To: Stephen Farrell <stephen.farrell@cs.tcd.ie>, Eric Rescorla
 <ekr@rtfm.com>, Christopher Wood <caw@heapingbits.net>
Cc: "TLS@ietf.org" <tls@ietf.org>
References: <EB7DEE42-8EC4-4347-BA10-0EBF90CBF398@heapingbits.net>
 <CABcZeBP1RcZDdXrmuu9DEg5jhntzpKPCwCoSRjUfH_W=cFOCpw@mail.gmail.com>
 <6b52f482-3a5e-ed0f-232a-68b888d00a2a@cs.tcd.ie>
From: Christian Huitema <huitema@huitema.net>
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Message-ID: <259571bf-6001-390d-7b22-6a4f19330c39@huitema.net>
Date: Sun, 22 Mar 2020 15:59:22 -0700
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Archived-At:
 <https://mailarchive.ietf.org/arch/msg/tls/NWmTONIAIIych78RkMTG7IApduA>
Subject: Re: [TLS] Dropping "do not stick out" from ECHO
Precedence: list

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From: Christian Huitema <huitema@huitema.net>
To: Stephen Farrell <stephen.farrell@cs.tcd.ie>, Eric Rescorla
 <ekr@rtfm.com>, Christopher Wood <caw@heapingbits.net>
Cc: "TLS@ietf.org" <tls@ietf.org>
Message-ID: <259571bf-6001-390d-7b22-6a4f19330c39@huitema.net>
Subject: Re: [TLS] Dropping "do not stick out" from ECHO
References: <EB7DEE42-8EC4-4347-BA10-0EBF90CBF398@heapingbits.net>
 <CABcZeBP1RcZDdXrmuu9DEg5jhntzpKPCwCoSRjUfH_W=cFOCpw@mail.gmail.com>
 <6b52f482-3a5e-ed0f-232a-68b888d00a2a@cs.tcd.ie>
In-Reply-To: <6b52f482-3a5e-ed0f-232a-68b888d00a2a@cs.tcd.ie>

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On 3/22/2020 3:23 PM, Stephen Farrell wrote:
> Hiya,
>
> I was wondering what I wanted to say about this, until...
>
> On 22/03/2020 22:16, Eric Rescorla wrote:
>> I think we should relax this requirement. It's turning out to be hard
>> enough to design ECHO as-is.
>>
>> If/when we get ECHO fully designed and widely deployed, we can then tr=
y to
>> find designs which use the same basic design but are more stealthy.
>>
>> Trying to fix everything at once makes the best the enemy of the good.=

> Yeah, that's about right. Well said.
>
> I very much like the idea of working on a more-stealthy
> mode later.
>
> I think we might be able to go even further in terms
> of simplifying ECHO in various ways that can make it
> easier to implement and deploy now without affecting
> the security properties/analysis. (I think I've whined
> about those on the list before but can regurgitate if
> useful:-)


I agree with Stephen. If we have a solid & verified spec, let's deploy
it. Then conduct an effort to mitigate the sticking out problem. I can
see a number of plausible ways to do that. Greasing is one. Actually
using the extension even for sites that have just one SNI, but want to
hide usage of multiple ALPN. In the case of QUIC, using the extension to
negotiate a secret and protect the Initial packets. If everybody does
it, the cost of blocking becomes very large.

-- Christian Huitema



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