Enhance channel key handling: unify retrieval for Public and hashtag channels, and clarify key derivation process in documentation

Author: MrAlders0n

.github/copilot-instructions.md

@@ -120,9 +120,14 @@ Used by `startAutoCountdown()`, `startRxListeningCountdown()`, cooldown logic.
 ### 2. Channel Hash & Decryption
 **Pre-computed at startup**:
 ```javascript
-WARDRIVING_CHANNEL_KEY = await deriveChannelKey("#wardriving");  // PBKDF2 SHA-256
+WARDRIVING_CHANNEL_KEY = await deriveChannelKey("#wardriving");  // SHA-256 for hashtag channels
 WARDRIVING_CHANNEL_HASH = await computeChannelHash(key);        // PSK channel identifier
 ```
+
+**Channel Key Types**:
+- **Hashtag channels** (`#wardriving`, `#testing`, `#ottawa`): Keys derived via SHA-256 of channel name
+- **Public channel** (`Public`, no hashtag): Uses fixed key `8b3387e9c5cdea6ac9e5edbaa115cd72` (default MeshCore channel)
+
 Used for:
 - Repeater echo detection (match `channelHash` in received packets)
 - Message decryption (AES-ECB via aes-js library)

content/wardrive.js

@@ -67,9 +67,16 @@ const ADVERT_HEADER = 0x11;                   // Header byte for ADVERT packets
 
 // RX Packet Filter Configuration
 const MAX_RX_PATH_LENGTH = 9;                 // Maximum path length for RX packets (drop if exceeded to filter corrupted packets)
-const RX_ALLOWED_CHANNELS = ['#wardriving', '#public', '#testing', '#ottawa']; // Allowed channels for RX wardriving
+const RX_ALLOWED_CHANNELS = ['#wardriving', 'Public', '#testing', '#ottawa']; // Allowed channels for RX wardriving (Public uses fixed key, hashtag channels use SHA-256 derivation)
 const RX_PRINTABLE_THRESHOLD = 0.80;          // Minimum printable character ratio for GRP_TXT (80%)
 
+// Fixed key for Public channel (default MeshCore channel without hashtag)
+// This is a well-known key used by all MeshCore devices for the default Public channel
+const PUBLIC_CHANNEL_FIXED_KEY = new Uint8Array([
+  0x8b, 0x33, 0x87, 0xe9, 0xc5, 0xcd, 0xea, 0x6a,
+  0xc9, 0xe5, 0xed, 0xba, 0xa1, 0x15, 0xcd, 0x72
+]);
+
 // Pre-computed channel hash and key for the wardriving channel
 // These will be computed once at startup and used for message correlation and decryption
 let WARDRIVING_CHANNEL_HASH = null;
@@ -94,7 +101,7 @@ let DEVICE_MODELS = [];
     // Initialize all allowed RX channels
     debugLog(`[INIT] Pre-computing hashes/keys for ${RX_ALLOWED_CHANNELS.length} allowed RX channels...`);
     for (const channelName of RX_ALLOWED_CHANNELS) {
-      const key = await deriveChannelKey(channelName);
+      const key = await getChannelKey(channelName);
       const hash = await computeChannelHash(key);
       RX_CHANNEL_MAP.set(hash, { name: channelName, key: key });
       debugLog(`[INIT] ${channelName} -> hash=0x${hash.toString(16).padStart(2, '0')}`);
@@ -1711,6 +1718,9 @@ async function primeGpsOnce() {
  * This allows any hashtag channel to be used (e.g., #wardriving, #wardrive, #test).
  * Channel names must start with # and contain only a-z, 0-9, and dashes.
  * 
+ * NOTE: This function is ONLY for hashtag channels. The "Public" channel (without hashtag)
+ * uses a fixed key defined in PUBLIC_CHANNEL_FIXED_KEY constant.
+ * 
  * Algorithm: sha256(channelName).subarray(0, 16)
  * 
  * @param {string} channelName - The hashtag channel name (e.g., "#wardriving")
@@ -1758,6 +1768,21 @@ async function deriveChannelKey(channelName) {
   return channelKey;
 }
 
+/**
+ * Get channel key for any channel (handles both Public and hashtag channels)
+ * Provides a unified interface for retrieving channel keys regardless of type
+ * @param {string} channelName - Channel name (e.g., "Public", "#wardriving", "#testing")
+ * @returns {Promise<Uint8Array>} The 16-byte channel key
+ */
+async function getChannelKey(channelName) {
+  if (channelName === 'Public') {
+    debugLog(`[CHANNEL] Using fixed key for Public channel`);
+    return PUBLIC_CHANNEL_FIXED_KEY;
+  } else {
+    return await deriveChannelKey(channelName);
+  }
+}
+
 // ---- Channel helpers ----
 async function createWardriveChannel() {
   if (!state.connection) throw new Error("Not connected");