diff --git a/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt b/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt
index da70abf..a29569d 100644
--- a/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt
+++ b/android/app/src/main/java/com/eddy/atomrelay/BleRelayManager.kt
@@ -7,6 +7,10 @@ import android.content.Context
 import android.os.Handler
 import android.os.Looper
 import java.util.UUID
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+import javax.crypto.Mac
+import javax.crypto.spec.SecretKeySpec
 
 class BleRelayManager(
     private val context: Context,
@@ -20,6 +24,8 @@ class BleRelayManager(
         private const val SCAN_TIMEOUT_MS = 30000L
         private const val RECONNECT_DELAY_MS = 2000L
         private const val MAX_SCAN_RETRIES = 3
+        private const val HMAC_PKT_SIZE = 37
+        private const val HMAC_LEN = 32
     }
 
     private var bluetoothGatt: BluetoothGatt? = null
@@ -37,9 +43,52 @@ class BleRelayManager(
     fun stopScan() {}
     fun sendRelayCommand(cmd: Byte) {}
     fun disconnect() {}
-    fun updateKeys() {}
-    fun resetTriedAddresses() {}
+    fun updateKeys() {
+        loadState()
+    }
+
+    fun resetTriedAddresses() {
+        triedAddresses.clear()
+    }
+
     fun hasPermissions(): Boolean = false
     fun getRequiredPermissions(): Array<String> = emptyArray()
-    fun destroy() {}
+
+    fun destroy() {
+        handler.removeCallbacksAndMessages(null)
+    }
+
+    private fun loadState() {
+        val prefs = PrefsHelper.getPrefs(context)
+        val hexKey = prefs.getString(PrefsHelper.PREF_KEY, null)
+        hmacKey = hexKey?.let { hexStringToBytes(it) }
+        val hexUuid = prefs.getString(PrefsHelper.PREF_UUID, null)
+        deviceUuid = hexUuid?.let { hexStringToBytes(it) }
+        seq = prefs.getInt(PrefsHelper.PREF_SEQ, 1).coerceAtMost(PrefsHelper.SEQ_MAX)
+    }
+
+    private fun hexStringToBytes(hex: String): ByteArray? {
+        val cleaned = hex.uppercase().filter { it in "0123456789ABCDEF" }
+        if (cleaned.isEmpty() || cleaned.length % 2 != 0) return null
+        return cleaned.chunked(2).map { it.toInt(16).toByte() }.toByteArray()
+    }
+
+    private fun hmacSha256(data: ByteArray, key: ByteArray): ByteArray {
+        val mac = Mac.getInstance("HmacSHA256")
+        mac.init(SecretKeySpec(key, "HmacSHA256"))
+        return mac.doFinal(data)
+    }
+
+    private fun buildPacket(cmd: Byte, key: ByteArray): ByteArray {
+        val seqBytes = ByteBuffer.allocate(4).order(ByteOrder.BIG_ENDIAN).putInt(seq).array()
+        val hmacData = ByteArray(5)
+        hmacData[0] = cmd
+        System.arraycopy(seqBytes, 0, hmacData, 1, 4)
+        val hmac = hmacSha256(hmacData, key)
+        val packet = ByteArray(HMAC_PKT_SIZE)
+        packet[0] = cmd
+        System.arraycopy(seqBytes, 0, packet, 1, 4)
+        System.arraycopy(hmac, 0, packet, 5, HMAC_LEN)
+        return packet
+    }
 }