Added compatibility between nodes on different Presets through Mesh via UDP

src/mesh/Channels.cpp

@@ -422,6 +422,29 @@ bool Channels::decryptForHash(ChannelIndex chIndex, ChannelHash channelHash)
     }
 }
 
+bool Channels::setDefaultPresetCryptoForHash(ChannelHash channelHash)
+{
+    // Iterate all known presets
+    for (int preset = _meshtastic_Config_LoRaConfig_ModemPreset_MIN; preset <= _meshtastic_Config_LoRaConfig_ModemPreset_MAX; ++preset) {
+        const char *name = DisplayFormatters::getModemPresetDisplayName((meshtastic_Config_LoRaConfig_ModemPreset)preset, false);
+        if (!name) continue;
+        if (strcmp(name, "Invalid") == 0) continue; // skip invalid placeholder
+        uint8_t h = xorHash((const uint8_t *)name, strlen(name));
+        // Expand default PSK alias 1 to actual bytes and xor into hash
+        uint8_t tmp = h ^ xorHash(defaultpsk, sizeof(defaultpsk));
+        if (tmp == channelHash) {
+            // Set crypto to defaultpsk and report success
+            CryptoKey k;
+            memcpy(k.bytes, defaultpsk, sizeof(defaultpsk));
+            k.length = sizeof(defaultpsk);
+            crypto->setKey(k);
+            LOG_INFO("Matched default preset '%s' for hash 0x%x; set default PSK", name, channelHash);
+            return true;
+        }
+    }
+    return false;
+}
+
 /** Given a channel index setup crypto for encoding that channel (or the primary channel if that channel is unsecured)
  *
  * This method is called before encoding outbound packets

src/mesh/Channels.h

@@ -94,6 +94,8 @@ class Channels
 
     bool ensureLicensedOperation();
 
+    bool setDefaultPresetCryptoForHash(ChannelHash channelHash);
+
   private:
     /** Given a channel index, change to use the crypto key specified by that index
      *

src/mesh/FloodingRouter.cpp

@@ -68,6 +68,13 @@ bool FloodingRouter::isRebroadcaster()
 void FloodingRouter::perhapsRebroadcast(const meshtastic_MeshPacket *p)
 {
     if (!isToUs(p) && (p->hop_limit > 0) && !isFromUs(p)) {
+        // If this packet arrived via UDP and is still encrypted, skip rebroadcast.
+        // We expect the router to decode and then re-encode to our local preset before sending.
+        if (p->transport_mechanism == meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MULTICAST_UDP &&
+            p->which_payload_variant == meshtastic_MeshPacket_encrypted_tag) {
+            LOG_DEBUG("Skip rebroadcast of UDP-encrypted packet; awaiting local decode/re-encode");
+            return;
+        }
         if (p->id != 0) {
             if (isRebroadcaster()) {
                 meshtastic_MeshPacket *tosend = packetPool.allocCopy(*p); // keep a copy because we will be sending it

src/mesh/Router.cpp

@@ -416,6 +416,27 @@ DecodeState perhapsDecode(meshtastic_MeshPacket *p)
             }
         }
     }
+
+    // Fallback: for UDP multicast, try default preset names with default PSK if normal channel match failed
+    if (!decrypted && p->transport_mechanism == meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MULTICAST_UDP) {
+        if (channels.setDefaultPresetCryptoForHash(p->channel)) {
+            memcpy(bytes, p->encrypted.bytes, rawSize);
+            crypto->decrypt(p->from, p->id, rawSize, bytes);
+
+            meshtastic_Data decodedtmp;
+            memset(&decodedtmp, 0, sizeof(decodedtmp));
+            if (pb_decode_from_bytes(bytes, rawSize, &meshtastic_Data_msg, &decodedtmp) &&
+                decodedtmp.portnum != meshtastic_PortNum_UNKNOWN_APP) {
+                p->decoded = decodedtmp;
+                p->which_payload_variant = meshtastic_MeshPacket_decoded_tag;
+                // Map to our primary channel index so subsequent processing and re-encoding use local preset
+                chIndex = channels.getPrimaryIndex();
+                decrypted = true;
+            } else {
+                LOG_WARN("UDP fallback decode attempted but failed for hash 0x%x", p->channel);
+            }
+        }
+    }
     if (decrypted) {
         // parsing was successful
         p->channel = chIndex; // change to store the index instead of the hash

src/mesh/udp/UdpMulticastHandler.h

@@ -54,6 +54,7 @@ class UdpMulticastHandler final
         LOG_DEBUG("Decoding MeshPacket from UDP len=%u", packetLength);
         bool isPacketDecoded = pb_decode_from_bytes(packet.data(), packetLength, &meshtastic_MeshPacket_msg, &mp);
         if (isPacketDecoded && router && mp.which_payload_variant == meshtastic_MeshPacket_encrypted_tag) {
+            mp.transport_mechanism = meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MULTICAST_UDP;
             mp.pki_encrypted = false;
             mp.public_key.size = 0;
             memset(mp.public_key.bytes, 0, sizeof(mp.public_key.bytes));