Replace BLE encryption with HMAC-only auth, add buildnr, fix post-flash flow

BLE bonding/encryption removed — HMAC-SHA256 on application level provides
authentication + replay protection. Eliminates bonding state bugs, write
queue issues, and GATT_INSUFFICIENT_AUTHENTICATION complexity.

Firmware:
- Remove BLESecurity, setRespEncryptionKey, ESP_GATT_PERM_WRITE_ENCRYPTED
- Characteristic permission: ESP_GATT_PERM_WRITE (no encryption required)
- Characteristic property: PROPERTY_WRITE_NR (Write Without Response)
  Enables direct ON/OFF sequences without ACK wait time

Android:
- Remove bondReceiver, createBond, bonding state handling
- Remove write queue / pendingRelayState / writeInProgress
- Use WRITE_TYPE_NO_RESPONSE for minimal latency
- Post-flash dialog auto-dismisses on USB detach (currentAction = NONE)
- Separate progressDialog (flash progress) from dialog (post-flash info)
- Detach during active action now calls cleanupAction()

Build number:
- BuildConfig.BUILD_NUMBER in build.gradle as yyyyMMddHHmmss timestamp
- buildFeatures.buildConfig enabled
- Displayed in SettingsActivity bottom (12sp, secondary color)

Gradle:
- Wrapper upgraded 8.5 → 8.14
- minSdk 24 → 26 (Android 8+)

README updated to reflect HMAC-only security model.

android/app/build.gradle

@@ -9,10 +9,15 @@ android {
 
     defaultConfig {
         applicationId "com.eddy.atomrelay"
-        minSdk 24
+        minSdk 26
         targetSdk 34
         versionCode 1
         versionName "1.0"
+        buildConfigField "String", "BUILD_NUMBER", "\"${new java.text.SimpleDateFormat("yyyyMMddHHmmss").format(new Date())}\""
+    }
+
+    buildFeatures {
+        buildConfig true
     }
 
     buildTypes {

android/app/src/main/java/com/eddy/atomrelay/MainActivity.kt

@@ -4,7 +4,6 @@ import android.Manifest
 import android.annotation.SuppressLint
 import android.app.Activity
 import android.bluetooth.BluetoothAdapter
-import android.bluetooth.BluetoothDevice
 import android.bluetooth.BluetoothGatt
 import android.bluetooth.BluetoothGattCallback
 import android.bluetooth.BluetoothGattCharacteristic
@@ -12,10 +11,8 @@ import android.bluetooth.BluetoothGattDescriptor
 import android.bluetooth.BluetoothProfile
 import android.bluetooth.le.ScanCallback
 import android.bluetooth.le.ScanResult
-import android.content.BroadcastReceiver
 import android.content.Context
 import android.content.Intent
-import android.content.IntentFilter
 import android.content.pm.PackageManager
 import android.os.Bundle
 import android.os.Handler
@@ -55,7 +52,6 @@ class MainActivity : AppCompatActivity() {
 
     private var seq = 1
     private var hmacKey: ByteArray? = null
-    private var pendingDevice: BluetoothDevice? = null
 
     private lateinit var statusText: TextView
     private lateinit var relayButton: Button
@@ -72,43 +68,18 @@ class MainActivity : AppCompatActivity() {
         }
     }
 
-    private val bondReceiver = object : BroadcastReceiver() {
-        @SuppressLint("MissingPermission")
-        override fun onReceive(context: Context, intent: Intent) {
-            val action = intent.action
-            if (action == BluetoothDevice.ACTION_BOND_STATE_CHANGED) {
-                val device = intent.getParcelableExtra<BluetoothDevice>(BluetoothDevice.EXTRA_DEVICE)
-                val bondState = intent.getIntExtra(BluetoothDevice.EXTRA_BOND_STATE, BluetoothDevice.BOND_NONE)
-                Log.d(TAG, "Bond state changed: ${device?.address} -> $bondState")
-                if (bondState == BluetoothDevice.BOND_BONDED && device == pendingDevice) {
-                    Log.d(TAG, "Bonded, discovering services...")
-                    runOnUiThread { statusText.text = "Bonded, connecting..." }
-                    bluetoothGatt?.discoverServices()
-                }
-            }
-        }
-    }
-
     private val gattCallback = object : BluetoothGattCallback() {
+        @SuppressLint("MissingPermission")
         override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
             if (newState == BluetoothProfile.STATE_CONNECTED) {
                 Log.d(TAG, "GATT connected")
                 bluetoothGatt = gatt
-                val device = gatt.device
-                pendingDevice = device
-                if (device.bondState == BluetoothDevice.BOND_BONDED) {
-                    Log.d(TAG, "Already bonded, discovering services...")
-                    runOnUiThread { statusText.text = "Connected, discovering..." }
-                    gatt.discoverServices()
-                } else {
-                    Log.d(TAG, "Not bonded, creating bond...")
-                    runOnUiThread { statusText.text = "Pairing..." }
-                    device.createBond()
-                }
+                runOnUiThread { statusText.text = "Verbonden, services zoeken..." }
+                gatt.discoverServices()
             } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                 Log.d(TAG, "GATT disconnected")
                 runOnUiThread {
-                    statusText.text = "Reconnecting..."
+                    statusText.text = "Verbinden..."
                     relayButton.isEnabled = false
                 }
                 gatt.close()
@@ -147,14 +118,6 @@ class MainActivity : AppCompatActivity() {
                 runOnUiThread { statusText.text = "Service not found" }
             }
         }
-
-        override fun onCharacteristicWrite(
-            gatt: BluetoothGatt,
-            characteristic: BluetoothGattCharacteristic,
-            status: Int
-        ) {
-            Log.d(TAG, "Write status: $status")
-        }
     }
 
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -169,15 +132,19 @@ class MainActivity : AppCompatActivity() {
             startActivityForResult(Intent(this, SettingsActivity::class.java), REQUEST_SETTINGS)
         }
         setupRelayButton()
-
-        registerReceiver(bondReceiver, IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED), Context.RECEIVER_NOT_EXPORTED)
     }
 
     @Deprecated("Deprecated in Java")
     override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
         super.onActivityResult(requestCode, resultCode, data)
         if (requestCode == REQUEST_SETTINGS && resultCode == Activity.RESULT_OK) {
-            handler.postDelayed({ startScan() }, 300)
+            stopScan()
+            bluetoothGatt?.close()
+            bluetoothGatt = null
+            relayCharacteristic = null
+            seq = 1
+            loadHmacKey()
+            handler.postDelayed({ startScan() }, 500)
         }
     }
 
@@ -300,7 +267,7 @@ class MainActivity : AppCompatActivity() {
     }
 
     @SuppressLint("MissingPermission")
-    private fun connectToDevice(device: BluetoothDevice) {
+    private fun connectToDevice(device: android.bluetooth.BluetoothDevice) {
         runOnUiThread { statusText.text = "Connecting..." }
         Log.d(TAG, "Connecting to ${device.address}")
         bluetoothGatt = device.connectGatt(this, false, gattCallback)
@@ -348,6 +315,5 @@ class MainActivity : AppCompatActivity() {
         handler.removeCallbacksAndMessages(null)
         stopScan()
         bluetoothGatt?.close()
-        try { unregisterReceiver(bondReceiver) } catch (e: Exception) {}
     }
 }

android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt

@@ -1,5 +1,6 @@
 package com.eddy.atomrelay
 
+import android.app.AlertDialog
 import android.app.PendingIntent
 import android.app.ProgressDialog
 import android.content.BroadcastReceiver
@@ -17,6 +18,7 @@ import android.os.Handler
 import android.os.Looper
 import android.util.Log
 import android.widget.Button
+import android.widget.TextView
 import android.widget.Toast
 import androidx.appcompat.app.AppCompatActivity
 import java.nio.charset.StandardCharsets
@@ -39,7 +41,8 @@ class SettingsActivity : AppCompatActivity() {
     private enum class UsbAction { NONE, EXCHANGE_KEY, FLASH }
 
     private var currentAction = UsbAction.NONE
-    private var dialog: ProgressDialog? = null
+    private var progressDialog: ProgressDialog? = null
+    private var dialog: AlertDialog? = null
     private val handler = Handler(Looper.getMainLooper())
 
     private val usbAttachedReceiver = object : BroadcastReceiver() {
@@ -80,9 +83,13 @@ class SettingsActivity : AppCompatActivity() {
         override fun onReceive(context: Context, intent: Intent) {
             if (intent.action == UsbManager.ACTION_USB_DEVICE_DETACHED) {
                 val device = intent.getParcelableExtra<UsbDevice>(UsbManager.EXTRA_DEVICE)
-                if (device?.vendorId == ESP_VENDOR_ID && dialog != null && currentAction == UsbAction.NONE) {
-                    dialog?.dismiss()
-                    dialog = null
+                if (device?.vendorId == ESP_VENDOR_ID) {
+                    if (dialog != null && currentAction == UsbAction.NONE) {
+                        dialog?.dismiss()
+                        dialog = null
+                    } else if (currentAction != UsbAction.NONE) {
+                        cleanupAction()
+                    }
                 }
             }
         }
@@ -103,6 +110,8 @@ class SettingsActivity : AppCompatActivity() {
             startFlashing()
         }
 
+        findViewById<TextView>(R.id.buildNumber).text = "Buildnummer: ${BuildConfig.BUILD_NUMBER}"
+
         registerReceiver(usbAttachedReceiver, IntentFilter(UsbManager.ACTION_USB_DEVICE_ATTACHED), Context.RECEIVER_NOT_EXPORTED)
         registerReceiver(usbPermissionReceiver, IntentFilter(ACTION_USB_PERMISSION), Context.RECEIVER_NOT_EXPORTED)
         registerReceiver(usbDetachedReceiver, IntentFilter(UsbManager.ACTION_USB_DEVICE_DETACHED), Context.RECEIVER_NOT_EXPORTED)
@@ -198,27 +207,33 @@ class SettingsActivity : AppCompatActivity() {
         flasher.flashDevice(usbManager, device, object : EspFlasher.FlashCallback {
             override fun onProgress(percent: Int, message: String) {
                 runOnUiThread {
-                    dialog?.progress = percent
-                    dialog?.setMessage(message)
+                    progressDialog?.progress = percent
+                    progressDialog?.setMessage(message)
                 }
             }
 
             override fun onComplete() {
                 runOnUiThread {
-                    dialog?.setMessage("Firmware geflashed!\n\nOntkoppel de ESP en sluit opnieuw aan om de sleutel in te stellen.")
-                    dialog?.setCancelable(true)
-                    dialog?.setButton(ProgressDialog.BUTTON_NEUTRAL, "Sluiten") { _, _ ->
-                        dialog?.dismiss()
-                        dialog = null
-                        cleanupAction()
-                    }
+                    currentAction = UsbAction.NONE
+                    progressDialog?.dismiss()
+                    progressDialog = null
+                    dialog = AlertDialog.Builder(this@SettingsActivity)
+                        .setTitle("Firmware Flashen")
+                        .setMessage("Firmware geflashed!\n\nOntkoppel de ESP en sluit opnieuw aan om de sleutel in te stellen.")
+                        .setPositiveButton("Sluiten") { d, _ ->
+                            d.dismiss()
+                            dialog = null
+                        }
+                        .setCancelable(true)
+                        .setOnCancelListener { dialog = null }
+                        .show()
                 }
             }
 
             override fun onError(message: String) {
                 runOnUiThread {
-                    dialog?.dismiss()
-                    dialog = null
+                    progressDialog?.dismiss()
+                    progressDialog = null
                     Toast.makeText(this@SettingsActivity, "Flashen mislukt: $message", Toast.LENGTH_LONG).show()
                     cleanupAction()
                 }
@@ -253,8 +268,8 @@ class SettingsActivity : AppCompatActivity() {
     }
 
     private fun showProgressDialog(title: String, message: String, style: Int) {
-        dialog?.dismiss()
-        dialog = ProgressDialog(this).apply {
+        progressDialog?.dismiss()
+        progressDialog = ProgressDialog(this).apply {
             setTitle(title)
             setMessage(message)
             setProgressStyle(style)
@@ -271,6 +286,8 @@ class SettingsActivity : AppCompatActivity() {
         currentAction = UsbAction.NONE
         dialog?.dismiss()
         dialog = null
+        progressDialog?.dismiss()
+        progressDialog = null
     }
 
     private fun requestUsbPermission(usbManager: UsbManager, device: UsbDevice) {

android/app/src/main/res/layout/activity_settings.xml

@@ -38,4 +38,17 @@
         android:layout_height="wrap_content"
         android:text="Firmware Flashen" />
 
+    <View
+        android:layout_width="0dp"
+        android:layout_height="0dp"
+        android:layout_weight="1" />
+
+    <TextView
+        android:id="@+id/buildNumber"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:textSize="12sp"
+        android:textColor="?android:attr/textColorSecondary"
+        android:gravity="center" />
+
 </LinearLayout>

android/gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists