+ /*
+ * If
+ * we are a server
+ * AND
+ * we have no key_share
+ * THEN
+ * If
+ * we didn't already send a HelloRetryRequest
+ * AND
+ * the client sent a key_share extension
+ * AND
+ * (we are not resuming
+ * OR the kex_mode allows key_share resumes)
+ * AND
+ * a shared group exists
+ * THEN
+ * send a HelloRetryRequest
+ * ELSE If
+ * we are not resuming
+ * OR
+ * the kex_mode doesn't allow non key_share resumes
+ * THEN
+ * fail;
+ */
+ if (s->server && s->s3->peer_tmp == NULL) {
+ /* No suitable share */
+ if (s->hello_retry_request == 0 && sent
+ && (!s->hit
+ || (s->ext.psk_kex_mode & TLSEXT_KEX_MODE_FLAG_KE_DHE)
+ != 0)) {
+ const unsigned char *pcurves, *pcurvestmp, *clntcurves;
+ size_t num_curves, clnt_num_curves, i;
+ unsigned int group_id;
+
+ /* Check a shared group exists */
+
+ /* Get the clients list of supported groups. */
+ if (!tls1_get_curvelist(s, 1, &clntcurves, &clnt_num_curves)) {
+ *al = SSL_AD_INTERNAL_ERROR;
+ SSLerr(SSL_F_FINAL_KEY_SHARE, ERR_R_INTERNAL_ERROR);
+ return 0;
+ }
+
+ /* Get our list of available groups */
+ if (!tls1_get_curvelist(s, 0, &pcurves, &num_curves)) {
+ *al = SSL_AD_INTERNAL_ERROR;
+ SSLerr(SSL_F_FINAL_KEY_SHARE, ERR_R_INTERNAL_ERROR);
+ return 0;
+ }
+
+ /* Find the first group we allow that is also in client's list */
+ for (i = 0, pcurvestmp = pcurves; i < num_curves;
+ i++, pcurvestmp += 2) {
+ group_id = pcurvestmp[0] << 8 | pcurvestmp[1];
+
+ if (check_in_list(s, group_id, clntcurves, clnt_num_curves, 1))
+ break;
+ }
+
+ if (i < num_curves) {
+ /* A shared group exists so send a HelloRetryRequest */
+ s->s3->group_id = group_id;
+ s->hello_retry_request = 1;
+ return 1;
+ }
+ }
+ if (!s->hit
+ || (s->ext.psk_kex_mode & TLSEXT_KEX_MODE_FLAG_KE) == 0) {
+ /* Nothing left we can do - just fail */
+ *al = SSL_AD_HANDSHAKE_FAILURE;
+ SSLerr(SSL_F_FINAL_KEY_SHARE, SSL_R_NO_SUITABLE_KEY_SHARE);
+ return 0;
+ }
+ }
+
+ /* We have a key_share so don't send any more HelloRetryRequest messages */
+ if (s->server)
+ s->hello_retry_request = 0;