ikev1: Add fragmentation support for Windows peers

I still think ipsec/l2tp with fragmentation support is a useful
fallback option in case the Windows IKEv2 connection fails because
of fragmentation problems.

Tested with Windows XP, 7 and 8.1.

src/libcharon/sa/ike_sa.c

@@ -16,6 +16,28 @@
  * for more details.
  */
 
+/*
+ * Copyright (c) 2014 Volker Rümelin
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
 #include <string.h>
 #include <sys/stat.h>
 #include <errno.h>
@@ -1024,6 +1046,14 @@ METHOD(ike_sa_t, generate_message_fragmented, status_t,
 				break;
 			case FRAGMENTATION_YES:
 				use_frags = supports_extension(this, EXT_IKE_FRAGMENTATION);
+				if (use_frags && this->version == IKEV1 &&
+					supports_extension(this, EXT_MS_WINDOWS))
+				{
+					/* It seems Windows 7 and 8 peers only accept proprietary
+					 * fragmented messages if they expect certificates. */
+					use_frags = message->get_payload(message,
+													 PLV1_CERTIFICATE) != NULL;
+				}
 				break;
 			default:
 				break;