Re: [TLS] Fixing TLS

Eric Rescorla <ekr@rtfm.com> Tue, 12 January 2016 17:42 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 12 Jan 2016 09:41:26 -0800
Message-ID: <CABcZeBNKdWzWH78KVshPAt0J1Sj3sWEi-UQX0=nCpLNWnCkxUg@mail.gmail.com>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] Fixing TLS
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On Tue, Jan 12, 2016 at 9:17 AM, Ilari Liusvaara <ilariliusvaara@welho.com>;
wrote:
>
> > - Drop 99% of all cipher suites, leaving one traditional one (DHE +
> AES-CBC +
> >   HMAC-SHA2 + RSA-SHA2/PSK for auth) and one ECC one (ECDHE + AES-GCM +
> HMAC-
> >   SHA2 + ECDSA-SHA2/PSK for auth) as must's (with a strong preference
> for OCB
> >   instead of GCM as the AEAD if it were freely available).
>
> DHE has serious problems. While the present TLS 1.3 way of doing DHE
> isn't totally horrible, advertise DHE and you can get downnegotiation to
> TLS 1.2 DHE, and now you are screwed.
>

Nit: this shouldn't be possible with the anti-downgrade mechanism that was
introduced
in draft-11 because the server's signature will cover the random value. If
you area
aware of an issue here, I would appreciate more information.

-Ekr