Re: [TLS] draft-ietf-tls-esni feedback

Stephen Farrell <stephen.farrell@cs.tcd.ie> Mon, 21 October 2019 20:46 UTC

Return-Path: <stephen.farrell@cs.tcd.ie>
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 4317E120A65 for <tls@ietfa.amsl.com>; Mon, 21 Oct 2019 13:46:23 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.3
X-Spam-Level:
X-Spam-Status: No, score=-4.3 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=cs.tcd.ie
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 hnqH3w4qlzOu for <tls@ietfa.amsl.com>; Mon, 21 Oct 2019 13:46:20 -0700 (PDT)
Received: from mercury.scss.tcd.ie (mercury.scss.tcd.ie [134.226.56.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 7A9081209C9 for <tls@ietf.org>; Mon, 21 Oct 2019 13:46:20 -0700 (PDT)
Received: from localhost (localhost [127.0.0.1]) by mercury.scss.tcd.ie (Postfix) with ESMTP id A1145BE4C; Mon, 21 Oct 2019 21:46:17 +0100 (IST)
X-Virus-Scanned: Debian amavisd-new at scss.tcd.ie
Received: from mercury.scss.tcd.ie ([127.0.0.1]) by localhost (mercury.scss.tcd.ie [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id DA42XfMf6Mon; Mon, 21 Oct 2019 21:46:16 +0100 (IST)
Received: from [10.244.2.119] (95-45-153-252-dynamic.agg2.phb.bdt-fng.eircom.net [95.45.153.252]) by mercury.scss.tcd.ie (Postfix) with ESMTPSA id 051EABE39; Mon, 21 Oct 2019 21:46:16 +0100 (IST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cs.tcd.ie; s=mail; t=1571690776; bh=bm4S7QtdnjidcDk5kw/ncTZgtiX+bFxAOCSaO/tXu3M=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=qZ1SJBmI3GnYTSAoqWXa12iFrMf0tlkdA+R3U3QRcixefjHvukOwPFhPFkQ0VX9EN 4QtZroY9IZQ/nafkPkfIOkg7HHKS9w8diJ5gBiI+H93YBagwTDpecjPcTuSvgQM9Lh fOapkUxXhQI/lGKhAhCMryLivKzQGl1eBY2ckz1g=
To: Eric Rescorla <ekr@rtfm.com>
Cc: Rob Sayre <sayrer@gmail.com>, "TLS@ietf.org" <tls@ietf.org>
References: <CAChr6Sw3f7du3JYxfcWSZje1zjDzsRBQyDjob-AvzjWeZzKW7g@mail.gmail.com> <CABcZeBPbw_KOo_ieSqkksYPeLtb9DufBz628oFPYc_Ue4S9iww@mail.gmail.com> <CAChr6SwB+7Jt2TLJSQh3q=Roizdt2=9jCBa9nq8KRxRo=86uZQ@mail.gmail.com> <CABcZeBNBtDK7q175tseEUiCVds=khj4xXYJZRf7GU9VGNDJ_Tg@mail.gmail.com> <CAChr6Sz6xHtFWjOKrLp3sp9MpC-SoU9Sx=vk22ditjShA7B=Kg@mail.gmail.com> <CABcZeBOnE+gyNu7GarAfO0bptoPfzQQ=VKeWLdpJBDM=E4yhzg@mail.gmail.com> <CAChr6SxWE66jPRbnBRtwNSn3L+uNFkoFBbYNOBAkKDN05qotoA@mail.gmail.com> <CABcZeBOy8ogJrmFajxX1pqjqgnE61gE=c3CWz+pp34NWHmGKbw@mail.gmail.com> <03e15760-dfce-cd7b-baea-56ac70d92192@cs.tcd.ie> <CABcZeBMquubsGvt8UssiyFU_ZuQK67rHN_KBXY+iKSNayJFZew@mail.gmail.com> <d9402fe2-2ab3-f60f-c478-dc1df5bd4402@cs.tcd.ie> <CABcZeBNC9YBGMs0b84DFDB-FU7fKXpzX+HP1H5KRcjYJ7kXr3w@mail.gmail.com>
From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
Openpgp: id=5BB5A6EA5765D2C5863CAE275AB2FAF17B172BEA; url=
Autocrypt: addr=stephen.farrell@cs.tcd.ie; prefer-encrypt=mutual; keydata= mQINBFo9UDIBEADUH4ZPcUnX5WWRWO4kEkHea5Y5eEvZjSwe/YA+G0nrTuOU9nemCP5PMvmh 5Cg8gBTyWyN4Z2+O25p9Tja5zUb+vPMWYvOtokRrp46yhFZOmiS5b6kTq0IqYzsEv5HI58S+ QtaFq978CRa4xH9Gi9u4yzUmT03QNIGDXE37honcAM4MOEtEgvw4fVhVWJuyy3w//0F2tzKr EMjmL5VGuD/Q9+G/7abuXiYNNd9ZFjv4625AUWwy+pAh4EKzS1FE7BOZp9daMu9MUQmDqtZU bUv0Q+DnQAB/4tNncejJPz0p2z3MWCp5iSwHiQvytYgatMp34a50l6CWqa13n6vY8VcPlIqO Vz+7L+WiVfxLbeVqBwV+4uL9to9zLF9IyUvl94lCxpscR2kgRgpM6A5LylRDkR6E0oudFnJg b097ZaNyuY1ETghVB5Uir1GCYChs8NUNumTHXiOkuzk+Gs4DAHx/a78YxBolKHi+esLH8r2k 4LyM2lp5FmBKjG7cGcpBGmWavACYEa7rwAadg4uBx9SHMV5i33vDXQUZcmW0vslQ2Is02NMK 7uB7E7HlVE1IM1zNkVTYYGkKreU8DVQu8qNOtPVE/CdaCJ/pbXoYeHz2B1Nvbl9tlyWxn5Xi HzFPJleXc0ksb9SkJokAfwTSZzTxeQPER8la5lsEEPbU/cDTcwARAQABtDJTdGVwaGVuIEZh cnJlbGwgKDIwMTcpIDxzdGVwaGVuLmZhcnJlbGxAY3MudGNkLmllPokCQAQTAQgAKgIbAwUJ CZQmAAULCQgHAgYVCAkKCwIEFgIDAQIeAQIXgAUCWj6jdwIZAQAKCRBasvrxexcr6o7QD/9m x9DPJetmW794RXmNTrbTJ44zc/tJbcLdRBh0KBn9OW/EaAqjDmgNJeCMyJTKr1ywaps8HGUN hLEVkc14NUpgi4/Zkrbi3DmTp25OHj6wXBS5qVMyVynTMEIjOfeFFyxG+48od+Xn7qg6LT7G rHeNf+z/r0v9+8eZ1Ip63kshQDGhhpmRMKu4Ws9ZvTW2ACXkkTFaSGYJj3yIP4R6IgwBYGMz DXFX6nS4LA1s3pcPNxOgrvCyb60AiJZTLcOk/rRrpZtXB1XQc23ZZmrlTkl2HaThL6w3YKdi Ti1NbuMeOxZqtXcUshII45sANm4HuWNTiRh93Bn5bN6ddjgsaXEZBKUBuUaPBl7gQiQJcAlS 3MmGgVS4ZoX8+VaPGpXdQVFyBMRFlOKOC5XJESt7wY0RE2C8PFm+5eywSO/P1fkl9whkMgml 3OEuIQiP2ehRt/HVLMHkoM9CPQ7t6UwdrXrvX+vBZykav8x9U9M6KTgfsXytxUl6Vx5lPMLi 2/Jrsz6Mzh/IVZa3xjhq1OLFSI/tT2ji4FkJDQbO+yYUDhcuqfakDmtWLMxecZsY6O58A/95 8Qni6Xeq+Nh7zJ7wNcQOMoDGj+24di2TX1cKLzdDMWFaWzlNP5dB5VMwS9Wqj1Z6TzKjGjru q8soqohwb2CK9B3wzFg0Bs1iBI+2RuFnxLkCDQRaPVAyARAA+g3R0HzGr/Dl34Y07XqGqzq5 SU0nXIu9u8Ynsxj7gR5qb3HgUWYEWrHW2jHOByXnvkffucf5yzwrsvw8Q8iI8CFHiTYHPpey 4yPVn6R0w/FOMcY70eTIu/k6EEFDlDbs09DtKcrsT9bmN0XoRxITlXwWTufYqUnmS+YkAuk+ TLCtUin7OdaS2uU6Ata3PLQSeM2ZsUQMmYmHPwB9rmf+q2I005AJ9Q1SPQ2KNg/8xOGxo13S VuaSqYRQdpV93RuCOzg4vuXtR+gP0KQrus/P2ZCEPvU9cXF/2MIhXgOz207lv3iE2zGyNXld /n8spvWk+0bH5Zqd9Wcba/rGcBhmX9NKKDARZqjkv/zVEP1X97w1HsNYeUFNcg2lk9zQKb4v l1jx/Uz8ukzH2QNhU4R39dbF/4AwWuSVkGW6bTxHJqGs6YimbfdQqxTzmqFwz3JP0OtXX5q/ 6D4pHwcmJwEiDNzsBLl6skPSQ0Xyq3pua/qAP8MVm+YxCxJQITqZ8qjDLzoe7s9X6FLLC/DA L9kxl5saVSfDbuI3usH/emdtn0NA9/M7nfgih92zD92sl1yQXHT6BDa8xW1j+RU4P+E0wyd7 zgB2UeYgrp2IIcfG+xX2uFG5MJQ/nYfBoiALb0+dQHNHDtFnNGY3Oe8z1M9c5aDG3/s29QbJ +w7hEKKo9YMAEQEAAYkCJQQYAQgADwUCWj1QMgIbDAUJCZQmAAAKCRBasvrxexcr6qwvD/9b Rek3kfN8Q+jGrKl8qwY8HC5s4mhdDJZI/JP2FImf5J2+d5/e8UJ4fcsT79E0/FqX3Z9wZr6h sofPqLh1/YzDsYkZDHTYSGrlWGP/I5kXwUmFnBZHzM3WGrL3S7ZmCYMdudhykxXXjq7M6Do1 oxM8JofrXGtwBTLv5wfvvygJouVCVe87Ge7mCeY5vey1eUi4zSSF1zPpR6gg64w2g4TXM5qt SwkZVOv1g475LsGlYWRuJV8TA67yp1zJI7HkNqCo8KyHX0DPOh9c+Sd9ZX4aqKfqH9HIpnCL AYEgj7vofeix7gM3kQQmwynqq32bQGQBrKJEYp2vfeO30VsVx4dzuuiC5lyjUccVmw5D72J0 FlGrfEm0kw6D1qwyBg0SAMqamKN6XDdjhNAtXIaoA2UMZK/vZGGUKbqTgDdk0fnzOyb2zvXK CiPFKqIPAqKaDHg0JHdGI3KpQdRNLLzgx083EqEc6IAwWA6jSz+6lZDV6XDgF0lYqAYIkg3+ 6OUXUv6plMlwSHquiOc/MQXHfgUP5//Ra5JuiuyCj954FD+MBKIj8eWROfnzyEnBplVHGSDI ZLzL3pvV14dcsoajdeIH45i8DxnVm64BvEFHtLNlnliMrLOrk4shfmWyUqNlzilXN2BTFVFH 4MrnagFdcFnWYp1JPh96ZKjiqBwMv/H0kw==
Message-ID: <c7ada021-1ccf-1dc5-d7e3-a5f893f116ee@cs.tcd.ie>
Date: Mon, 21 Oct 2019 21:46:10 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0
MIME-Version: 1.0
In-Reply-To: <CABcZeBNC9YBGMs0b84DFDB-FU7fKXpzX+HP1H5KRcjYJ7kXr3w@mail.gmail.com>
Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="EQorT9tmOa6dYMubHT9uKdW7qfIP1bOup"
Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/S2wuAC3D5N_eblGerYPux61ek_s>
Subject: Re: [TLS] draft-ietf-tls-esni feedback
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: Mon, 21 Oct 2019 20:46:23 -0000

Hiya,

On 21/10/2019 21:02, Eric Rescorla wrote:
>> Sure, but the point holds though. If ESNIKeys are changed every
>> N seconds, and any new certificate is loaded during that time,
>> then the server operator can't tell the lengths that the CAs
>> might produce in future. So with the current design 260-always is
>> the only thing a server-operator (or really an ESNIKeys generator
>> who may be a slightly different entity) can rely on in general.
>>
> I don't believe that this claim is correct in general. Remember that these
> records are stored in the DNS under the name that becomes the SNI, so,
> absent wildcards, ths eet of names is in fact known, regardless of what
> happens to be in the certificate.

Depends which "in general" is more general I guess.

Wildcards do exist in the DNS, though TBH I'm not really
familiar with how they're implemented in authoritatives.

But even ignoring those, deployment models where the
ESNIKeys are generated by the TLS server operator, but
DNS records are published by a different entity (say the
owner of the name or registrar) ought not be precluded
I think. Supporting such a model I think more or less
requires setting padding_length to 260 or else risking
a failure nobody will notice (if browsers fall back to
cleartext SNI) or know how to diagnose if they do.

And even in the case of a monolithic service that does it
all for every name, I think it'd still likely pick 260
in order to avoid having to exercise/write the code to
detect and react to a need to increase the padding_length.
("Holy crap - you mean I need to re-publish everyone's
ESNIKeys just because this bozo has a really long name?
Who made that up?")

I really can't see what'd motivate anyone to publish
ESNIKeys with a padding_length < 260 tbh (well, other
than not having thought it through;-). Anything <260
just seems to be asking for later problems.

S.