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

Ben Schwartz <bemasc@google.com> Mon, 25 November 2019 19:25 UTC

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From: Ben Schwartz <bemasc@google.com>
Date: Mon, 25 Nov 2019 14:25:36 -0500
Message-ID: <CAHbrMsC8=5fKmmKaNSPiZY42vLmfVLdUYNiwWqox3jJ0H53bxg@mail.gmail.com>
To: Rob Sayre <sayrer@gmail.com>
Cc: "TLS@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] ESNI: Tracking and blocking via record_digest
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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
>
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