Remote wipe: user interface

app/src/main/java/eu/faircode/email/FragmentOptionsPrivacy.java

@@ -20,6 +20,8 @@ package eu.faircode.email;
 */
 
 import android.app.Dialog;
+import android.content.ClipData;
+import android.content.ClipboardManager;
 import android.content.Context;
 import android.content.DialogInterface;
 import android.content.Intent;
@@ -44,6 +46,7 @@ import android.widget.EditText;
 import android.widget.ImageButton;
 import android.widget.Spinner;
 import android.widget.TextView;
+import android.widget.Toast;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
@@ -93,7 +96,9 @@ public class FragmentOptionsPrivacy extends FragmentBase implements SharedPrefer
     private SwitchCompat swDisconnectAutoUpdate;
     private SwitchCompat swDisconnectLinks;
     private SwitchCompat swDisconnectImages;
+    private SwitchCompat swMnemonic;
     private Button btnClearAll;
+    private TextView tvMnemonic;
 
     private Group grpSafeBrowsing;
 
@@ -104,7 +109,8 @@ public class FragmentOptionsPrivacy extends FragmentBase implements SharedPrefer
             "pin", "biometrics", "biometrics_timeout", "autolock", "autolock_nav",
             "client_id", "display_hidden", "incognito_keyboard", "secure",
             "generic_ua", "safe_browsing", "load_emoji",
-            "disconnect_auto_update", "disconnect_links", "disconnect_images"
+            "disconnect_auto_update", "disconnect_links", "disconnect_images",
+            "wipe_mnemonic"
     };
 
     @Override
@@ -151,7 +157,9 @@ public class FragmentOptionsPrivacy extends FragmentBase implements SharedPrefer
         swDisconnectAutoUpdate = view.findViewById(R.id.swDisconnectAutoUpdate);
         swDisconnectLinks = view.findViewById(R.id.swDisconnectLinks);
         swDisconnectImages = view.findViewById(R.id.swDisconnectImages);
+        swMnemonic = view.findViewById(R.id.swMnemonic);
         btnClearAll = view.findViewById(R.id.btnClearAll);
+        tvMnemonic = view.findViewById(R.id.tvMnemonic);
 
         grpSafeBrowsing = view.findViewById(R.id.grpSafeBrowsing);
 
@@ -446,6 +454,31 @@ public class FragmentOptionsPrivacy extends FragmentBase implements SharedPrefer
             }
         });
 
+        swMnemonic.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
+            @Override
+            public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
+                if (checked) {
+                    byte[] entropy = MnemonicHelper.generate();
+                    String mnemonic = MnemonicHelper.get(entropy);
+                    prefs.edit().putString("wipe_mnemonic", Helper.hex(entropy)).apply();
+                    tvMnemonic.setText(mnemonic);
+
+                    Context context = compoundButton.getContext();
+                    ClipboardManager cbm = (ClipboardManager) context.getSystemService(Context.CLIPBOARD_SERVICE);
+                    if (cbm == null)
+                        return;
+
+                    ClipData clip = ClipData.newPlainText(getString(R.string.app_name), mnemonic);
+                    cbm.setPrimaryClip(clip);
+                    ToastEx.makeText(context, R.string.title_clipboard_copied, Toast.LENGTH_LONG).show();
+
+                } else {
+                    prefs.edit().remove("wipe_mnemonic").apply();
+                    tvMnemonic.setText(null);
+                }
+            }
+        });
+
         // Initialize
         FragmentDialogTheme.setBackground(getContext(), view, false);
 
@@ -546,6 +579,10 @@ public class FragmentOptionsPrivacy extends FragmentBase implements SharedPrefer
         swDisconnectAutoUpdate.setChecked(prefs.getBoolean("disconnect_auto_update", false));
         swDisconnectLinks.setChecked(prefs.getBoolean("disconnect_links", true));
         swDisconnectImages.setChecked(prefs.getBoolean("disconnect_images", false));
+
+        String mnemonic = prefs.getString("wipe_mnemonic", null);
+        swMnemonic.setChecked(mnemonic != null);
+        tvMnemonic.setText(mnemonic == null ? null : MnemonicHelper.get(mnemonic));
     }
 
     public static class FragmentDialogPin extends FragmentDialogBase {

app/src/main/java/eu/faircode/email/MnemonicHelper.java

@@ -0,0 +1,58 @@
+package eu.faircode.email;
+
+/*
+    This file is part of FairEmail.
+
+    FairEmail is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    FairEmail is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with FairEmail.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2018-2022 by Marcel Bokhorst (M66B)
+*/
+
+import java.security.SecureRandom;
+
+import io.github.novacrypto.bip39.MnemonicGenerator;
+import io.github.novacrypto.bip39.Words;
+import io.github.novacrypto.bip39.wordlists.English;
+
+public class MnemonicHelper {
+    // https://github.com/NovaCrypto/BIP39
+
+    static String get(byte[] entropy) {
+        StringBuilder sb = new StringBuilder();
+        new SecureRandom().nextBytes(entropy);
+        new MnemonicGenerator(English.INSTANCE).createMnemonic(entropy, sb::append);
+        return sb.toString();
+    }
+
+    static String get(String hex) {
+        return get(fromHex(hex));
+    }
+
+    static byte[] generate() {
+        byte[] entropy = new byte[Words.TWELVE.byteLength()];
+        new SecureRandom().nextBytes(entropy);
+        return entropy;
+    }
+
+    private static byte[] fromHex(String hex) {
+        int len = hex.length();
+        byte[] data = new byte[len / 2];
+        for (int i = 0; i < len; i += 2) {
+            data[i / 2] =
+                    (byte) ((Character.digit(hex.charAt(i), 16) << 4) +
+                            Character.digit(hex.charAt(i + 1), 16));
+        }
+        return data;
+    }
+}