[openssl-users] ecc negotiation

Matt Caswell matt at openssl.org
Sun Apr 5 22:46:00 UTC 2015

On 05/04/15 23:42, Matt Caswell wrote:
> On 05/04/15 22:04, David Rufino wrote:
>> Hello, 
>> It's possible I'm doing something wrong here, but I can't seem to
>> negotiate ecdhe with an elliptic curve other than P-256. To reproduce
>> the issue, using openssl 1.0.2 
>> openssl s_server  -key server.key -cert server.crt -msg -debug -dhparam
>> dhparam.pem  -cipher ECDHE-RSA-AES128-SHA -tls1_2 
>> gnutls-cli -p 4433 -d 4 --insecure
>> which gives the error 
>> :SSL routines:ssl3_get_client_hello:no shared cipher:s3_srvr.c:1366: 
>> changing to p256r1 succeeds. is there a particular why the negotation
>> would fail with p224 ? my understanding is that openssl supports all the
>> nist curves. 
> Try adding "-named_curve secp224r1" to your s_server arguments. This
> specifies the curve to use for ECDHE keys. The default if you don't
> specify a named curve is P-256 which is why it works when you are using
> that curve.

BTW, you can also use "-named_curve auto", which will just pick an
appropriate curve.


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