Re: [TLS] (no subject)

Eric Rescorla <ekr@rtfm.com> Fri, 10 March 2017 02:55 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 9 Mar 2017 16:58:59 -0800
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To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] (no subject)
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Landed.

Also, see the follow up PR to make implementation easier:
https://github.com/tlswg/tls13-spec/pull/904


On Thu, Mar 9, 2017 at 4:41 AM, Ilari Liusvaara <ilariliusvaara@welho.com>
wrote:

> On Thu, Mar 09, 2017 at 12:50:03PM +0100, Hubert Kario wrote:
> > On Thursday, 9 February 2017 22:17:33 CET Eric Rescorla wrote:
> > > Hi folks,
> > >
> > > We need to close on an issue about the size of the
> > > state in the HelloRetryRequest. Because we continue the transcript
> > > after HRR, if you want a stateless HRR the server needs to incorporate
> > > the hash state into the cookie. However, this has two issues:
> >
> > Isn't the whole CH2 supposed to be deterministically created from CH1
> and HRR?
>
> No.
>
> Neither CH1 nor CH2 are deterministic w.r.t. one another.
>
> > So you should be able (as the server) to recreate the CH1 given the hash
> (or
> > better yet, keyed HMAC) of the CH1 fairly easily? Bonus point: you
> > automatically reject technically malformed CH2 messages (ones with more
> > changes than prescribed) as you won't be able to create a CH1 that
> creates the
> > matching HMAC.
>
> Actually, you can't create CH1 from just CH2. Back some versions it was
> merely very annoying to do so, now (as in -18), you can't do it at all.
>
>
> -Ilari
>
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