Enforcing group / key_share order in TLS1.3

Sebastian Andrzej Siewior openssl-dev at ml.breakpoint.cc
Mon Jan 13 22:21:37 UTC 2020

On 2020-01-13 11:23:35 [+0000], Matt Caswell wrote:
> The current behaviour is that the first key share we see that also
> exists in our supported groups list is the one that we use. There isn't
> a way at the moment to configure things in order to specify a preference
> order.
> https://github.com/openssl/openssl/blob/bbe486cf6154df3d3aaedbae6c5b82d4ed31a5f8/ssl/statem/extensions_srvr.c#L662-L720

Okay so there isn't a knob yet. Thank you for confirming.

> It wouldn't be too difficult to amend the above logic to select the key
> share that is highest in the server's supported group list. But that
> would be a new feature and wouldn't be backported to 1.1.1.
> PRs to make that change welcome.

Thanks, done.

> Matt

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