I support this. It increases privacy, increase protection against implementation bugs (which have been common), and significantly simplifies analysis of the protocol and future extensions. Ephemeral and static keys should never use the same code point without additional negotiation.
Cheers, John Preuß Mattsson On Sun, Mar 15, 2026 at 9:25 PM Martin Thomson <[email protected]<mailto:[email protected]>> wrote: Proposal: Prohibit key share reuse in TLS 1.3. Reason: TLS security depends on uniqueness of key shares. In ECDH, it can be sufficient for one peer to generate a fresh share. However, a recommendation against reuse does not prevent BOTH peers from reusing shares. In that case, session transcripts will only be divergent based on {Client|Server}Hello.random. The shared secrets will be duplicated between connections. This is a bad outcome. Fixing that could be achieved with signaling or rules. ... or simply prohibiting key share reuse. The reasons we tolerated reuse in the past remain, but their relevance has faded: it is now more likely the case that fresh keygen for every connection is sufficiently cheap that the added code for reuse isn't worth it. Logistics: TLS 1.3 is in AUTH48. So this isn't trivial from a procedural perspective. However. I think that this is trivial from a text perspective. I think that it's worthwhile if possible. _______________________________________________ TLS mailing list -- [email protected]<mailto:[email protected]> To unsubscribe send an email to [email protected]<mailto:[email protected]>
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