Re: [TLS] Computation of static secret in anonymous DH

Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Wed, 17 June 2015 15:05 UTC

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Date: Wed, 17 Jun 2015 18:05:05 +0300
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] Computation of static secret in anonymous DH
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On Wed, Jun 17, 2015 at 05:56:23AM -0700, Eric Rescorla wrote:
> On Wed, Jun 17, 2015 at 1:25 AM, Ilari Liusvaara <
> ilari.liusvaara@elisanet.fi> wrote:
> 
> > On Wed, Jun 17, 2015 at 07:33:31AM +0000, Douglas Stebila wrote:
> > > In the DH-based draft of TLS 1.3 (
> > https://github.com/ekr/tls13-spec/blob/ietf92_materials/draft-ietf-tls-tls13-dh-based.txt
> > ),
> > > how is the ServerParameters message containing the static secret SS
> > > constructed in the unauthenticated setting?
> >
> > There's much newer version in ekr/tls13-spec#WIP_draft_06
> > (seems to have fixed most of the mistakes in the original WIP)
> >
> 
> Don't worry, I'm sure there are plenty of mistakes left!

Such as how keys for TLS exporters are derived? Trying to
search for 'export' or 'extractor' only gives changelog
entry about fixing used key...

Editor's copy says exporters use master secret (not quite
ideal).

> > It also does not say what master key to use for handshake
> > encryption key derivation. I presume tmp2.
> >
> 
> " For handshake records, this means the ephemeral secret (ES)"
> 
> This whole section is still under active development, though.
 
I was thinking about avoiding using ES twice (since it is not
secured against THS-style attacks, while tmp2 is).


-Ilari