Added XTEA and Pearson Hashing.

Improved message encryption for RF24.

core/MyMessage.h

@@ -36,9 +36,16 @@
 #include <stdint.h>
 #endif
 
+
 #define PROTOCOL_VERSION	(2u)	//!< The version of the protocol
 #define MAX_MESSAGE_LENGTH	(32u)	//!< The maximum size of a message (including header)
+#if (defined (MY_MESSAGE_ENABLE_HASH) && defined(MY_MESSAGE_ENABLE_NONCE))
+#define HEADER_SIZE			(11u)	//!< The size of the header
+#elif (defined (MY_MESSAGE_ENABLE_HASH) || defined(MY_MESSAGE_ENABLE_NONCE))
+#define HEADER_SIZE			(9u)	//!< The size of the header
+#else
 #define HEADER_SIZE			(7u)	//!< The size of the header
+#endif
 #define MAX_PAYLOAD (MAX_MESSAGE_LENGTH - HEADER_SIZE) //!< The maximum size of a payload depends on #MAX_MESSAGE_LENGTH and #HEADER_SIZE
 
 /// @brief The command field (message-type) defines the overall properties of a message
@@ -495,6 +502,15 @@ typedef union {
 	 * 3 bit - Payload data type
 	 */
 	uint8_t command_ack_payload;
+	
+#if defined (MY_MESSAGE_ENABLE_NONCE)
+	// The salt/nonce need to be in the first XTEA block
+	uint16_t _nounce; 		// 16 bit - nounce
+#endif
+
+#if defined (MY_MESSAGE_ENABLE_HASH)
+	uint16_t _hash;				// 16 bit - CRC16 checksum
+#endif
 
 	uint8_t type; ///< 8 bit - Type varies depending on command
 	uint8_t sensor; ///< 8 bit - Id of sensor that this message concerns.