Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-00.txt

Peter Gutmann <> Fri, 25 July 2014 04:10 UTC

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From: Peter Gutmann <>
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Thread-Topic: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-00.txt
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Date: Fri, 25 Jul 2014 04:10:23 +0000
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Subject: Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-00.txt
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Andrey Jivsov <> writes:

>* It adds only one bit of security
>* an implementation that shares code between IKE and TLS will need to store
>an additional hardcoded prime.

* The IKE values have been around since before IKE (in the form of Oakley),
nearly twenty years.  These new values have been around since last Wednesday.
This could mean a difference in anything from 0 to 1024, 2048, or whatever
bits of security (0 bits if they're no better or worse, the full bitsize if
they turn out to have some issue that the existing, well-proven ones don't).

>Most people will not have strong preferences here, I assume.

Well I do, the RFC 3526 values are already used in SSH (alongside IKE), and
I've been using them in TLS as well.  I really don't want to have to implement
a whole new set of gratuitously incompatible parameters.

All we need in order to deal with this is a signalling mechanism for which set
of parameters to use.  The RFC should provide this, and reference a standard
set of parameters, i.e. the IKE/SSH/whatever ones.  Alongside this there could
be a second RFC, "Additional parameters for xxx", which contains the new
parameters, although I can't see why anyone would want them.

(OK, there's always the "as a spare in case the existing ones fail", it's a
pretty thin argument but I can accept it.  Just make the standard RFC 3526
ones the default and have any new ones as a backup).