Re: [TLS] Genart last call review of draft-ietf-tls-exported-authenticator-09

Eric Rescorla <ekr@rtfm.com> Thu, 10 October 2019 14:36 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 A29361200C1 for <tls@ietfa.amsl.com>; Thu, 10 Oct 2019 07:36:58 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.896
X-Spam-Level:
X-Spam-Status: No, score=-1.896 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_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_NONE=0.001, URIBL_BLOCKED=0.001] 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 f_hp_6WrAvbM for <tls@ietfa.amsl.com>; Thu, 10 Oct 2019 07:36:54 -0700 (PDT)
Received: from mail-lf1-x129.google.com (mail-lf1-x129.google.com [IPv6:2a00:1450:4864:20::129]) (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 75048120018 for <tls@ietf.org>; Thu, 10 Oct 2019 07:36:53 -0700 (PDT)
Received: by mail-lf1-x129.google.com with SMTP id c195so4568735lfg.9 for <tls@ietf.org>; Thu, 10 Oct 2019 07:36:53 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rtfm-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=BKbxl0Llj5SNsAm7793ZM2v7TvXBNai78KLepuMeQaI=; b=cm535rWRFfVG5pEXHY13X1Cxy8KirO5IpokuvnGpHTy/Dof3bn57ly4knxq0PKQqK+ tYmL5PUzLspwrP+ECedp71RFk9Dt4UFf5DkH2URe/jaRfemO+esOuCrcAkYO2e0Jcpk0 O6FelrbJgZfL/3OJ6cJ1zpytdqYDi/9IDgYdnPpzytO9DpvWOIVTxChJWdy5q5jEqRUt NCIIaMZyMScnDr6FpChh2w3rl0qhC6dhdJzjYSAkFWwS8HsHVY3O24ftl8niV6tUFEdG QkcVlVSxiSqAJo6BVHPbiuTfIRTl5hlYot6bhPFCDWm1DQhUxYq8KYkUMUaFDFhuNrcK Nreg==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=BKbxl0Llj5SNsAm7793ZM2v7TvXBNai78KLepuMeQaI=; b=ZyXaXNQkEBlK407AGXqv6RKNGo632FQiqp8ZMgfPHC8/yhcxYqPRq1x6Y2dMegQ6T7 YlYOE+Xg+HOyckwQgQVSK74mMFw108SOGM0Lg1dgjSbHXuZcUN1RKFE16lhmZVOui2s2 kZPHHejLEb2IjtVm5j6eF2w2SdVkb6eZv9VxvVj7y6oDIzdCSwCIEm3ohbEzHdWwNHV8 eKQr7Pc+wBYY4PoYNKbVtUTp2tnAOv4xoCz3G5PZk5r5cHTRg+3M2PZaMLIKm9zwOXqX qlQPILAiTHt7AWm261G8NVQops1dVwCJWnBBSnPdYdwTRHwMFkZimob3PM0AvC1n25Ku LYwQ==
X-Gm-Message-State: APjAAAV9uMdF4FALJCGVbBF+Z3NpF4zBkLPIklwLth27Gs/3Y8aQvjLm 92l5S/8OtgPLLdXZ+iPD1JEJhq0MRPrAVKKf/jpTZA==
X-Google-Smtp-Source: APXvYqzRaG8qyJyEcZEeeVKE7QEik+mtfFWHKUfiDRJtwg6KAxpNFPkzX2pwHNidvn73IKy1ZDXxpnkajq3tfUzjZsU=
X-Received: by 2002:a19:7404:: with SMTP id v4mr1223420lfe.129.1570718211653; Thu, 10 Oct 2019 07:36:51 -0700 (PDT)
MIME-Version: 1.0
References: <156249708979.14501.13745976049183757305@ietfa.amsl.com> <CAFDDyk8iG0R2rT7x-t7fHkFxcYBBkf8j1-mg1xbexoh8gXts6A@mail.gmail.com> <7BDE969A-7B5F-4979-B4E9-7E6C03C0A1B1@ericsson.com> <CAFDDyk_yoOu01nBPrBj_AVBugFRGUCOthYDysOuAGCrKNWG8dg@mail.gmail.com> <57E5EB36-6A59-45A7-A2F4-1E1626391742@ericsson.com> <CAFDDyk-T_+RHDwEJ+8AQFTvZKykPxwd+A5+8xiZp22bOs48S8w@mail.gmail.com> <0cf4806b-3825-4d25-8be0-13c27533b08d@www.fastmail.com> <CAFDDyk-JyDTfk3JpfvtDZpWcKXE3Nd14oegbeMDetnHkCLr-wA@mail.gmail.com>
In-Reply-To: <CAFDDyk-JyDTfk3JpfvtDZpWcKXE3Nd14oegbeMDetnHkCLr-wA@mail.gmail.com>
From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 10 Oct 2019 07:36:14 -0700
Message-ID: <CABcZeBPNwf6sUg-9hpAS1scfnU-KqpEXDmG430Tw0V+rGGXoVw@mail.gmail.com>
To: Nick Sullivan <nick=40cloudflare.com@dmarc.ietf.org>
Cc: Martin Thomson <mt@lowentropy.net>, "<tls@ietf.org>" <tls@ietf.org>
Content-Type: multipart/alternative; boundary="0000000000000c569e05948f5561"
Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/KxeUWqv7VKmvMtbxTv13-pPcPMM>
Subject: Re: [TLS] Genart last call review of draft-ietf-tls-exported-authenticator-09
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.29
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, 10 Oct 2019 14:36:59 -0000

Well, DTLS is one of the primary consumers of exporters
https://tools.ietf.org/rfcmarkup?doc=5764, so as a practical matter I think
we've accepted that. I'm not aware of a practical problem with exporters
and DTLS, but if there is one, we should document it and address it.

-Ekr


On Thu, Oct 10, 2019 at 7:08 AM Nick Sullivan <nick=
40cloudflare.com@dmarc.ietf.org>; wrote:

> The main concern I had about including DTLS explicitly in this document
> was because exporters are not officially defined for DTLS. However, some
> other documents assume they are portable so maybe this is an overly
> conservative choice.
>
> On Wed, Oct 9, 2019 at 6:26 PM Martin Thomson <mt@lowentropy.net>; wrote:
>
>> I think that the DTLS thing doesn't require as much rewriting as
>> observed.  Just say that when you say "TLS" you mean "TLS or DTLS"
>> somewhere up front.
>>
>> As to what a transport needs to provide, I think that there is no real
>> text to add regarding DTLS.  You *could* say that as the application
>> protocol is responsible for carrying the messages, might find that using a
>> DTLS connection introduces new problems.  Specially, these are big messages
>> and they are likely to require fragmentation and reassembly if DTLS is
>> used.  Also, if the protocol depends on these messages being reliably
>> delivered, it will want to provide some sort of loss recovery mechanism.
>>
>> On Thu, Oct 10, 2019, at 11:47, Nick Sullivan wrote:
>> > Thanks again for your review! The PR is on Github
>> > (https://github.com/tlswg/tls-exported-authenticator/pull/50) and will
>> > be incorporated into a new version of the document that addresses both
>> > your comments and those by Yaron Sheffer.
>> >
>> > On Thu, Sep 19, 2019 at 11:29 PM Christer Holmberg
>> > <christer.holmberg@ericsson.com>; wrote:
>> > > Hi,
>> > >
>> > >  >Some answers to your questions inline. I'm not sure further changes
>> along the lines suggested here are needed, but I'm open to arguments that
>> point in that direction.
>> > >
>> > >  I am mostly fine with your answers. Just a couple of comments inline
>> still.
>> > >
>> > >  ---
>> > >
>> > >  MIN_2:
>> > >
>> > >  >>>> Can the mechanism be used also for DTLS?
>> > >  >>>
>> > >  >>> I think the answer is yes. I don't see any reason to disallow
>> the use of Exported Authenticators in DTLS.
>> > >  >>
>> > >  >> Would it be useful to clarify that?
>> > >  >
>> > >  > Going through what the modified text would look like, it seems
>> like a substantial amount of re-writing (even the title!) for what amounts
>> to an unclear use case.
>> > >  > Keeping in mind that DTLS 1.3 hasn't been finalized and doesn't
>> directly define exporters, I'm disinclined to define how EAs would work
>> with DTLS. If someone
>> > >  > has a strong use case for EA in DTLS, it may be worth considering
>> it.
>> > >
>> > >  Would it then be useful with a statement saying that it might be
>> possible to use exporters also with DTLS, but that such usage is outside
>> the scope of the document and needs to be specified in a separate document?
>> >
>> > I added a line to this effect.
>> > >
>> > >  ---
>> > >
>> > >  MIN_3:
>> > >
>> > >  >>>> The documents talk about additional certificates. If I only
>> have one additional
>> > >  >>>> certificate, can I use that for multiple authenticators
>> throughout the TLS
>> > >  >>>> session?
>> > >  >>>
>> > >  >>> Yes, there is nothing disallowing the creation of multiple
>> exported authenticators with the same certificate.
>> > >  >>
>> > >  >> Would it be useful to clarify that?
>> > >  >
>> > >  > I'm not convinced this is a realistic use case. Since exported
>> authenticators are based on the exporter, there is no inherent ordering.
>> > >  > If you re-authenticate with the same certificate, there's nothing
>> asserting freshness of the second certificate. Is there something in
>> > >  > the text that suggests that using a certificate multiple times is
>> disallowed? If there's no suggestion that this is not possible that
>> > >  > needs to be corrected, I don't see the benefit of calling out this
>> specific use case.
>> > >
>> > >  I don't think there is any text suggesting that it is disallowed.
>> But, if you don't think it is a realistic use case I'll take your word for
>> it :)
>> > >
>> > >  ---
>> > >
>> > >  ED_2:
>> > >
>> > >  >>>> Section 3 says: "The authenticator request is a structured
>> message that can be
>> > >  >>>> created..." Section 4 says: "The authenticator is a structured
>> message that can
>> > >  >>>> be exported..."
>> > >  >>>>
>> > >  >>>> In the 2nd paragraph of Section 4 it is stated that
>> "authenticator" is sent
>> > >  >>>> based on an "authenticator request". I wonder if that could be
>> stated already
>> > >  >>>> in the beginning of Section 4, to further clarify the
>> difference between them.
>> > >  >>>> E.g.,
>> > >  >>>>
>> > >  >>>> "The authenticator is a structured message, triggered by an
>> authenticator
>> > >  >>>> request, that can be exported from either party of a TLS
>> connection."
>> > >  >>>
>> > >  >>> The issue is that servers can generate spontaneous exported
>> authenticators without
>> > >  >>> an authenticator request.
>> > >  >>
>> > >  >> Where is this written? Did I miss it?
>> > >  >
>> > >  > Section 4:
>> > >  > An authenticator message can be constructed by either the client or
>> > >  > the server given an established TLS connection, a certificate, and
>> a
>> > >  > corresponding private key. Clients MUST NOT send an authenticator
>> > >  > without a preceding authenticator request; for servers an
>> > >  > authenticator request is optional. For authenticators that do not
>> > >  > correspond to authenticator requests, the
>> certificate_request_context
>> > >  > is chosen by the server.
>> > >
>> > >  Ok. Looks good.
>> > >
>> > >  Regards,
>> > >
>> > >  Christer
>> > >
>> > >
>> > _______________________________________________
>> > TLS mailing list
>> > TLS@ietf.org
>> > https://www.ietf.org/mailman/listinfo/tls
>> >
>>
>> _______________________________________________
>> TLS mailing list
>> TLS@ietf.org
>> https://www.ietf.org/mailman/listinfo/tls
>>
> _______________________________________________
> TLS mailing list
> TLS@ietf.org
> https://www.ietf.org/mailman/listinfo/tls
>