Added support for encryption and decryption of the packetbuf if macros

NETSTACK_ENCRYPT and NETSTACK_DECRYPT are defined. Those are intended
to be called as functions NETSTACK_ENCRYPT() and NETSTACK_DECRYPT() to
encrypt and decrypt the packetbuf, respectively. If needed, an
initialization function by the name NETSTACK_ENCRYPTION_INIT() can
also be defined.

core/net/mac/contikimac.c

@@ -626,6 +626,12 @@ send_packet(mac_callback_t mac_callback, void *mac_callback_ptr, struct rdc_buf_
 
   packetbuf_compact();
 
+#ifdef NETSTACK_ENCRYPT
+  NETSTACK_ENCRYPT();
+#endif /* NETSTACK_ENCRYPT */
+
+  transmit_len = packetbuf_totlen();
+
   NETSTACK_RADIO.prepare(packetbuf_hdrptr(), transmit_len);
 
   /* Remove the MAC-layer header since it will be recreated next time around. */
@@ -915,7 +921,11 @@ input_packet(void)
   }
 
   /*  printf("cycle_start 0x%02x 0x%02x\n", cycle_start, cycle_start % CYCLE_TIME);*/
-  
+
+#ifdef NETSTACK_DECRYPT
+  NETSTACK_DECRYPT();
+#endif /* NETSTACK_DECRYPT */
+
   if(packetbuf_totlen() > 0 && NETSTACK_FRAMER.parse() >= 0) {
 
 #if WITH_CONTIKIMAC_HEADER

core/net/mac/nullrdc.c

@@ -114,6 +114,10 @@ send_packet(mac_callback_t sent, void *ptr)
     ret = MAC_TX_ERR_FATAL;
   } else {
 
+#ifdef NETSTACK_ENCRYPT
+    NETSTACK_ENCRYPT();
+#endif /* NETSTACK_ENCRYPT */
+
 #if NULLRDC_802154_AUTOACK
     int is_broadcast;
     uint8_t dsn;
@@ -213,6 +217,10 @@ send_list(mac_callback_t sent, void *ptr, struct rdc_buf_list *buf_list)
 static void
 packet_input(void)
 {
+#ifdef NETSTACK_DECRYPT
+    NETSTACK_DECRYPT();
+#endif /* NETSTACK_DECRYPT */
+
 #if NULLRDC_802154_AUTOACK
   if(packetbuf_datalen() == ACK_LEN) {
     /* Ignore ack packets */

core/net/netstack.c

@@ -46,5 +46,9 @@ netstack_init(void)
   NETSTACK_RDC.init();
   NETSTACK_MAC.init();
   NETSTACK_NETWORK.init();
+
+#ifdef NETSTACK_ENCRYPTION_INIT
+  NETSTACK_ENCRYPTION_INIT();
+#endif /* NETSTACK_ENCRYPTION_INIT */
 }
 /*---------------------------------------------------------------------------*/