Re: [TLS] Finished stuffing/PSK Binders

Ilari Liusvaara <ilariliusvaara@welho.com> Sun, 09 October 2016 13:58 UTC

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Date: Sun, 9 Oct 2016 16:58:17 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] Finished stuffing/PSK Binders
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On Fri, Oct 07, 2016 at 08:01:43AM -0700, Eric Rescorla wrote:
> After the discussion on PR #615, I took another pass at this with some
> help from the research community. Please see:
> 
>    https://github.com/tlswg/tls13-spec/pull/672
> 

Also, an observation: This seems to interact in somewhat annoying way
with stateless HRR.

Basically, CH reconstruction no longer works properly, so one needs to
have a  freezeable PRF hash (and most implementations of hashes can not
be frozen).

And server not supporting PSK does not help here.


(BTW: Simlar thing comes up if you try to freeze an established TLS
session: Currently you need to freeze a hash due to post-handshake
authentication, even if you don't support it. Nothing else in TLS
1.2 or 1.3 needs hash freezing for established session).


-Ilari