Re: [TLS] Premaster/Master convention

Watson Ladd <watsonbladd@gmail.com> Thu, 31 July 2014 02:51 UTC

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Date: Wed, 30 Jul 2014 19:51:24 -0700
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From: Watson Ladd <watsonbladd@gmail.com>
To: Michael StJohns <msj@nthpermutation.com>
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Subject: Re: [TLS] Premaster/Master convention
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On Wed, Jul 30, 2014 at 7:56 AM, Michael StJohns <msj@nthpermutation.com> wrote:
> Given that TLS1.3 only does KeyAgreement, is there still any reason for the
> premaster -> master_secret derivation step?  We do (KA)->premaster and then
> premaster -> master and then master->(session keys).   We could probably do
> (KA)->master->(session keys) where the master secret is now the KA shared
> secret rather than premaster.
>
> 1) Is there any security reason for retaining the extra step given there is
> no longer a KeyTransport mechanism in TLS1.3?
> 2) Are there other *good* - non-security - reasons for retaining the extra
> step?

Ideally the handshake would simply supply key material to a transport
protocol, and meet standard security conditions.
(some CK variant, and I've not included renegotiation). To do this the
premaster->master step is fine, but the Finished
message needs to be changed. (Yes, miTLS exists. It has to do all sort
of nonstandard assumptions to work).

Sincerely,
Watson Ladd

>
> Mike
>
>
>
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