Set username and random password on first start.

src/androidTest/java/com/nutomic/syncthingandroid/test/syncthing/SyncthingServiceTest.java

@@ -2,6 +2,7 @@ package com.nutomic.syncthingandroid.test.syncthing;
 
 import android.content.Context;
 import android.content.Intent;
+import android.content.SharedPreferences;
 import android.preference.PreferenceManager;
 import android.test.ServiceTestCase;
 import android.test.suitebuilder.annotation.MediumTest;
@@ -109,4 +110,11 @@ public class SyncthingServiceTest extends ServiceTestCase<SyncthingService> {
         assertTrue(publicKey.exists());
     }
 
+    public void testPassword() {
+        startService(new Intent(getContext(), SyncthingService.class));
+        SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getContext());
+        assertNotNull(sp.getString("gui_user", null));
+        assertEquals(20, sp.getString("gui_password", null).length());
+    }
+
 }

src/main/java/com/nutomic/syncthingandroid/fragments/SettingsFragment.java

@@ -1,5 +1,6 @@
 package com.nutomic.syncthingandroid.fragments;
 
+import android.content.SharedPreferences;
 import android.content.pm.PackageManager;
 import android.os.Bundle;
 import android.preference.CheckBoxPreference;
@@ -27,11 +28,16 @@ public class SettingsFragment extends PreferenceFragment
     private static final String TAG = "SettingsFragment";
 
     private static final String SYNCTHING_OPTIONS_KEY = "syncthing_options";
-    private static final String SYNCTHING_GUI_KEY = "syncthing_gui";
+    private static final String SYNCTHING_GUI_KEY     = "syncthing_gui";
-    private static final String DEVICE_NAME_KEY = "DeviceName";
+    private static final String DEVICE_NAME_KEY       = "DeviceName";
     private static final String USAGE_REPORT_ACCEPTED = "URAccepted";
-    private static final String EXPORT_CONFIG = "export_config";
+    private static final String ADDRESS               = "Address";
-    private static final String IMPORT_CONFIG = "import_config";
+    private static final String GUI_USER              = "gui_user";
+    private static final String GUI_PASSWORD          = "gui_password";
+    private static final String USER_TLS              = "UseTLS";
+    private static final String EXPORT_CONFIG         = "export_config";
+    private static final String IMPORT_CONFIG         = "import_config";
+    private static final String STTRACE               = "sttrace";
 
     private static final String SYNCTHING_VERSION_KEY = "syncthing_version";
 
@@ -72,18 +78,15 @@ public class SettingsFragment extends PreferenceFragment
                         break;
                     default:
                         value = api.getValue(RestApi.TYPE_OPTIONS, pref.getKey());
-
-
                 }
                 applyPreference(pref, value);
             }
 
-            for (int i = 0; i < mGuiScreen.getPreferenceCount(); i++) {
+            Preference address = mGuiScreen.findPreference(ADDRESS);
-                Preference pref = mGuiScreen.getPreference(i);
+            applyPreference(address, api.getValue(RestApi.TYPE_GUI, ADDRESS));
-                pref.setOnPreferenceChangeListener(SettingsFragment.this);
+
-                String value = api.getValue(RestApi.TYPE_GUI, pref.getKey());
+            Preference tls = mGuiScreen.findPreference(USER_TLS);
-                applyPreference(pref, value);
+            applyPreference(tls, api.getValue(RestApi.TYPE_GUI, USER_TLS));
-            }
         }
     }
 
@@ -122,26 +125,33 @@ public class SettingsFragment extends PreferenceFragment
                 findPreference(SyncthingService.PREF_SYNC_ONLY_CHARGING);
         mSyncOnlyWifi = (CheckBoxPreference) findPreference(SyncthingService.PREF_SYNC_ONLY_WIFI);
         Preference appVersion = screen.findPreference(APP_VERSION_KEY);
+        mOptionsScreen = (PreferenceScreen) screen.findPreference(SYNCTHING_OPTIONS_KEY);
+        mGuiScreen = (PreferenceScreen) screen.findPreference(SYNCTHING_GUI_KEY);
+        Preference user = screen.findPreference(GUI_USER);
+        Preference password = screen.findPreference(GUI_PASSWORD);
+        Preference sttrace = findPreference(STTRACE);
+
         try {
             appVersion.setSummary(getActivity().getPackageManager()
                     .getPackageInfo(getActivity().getPackageName(), 0).versionName);
         } catch (PackageManager.NameNotFoundException e) {
             Log.d(TAG, "Failed to get app version name");
         }
-        mOptionsScreen = (PreferenceScreen) screen.findPreference(SYNCTHING_OPTIONS_KEY);
-        mGuiScreen = (PreferenceScreen) screen.findPreference(SYNCTHING_GUI_KEY);
 
         mAlwaysRunInBackground.setOnPreferenceChangeListener(this);
         mSyncOnlyCharging.setOnPreferenceChangeListener(this);
         mSyncOnlyWifi.setOnPreferenceChangeListener(this);
         screen.findPreference(EXPORT_CONFIG).setOnPreferenceClickListener(this);
         screen.findPreference(IMPORT_CONFIG).setOnPreferenceClickListener(this);
+        user.setOnPreferenceChangeListener(this);
+        password.setOnPreferenceChangeListener(this);
         // Force summary update and wifi/charging preferences enable/disable.
         onPreferenceChange(mAlwaysRunInBackground, mAlwaysRunInBackground.isChecked());
-        Preference sttrace = findPreference("sttrace");
         sttrace.setOnPreferenceChangeListener(this);
-        sttrace.setSummary(PreferenceManager
+
-                .getDefaultSharedPreferences(getActivity()).getString("sttrace", ""));
+        SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getActivity());
+        user.setSummary(sp.getString("gui_user", ""));
+        sttrace.setSummary(sp.getString("sttrace", ""));
     }
 
     @Override
@@ -171,7 +181,7 @@ public class SettingsFragment extends PreferenceFragment
     @Override
     public boolean onPreferenceChange(Preference preference, Object o) {
         // Convert new value to integer if input type is number.
-        if (preference instanceof EditTextPreference) {
+        if (preference instanceof EditTextPreference && !preference.getKey().equals(GUI_PASSWORD)) {
             EditTextPreference pref = (EditTextPreference) preference;
             if ((pref.getEditText().getInputType() & InputType.TYPE_CLASS_NUMBER) > 0) {
                 try {
@@ -193,7 +203,6 @@ public class SettingsFragment extends PreferenceFragment
                     : R.string.always_run_in_background_disabled);
             mSyncOnlyCharging.setEnabled((Boolean) o);
             mSyncOnlyWifi.setEnabled((Boolean) o);
-
         } else if (preference.getKey().equals(DEVICE_NAME_KEY)) {
             RestApi.Device old = mSyncthingService.getApi().getLocalDevice();
             RestApi.Device updated = new RestApi.Device();
@@ -211,16 +220,34 @@ public class SettingsFragment extends PreferenceFragment
                     preference.getKey().equals("GlobalAnnServers");
             mSyncthingService.getApi().setValue(RestApi.TYPE_OPTIONS, preference.getKey(), o,
                     isArray, getActivity());
-        } else if (mGuiScreen.findPreference(preference.getKey()) != null) {
+        } else if (preference.getKey().equals(ADDRESS) || preference.getKey().equals(USER_TLS)) {
             mSyncthingService.getApi().setValue(
                     RestApi.TYPE_GUI, preference.getKey(), o, false, getActivity());
-        } else if (preference.getKey().equals("sttrace")) {
+        }
-            // Avoid any code injection.
+
-            if (!((String) o).matches("[a-z,]*")) {
+        // Avoid any code injection.
-                Log.w(TAG, "Only a-z and ',' are allowed in STTRACE options");
+        int error = 0;
-                return false;
+        if (preference.getKey().equals(STTRACE)) {
-            }
+            if (((String) o).matches("[a-z, ]*"))
-            ((SyncthingActivity) getActivity()).getApi().requireRestart(getActivity());
+                mSyncthingService.getApi().requireRestart(getActivity());
+            else
+                error = R.string.toast_invalid_sttrace;
+        } else if (preference.getKey().equals(GUI_USER)) {
+            String s = (String) o;
+            if (!s.contains(":") && !s.contains("'"))
+                mSyncthingService.getApi().requireRestart(getActivity());
+            else
+                error = R.string.toast_invalid_username;
+        } else if (preference.getKey().equals(GUI_PASSWORD)) {
+            String s = (String) o;
+            if (!s.contains(":") && !s.contains("'"))
+                mSyncthingService.getApi().requireRestart(getActivity());
+            else
+                error = R.string.toast_invalid_password;
+        }
+        if (error != 0) {
+            Toast.makeText(getActivity(), error, Toast.LENGTH_SHORT).show();
+            return false;
         }
 
         return true;

src/main/java/com/nutomic/syncthingandroid/syncthing/SyncthingRunnable.java

@@ -12,6 +12,7 @@ import java.io.DataOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.util.Map;
 
 /**
  * Runs the syncthing binary from command line, and prints its output to logcat.
@@ -42,20 +43,25 @@ public class SyncthingRunnable implements Runnable {
 
     @Override
     public void run() {
-        SharedPreferences pm = PreferenceManager.getDefaultSharedPreferences(mContext);
+        SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(mContext);
         DataOutputStream dos = null;
         int ret = 1;
         Process process = null;
         try {
             // Loop to handle syncthing restarts (these always have an error code of 3).
             do {
-                process = Runtime.getRuntime().exec("sh");
+                ProcessBuilder pb = new ProcessBuilder("sh");
+                Map<String, String> env = pb.environment();
+                // Set home directory to data folder for web GUI folder picker.
+                env.put("HOME", Environment.getExternalStorageDirectory().getAbsolutePath());
+                env.put("STTRACE", sp.getString("sttrace", ""));
+                env.put("STNORESTART", "1");
+                env.put("STNOUPGRADE", "1");
+                env.put("STGUIAUTH", sp.getString("gui_user", "") + ":" +
+                        sp.getString("gui_password", ""));
+                process = pb.start();
+
                 dos = new DataOutputStream(process.getOutputStream());
-                // Set home directory to data folder for syncthing to use.
-                dos.writeBytes("HOME=" + Environment.getExternalStorageDirectory() + " ");
-                dos.writeBytes("STTRACE=" + pm.getString("sttrace", "") + " ");
-                dos.writeBytes("STNORESTART=1 ");
-                dos.writeBytes("STNOUPGRADE=1 ");
                 // Call syncthing with -home (as it would otherwise use "~/.config/syncthing/".
                 dos.writeBytes(mCommand + " -home " + mContext.getFilesDir() + "\n");
                 dos.writeBytes("exit\n");

src/main/java/com/nutomic/syncthingandroid/syncthing/SyncthingService.java

@@ -12,6 +12,7 @@ import android.content.Intent;
 import android.content.IntentFilter;
 import android.content.SharedPreferences;
 import android.os.AsyncTask;
+import android.os.Build;
 import android.os.Environment;
 import android.os.IBinder;
 import android.preference.PreferenceManager;
@@ -24,6 +25,7 @@ import com.nutomic.syncthingandroid.activities.MainActivity;
 import com.nutomic.syncthingandroid.activities.SettingsActivity;
 import com.nutomic.syncthingandroid.util.ConfigXml;
 import com.nutomic.syncthingandroid.util.FolderObserver;
+import com.nutomic.syncthingandroid.util.PRNGFixes;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -32,6 +34,7 @@ import java.io.FilenameFilter;
 import java.io.IOException;
 import java.lang.ref.WeakReference;
 import java.nio.channels.FileChannel;
+import java.security.SecureRandom;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedList;
@@ -261,6 +264,26 @@ public class SyncthingService extends Service {
      */
     @Override
     public void onCreate() {
+        PRNGFixes.apply();
+        SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
+
+        // Make sure this is also done for existing installs. We can replace this check with
+        // {@link #isFirstStart()} after a while.
+        if (!sp.getBoolean("default_user_pw_set", false)) {
+            sp.edit().putBoolean("default_user_pw_set", true).commit();
+            char[] chars =
+                    "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
+            StringBuilder sb = new StringBuilder();
+            SecureRandom random = new SecureRandom();
+            for (int i = 0; i < 20; i++)
+                sb.append(chars[random.nextInt(chars.length)]);
+
+            String user = Build.MODEL.replaceAll("[^a-zA-Z0-9 ]", "");
+            Log.i(TAG, "Generated GUI username and password (username is " + user + ")");
+            sp.edit().putString("gui_user", user)
+                     .putString("gui_password", sb.toString()).commit();
+        }
+
         mDeviceStateHolder = new DeviceStateHolder(SyncthingService.this);
         registerReceiver(mDeviceStateHolder, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
         new StartupTask().execute();

src/main/java/com/nutomic/syncthingandroid/util/PRNGFixes.java

@@ -0,0 +1,338 @@
+package com.nutomic.syncthingandroid.util;
+
+/*
+ * This software is provided 'as-is', without any express or implied
+ * warranty.  In no event will Google be held liable for any damages
+ * arising from the use of this software.
+ *
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, as long as the origin is not misrepresented.
+ */
+
+import android.os.Build;
+import android.os.Process;
+import android.util.Log;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.UnsupportedEncodingException;
+import java.security.NoSuchAlgorithmException;
+import java.security.Provider;
+import java.security.SecureRandom;
+import java.security.SecureRandomSpi;
+import java.security.Security;
+
+/**
+ * Fixes for the output of the default PRNG having low entropy.
+ *
+ * The fixes need to be applied via {@link #apply()} before any use of Java
+ * Cryptography Architecture primitives. A good place to invoke them is in the
+ * application's {@code onCreate}.
+ *
+ * @see <a href="http://android-developers.blogspot.jp/2013/08/some-securerandom-thoughts.html">Android Developers Blog Post</a>
+ */
+public final class PRNGFixes {
+
+    private static final int VERSION_CODE_JELLY_BEAN = 16;
+    private static final int VERSION_CODE_JELLY_BEAN_MR2 = 18;
+    private static final byte[] BUILD_FINGERPRINT_AND_DEVICE_SERIAL =
+            getBuildFingerprintAndDeviceSerial();
+
+    /** Hidden constructor to prevent instantiation. */
+    private PRNGFixes() {}
+
+    /**
+     * Applies all fixes.
+     *
+     * @throws SecurityException if a fix is needed but could not be applied.
+     */
+    public static void apply() {
+        applyOpenSSLFix();
+        installLinuxPRNGSecureRandom();
+    }
+
+    /**
+     * Applies the fix for OpenSSL PRNG having low entropy. Does nothing if the
+     * fix is not needed.
+     *
+     * @throws SecurityException if the fix is needed but could not be applied.
+     */
+    private static void applyOpenSSLFix() throws SecurityException {
+        if ((Build.VERSION.SDK_INT < VERSION_CODE_JELLY_BEAN)
+                || (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2)) {
+            // No need to apply the fix
+            return;
+        }
+
+        try {
+            // Mix in the device- and invocation-specific seed.
+            Class.forName("org.apache.harmony.xnet.provider.jsse.NativeCrypto")
+                    .getMethod("RAND_seed", byte[].class)
+                    .invoke(null, generateSeed());
+
+            // Mix output of Linux PRNG into OpenSSL's PRNG
+            int bytesRead = (Integer) Class.forName(
+                    "org.apache.harmony.xnet.provider.jsse.NativeCrypto")
+                    .getMethod("RAND_load_file", String.class, long.class)
+                    .invoke(null, "/dev/urandom", 1024);
+            if (bytesRead != 1024) {
+                throw new IOException(
+                        "Unexpected number of bytes read from Linux PRNG: "
+                                + bytesRead);
+            }
+        } catch (Exception e) {
+            throw new SecurityException("Failed to seed OpenSSL PRNG", e);
+        }
+    }
+
+    /**
+     * Installs a Linux PRNG-backed {@code SecureRandom} implementation as the
+     * default. Does nothing if the implementation is already the default or if
+     * there is not need to install the implementation.
+     *
+     * @throws SecurityException if the fix is needed but could not be applied.
+     */
+    private static void installLinuxPRNGSecureRandom()
+            throws SecurityException {
+        if (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2) {
+            // No need to apply the fix
+            return;
+        }
+
+        // Install a Linux PRNG-based SecureRandom implementation as the
+        // default, if not yet installed.
+        Provider[] secureRandomProviders =
+                Security.getProviders("SecureRandom.SHA1PRNG");
+        if ((secureRandomProviders == null)
+                || (secureRandomProviders.length < 1)
+                || (!LinuxPRNGSecureRandomProvider.class.equals(
+                secureRandomProviders[0].getClass()))) {
+            Security.insertProviderAt(new LinuxPRNGSecureRandomProvider(), 1);
+        }
+
+        // Assert that new SecureRandom() and
+        // SecureRandom.getInstance("SHA1PRNG") return a SecureRandom backed
+        // by the Linux PRNG-based SecureRandom implementation.
+        SecureRandom rng1 = new SecureRandom();
+        if (!LinuxPRNGSecureRandomProvider.class.equals(
+                rng1.getProvider().getClass())) {
+            throw new SecurityException(
+                    "new SecureRandom() backed by wrong Provider: "
+                            + rng1.getProvider().getClass());
+        }
+
+        SecureRandom rng2;
+        try {
+            rng2 = SecureRandom.getInstance("SHA1PRNG");
+        } catch (NoSuchAlgorithmException e) {
+            throw new SecurityException("SHA1PRNG not available", e);
+        }
+        if (!LinuxPRNGSecureRandomProvider.class.equals(
+                rng2.getProvider().getClass())) {
+            throw new SecurityException(
+                    "SecureRandom.getInstance(\"SHA1PRNG\") backed by wrong"
+                            + " Provider: " + rng2.getProvider().getClass());
+        }
+    }
+
+    /**
+     * {@code Provider} of {@code SecureRandom} engines which pass through
+     * all requests to the Linux PRNG.
+     */
+    private static class LinuxPRNGSecureRandomProvider extends Provider {
+
+        public LinuxPRNGSecureRandomProvider() {
+            super("LinuxPRNG",
+                    1.0,
+                    "A Linux-specific random number provider that uses"
+                            + " /dev/urandom");
+            // Although /dev/urandom is not a SHA-1 PRNG, some apps
+            // explicitly request a SHA1PRNG SecureRandom and we thus need to
+            // prevent them from getting the default implementation whose output
+            // may have low entropy.
+            put("SecureRandom.SHA1PRNG", LinuxPRNGSecureRandom.class.getName());
+            put("SecureRandom.SHA1PRNG ImplementedIn", "Software");
+        }
+    }
+
+    /**
+     * {@link SecureRandomSpi} which passes all requests to the Linux PRNG
+     * ({@code /dev/urandom}).
+     */
+    public static class LinuxPRNGSecureRandom extends SecureRandomSpi {
+
+        /*
+         * IMPLEMENTATION NOTE: Requests to generate bytes and to mix in a seed
+         * are passed through to the Linux PRNG (/dev/urandom). Instances of
+         * this class seed themselves by mixing in the current time, PID, UID,
+         * build fingerprint, and hardware serial number (where available) into
+         * Linux PRNG.
+         *
+         * Concurrency: Read requests to the underlying Linux PRNG are
+         * serialized (on sLock) to ensure that multiple threads do not get
+         * duplicated PRNG output.
+         */
+
+        private static final File URANDOM_FILE = new File("/dev/urandom");
+
+        private static final Object sLock = new Object();
+
+        /**
+         * Input stream for reading from Linux PRNG or {@code null} if not yet
+         * opened.
+         *
+         * @GuardedBy("sLock")
+         */
+        private static DataInputStream sUrandomIn;
+
+        /**
+         * Output stream for writing to Linux PRNG or {@code null} if not yet
+         * opened.
+         *
+         * @GuardedBy("sLock")
+         */
+        private static OutputStream sUrandomOut;
+
+        /**
+         * Whether this engine instance has been seeded. This is needed because
+         * each instance needs to seed itself if the client does not explicitly
+         * seed it.
+         */
+        private boolean mSeeded;
+
+        @Override
+        protected void engineSetSeed(byte[] bytes) {
+            try {
+                OutputStream out;
+                synchronized (sLock) {
+                    out = getUrandomOutputStream();
+                }
+                out.write(bytes);
+                out.flush();
+            } catch (IOException e) {
+                // On a small fraction of devices /dev/urandom is not writable.
+                // Log and ignore.
+                Log.w(PRNGFixes.class.getSimpleName(),
+                        "Failed to mix seed into " + URANDOM_FILE);
+            } finally {
+                mSeeded = true;
+            }
+        }
+
+        @Override
+        protected void engineNextBytes(byte[] bytes) {
+            if (!mSeeded) {
+                // Mix in the device- and invocation-specific seed.
+                engineSetSeed(generateSeed());
+            }
+
+            try {
+                DataInputStream in;
+                synchronized (sLock) {
+                    in = getUrandomInputStream();
+                }
+                synchronized (in) {
+                    in.readFully(bytes);
+                }
+            } catch (IOException e) {
+                throw new SecurityException(
+                        "Failed to read from " + URANDOM_FILE, e);
+            }
+        }
+
+        @Override
+        protected byte[] engineGenerateSeed(int size) {
+            byte[] seed = new byte[size];
+            engineNextBytes(seed);
+            return seed;
+        }
+
+        private DataInputStream getUrandomInputStream() {
+            synchronized (sLock) {
+                if (sUrandomIn == null) {
+                    // NOTE: Consider inserting a BufferedInputStream between
+                    // DataInputStream and FileInputStream if you need higher
+                    // PRNG output performance and can live with future PRNG
+                    // output being pulled into this process prematurely.
+                    try {
+                        sUrandomIn = new DataInputStream(
+                                new FileInputStream(URANDOM_FILE));
+                    } catch (IOException e) {
+                        throw new SecurityException("Failed to open "
+                                + URANDOM_FILE + " for reading", e);
+                    }
+                }
+                return sUrandomIn;
+            }
+        }
+
+        private OutputStream getUrandomOutputStream() throws IOException {
+            synchronized (sLock) {
+                if (sUrandomOut == null) {
+                    sUrandomOut = new FileOutputStream(URANDOM_FILE);
+                }
+                return sUrandomOut;
+            }
+        }
+    }
+
+    /**
+     * Generates a device- and invocation-specific seed to be mixed into the
+     * Linux PRNG.
+     */
+    private static byte[] generateSeed() {
+        try {
+            ByteArrayOutputStream seedBuffer = new ByteArrayOutputStream();
+            DataOutputStream seedBufferOut =
+                    new DataOutputStream(seedBuffer);
+            seedBufferOut.writeLong(System.currentTimeMillis());
+            seedBufferOut.writeLong(System.nanoTime());
+            seedBufferOut.writeInt(Process.myPid());
+            seedBufferOut.writeInt(Process.myUid());
+            seedBufferOut.write(BUILD_FINGERPRINT_AND_DEVICE_SERIAL);
+            seedBufferOut.close();
+            return seedBuffer.toByteArray();
+        } catch (IOException e) {
+            throw new SecurityException("Failed to generate seed", e);
+        }
+    }
+
+    /**
+     * Gets the hardware serial number of this device.
+     *
+     * @return serial number or {@code null} if not available.
+     */
+    private static String getDeviceSerialNumber() {
+        // We're using the Reflection API because Build.SERIAL is only available
+        // since API Level 9 (Gingerbread, Android 2.3).
+        try {
+            return (String) Build.class.getField("SERIAL").get(null);
+        } catch (Exception ignored) {
+            return null;
+        }
+    }
+
+    private static byte[] getBuildFingerprintAndDeviceSerial() {
+        StringBuilder result = new StringBuilder();
+        String fingerprint = Build.FINGERPRINT;
+        if (fingerprint != null) {
+            result.append(fingerprint);
+        }
+        String serial = getDeviceSerialNumber();
+        if (serial != null) {
+            result.append(serial);
+        }
+        try {
+            return result.toString().getBytes("UTF-8");
+        } catch (UnsupportedEncodingException e) {
+            throw new RuntimeException("UTF-8 encoding not supported");
+        }
+    }
+}

src/main/res/values/strings.xml

@@ -274,6 +274,15 @@ Please report any problems you encounter via Github.</string>
     <!-- Title for the preference to set STTRACE parameters -->
     <string name="sttrace_title">Debug Options</string>
 
+    <!-- Toast after entering invalid STTRACE params -->
+    <string name="toast_invalid_sttrace">Only a-z and \',\' are allowed in STTRACE options</string>
+
+    <!-- Toast after entering invalid username -->
+    <string name="toast_invalid_username">Characters : and \' are not allowed in username</string>
+
+    <!-- Toast after entering invalid password -->
+    <string name="toast_invalid_password">Characters : and \' are not allowed in password</string>
+
     <string name="category_about">About</string>
 
     <!-- Settings item that opens issue tracker -->

src/main/res/xml/app_settings.xml

@@ -93,15 +93,12 @@
                 android:persistent="false" />
 
             <EditTextPreference
-                android:key="User"
+                android:key="gui_user"
-                android:title="@string/gui_user"
+                android:title="@string/gui_user" />
-                android:persistent="false" />
 
             <EditTextPreference
-                android:key="Password"
+                android:key="gui_password"
-                android:title="@string/gui_password"
+                android:title="@string/gui_password" />
-                android:inputType="textPassword"
-                android:persistent="false" />
 
             <CheckBoxPreference
                 android:key="UseTLS"