Re: [TLS] Another INRIA bug in TLS

Martin Thomson <martin.thomson@gmail.com> Fri, 22 May 2015 21:10 UTC

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Date: Fri, 22 May 2015 14:10:39 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
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Subject: Re: [TLS] Another INRIA bug in TLS
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On 22 May 2015 at 13:55, Daniel Kahn Gillmor <dkg@fifthhorseman.net>; wrote:
> I'm considering adding a Miller-Rabin primality check for the group
> modulus to negotiated-ff-dhe's "Local Policy for Custom Groups" section:

Please don't.  I like the statement you have already:

   Compatible clients that are willing to accept FFDHE ciphersuites from
   non-compatible servers may have local policy about what custom FFDHE
   groups they are willing to accept.  This local policy presents a risk
   to clients, who may accept weakly-protected communications from
   misconfigured servers.

More words aren't going to change that.  In fact, I can see only harm
in going further.  I would even go so far as to remove the two
paragraphs that follow this.  SHOULD >= 1024 isn't really advice that
I'm comfortable with.