Re: [TLS] Distinguishing between external/resumption PSKs

Rob Sayre <sayrer@gmail.com> Fri, 20 September 2019 23:37 UTC

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From: Rob Sayre <sayrer@gmail.com>
Date: Fri, 20 Sep 2019 16:37:42 -0700
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To: Mohit Sethi M <mohit.m.sethi=40ericsson.com@dmarc.ietf.org>
Cc: Richard Barnes <rlb@ipv.sx>, Nico Williams <nico@cryptonector.com>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Distinguishing between external/resumption PSKs
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On Fri, Sep 20, 2019 at 1:07 AM Mohit Sethi M <mohit.m.sethi=
40ericsson.com@dmarc.ietf.org>; wrote:

> Chrisitian Huitema rightly points out that having free from PSKIdentity is
> good from a privacy perspective as an attacker cannot distinguish between
> initial authentication and resumption. However, if the server first has to
> lookup the resumption PSKs table before checking for any matching external
> PSKs, the timing information would leak that nonetheless.
>

This timing issue is a good concern to raise.

However, it made me wonder why the various ESNI drafts don't allow any
ClientHello field or extension to be encrypted.

thanks,
Rob