[openssl-users] ecc negotiation

[Matt Caswell]

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 127.0.0.1 -p 4433 -d 4 --insecure
>> --priority="NORMAL:-KX-ALL:+ECDHE-RSA:-CURVE-ALL:+CURVE-SECP224R1" 
>>
>> 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.

Matt