Re: [TLS] TLS 1.2 Long-term Support Profile draft posted

Peter Gutmann <pgut001@cs.auckland.ac.nz> Sat, 19 March 2016 09:31 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Hubert Kario <hkario@redhat.com>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] TLS 1.2 Long-term Support Profile draft posted
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Date: Sat, 19 Mar 2016 09:30:26 +0000
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Subject: Re: [TLS] TLS 1.2 Long-term Support Profile draft posted
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Hubert Kario <hkario@redhat.com>; writes:

>also, if it really is supposed to be Long Term Support, why it doesn't say
>anything about implementation explicitly being able to handle big key sizes?
>both RSA and DHE?

I've deliberately avoided getting into that because it's such a rathole,
you've got everything from the NIST numerologists at one extreme to the "good
enough for now" folks at the other, and you'll never get any consensus because
there are completely different worldviews involved.  A possible median is:

Implementations SHOULD choose public-key algorithm key sizes that are
appropriate for the situation, weighted by the value of the information being
protected, the probability of an attack, and the ability of the hardware to
deal with large keys.  For example a SCADA system being used to switch a
ventilator on and off doesn't require anywhere near the keysize-based security
of a system used to transfer classified information.  One way to avoid having
to use very large public keys is to switch keys periodically.  This can be
done by regenerating DH parameters in a background thread and rolling them
over from time to time, or if this isn't possible, by pre-generating a
selection of DH parameters and choosing one at random for each new handshake,
or again rolling them over from time to time.

>I might have missed, but where is the specification of the acceptable
>signature algorithms (hash especially) on Server and Client Key Exchange
>messages?

That's implicit in the cipher suites, RSA or ECDSA + SHA256.

Peter.