Re: [TLS] Adoption call for Deprecating Obsolete Key Exchange Methods in TLS

Viktor Dukhovni <ietf-dane@dukhovni.org> Sat, 31 July 2021 16:11 UTC

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From: Viktor Dukhovni <ietf-dane@dukhovni.org>
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Subject: Re: [TLS] Adoption call for Deprecating Obsolete Key Exchange Methods in TLS
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On Sat, Jul 31, 2021 at 12:57:39PM +0000, Peter Gutmann wrote:
> Viktor Dukhovni <ietf-dane@dukhovni.org> writes:
> 
> >I strongly doubt there's a non-negligible server population with weak locally
> >generated groups.
> 
> Would you care to rephrase that so we can make sure you're saying what we
> think you're saying in order to disagree with it?

OK, who goes around bothering to actually generate custom DH parameters,
and with what tools, but then does not use a "strong" (Sophie Germain)
prime?

The only weakness I expect to encounter is a deprecated size of e.g.
512, 768 or 1024 bits.  Clients can easily detect that and enforce a
floor, but of course still don't get to negotiate a minimum.

Clients also don't get to negotiate the size of the server's RSA public
key, or as you mentioned various other ways for the server to not screw
up.

-- 
    Viktor.