diff --git a/articles/lorawan3.html b/articles/lorawan3.html index 39613f32e..982447ea5 100644 --- a/articles/lorawan3.html +++ b/articles/lorawan3.html @@ -82,7 +82,8 @@
  • 9.2 Message Interval
  • 10 Rerun The Firmware
    • -
  • 11 LoRaWAN Nonce
    • +
  • 11 LoRaWAN Nonce
  • 12 LoRaWAN Event Loop
  • 13 NimBLE Porting Layer
  • 14 GPIO Interrupts
    • @@ -746,53 +747,81 @@ CHANNEL MASK: 0003

    Join LoRaWAN Network

    11 LoRaWAN Nonce

    Why did we configure NuttX to provide a Strong Random Number Generator with Entropy Pool?

    -

    The Strong Random Number Generator fixes a Nonce Quirk in our LoRaWAN Library that we observed during development.

    +

    The Strong Random Number Generator fixes a Nonce Quirk in our LoRaWAN Library that we observed during development…

    + +

    Now suppose the LoRaWAN Library crashes our device due to a bug. Watch what happens…

    +
    + + + + + + + + +
    Our DeviceLoRaWAN Gateway
    1️⃣ Here is Nonce 1
    2️⃣ OK I accept Nonce 1
    3️⃣ (Device crashes and restarts)
    4️⃣ Here is Nonce 1
    5️⃣ (Rejects Nonce 1 because it’s repeated)
    6️⃣ Here is Nonce 2
    7️⃣ OK I accept Nonce 2
    8️⃣ (Device crashes and restarts)
    +
    +

    If our device keeps crashing, the LoRaWAN Gateway will eventually reject a whole bunch of Nonces: 1, 2, 3, 4, …

    +

    (Which makes development super slow and frustrating)

    +

    Thus we generate LoRaWAN Nonces with a Strong Random Number Generator instead.

    +

    (Random Numbers that won’t repeat upon restarting)

    +

    11.1 Random Number Generator

    TODO

    From nuttx.c

    /// Get random devnonce from the Random Number Generator
 SecureElementStatus_t SecureElementRandomNumber( uint32_t* randomNum ) {
-    //  Open the Random Number Generator /dev/urandom
-    int fd = open("/dev/urandom", O_RDONLY);
-    assert(fd > 0);
+  //  Open the Random Number Generator /dev/urandom
+  int fd = open("/dev/urandom", O_RDONLY);
+  assert(fd > 0);
 
-    //  Read the random number
-    read(fd, randomNum, sizeof(uint32_t));
-    close(fd);
+  //  Read the random number
+  read(fd, randomNum, sizeof(uint32_t));
+  close(fd);
 
-    printf("SecureElementRandomNumber: 0x%08lx\n", *randomNum);
-    return SECURE_ELEMENT_SUCCESS;
+  printf("SecureElementRandomNumber: 0x%08lx\n", *randomNum);
+  return SECURE_ELEMENT_SUCCESS;
 }

    TODO

    From LoRaMacCrypto.c

    -
    LoRaMacCryptoStatus_t LoRaMacCryptoPrepareJoinRequest( LoRaMacMessageJoinRequest_t* macMsg )
-{
-    if( macMsg == 0 )
-    {
-        return LORAMAC_CRYPTO_ERROR_NPE;
-    }
-    KeyIdentifier_t micComputationKeyID = NWK_KEY;
+
    LoRaMacCryptoStatus_t LoRaMacCryptoPrepareJoinRequest( LoRaMacMessageJoinRequest_t* macMsg ) {
+  if( macMsg == 0 ) {
+    return LORAMAC_CRYPTO_ERROR_NPE;
+  }
+  KeyIdentifier_t micComputationKeyID = NWK_KEY;
 
-    // Add device nonce
 #if ( USE_RANDOM_DEV_NONCE == 1 )
-    uint32_t devNonce = 0;
-    SecureElementRandomNumber( &devNonce );
-    CryptoNvm->DevNonce = devNonce;
+  //  Get Nonce from Random Number Generator
+  uint32_t devNonce = 0;
+  SecureElementRandomNumber( &devNonce );
+  CryptoNvm->DevNonce = devNonce;
 #else
-    CryptoNvm->DevNonce++;
+  //  Init Nonce to 1
+  CryptoNvm->DevNonce++;
 #endif
-    macMsg->DevNonce = CryptoNvm->DevNonce;
    
+  macMsg->DevNonce = CryptoNvm->DevNonce;

    TODO

    From LoRaMacCrypto.h

    /*!
  * Indicates if a random devnonce must be used or not
  */
 #ifdef __NuttX__  //  For NuttX: Get random devnonce from the Random Number Generator
-#define USE_RANDOM_DEV_NONCE                        1
+#define USE_RANDOM_DEV_NONCE 1
 #else
-#define USE_RANDOM_DEV_NONCE                        0
+#define USE_RANDOM_DEV_NONCE 0
 #endif  //  __NuttX__

    What happens if we don’t select the Entropy Pool?

    TODO

    +

    Non Volatile Memory

    Our #NuttX App resends the same Nonce to the #LoRaWAN Gateway … Which (silently) rejects the Join Request due to Duplicate Nonce … Let’s fix our Random Number Generator

    TODO34