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, 8 insertions, 1 deletions

diff --git a/CHANGES b/CHANGES
index 8600b8166c..397ff2c6e1 100644
--- a/CHANGES
+++ b/CHANGES
@@ -396,7 +396,14 @@
      whose return value is often ignored. 
      [Steve Henson]
 
- Changes between 1.0.2 and 1.0.2a [xx XXX xxxx]
+ Changes between 1.0.2a and 1.0.2b [xx XXX xxxx]
+
+  *) Only support 256-bit or stronger elliptic curves with the
+     'ecdh_auto' setting (server) or by default (client). Of supported
+     curves, prefer P-256 (both).
+     [Emilia Kasper]
+
+ Changes between 1.0.2 and 1.0.2a [19 Mar 2015]
 
   *) ClientHello sigalgs DoS fix