[TLS] drop ffdhe2048? (was: I-D Action: draft-ietf-tls-negotiated-ff-dhe-10.txt)

Dave Garrett <davemgarrett@gmail.com> Wed, 03 June 2015 21:52 UTC

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From: Dave Garrett <davemgarrett@gmail.com>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Date: Wed, 3 Jun 2015 17:52:10 -0400
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Subject: [TLS] drop ffdhe2048? (was: I-D Action: draft-ietf-tls-negotiated-ff-dhe-10.txt)
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On Wednesday, June 03, 2015 05:36:30 pm Dave Garrett wrote:
> pick either a strong curve to do ECDHE or a strong group to do FFDHE

On the topic of "strong":

https://tools.ietf.org/html/draft-ietf-tls-negotiated-ff-dhe-10#appendix-A.1

estimated symmetric-equivalent strengths:
ffdhe2048:  103 bits
ffdhe3072:  125 bits
ffdhe4096:  150 bits
ffdhe6144:  175 bits
ffdhe8192:  192 bits

If we only wish to support strong groups, then we should consider dropping ffdhe2048 and require ffdhe3072 or higher. (likewise, prohibit all curves under a ~128 bit security level)

Also, a ~256 bit security level FFDHE group should probably be in the list, even if its performance is crap.


Dave