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Re: [TLS] ESNI: Tracking and blocking via record_digest

Rob Sayre <sayrer@gmail.com> Tue, 26 November 2019 03:47 UTC

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From: Rob Sayre <sayrer@gmail.com>
Date: Mon, 25 Nov 2019 19:47:23 -0800
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To: Christian Huitema <huitema@huitema.net>
Cc: Ben Schwartz <bemasc@google.com>, "TLS@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] ESNI: Tracking and blocking via record_digest
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Yes, and this concern is covered well by the draft in GitHub, imho.

thanks,
Rob

On Mon, Nov 25, 2019 at 7:33 PM Christian Huitema <huitema@huitema.net>
wrote:

> Actually there is one use case in which the anonymity set is size 1 --
> mobile servers. The name of the mobile server cannot be deduced from its
> temporary address. It can also not be deduced from the ESNI. But it can be
> deduced from the record digest. The mobile server who wants to maintain
> privacy will want to use ESNI without a record digest,  at the cost of
> course of trial decryption.
>
>
> -- Christian Huitema
> On 11/26/2019 4:37 AM, Rob Sayre wrote:
>
> You're right, this is all there in the draft. It's just scattered around a
> bit, and "anonymity set" is used only once and not defined.
>
> I filed an issue https://github.com/tlswg/draft-ietf-tls-esni/issues/204
> in case the editors want to consolidate text on this concern.
>
> thanks,
> Rob
>
>
> On Mon, Nov 25, 2019 at 11:25 AM Ben Schwartz <bemasc@google.com> wrote:
>
>> The record_digest, like the ESNIConfig itself, is intended to be constant
>> across all domains that form an anonymity set (i.e. O(1) ESNIConfigs per
>> CDN).  Thus, the record_digest reveals no additional information to an
>> onlooker who can observe the server IP.
>>
>> On Mon, Nov 25, 2019 at 2:03 PM Rob Sayre <sayrer@gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I see the issue of tracking and blocking via record_digest has come up a
>>> few times in the github repository, but I don't understand the resolution.
>>>
>>> If someone wanted to observe or block traffic to "example.com",
>>> couldn't they retrieve the ESNI keys, calculate the record_digest
>>> themselves, and then use that to spot traffic to "example.com"?
>>>
>>> Is the idea that DNS providers will vary the shared keys?
>>>
>>> thanks,
>>> Rob
>>>
>>> _______________________________________________
>>> TLS mailing list
>>> TLS@ietf.org
>>> https://www.ietf.org/mailman/listinfo/tls
>>>
>>
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