[openssl-dev] rejecting elliptic_curves/supported_groups in ServerHello (new behavior in master/1.1.1 vs 1.1.0)

[Dr. Stephen Henson]

On Wed, Oct 04, 2017, Mahesh Bhoothapuri wrote:

> Thanks for the hint.  The problem is fixed.
> 
> Server was setting:
> 
> if (SSL_CTX_set1_groups_list(ctx, "X25519:P-256") == 0) {
> //
> }
> 
> The call succeeds.
> 
> But the old TLS 1.2 code was setting:
> 
>             int nid = NID_X9_62_prime256v1;
>             EC_KEY* ecdh = EC_KEY_new_by_curve_name(nid);
>             if (ecdh == NULL)
>             {
>                //error
>             }
>             SSL_CTX_set_tmp_ecdh(ctx, ecdh);
> 
> After disabling this, the server responds with the right group - X25519.
> 

Yes that's the problem. By doing that you're replacing the groups list with a
single curve.

Steve.
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org