On 15.05.2013 20:52, Dave Thompson wrote:

> I can't easily test at the moment (even assuming your client is OpenSSL), 
> but I speculate that in SSL3 mode the client doesn't send (Client)Hello 
> extensions for SupportedCurves and SupportedPointFormats,

Correct.

> and in TLS 
> mode(s?) it does.

Correct again.

> If those extensions are present but don't include 
> the named curve or unnamed generic type (your case) and pointformat 
> used by your EC cert/key,

Pointformat shouldn't be the problem as I'm not using point compression.
But indeed the TLS 1.2 client only sends a list of 25 permissible
curves. Only sect/secp are included curiously although my openssl client
does internally also know, for example, about the wap-wsg and X9.62
curves. But those are not included in the Client Hello request.

And there's definitely no "unnamed generic type" included in the
request. Is there any way I can make openssl include that?

> OpenSSL server logic won't consider that 
> EC cert/key as a candidate for this client/session. Unless there's 
> another cert/key configured, or non-PK alternatives like PSK or SRP,
> acceptable to the client, you'll get "no shared cipher".

This is highly problematic, as custom curves (like the Brainpool curves
I need to use, which aren't even included in stock openssl) are then
therefore rendered dysfunctional.

Even worse is that even if I would somehow get the s_client/s_server
test running, I ultimately need to transfer the results to openvpn
(where I have even less control about openssl intrinsics).

You mentioned that you aren't able to easily reproduce this -- I could
provide either complete keys/certificates for testing purposes or a pcap
dump (just did it to confirm your assertions about SupportedCurves and
SupportedPointFormats held true). Is either going to be helpful to you?

Best regards,
Johannes
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