Re: [TLS] Refactoring the negotiation syntax

Ilari Liusvaara <ilariliusvaara@welho.com> Thu, 14 July 2016 11:44 UTC

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Date: Thu, 14 Jul 2016 14:44:43 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] Refactoring the negotiation syntax
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On Thu, Jul 14, 2016 at 11:32:00AM +0300, Ilari Liusvaara wrote:
> 
> I was thinking of just scanning the server key_share in order the groups
> appear... With no mixing if no key_share is absent.
> 
> This would unify DHE-PSK and PSK for purposes of later handshake.
> 
> Would need a way to ensure that some mixing happened tho!

Thinking some more about this:

- The initial value for the chain secret should be empty string, not
  L zeroes. If hash function is well-behaved (and most are), then
  empty and L zeroes are the same if passed as salt to HKDF-Extract,
  but empty string would cause an internal fault in derive_secret.
- One should ensure that the default type is "certificate
  authentication" and that this can't be changed without mixing in
  a secret.
- One needs to require that at least one secret mixing occurs in
  processing of CH/SH.


-Ilari