUUFx9h863APxB31Poy-czNpYS1+HwZjyQxn6wEw@mail.gmail.com> <b76b0d82-5714-4e1e-82ff-3f8af59c2c3e@Spark> <140080C241BAA1419B58F093108F9EDC1678CD1A@UK-MAL-MBOX-02.dyson.global.corp>
From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 8 Mar 2018 15:24:53 -0800
Message-ID: <CABcZeBNowz0irFwU-hJkrbV=zJhW4Vgtn5=e6zvm_NU2ZAG7_g@mail.gmail.com>
To: Tony Putman <Tony.Putman@dyson.com>
Cc: "<tls@ietf.org>" <tls@ietf.org>, Christopher Wood <christopherwood07@gmail.com>
Content-Type: multipart/alternative; boundary="94eb2c072d760dc9220566eefee4"
Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/0Zh-5MpIVqcKB_L3vnluZswT2iE>
Subject: Re: [TLS] Semi-Static Diffie-Hellman Key Establishment for TLS 1.3
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: "This is the mailing list for the Transport Layer Security working group of the IETF." <tls.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tls>, <mailto:tls-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/tls/>
List-Post: <mailto:tls@ietf.org>
List-Help: <mailto:tls-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tls>, <mailto:tls-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 08 Mar 2018 23:25:38 -0000

On Thu, Mar 8, 2018 at 9:41 AM, Tony Putman <Tony.Putman@dyson.com> wrote:

> Hi Ekr,
>
>
>
> Firstly, thanks for this. My primary reason for putting together
> draft-putman was to propose a handshake exchange which only uses a single
> asymmetric algorithm. If this proposal is extended to include raw public
> keys (I think these are already supported, but not mentioned in the text)
> and an ECDH-based MAC for client authentication, then this satisfies my
> constraints.
>

Yep, that should actually work just fine.


As a single data point, I can state that some of the IoT products that I'm
> working with already use static ECDH keys for client authentication (though
> not within TLS).
>



>
>
> Although OPTLS is able to use 0-RTT, I don't see how this capability could
> be used in this implementation, even if the client knows the server static
> key. Because SS is only included in the key schedule when the master secret
> is generated, the client_early_traffic_secret has no input secret.
> Conversely, if the SS is included in the key schedule as the PSK, then the
> certificate cannot be decrypted by a client which does not have the server
> static key.
>

Yes, I agree with you. OPTLS had a less linear key schedule. I think if you
wanted to do 0-RTT you would have to have it be a pretend PSK as you
suggest in your draft.


I think that this and draft-putman are not competing, but rather that they
> serve different use case
>

Agreed. It sounds like you have a set of use cases where you know how to
predistribute the server key? This is the part we found challenging int he
web context.

-Ekr





> s. They could be synergistic, such that this draft provides a mechanism
> for distributing a static key which could later be used in a draft-putman
> exchange; however, the natural continuation would be to use a resumption
> PSK, so this would only be useful if there were a long gap between session,
> which seems unlikely.
>
>
>
> Regards,
>
> Tony
>
>
>
> *From:* TLS [mailto:tls-bounces@ietf.org] *On Behalf Of *Christopher Wood
> *Sent:* 07 March 2018 01:26
> *To:* <tls@ietf.org>rg>; Eric Rescorla
> *Subject:* Re: [TLS] Semi-Static Diffie-Hellman Key Establishment for TLS
> 1.3
>
>
>
> Thanks for putting this together! I’m in favor of the mechanism and look
> forward to discussing it. Negotiating with signature_algorithms is a simple
> way to roll this out, it fits in cleanly with the key schedule, and the
> benefits outlined in the introduction (PRNG hardening, plausible
> deniability, etc.) seem worth the effort. Although the approach has its
> roots in OPTLS, we will certainly need to re-assess its impact on the
> handshake. (I know of some folks actively working on this.) We also need to
> spend more time thinking about the open issues — specifically, the story
> around early data encryption. This variant has the benefit of enabling
> early data with public key encryption, as opposed to (trackable) symmetric
> key encryption. It’s unclear to me whether or not we need to address the
> static share publication issue for this benefit.
>
>
>
> Anyway, thanks again for the draft. I’ll read it carefully before London.
>
>
> Best,
>
> Chris
>
>
> On Mar 5, 2018, 4:14 PM -0500, Eric Rescorla <ekr@rtfm.com>om>, wrote:
>
> Hi folks,
>
>
>
> Here's another entry in the DH-only pile.
>
>
>
> I've just posted:
>
>    draft-rescorla-tls13-semistatic-dh-00
>
>
>
> This implements a semi-static DH exchange mostly borrowed from
>
> OPTLS [0]. There are obviously connections with draft-putman, but
>
> this is more oriented towards implementing a 1-RTT style
>
> exchange where the client has no foreknowledge of the server's
>
> capabilities (though it's extensible to 0-RTT) than towards
>
> pre-distributed DH keys, and has less invasive changes to the
>
> key schedule.
>
>
>
> We'd like 10 minutes to discuss this in London.
>
>
>
> Thanks,
>
> -Ekr
>
>
>
> [0] http://ieeexplore.ieee.org/abstract/document/7467348/
>
>
>
>
>
>
>
> _______________________________________________
> TLS mailing list
> TLS@ietf.org
> https://www.ietf.org/mailman/listinfo/tls
>
> Dyson Technology Limited, company number 01959090, Tetbury Hill,
> Malmesbury, SN16 0RP, UK.
> This message is intended solely for the addressee and may contain
> confidential information. If you have received this message in error,
> please immediately and permanently delete it, and do not use, copy or
> disclose the information contained in this message or in any attachment.
> Dyson may monitor email traffic data and content for security & training.
>