EAP-TLS with TLS 1.3

[Stefan Winter]

Hi,

I'm currently looking at
https://www.ietf.org/id/draft-mattsson-eap-tls13-02.txt.

It states that:

   While Elliptic Curve Cryptography (ECC) was optional for earlier
   version of TLS, TLS 1.3 mandates support of ECC (see Section 9 of
   [I-D.ietf-tls-tls13]).  To avoid fragmentation, the use of ECC in
   certificates, signature algorithms, and groups are RECOMMENDED when
   using EAP-TLS with TLS 1.3 or higher.

That sounds like useful avice.

I'm wondering though what to do if you have a diverse variety of client
devices doing EAP; some of which only do TLS 1.2 while others do TLS 1.3.

The EAP server can only present one certificate to its incoming peer
connections.

If it has a ECDSA certificate, there's a chance for an interop problem
with TLS 1.2 clients not supporting the needed cipher suites.

If it has a RSA certificate, it misses out on the small-cert benefits.

I wonder if it's possible to have both certificates available to the
server, with a late selection: depending on which TLS version has been
negotiated, present one cert or the other.

Is that kind of stuff doable?

It would certainly make a transition easier...

Greetings,

Stefan Winter

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