Re: [secdir] [Captive-portals] Secdir last call review of draft-ietf-capport-rfc7710bis-04

Erik Kline <ek.ietf@gmail.com> Mon, 08 June 2020 00:21 UTC

Return-Path: <ek.ietf@gmail.com>
X-Original-To: secdir@ietfa.amsl.com
Delivered-To: secdir@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id B0D323A081D; Sun, 7 Jun 2020 17:21:38 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.097
X-Spam-Level:
X-Spam-Status: No, score=-2.097 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-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=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 GYEwWsD73HjX; Sun, 7 Jun 2020 17:21:36 -0700 (PDT)
Received: from mail-oi1-x22e.google.com (mail-oi1-x22e.google.com [IPv6:2607:f8b0:4864:20::22e]) (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 AAE213A081B; Sun, 7 Jun 2020 17:21:36 -0700 (PDT)
Received: by mail-oi1-x22e.google.com with SMTP id b8so13793062oic.1; Sun, 07 Jun 2020 17:21:36 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=ul/pKUBYhT3ElTPxUa5XW2WJhFhZtzsIbR3LM5yH9OI=; b=LB3NactwP6tG1/h8zKbB7A+otgqobDexC5mLqEFEqBgKKOviCUyuFP9lqEzaGyqUfU KBASiGYWwheeHqO36dIB1c/HXgSc/xkFjifCUhAT+OWqC38lWyX33WtLaM3iYG3nt6qW 9drB0PSvzJ75a4qy3a8AoLWPPKas7FoQEdJ7warrHmfr2Ola4wiG/ynK22zy/9Mu/aXf dgxZJUz+brIprHpobh004iA3UEmB+cEzC6M3wGQjTblSpVrLgf11oRTVXhOL9Nxqn5LU fCL7M15U1+ouwZcIuArg2HmNvt7H7OY8pLtReeecb86oKdzuCtj40JaDGqBroyd9XCxx lxqg==
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:content-transfer-encoding; bh=ul/pKUBYhT3ElTPxUa5XW2WJhFhZtzsIbR3LM5yH9OI=; b=PrO1C8AE6tZn0ZgH7+Q3ETuvPBNMCZ9Yq7Sj1j/fV79JZeAm6VVL8jkujbYEibAyOQ sON6vDI4GHbYXC7+rEYpXXwgW3luDZuXX76I9HLjF0BZOzwJr4xCHHSQ5FMUvpDCGxcm clYxsW7FUEhe33bRRRrmC9RBi5O5WjazDZw/gPF9OdfDggtC9cLo/zwxWtctdBCnx3qy 9vCk9iRKVbVCQoF014/8Z+4cJ9HlDyYvkmygfYMBDe1oV8XoMg8yMdl0qobrCup0tFIZ lrW7NO88ajUJ9aoLONnOaKcrj0MpguTxKJVVCnUVUQNXz+ZluTIE7J01A9DDvXg20goc KS7Q==
X-Gm-Message-State: AOAM5319IeCEb4Ecvc7UPnQ54BK29IzTGCiQSmfZxSidj7rJzRkwjCx5 Uso4n3y9N4TqTw5nBteIuxr8WwOC3EQFjMmVaiI=
X-Google-Smtp-Source: ABdhPJwE2YaUIavpw8BYoJlRcKAX3d9nCXr/C050J5Q7bdqnHZh5xIu511k0gxhXFaYs8MtPzeyQ4OM36nRNGtbvz5g=
X-Received: by 2002:aca:da55:: with SMTP id r82mr9284999oig.100.1591575695944; Sun, 07 Jun 2020 17:21:35 -0700 (PDT)
MIME-Version: 1.0
References: <CADNypP-MYk31mt2v8sqzYd583cTqHbfB4r6J0V_Lq5T7KuDsxg@mail.gmail.com> <AE32B5DA-FE7F-4691-8C2C-B0E5E9403EC8@apple.com> <CADNypP_BycOUSRiwQyvBfbDeM6-pVBQhvnyQkO4bsB-zstLZtg@mail.gmail.com>
In-Reply-To: <CADNypP_BycOUSRiwQyvBfbDeM6-pVBQhvnyQkO4bsB-zstLZtg@mail.gmail.com>
From: Erik Kline <ek.ietf@gmail.com>
Date: Sun, 7 Jun 2020 17:21:25 -0700
Message-ID: <CAMGpriXL30fqPSkoReoS7z94BLOsS2Z=UBbbDhEvRXO2h=PFrA@mail.gmail.com>
To: Rifaat Shekh-Yusef <rifaat.s.ietf@gmail.com>
Cc: Tommy Pauly <tpauly@apple.com>, captive-portals <captive-portals@ietf.org>, Martin Thomson <mt@lowentropy.net>, Benjamin Kaduk <kaduk@mit.edu>, Barry Leiba <barryleiba@computer.org>, IETF SecDir <secdir@ietf.org>, d.thakore@cablelabs.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: <https://mailarchive.ietf.org/arch/msg/secdir/iuECBeVUjqhz58ctffFmZaJ9xak>
Subject: Re: [secdir] [Captive-portals] Secdir last call review of draft-ietf-capport-rfc7710bis-04
X-BeenThere: secdir@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Security Area Directorate <secdir.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/secdir>, <mailto:secdir-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/secdir/>
List-Post: <mailto:secdir@ietf.org>
List-Help: <mailto:secdir-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/secdir>, <mailto:secdir-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 08 Jun 2020 00:21:39 -0000

I think there are two separate things here.

[1] The use of HTTPS allows the client to authenticate the API and
interactive URLs the same way a browser would be confident it's
talking to amazon.com, for example.

I think in this sense, the text is correct.

[2] There is, however, no way to know whether
bobshouseofportals.example.com is the authoritative captive portal
service for the MyCoffeeShop ESSID.

We should have this explicitly stated somewhere.  I couldn't quickly
find such a section, but perhaps I should add some text about this to
the 7710bis Security Considerations or thereabouts.

On Sat, Jun 6, 2020 at 1:02 PM Rifaat Shekh-Yusef
<rifaat.s.ietf@gmail.com> wrote:
>
> Hi Tommy,
>
> You will probably need to do more than just dropping this specific sentence, because the text just before this sentence talks about the client authenticating the server and allowing the user to be confident of the server and its identity.
>
> Regards,
>  Rifaat
>
>
> On Tue, Jun 2, 2020 at 1:33 AM Tommy Pauly <tpauly@apple.com> wrote:
>>
>> Hi Rifaat,
>>
>> Your comments make it clear that the recommendation to make the API server name visible isn’t necessarily clear. I think it’s not a harmful thing to show, as a way to give troubleshooting information and transparency to the user, but it is not a security-critical point.
>>
>> It seems appropriate to either explain the rationale more in depth, or remove that sentence entirely to avoid the misinterpretation.
>>
>> Do others in the CAPPORT group have thoughts on this sentence, and any background on why we decided to go that way? Would there be any objections to removing the sentence?
>>
>> Thanks,
>> Tommy
>>
>> On Jun 1, 2020, at 6:05 PM, Rifaat Shekh-Yusef <rifaat.s.ietf@gmail.com> wrote:
>>
>> 
>>
>>
>> On Sun, May 31, 2020 at 2:07 AM Erik Kline <ek.ietf@gmail.com> wrote:
>>>
>>> On Wed, May 20, 2020 at 4:37 AM Rifaat Shekh-Yusef
>>> <rifaat.s.ietf@gmail.com> wrote:
>>> >
>>> > Adding SecDir back to this thread.
>>> >
>>> >
>>> > >Martin Thomson <mt@lowentropy.net> Tue, 19 May 2020 01:02 UTCShow header
>>> > >
>>> > >On Tue, May 19, 2020, at 07:08, Rifaat Shekh-Yusef wrote:
>>> > >>    it provides the client of the API
>>> > >>    an opportunity to authenticate the server that is hosting the API.
>>> > >>    This authentication is aimed at *allowing a user to be reasonably
>>> > >>    confident that the entity providing the Captive Portal API has a
>>> > >>    valid certificate for the hostname in the URI*
>>> > >[...]
>>> > >> An end user should be able to validate that the name is example.com and
>>> > >> not any other form of the URI.
>>> > >> It would be much more difficult for the end user to make sense and
>>> > >> validate an IP address.
>>> > >
>>> > >I think that you missed the point of my comments.  This validation, performed by
>>> > >a user, has no meaningful security value.  The text you cite says that the server
>>> > >has a certificate for the name it chooses, which is not the same as "has a certificate
>>> > >for a name the client expects".  The difference is important.
>>> > >
>>> >
>>> > This is not the way I read these statements from section 4.1 titled Server Authentication.
>>> >
>>> > Here is the use case I have in mind when I read this section:
>>> > If I walk into an airport and I see an ad for a paid Internet service from example.com, then as an
>>> > end user it is reasonable to expect that I would have some ability to make sense of the name
>>> > presented to me and make sure it is from example.com if I choose to get such a service.
>>> >
>>> > If this is not the case, then yo might want to make it clear that this is not about Server Authentication
>>> > as the title of the section and the text inside that section is suggesting.
>>>
>>> If we changed the API document's section 4.1 title from "Server
>>> Authentication" to "API Server Authentication", would that be more
>>> clear?
>>>
>>> I reality, users should never see the API URL.
>>
>>
>> The following is a quote from section 4.1 of the API document, which implies otherwise:
>> "The hostname of the API SHOULD be displayed to the user in order to indicate the entity which is providing the API service."
>>
>> Regards,
>>  Rifaat
>>
>>
>>
>>>
>>> They'll just be
>>> connecting to "Cool Cafe" or "Awesome Bookshop" ESSIDs.  If anything
>>> will only be one or both of the "user-portal-url" or "venue-info-url"
>>> URLs that might be visible in the browser that's opened for the user's
>>> interaction.
>>>
>>> -ek
>>>
>>> > Regards,
>>> >  Rifaat
>>> >
>>> >
>>> >
>>> > >In a typical web scenario, a person types a string in and (ignore the case where there
>>> > >is an extra hop via a search engine) that string determines what is acceptable as a
>>> > >server identity.  The exposure to confusables is limited (under a set of other assumptions,
>>> > >HSTS, etc...).  Here, the network has free reign to do as they choose with homoglyphs and
>>> > >other such nonsense.  Any expectation you might have about this really being a trustworthy
>>> > >entity is meaningless in this context.
>>> > >
>>> > >There are protections against this, but they all lie firmly in the anti-phishing domain.
>>> > >Most of those rely on having a certificate though, so the requirement for HTTPS is in
>>> > >service of that, not in terms of ensuring that an untrained human can make a security
>>> > >critical decision based on poisoned information.
>>> >
>>> > On Mon, May 18, 2020 at 5:08 PM Rifaat Shekh-Yusef <rifaat.s.ietf@gmail.com> wrote:
>>> >>
>>> >> Adding Ben.
>>> >>
>>> >>
>>> >> On Sun, May 17, 2020 at 9:26 PM Martin Thomson <mt@lowentropy.net> wrote:
>>> >>>
>>> >>> Adding more lists..
>>> >>>
>>> >>> On Sun, May 17, 2020, at 02:50, Rifaat Shekh-Yusef wrote:
>>> >>> > > Here is a quote form the API document:
>>> >>> > > "The hostname of the API SHOULD be displayed to the user in order to indicate the entity which is providing the API service."
>>> >>> > >
>>> >>> > > This seems to suggest that the user is expected to inspect the displayed name and make sure it is make sense in the context of whoever is providing that service.
>>> >>>
>>> >>> I don't think that is the case.  If this were a security mechanism, then it would use "MUST".  This is likely for the purpose of enabling some sort of accountability.  In other words, this is to offer maximal information about what is going on.
>>> >>>
>>> >> Here is the sentence just before the above quote from the API document:
>>> >>
>>> >>    it provides the client of the API
>>> >>    an opportunity to authenticate the server that is hosting the API.
>>> >>    This authentication is aimed at allowing a user to be reasonably
>>> >>    confident that the entity providing the Captive Portal API has a
>>> >>    valid certificate for the hostname in the URI
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>>
>>> >>> > > Since this would be an easier attack compared to the interception attack, and IP address is still permitted, then an attacker might force the use of IP address to make it harder for the user to make sense of the displayed name.
>>> >>>
>>> >>> I don't think that is materially different than getting a name with confusable characters (or using the prefix hack, example.com.<some-guid>.example, in an attempt to confuse).
>>> >>
>>> >>
>>> >> An end user should be able to validate that the name is example.com and not any other form of the URI.
>>> >> It would be much more difficult for the end user to make sense and validate an IP address.
>>> >>
>>> >> Regards,
>>> >>  Rifaat
>>> >>
>>> > _______________________________________________
>>> > Captive-portals mailing list
>>> > Captive-portals@ietf.org
>>> > https://www.ietf.org/mailman/listinfo/captive-portals