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Re: [TLS] PSK in 1.3?

Stephen Checkoway <s@pahtak.org> Mon, 23 February 2015 20:56 UTC

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From: Stephen Checkoway <s@pahtak.org>
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To: Dan Harkins <dharkins@lounge.org>
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Cc: Alex Elsayed <eternaleye@gmail.com>, tls@ietf.org
Subject: Re: [TLS] PSK in 1.3?
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On Feb 23, 2015, at 12:34 PM, Dan Harkins <dharkins@lounge.org> wrote:

> On Sat, February 21, 2015 12:45 am, Alex Elsayed wrote:
>> No, its model is "For shared keys drawn uniformly from {0,1}^n, this is
>> secure".
> 
>  No, it's not. If n=8 then the attack is trivial and succeeds almost
> instantaneously. If n=128 then with high probability a dictionary attack
> will not be successful. But in neither case is that "secure".

What is your definition of secure then?

If drawing uniformly at random from {0,1}^n is not secure for any n, then doesn't that say that there is no way to use TLS securely? The master secret is merely a number in {0,1}^384, after all. And common (EC)DHE key exchanges involve a secret in {0,1}^n for n in [160, 256].

-- 
Stephen Checkoway

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