Re: [TLS] Another IRINA bug in TLS

Florian Weimer <fweimer@redhat.com> Thu, 21 May 2015 11:10 UTC

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Date: Thu, 21 May 2015 13:09:26 +0200
From: Florian Weimer <fweimer@redhat.com>
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Subject: Re: [TLS] Another IRINA bug in TLS
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On 05/21/2015 10:09 AM, Nikos Mavrogiannopoulos wrote:
> On Thu, 2015-05-21 at 10:01 +0200, Florian Weimer wrote:
> 
>> But removing that support is going to be tricky.  If the server has only
>> export-grade DH parameters (but does not actually support export cipher
>> suites), and it is willing to negotiate DHE cipher suites, you end up
>> with an interop failure, although you could well negotiate a reasonable
>> secure connection without a forward secrecy cipher suite.
>> Maybe we need SCSVs which express constraints on the size of the DH
>> prime?  If the server cannot match the constraints due to its
>> configuration, then it would not use forward secrecy.  That would give
>> (me at least) much more confidence for large-scale roll-out.
> 
> I think it would make sense to push for adoption of:
> https://tools.ietf.org/html/draft-ietf-tls-negotiated-ff-dhe-09

Interesting.  But do we want to encourage the use of additional magic
primes?

> However, that would not solve the incompatibility issue with old
> servers.

You mean, if the client rejects handshakes with defective primes, it
will not be able to connect to servers which use them?

-- 
Florian Weimer / Red Hat Product Security