From 3303c77e2a46bab857ef57d6171a93eb2833bd7c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?King=20K=C3=A9vin?= <kingkevin@cuvoodoo.info>
Date: Tue, 10 Nov 2015 22:32:28 +0100
Subject: [PATCH] add CRC in receiver

---
 rpi/spark_counter_receiver.cpp | 60 ++++++++++++++++++++++++++++++----
 1 file changed, 53 insertions(+), 7 deletions(-)

diff --git a/rpi/spark_counter_receiver.cpp b/rpi/spark_counter_receiver.cpp
index ef6fe58..2ff4a6a 100644
--- a/rpi/spark_counter_receiver.cpp
+++ b/rpi/spark_counter_receiver.cpp
@@ -19,7 +19,6 @@
  * they are then stored in an InfluxDB time series database using the HTTP API
  * to send values to the database the curl library is required
  */
-
 #include <unistd.h>
 #include <string.h>
 #include <stdio.h>
@@ -29,6 +28,9 @@
 #include <RF24/RF24.h> // http://tmrh20.github.io/RF24 library to communicate to the nRF24L01+
 #include <curl/curl.h> // curl library to send the measurement data to the influxDB.
 #include "aes.h" // AES library (from tiny-AES128-C)
+#include "crc16.h" // CRC Computations (from AVR libc)
+
+//#define DEBUG 1
 
 // Setup for RPi B1 GPIO 22 CE and CE0 CSN with SPI Speed @ 8Mhz
 RF24 radio(RPI_V2_GPIO_P1_22, BCM2835_SPI_CS0, BCM2835_SPI_SPEED_8MHZ);
@@ -77,32 +79,76 @@ int main(int argc, char** argv){
       uint8_t size = radio.getDynamicPayloadSize();
       radio.read(&payload,size);
 
-/*
+#ifdef DEBUG
       printf("got %d bytes:",size);
       for (uint8_t i=0; i<size; i++) {
         printf(" %02x",payload[i]);
       }
       printf("\n");
-*/
+#endif
 
       // got through payload
-      if (size!=1+16) {
+      if (size!=1+4*4+1) {
+#ifdef DEBUG
+		printf("wrong size: expected %d, got %d\n",18,size);
+#endif
         continue;
       }
       uint8_t id = payload[0]; // the meter id (0 is myself, used for unknown source)
-      float voltage, current, power, energy; // the values coming from the meter
+      if (id!=1) { // there is only one source for power measurement
+#ifdef DEBUG
+        printf("wrong id: expected %d, got %d\n",1,id);
+#endif
+        continue;
+      }
       uint8_t values[16]; // the encrypted values block
-      AES128_ECB_decrypt(&payload[1], key, values); // decrypt payload
+      AES128_ECB_decrypt(&payload[1], key, values); // decrypt values
+#ifdef DEBUG
+      printf("decrypted values:");
+      for (uint8_t i=0; i<sizeof(values); i++) {
+        printf(" %02x",values[i]);
+      }
+      printf("\n");
+#endif
       for (uint8_t i=0; i<sizeof(values) && i<sizeof(iv); i++) { // use CBC mode
         values[i] ^= iv[i]; // XOR with last IV
       }
+#ifdef DEBUG
+      printf("XORed values:");
+      for (uint8_t i=0; i<sizeof(values); i++) {
+        printf(" %02x",values[i]);
+      }
+      printf("\n");
+#endif
       memcpy(iv,&payload[1],sizeof(iv)); // save next IV
+      // check CRC of plain values
+      uint8_t crc = 0;
+      for (uint8_t i = 0; i < sizeof(values); i++) {
+        crc = _crc_ibutton_update(crc, values[i]); // calculate CRC
+      }
+      crc = _crc_ibutton_update(crc, payload[17]); // this is the CRC
+      if (crc) { // wrong key or IV
+#ifdef DEBUG
+        printf("wrong CRC: expected %d, got %d\n",payload[17],crc);
+#endif
+        continue;
+      }
+      uint8_t invalid[sizeof(values)]; // used to indicate that the values are invalid
+      memset(invalid,0xff,sizeof(invalid)); // 0xff... is the invalid value
+      if (memcmp(invalid,values,sizeof(values))==0) { // values are invalid
+#ifdef DEBUG
+        printf("invalid values\n");
+#endif
+        continue;
+      }
+      // read values
+      float voltage, current, power, energy; // the values coming from the meter
       memcpy(&voltage,&values[0],4); // read voltage
       memcpy(&current,&values[4],4); // read current
       memcpy(&power,&values[8],4); // read power
       memcpy(&energy,&values[12],4); // read energy
-
       printf("meter: %d, voltage: %f V, current: %f A, power: %f W, energy: %f Wh\n",id,voltage,current,power,energy);
+      // submit values to database
       if (curl) {
         CURLcode res = CURLE_OK; // curl response
         char post[128*4] = {0}; // string to submit data to DB using POST request