Add MAC'd PC comms

5 files changed, 119 insertions, 59 deletions

diff --git a/arduino/src/.pc.cpp.swp b/arduino/src/.pc.cpp.swp
new file mode 100644
index 0000000..2c4fdeb
--- /dev/null
+++ b/arduino/src/.pc.cpp.swp
diff --git a/arduino/src/config.h b/arduino/src/config.h
index 126e51f..83597cf 100644
--- a/arduino/src/config.h
+++ b/arduino/src/config.h
@@ -21,7 +21,12 @@
 //#define DEBUG_KEYPAD_SIM 1
 /** Max length of message from rfid reader. */
 #define RF_MAX_BYTES (16)
+/** Length of MAC **/
+#define PC_MAC_SIZE (32)
 /** Max length of message from or to PC. */
-#define PC_MAX_BYTES (2+1+4+1+EMEM_HASH_SIZE*2+1+8+1)
+#define PC_MAX_BYTES (2+1+4+1+EMEM_HASH_SIZE*2+1+PC_MAC_SIZE*2+1)
 /** Period for quering rfid reader. */
 #define RF_PERIOD_MS (500)
+
+/** PC Communications MAC secret **/
+#define PC_MAC_SECRET ("hackme")
diff --git a/arduino/src/doorman.ino b/arduino/src/doorman.ino
index 384e936..10fba30 100644
--- a/arduino/src/doorman.ino
+++ b/arduino/src/doorman.ino
@@ -21,8 +21,9 @@
 #include "rf.h"
 #include "emem.h"
 
-//Global var
-unsigned char global_hash[EMEM_HASH_SIZE];
+// Global var
+/** Used to pass current command hash **/
+unsigned char g_Hash[EMEM_HASH_SIZE];
 /** Door control pin. */
 #define DOOR_CTRN (4)
 
diff --git a/arduino/src/emem.cpp b/arduino/src/emem.cpp
index 50fa99d..ae9fc83 100644
--- a/arduino/src/emem.cpp
+++ b/arduino/src/emem.cpp
@@ -4,7 +4,7 @@
 #include "config.h"
 
 // from doorman.ino
-extern unsigned char global_hash[];
+extern unsigned char g_Hash[];
 
 /**
  * Function reads record with given address from EEPROM. 
@@ -120,17 +120,17 @@ boolean emem_set_record(unsigned int adr,unsigned char * data) {
 void emem_print() {  
   unsigned int id;  
   for (int ii=0;ii<EMEM_HASH_SIZE;ii++){
-    global_hash[ii] = 0;
+    g_Hash[ii] = 0;
   }
   for (int ii=ENEM_MIN_ADR;ii<=EMEM_MAX_ADR;ii++){
-    if (emem_get_record(ii,&id,global_hash)){
+    if (emem_get_record(ii,&id,g_Hash)){
       Serial.print("REC,");
       Serial.print(ii,HEX);
       Serial.print(',');
       Serial.print(id,HEX);
       for (int jj=0;jj<EMEM_HASH_SIZE;jj++){
         Serial.print(',');
-        Serial.print(*(global_hash+jj),HEX);   
+        Serial.print(*(g_Hash+jj),HEX);   
       }
       Serial.println();
     } else {
diff --git a/arduino/src/pc.cpp b/arduino/src/pc.cpp
index 5c5841c..fb340b4 100644
--- a/arduino/src/pc.cpp
+++ b/arduino/src/pc.cpp
@@ -1,17 +1,21 @@
 #include <Arduino.h>
 #include <EEPROM.h>
 
+#include "sha256.h"
+
 #include "config.h"
 #include "pc.h"
 #include "emem.h"
 
-/** Global vatiable that holds last message from PC. Lenght is plus one for zero termination. */
+/** Global variable that holds last message from PC. Length is plus one for zero termination. */
 char pc_bytes[PC_MAX_BYTES+1];
 /** Flag set when next scan should send mid. */
 boolean pc_send_flag = false;
+/** Global varuiable that holds last MAC from PC. Length is 32 bytes, no termination. */
+unsigned char pc_mac[PC_MAC_SIZE];
 
 // from doorman.ino
-extern unsigned char global_hash[];
+extern unsigned char g_Hash[];
 
 /**
  * Function receives bytes from PC and parses them into message.
@@ -25,7 +29,7 @@ boolean pc_parse(){
     //read the incoming byte:
     in = Serial.read();
     if (in=='$') {
-      //Start
+      //Start condition
       pc_idx=0;
       pc_bytes[pc_idx]=in; 
       continue;
@@ -35,7 +39,7 @@ boolean pc_parse(){
       Serial.print("Got newline ");
       Serial.println(pc_idx);
 #endif //DEBUG
-      // what the fuck?
+      // Did we match the required length?
       if (pc_idx==PC_MAX_BYTES-2) {;
         pc_bytes[pc_idx+1]=in;
         pc_idx=0;
@@ -88,41 +92,62 @@ void pc_print(char code,unsigned int id,unsigned char * data) {
 
 /**
  * Handles communication with PC.
+ * Message structure is:
+ *  $<code>,<id>,<hash/data>,<token>,newline
+ * eg.:
+ *  $a,0000,dfdd69691a7af8c141cef1ce69b5196b327f71f40b54da3c4e673283dcebd9b7,\
+ *  e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
+ * where code is a command code, hash/data is a 32-byte piece of data in
+ * lowercase hexdigest, and token is a 32-byte MAC in lowecase hexdigest
+ *   
  */
 void pc_comm(){  
   if (pc_parse()){
 #ifdef DEBUG    
     Serial.print("I received: ");
     for (int ii=0;ii<PC_MAX_BYTES;ii++) {
-      Serial.print(pc_bytes[ii], HEX);
+      Serial.print(pc_bytes[ii]);
     }
 #endif //DEBUG
     pc_bytes[PC_MAX_BYTES]=0;
-    char code = 0;
-    unsigned int id = 0;
 
-    for (int ii=0;ii<EMEM_HASH_SIZE;ii++){
-      global_hash[ii]=0;
+    // Zero global hash
+    for (int i = 0; i < EMEM_HASH_SIZE; i++) {
+      g_Hash[i] = 0;
+    }
+    // Zero given MAC
+    for (int i = 0; i < PC_MAC_SIZE; i++) {
+      pc_mac[i] = 0;
     }
-    unsigned long token = 0;
  
-    //$a,0000,dfdd69691a7af8c141cef1ce69b5196b327f71f40b54da3c4e673283dcebd9b7,386855c3
-    code=pc_bytes[1];
-    char ids[5];
-    for (int ii=0;ii<4;ii++){
-      ids[ii]=pc_bytes[ii+3];
+    // Get code
+    char code = pc_bytes[1];
+    // Get ID
+    char id_string[5];
+    for (int i = 0; i < 4; i++) {
+      id_string[i] = pc_bytes[3 + i];
     }
-    ids[4]='\0';
-    sscanf(ids,"%d",&id);
-    for (int ii=0;ii<32;ii++){
+    id_string[4] = '\0';
+    unsigned short id;
+    sscanf(id_string, "%d", &id);
+
+    // Get hash
+    for (int i = 0; i < EMEM_HASH_SIZE; i++) {
       char hex[3];
-      hex[0]= pc_bytes[ii*2+8];
-      hex[1]= pc_bytes[ii*2+8+1];
-      hex[2]= 0;
-      sscanf(hex,"%02x",global_hash+ii);
+      hex[0] = pc_bytes[8+i*2];
+      hex[1] = pc_bytes[8+i*2+1];
+      hex[2] = 0;
+      sscanf(hex, "%02x", g_Hash + i);
     }
-    sscanf(pc_bytes+32*2+8+1,"%8lx",&token);
 
+    // Get MAC
+    for (int i = 0; i < PC_MAC_SIZE; i++) {
+      char hex[3];
+      hex[0] = pc_bytes[73+i*2];
+      hex[1] = pc_bytes[73+i*2+1];
+      hex[2] = 0;
+      sscanf(hex, "%02x", pc_mac + i);
+    }
       
 #ifdef DEBUG    
     Serial.print("CODE: ");
@@ -130,63 +155,92 @@ void pc_comm(){
     Serial.print(", ID: ");
     Serial.print(id, HEX);
     Serial.print(", HASH: ");
-    for (int ii=0; ii<EMEM_HASH_SIZE; ii++){
-      Serial.print(global_hash[ii], HEX);
+    for (int i = 0; i < EMEM_HASH_SIZE; i++) {
+      Serial.print(g_Hash[i], HEX);
       Serial.print(',');
     }  
     Serial.print(" TOKEN: ");    
-    Serial.print(token>>24 & 0x0ff, HEX);    
-    Serial.print(',');
-    Serial.print(token>>16 & 0x0ff, HEX);    
-    Serial.print(',');
-    Serial.print(token>>8 & 0x0ff, HEX);
-    Serial.print(',');
-    Serial.print(token & 0x0ff, HEX);
-    Serial.println();    
-    
+    for (int i = 0; i < PC_MAC_SIZE; i++) {
+      Serial.print(pc_mac[i], HEX);
+      if (i == PC_MAC_SIZE - 1)
+        Serial.println("");
+      else
+        Serial.print(',');
+    }  
+
+    // Check MAC
+    pc_bytes[1+1+1+4+1+EMEM_HASH_SIZE*2] = '\0';
+#ifdef DEBUG
+    Serial.print("MACing ");
+    Serial.println(pc_bytes);
+#endif //DEBUG
+    Sha256.initHmac((const uint8_t *)PC_MAC_SECRET, strlen(PC_MAC_SECRET));
+    Sha256.print(pc_bytes);
+    uint8_t *expected_mac = Sha256.resultHmac();
+    // anti-timing attack - xor all MAC bytes together, or-fold, check if null
+    uint8_t mac_result = 0;
+    for (int i = 0; i < PC_MAC_SIZE; i++) {
+      mac_result |= (pc_mac[i] ^ expected_mac[i]);
+    }
+#ifdef DEBUG
+    Serial.print("Expected MAC: ");
+    for (int i = 0; i < PC_MAC_SIZE; i++) {
+      Serial.print(expected_mac[i], HEX);
+      Serial.print(',');
+    }
+    Serial.println("");
+#endif
           
 #endif //DEBUG
-    if (0){
+    if (mac_result != 0){
 #ifdef DEBUG    
       Serial.println("WRONG TOKEN");
 #endif //DEBUG
-      pc_print('E', id, global_hash);  
-    } else if (pc_bytes[1]=='A' || pc_bytes[1]=='a'){
+      pc_print('E', id, g_Hash);  
+      return;
+    }
+   
+    if (code == 'A' || code == 'a') {
       //Add
-      if (id == 0)
-      {
+      if (id == 0) {
         id = emem_find_free();
       }
-      if (emem_find_data(global_hash)!=EMEM_INV_ADR){
+      if (emem_find_data(g_Hash) != EMEM_INV_ADR) {
         //Already have this data
 #ifdef DEBUG
         Serial.println("ADD FAILED, USER EXISTS");
 #endif 
-        pc_print('E',id,global_hash);
-      } else if (emem_set_record(id,global_hash)){
+        pc_print('E', id, g_Hash);
+        return;
+      }
+      if (emem_set_record(id, g_Hash)) {
 #ifdef DEBUG    
         Serial.println("ADD DONE");
 #endif //DEBUG
-        pc_print('C',id,global_hash);  
-      } else {
+        pc_print('C', id, g_Hash);  
+        return;
+      }
+
 #ifdef DEBUG    
-        Serial.println("ADD FAILED");
+      Serial.println("ADD FAILED");
 #endif //DEBUG
-        pc_print('E',id,global_hash);  
-      }
-    } else if (pc_bytes[1]=='R' || pc_bytes[1]=='r'){
-//        //Revoke
-      if (id==0) id=emem_find_data(global_hash);
+      pc_print('E', id, g_Hash);  
+      return;
+    }
+    
+    if (pc_bytes[1]=='R' || pc_bytes[1]=='r') {
+      if (id == 0)
+        id=emem_find_data(g_Hash);
       if (emem_del_record(id)){
 #ifdef DEBUG    
         Serial.println("REVOKE DONE");  
 #endif //DEBUG    
-        pc_print('K',id,global_hash);
+        pc_print('K',id,g_Hash);
       } else {
 #ifdef DEBUG    
         Serial.println("REVOKE FAILED");
 #endif //DEBUG    
-        pc_print('E',id,global_hash);
+        pc_print('E',id,g_Hash);
       }
     } else if (pc_bytes[1]=='Z' || pc_bytes[1]=='z'){
       //Zero eeprom