Only support >= 256-bit elliptic curves with ecdh_auto (server) or by default (client).

Also reorder preferences to prefer prime curves to binary curves, and P-256 to everything else.

The result:

$ openssl s_server -named_curves "auto"

This command will negotiate an ECDHE ciphersuite with P-256:

$ openssl s_client

This command will negotiate P-384:

$ openssl s_client -curves "P-384"

This command will not negotiate ECDHE because P-224 is disabled with "auto":

$ openssl s_client -curves "P-224"

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>

1 files changed, 2 insertions, 5 deletions

diff --git a/test/ssltest.c b/test/ssltest.c
index 95ba1a0..136bf9a 100644
--- a/test/ssltest.c
+++ b/test/ssltest.c
@@ -1494,12 +1494,9 @@ int main(int argc, char *argv[])
                 BIO_printf(bio_err, "unknown curve name (%s)\n", named_curve);
                 goto end;
             }
-        } else
-# ifdef OPENSSL_NO_EC2M
+        } else {
             nid = NID_X9_62_prime256v1;
-# else
-            nid = NID_sect163r2;
-# endif
+        }
 
         ecdh = EC_KEY_new_by_curve_name(nid);
         if (ecdh == NULL) {