1 files changed, 19 insertions, 5 deletions

diff --git a/src/lib/libssl/ssl_tlsext.c b/src/lib/libssl/ssl_tlsext.c
index 4cb7c5bf90..a0e2f7320b 100644
--- a/src/lib/libssl/ssl_tlsext.c
+++ b/src/lib/libssl/ssl_tlsext.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.c,v 1.62 2020/02/18 16:12:14 tb Exp $ */
+/* $OpenBSD: ssl_tlsext.c,v 1.63 2020/04/21 17:06:16 jsing Exp $ */
 /*
  * Copyright (c) 2016, 2017, 2019 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -1288,13 +1288,27 @@ tlsext_keyshare_server_parse(SSL *s, CBS *cbs, int *alert)
                         return 0;
 
                 /*
-                 * XXX support other groups later.
-                 * XXX enforce group can only appear once.
+                 * XXX - check key exchange against supported groups from client.
+                 * XXX - check that groups only appear once.
                  */
-                if (S3I(s)->hs_tls13.key_share == NULL ||
-                    tls13_key_share_group(S3I(s)->hs_tls13.key_share) != group)
+
+                /*
+                 * Ignore this client share if we're using earlier than TLSv1.3
+                 * or we've already selected a key share.
+                 */
+                if (S3I(s)->hs_tls13.max_version < TLS1_3_VERSION)
+                        continue;
+                if (S3I(s)->hs_tls13.key_share != NULL)
                         continue;
 
+                /* XXX - consider implementing server preference. */
+                if (!tls1_check_curve(s, group))
+                        continue;
+
+                /* Decode and store the selected key share. */
+                S3I(s)->hs_tls13.key_share = tls13_key_share_new(group);
+                if (S3I(s)->hs_tls13.key_share == NULL)
+                        goto err;
                 if (!tls13_key_share_peer_public(S3I(s)->hs_tls13.key_share,
                     group, &key_exchange))
                         goto err;