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

Eric Rescorla <ekr@rtfm.com> Wed, 03 June 2015 22:04 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Wed, 03 Jun 2015 15:03:54 -0700
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To: Dave Garrett <davemgarrett@gmail.com>
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Subject: Re: [TLS] drop ffdhe2048? (was: I-D Action: draft-ietf-tls-negotiated-ff-dhe-10.txt)
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Please see:
http://www.ietf.org/mail-archive/web/tls/current/msg14438.html


On Wed, Jun 3, 2015 at 2:52 PM, Dave Garrett <davemgarrett@gmail.com> wrote:

> 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
>
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