Re: [TLS] Certificate keyUsage enforcement question (new in RFC8446 Appendix E.8)

Peter Gutmann <pgut001@cs.auckland.ac.nz> Fri, 09 November 2018 06:19 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: "<tls@ietf.org>" <tls@ietf.org>
Thread-Topic: [TLS] Certificate keyUsage enforcement question (new in RFC8446 Appendix E.8)
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Date: Fri, 9 Nov 2018 06:19:32 +0000
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Subject: Re: [TLS] Certificate keyUsage enforcement question (new in RFC8446 Appendix E.8)
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Viktor Dukhovni <ietf-dane@dukhovni.org> writes:

>Well, ECDH keys (not really ECDSA) can do key agreement, and EC keys can be
>used for encryption with ECIES.

Sure, in theory, but in practice I've never seen an (EC)DH cert used in TLS
(despite actively looking for one, since it'd be a collectors item for the
cert collection [0]), and I doubt most implementations could even deal with
one if they saw one.  Also, I don't think any TLS implementation, or
specification, does ECIES.  So it's pretty much self-regulating...

Peter.

[0] I know some test certs were generated about 20 years ago to demonstrate
    X9.42 use in S/MIME, but that's all I'm aware of.