Re: [TLS] draft-ietf-tls-curve25519-01: Is public key validation necessary or helpful?

Ilari Liusvaara <ilariliusvaara@welho.com> Thu, 31 December 2015 20:20 UTC

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Date: Thu, 31 Dec 2015 22:20:43 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [TLS] draft-ietf-tls-curve25519-01: Is public key validation necessary or helpful?
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On Fri, Jan 01, 2016 at 06:22:00AM +1100, Martin Thomson wrote:
> On 31 December 2015 at 17:54, Ilari Liusvaara <ilariliusvaara@welho.com> wrote:
> > Zero checks can already be unit-tested/interop-tested just as well.
> 
> 
> What ekr said applies, but also this:

I thought the ekr's point was that if you need THS resistance, you
require EMS. If you don't, not much point worrying what properties
individual key exchanges have.
 
> Yes, you can test that a given implementation does the right checks,
> but you won't be checking during normal operation.  If you require
> session-hash, then every handshake includes that check and if someone
> messes up, the handshake just fails.  That far more visible.

I don't think the parts that actually matter are tested in normal
use. Unless you mean deimplementing entiere old TLS master secret
derivation...


-Ilari