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@ -82,7 +82,8 @@
<li><a href="#message-interval">9.2 Message Interval</a><ul></ul></li></ul></li>
<li><a href="#rerun-the-firmware">10 Rerun The Firmware</a><ul>
<li><a href="#check-lorawan-gateway-1">10.1 Check LoRaWAN Gateway</a><ul></ul></li></ul></li>
<li><a href="#lorawan-nonce">11 LoRaWAN Nonce</a><ul></ul></li>
<li><a href="#lorawan-nonce">11 LoRaWAN Nonce</a><ul>
<li><a href="#random-number-generator">11.1 Random Number Generator</a><ul></ul></li></ul></li>
<li><a href="#lorawan-event-loop">12 LoRaWAN Event Loop</a><ul></ul></li>
<li><a href="#nimble-porting-layer">13 NimBLE Porting Layer</a><ul></ul></li>
<li><a href="#gpio-interrupts">14 GPIO Interrupts</a><ul></ul></li>
@ -746,53 +747,81 @@ CHANNEL MASK: 0003</code></pre></div></li>
<p><img src="https://lupyuen.github.io/images/lorawan3-flow2.jpg" alt="Join LoRaWAN Network" /></p>
<h1 id="lorawan-nonce" class="section-header"><a href="#lorawan-nonce">11 LoRaWAN Nonce</a></h1>
<p><em>Why did we configure NuttX to provide a Strong Random Number Generator with Entropy Pool?</em></p>
<p>The Strong Random Number Generator fixes a <strong>Nonce Quirk</strong> in our LoRaWAN Library that we observed during development.</p>
<p>The Strong Random Number Generator fixes a <strong>Nonce Quirk</strong> in our LoRaWAN Library that we observed during development…</p>
<ul>
<li>
<p>Remember that our LoRaWAN Library <strong>sends a Nonce</strong> to the LoRaWAN Gateway every time it starts. (Pic above)</p>
</li>
<li>
<p>What’s a Nonce? It’s a <strong>Non-Repeating Number</strong> that prevents <a href="https://en.wikipedia.org/wiki/Replay_attack"><strong>Replay Attacks</strong></a></p>
</li>
<li>
<p>By default our LoRaWAN Library <strong>initialises the Nonce to 1</strong> and increments by 1 for every Join Network Request: 1, 2, 3, 4, …</p>
</li>
</ul>
<p>Now suppose the LoRaWAN Library <strong>crashes our device</strong> due to a bug. Watch what happens…</p>
<div><table><thead><tr><th><em>Our Device</em></th><th><em>LoRaWAN Gateway</em></th></tr></thead><tbody>
<tr><td>1️⃣ Here is Nonce 1</td><td></td></tr>
<tr><td></td><td>2️⃣ OK I accept Nonce 1</td></tr>
<tr><td>3️⃣ (Device crashes and restarts)</td><td></td></tr>
<tr><td>4️⃣ Here is Nonce 1</td><td></td></tr>
<tr><td></td><td>5️⃣ (Rejects Nonce 1 because it’s repeated)</td></tr>
<tr><td>6️⃣ Here is Nonce 2</td><td></td></tr>
<tr><td></td><td>7️⃣ OK I accept Nonce 2</td></tr>
<tr><td>8️⃣ (Device crashes and restarts)</td><td></td></tr>
</tbody></table>
</div>
<p>If our device keeps crashing, the LoRaWAN Gateway will eventually <strong>reject a whole bunch of Nonces</strong>: 1, 2, 3, 4, …</p>
<p>(Which makes development super slow and frustrating)</p>
<p>Thus we generate LoRaWAN Nonces with a <strong>Strong Random Number Generator</strong> instead.</p>
<p>(Random Numbers that won’t repeat upon restarting)</p>
<h2 id="random-number-generator" class="section-header"><a href="#random-number-generator">11.1 Random Number Generator</a></h2>
<p>TODO</p>
<p>From <a href="https://github.com/lupyuen/LoRaMac-node-nuttx/blob/master/src/nuttx.c#L140-L152">nuttx.c</a></p>
<div class="example-wrap"><pre class="language-c"><code>/// Get random devnonce from the Random Number Generator
SecureElementStatus_t SecureElementRandomNumber( uint32_t* randomNum ) {
// Open the Random Number Generator /dev/urandom
int fd = open(&quot;/dev/urandom&quot;, O_RDONLY);
assert(fd &gt; 0);
// Open the Random Number Generator /dev/urandom
int fd = open(&quot;/dev/urandom&quot;, O_RDONLY);
assert(fd &gt; 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(&quot;SecureElementRandomNumber: 0x%08lx\n&quot;, *randomNum);
return SECURE_ELEMENT_SUCCESS;
printf(&quot;SecureElementRandomNumber: 0x%08lx\n&quot;, *randomNum);
return SECURE_ELEMENT_SUCCESS;
}</code></pre></div>
<p>TODO</p>
<p>From <a href="https://github.com/lupyuen/LoRaMac-node-nuttx/blob/master/src/mac/LoRaMacCrypto.c#L980-L996">LoRaMacCrypto.c</a></p>
<div class="example-wrap"><pre class="language-c"><code>LoRaMacCryptoStatus_t LoRaMacCryptoPrepareJoinRequest( LoRaMacMessageJoinRequest_t* macMsg )
{
if( macMsg == 0 )
{
return LORAMAC_CRYPTO_ERROR_NPE;
}
KeyIdentifier_t micComputationKeyID = NWK_KEY;
<div class="example-wrap"><pre class="language-c"><code>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( &amp;devNonce );
CryptoNvm-&gt;DevNonce = devNonce;
// Get Nonce from Random Number Generator
uint32_t devNonce = 0;
SecureElementRandomNumber( &amp;devNonce );
CryptoNvm-&gt;DevNonce = devNonce;
#else
CryptoNvm-&gt;DevNonce++;
// Init Nonce to 1
CryptoNvm-&gt;DevNonce++;
#endif
macMsg-&gt;DevNonce = CryptoNvm-&gt;DevNonce;</code></pre></div>
macMsg-&gt;DevNonce = CryptoNvm-&gt;DevNonce;</code></pre></div>
<p>TODO</p>
<p>From <a href="https://github.com/lupyuen/LoRaMac-node-nuttx/blob/master/src/mac/LoRaMacCrypto.h#L58-L65">LoRaMacCrypto.h</a></p>
<div class="example-wrap"><pre class="language-c"><code>/*!
* 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__</code></pre></div>
<p><em>What happens if we don’t select the Entropy Pool?</em></p>
<p>TODO</p>
<p>Non Volatile Memory</p>
<p>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</p>
<p>TODO34</p>
<p><img src="https://lupyuen.github.io/images/lorawan3-chirpstack2a.png" alt="" /></p>