add optional assymetric payload encryption

This patch uses the NaCL library to en-/decrypt and authenticate the
payload suitable private and public keys are found. It
- adds crypto.h, containing all crypto logic (including the detection
  if the packet is to be en-/decrypted)
- adds nacl dependency to Makefile (including a switch between
  internal and external nacl)

It also
- changes Makefile to build with -Werror -Wextra
- builds warning-free

1 files changed, 13 insertions, 0 deletions

diff --git a/common.h b/common.h
index 5ce3c61..1a1bd5e 100644
--- a/common.h
+++ b/common.h
@@ -9,6 +9,10 @@
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/types.h>
+#include <net/if.h>
+#include <unistd.h>
+
+typedef unsigned char byte;
 
 /* the port users will be connecting to */
 #define SERVERPORT 4950
@@ -25,4 +29,13 @@
     exit(1);			\
   }
 
+#define E0P(Cmd, Msg) \
+  if ((Cmd) == NULL) {		\
+    perror(Msg);		\
+    exit(1);			\
+  }
+
+#define IGN(Cmd) \
+  if (Cmd) {}
+
 #endif // UDP_BROADCAST_COMMON