Simplify mnemonic generation

ATTRIBUTION.md

@@ -41,4 +41,3 @@ FairEmail uses:
 * [Cousine font](https://fonts.google.com/specimen/Cousine). By Steve Matteson. [Apache License 2.0](https://fonts.google.com/specimen/Cousine#license).
 * [Lato font](https://fonts.google.com/specimen/Lato). By Łukasz Dziedzic. [Apache License 2.0](https://fonts.google.com/specimen/Lato#license).
 * [Caladea font](https://fonts.google.com/specimen/Caladea). By Andrés Torresi, Carolina Giovanolli. [Apache License 2.0](https://fonts.google.com/specimen/Caladea#license).
-* [BIP39](https://github.com/NovaCrypto/BIP39). Copyright (C) 2017-2019 Alan Evans, NovaCrypto. [GNU General Public License v3.0](https://github.com/NovaCrypto/BIP39/blob/master/LICENCE.txt).

app/src/main/assets/ATTRIBUTION.md

@@ -41,4 +41,3 @@ FairEmail uses:
 * [Cousine font](https://fonts.google.com/specimen/Cousine). By Steve Matteson. [Apache License 2.0](https://fonts.google.com/specimen/Cousine#license).
 * [Lato font](https://fonts.google.com/specimen/Lato). By Łukasz Dziedzic. [Apache License 2.0](https://fonts.google.com/specimen/Lato#license).
 * [Caladea font](https://fonts.google.com/specimen/Caladea). By Andrés Torresi, Carolina Giovanolli. [Apache License 2.0](https://fonts.google.com/specimen/Caladea#license).
-* [BIP39](https://github.com/NovaCrypto/BIP39). Copyright (C) 2017-2019 Alan Evans, NovaCrypto. [GNU General Public License v3.0](https://github.com/NovaCrypto/BIP39/blob/master/LICENCE.txt).

app/src/main/java/io/github/novacrypto/bip39/wordlists/English.java → app/src/main/java/eu/faircode/email/BIP39.java

@@ -1,45 +1,7 @@
-/*
- *  BIP39 library, a Java implementation of BIP39
- *  Copyright (C) 2017-2019 Alan Evans, NovaCrypto
- *
- *  This program 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.
- *
- *  This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
- *
- *  Original source: https://github.com/NovaCrypto/BIP39
- *  You can contact the authors via github issues.
- */
+package eu.faircode.email;
 
-package io.github.novacrypto.bip39.wordlists;
-
-import io.github.novacrypto.bip39.WordList;
-
-/**
- * Source: https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt
- */
-public enum English implements WordList {
-    INSTANCE;
-
-    @Override
-    public String getWord(final int index) {
-        return words[index];
-    }
-
-    @Override
-    public char getSpace() {
-        return ' ';
-    }
-
-    private final static String[] words = new String[]{
+public class BIP39 {
+    public final static String[] words = new String[]{
             "abandon",
             "ability",
             "able",
@@ -2089,4 +2051,4 @@ public char getSpace() {
             "zone",
             "zoo"
     };
-}
+}

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

@@ -58,13 +58,12 @@
 import androidx.webkit.WebViewFeature;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.security.SecureRandom;
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
-
-import io.github.novacrypto.bip39.MnemonicGenerator;
-import io.github.novacrypto.bip39.Words;
-import io.github.novacrypto.bip39.wordlists.English;
+import java.util.ArrayList;
+import java.util.List;
 
 public class FragmentOptionsPrivacy extends FragmentBase implements SharedPreferences.OnSharedPreferenceChangeListener {
     private SwitchCompat swConfirmLinks;
@@ -107,6 +106,8 @@ public class FragmentOptionsPrivacy extends FragmentBase implements SharedPrefer
 
     private Group grpSafeBrowsing;
 
+    private final static int BIP39_WORDS = 6;
+
     private final static String[] RESET_OPTIONS = new String[]{
             "confirm_links", "check_links_dbl", "browse_links",
             "confirm_images", "ask_images", "html_always_images", "confirm_html", "ask_html",
@@ -463,12 +464,11 @@ public void onClick(View v) {
             @Override
             public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
                 if (checked) {
-                    // https://github.com/NovaCrypto/BIP39
-                    StringBuilder sb = new StringBuilder();
-                    byte[] entropy = new byte[Words.TWELVE.byteLength()];
-                    new SecureRandom().nextBytes(entropy);
-                    new MnemonicGenerator(English.INSTANCE).createMnemonic(entropy, sb::append);
-                    String mnemonic = sb.toString();
+                    List<String> words = new ArrayList<>();
+                    SecureRandom rnd = new SecureRandom();
+                    for (int i = 0; i < BIP39_WORDS; i++)
+                        words.add(BIP39.words[rnd.nextInt(2048)]);
+                    String mnemonic = TextUtils.join(" ", words);
 
                     prefs.edit().putString("wipe_mnemonic", mnemonic).apply();
                     tvMnemonic.setText(mnemonic);