Store the backup password encrypted

Closes #49

app/src/main/java/org/shadowice/flocke/andotp/Activities/BackupActivity.java

@@ -133,7 +133,7 @@ public class BackupActivity extends BaseActivity {
         LinearLayout backupCrypt = v.findViewById(R.id.button_backup_crypt);
         LinearLayout restoreCrypt = v.findViewById(R.id.button_restore_crypt);
 
-        if (settings.getBackupPassword().isEmpty()) {
+        if (settings.getBackupPasswordEnc().isEmpty()) {
             cryptSetup.setVisibility(View.VISIBLE);
             backupCrypt.setVisibility(View.GONE);
             restoreCrypt.setVisibility(View.GONE);
@@ -392,7 +392,7 @@ public class BackupActivity extends BaseActivity {
     /* Encrypted backup functions */
 
     private void doRestoreCrypt(Uri uri) {
-        String password = settings.getBackupPassword();
+        String password = settings.getBackupPasswordEnc();
 
         if (! password.isEmpty()) {
             if (StorageHelper.isExternalStorageReadable()) {
@@ -428,7 +428,7 @@ public class BackupActivity extends BaseActivity {
     }
 
     private void doBackupCrypt(Uri uri) {
-        String password = settings.getBackupPassword();
+        String password = settings.getBackupPasswordEnc();
 
         if (! password.isEmpty()) {
             if (StorageHelper.isExternalStorageWritable()) {

app/src/main/java/org/shadowice/flocke/andotp/Preferences/PasswordEncryptedPreference.java

@@ -33,19 +33,28 @@ import android.text.InputType;
 import android.text.TextWatcher;
 import android.text.method.PasswordTransformationMethod;
 import android.util.AttributeSet;
+import android.util.Base64;
 import android.view.View;
 import android.widget.Button;
 import android.widget.EditText;
 
 import org.shadowice.flocke.andotp.R;
+import org.shadowice.flocke.andotp.Utilities.EncryptionHelper;
+import org.shadowice.flocke.andotp.Utilities.KeyStoreHelper;
 
-public class PasswordPreference extends DialogPreference
+import java.nio.charset.StandardCharsets;
+import java.security.KeyPair;
+
+public class PasswordEncryptedPreference extends DialogPreference
     implements View.OnClickListener, TextWatcher {
 
     public enum Mode {
         PASSWORD, PIN
     }
 
+    public static final String KEY_ALIAS = "password";
+    private KeyPair key;
+
     private static final String DEFAULT_VALUE = "";
 
     private Mode mode = Mode.PASSWORD;
@@ -57,9 +66,15 @@ public class PasswordPreference extends DialogPreference
 
     private String value = DEFAULT_VALUE;
 
-    public PasswordPreference(Context context, AttributeSet attrs) {
+    public PasswordEncryptedPreference(Context context, AttributeSet attrs) {
         super(context, attrs);
 
+        try {
+            key = KeyStoreHelper.loadOrGenerateAsymmetricKeyPair(context, KEY_ALIAS);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+
         setDialogLayoutResource(R.layout.component_password);
     }
 
@@ -120,13 +135,31 @@ public class PasswordPreference extends DialogPreference
         return a.getString(index);
     }
 
+    private void encryptAndPersist(String value) {
+        try {
+            byte[] encBytes = EncryptionHelper.encrypt(key.getPublic(), value.getBytes(StandardCharsets.UTF_8));
+            persistString(Base64.encodeToString(encBytes, Base64.URL_SAFE));
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+    private void restoreAndDecrypt(String encValue) {
+        try {
+            byte[] encBytes = Base64.decode(encValue, Base64.URL_SAFE);
+            value = new String(EncryptionHelper.decrypt(key.getPrivate(), encBytes), StandardCharsets.UTF_8);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
     @Override
     protected void onSetInitialValue(boolean restorePersistedValue, Object defaultValue) {
         if (restorePersistedValue) {
-            value = getPersistedString(DEFAULT_VALUE);
+            restoreAndDecrypt(getPersistedString(DEFAULT_VALUE));
         } else {
             value = (String) defaultValue;
-            persistString(value);
+            encryptAndPersist(value);
         }
     }
 
@@ -138,7 +171,7 @@ public class PasswordPreference extends DialogPreference
                 break;
             case (R.id.btnSave):
                 value = passwordInput.getText().toString();
-                persistString(value);
+                encryptAndPersist(value);
 
                 getDialog().dismiss();
                 break;

app/src/main/java/org/shadowice/flocke/andotp/Utilities/EncryptionHelper.java

@@ -29,6 +29,8 @@ import java.security.InvalidAlgorithmParameterException;
 import java.security.InvalidKeyException;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.security.PrivateKey;
+import java.security.PublicKey;
 import java.security.SecureRandom;
 import java.util.Arrays;
 
@@ -41,7 +43,9 @@ import javax.crypto.spec.IvParameterSpec;
 import javax.crypto.spec.SecretKeySpec;
 
 public class EncryptionHelper {
-    private final static String ALGORITHM = "AES/GCM/NoPadding";
+    private final static String ALGORITHM_SYMMETRIC = "AES/GCM/NoPadding";
+    private final static String ALGORITHM_ASYMMETRIC = "RSA/ECB/PKCS1Padding";
+
     private final static int IV_LENGTH = 12;
 
     public static SecretKey generateSymmetricKeyFromPassword(String password)
@@ -51,30 +55,14 @@ public class EncryptionHelper {
         return new SecretKeySpec(sha.digest(password.getBytes(StandardCharsets.UTF_8)), "AES");
     }
 
-    public static byte[] encrypt(SecretKey secretKey, IvParameterSpec iv, byte[] plainText)
-            throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, UnsupportedEncodingException, BadPaddingException, IllegalBlockSizeException {
-        Cipher cipher = Cipher.getInstance(ALGORITHM);
-        cipher.init(Cipher.ENCRYPT_MODE, secretKey, iv);
-
-        return cipher.doFinal(plainText);
-    }
-
-    public static byte[] decrypt(SecretKey secretKey, IvParameterSpec iv, byte[] cipherText)
-            throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
-        Cipher cipher = Cipher.getInstance(ALGORITHM);
-        cipher.init(Cipher.DECRYPT_MODE, secretKey, iv);
-
-        return cipher.doFinal(cipherText);
-    }
-
-
     public static byte[] encrypt(SecretKey secretKey, byte[] plaintext)
             throws NoSuchPaddingException, BadPaddingException, InvalidKeyException, NoSuchAlgorithmException, IllegalBlockSizeException, UnsupportedEncodingException, InvalidAlgorithmParameterException {
         final byte[] iv = new byte[IV_LENGTH];
         new SecureRandom().nextBytes(iv);
 
-        byte[] cipherText = encrypt(secretKey, new IvParameterSpec(iv), plaintext);
+        Cipher cipher = Cipher.getInstance(ALGORITHM_SYMMETRIC);
-
+        cipher.init(Cipher.ENCRYPT_MODE, secretKey, new IvParameterSpec(iv));
+        byte[] cipherText = cipher.doFinal(plaintext);
 
         byte[] combined = new byte[iv.length + cipherText.length];
         System.arraycopy(iv, 0, combined, 0, iv.length);
@@ -83,11 +71,30 @@ public class EncryptionHelper {
         return combined;
     }
 
+    public static byte[] encrypt(PublicKey publicKey, byte[] plaintext)
+            throws NoSuchPaddingException, BadPaddingException, InvalidKeyException, NoSuchAlgorithmException, IllegalBlockSizeException, UnsupportedEncodingException, InvalidAlgorithmParameterException {
+        Cipher cipher = Cipher.getInstance(ALGORITHM_ASYMMETRIC);
+        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
+
+        return cipher.doFinal(plaintext);
+    }
+
     public static byte[] decrypt(SecretKey secretKey, byte[] cipherText)
             throws NoSuchPaddingException, InvalidKeyException, NoSuchAlgorithmException, IllegalBlockSizeException, BadPaddingException, InvalidAlgorithmParameterException {
         byte[] iv = Arrays.copyOfRange(cipherText, 0, IV_LENGTH);
-        byte[] cipher = Arrays.copyOfRange(cipherText, IV_LENGTH,cipherText.length);
+        byte[] encrypted = Arrays.copyOfRange(cipherText, IV_LENGTH, cipherText.length);
 
-        return decrypt(secretKey,new IvParameterSpec(iv), cipher );
+        Cipher cipher = Cipher.getInstance(ALGORITHM_SYMMETRIC);
+        cipher.init(Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec(iv));
+
+        return cipher.doFinal(encrypted);
+    }
+
+    public static byte[] decrypt(PrivateKey privateKey, byte[] cipherText)
+            throws NoSuchPaddingException, InvalidKeyException, NoSuchAlgorithmException, IllegalBlockSizeException, BadPaddingException, InvalidAlgorithmParameterException {
+        Cipher cipher = Cipher.getInstance(ALGORITHM_ASYMMETRIC);
+        cipher.init(Cipher.DECRYPT_MODE, privateKey);
+
+        return cipher.doFinal(cipherText);
     }
 }

app/src/main/java/org/shadowice/flocke/andotp/Utilities/KeyStoreHelper.java

@@ -32,7 +32,6 @@ import java.io.File;
 import java.io.IOException;
 import java.math.BigInteger;
 import java.security.GeneralSecurityException;
-import java.security.Key;
 import java.security.KeyPair;
 import java.security.KeyPairGenerator;
 import java.security.KeyStore;
@@ -41,7 +40,6 @@ import java.security.spec.AlgorithmParameterSpec;
 import java.util.Calendar;
 import java.util.GregorianCalendar;
 
-import javax.crypto.KeyGenerator;
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
 import javax.security.auth.x500.X500Principal;
@@ -49,13 +47,19 @@ import javax.security.auth.x500.X500Principal;
 public class KeyStoreHelper {
     private final static int KEY_LENGTH = 16;
 
-    private static AlgorithmParameterSpec generateAlgorithmSpec(Context context, String alias) {
+    public static KeyPair loadOrGenerateAsymmetricKeyPair(Context context, String alias)
+            throws GeneralSecurityException, IOException {
+        final KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
+        keyStore.load(null);
+
+        if (! keyStore.containsAlias(alias)) {
             final Calendar start = new GregorianCalendar();
             final Calendar end = new GregorianCalendar();
             end.add(Calendar.YEAR, 100);
 
+            AlgorithmParameterSpec spec;
             if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
-            return new KeyGenParameterSpec.Builder(alias, KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
+                spec = new KeyGenParameterSpec.Builder(alias, KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
                         .setCertificateSubject(new X500Principal("CN=" + alias))
                         .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)
                         .setCertificateSerialNumber(BigInteger.ONE)
@@ -63,7 +67,7 @@ public class KeyStoreHelper {
                         .setCertificateNotAfter(end.getTime())
                         .build();
             } else {
-            return new KeyPairGeneratorSpec.Builder(context)
+                spec = new KeyPairGeneratorSpec.Builder(context)
                         .setAlias(alias)
                         .setSubject(new X500Principal("CN=" + alias))
                         .setSerialNumber(BigInteger.ONE)
@@ -71,17 +75,10 @@ public class KeyStoreHelper {
                         .setEndDate(end.getTime())
                         .build();
             }
-    }
 
-    public static KeyPair loadOrGenerateAsymmetricKeyPair(Context context, String alias)
-            throws GeneralSecurityException, IOException {
-        final KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
-        keyStore.load(null);
-
-        if (! keyStore.containsAlias(alias)) {
             KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
 
-            gen.initialize(generateAlgorithmSpec(context, alias));
+            gen.initialize(spec);
             gen.generateKeyPair();
         }
 
@@ -89,21 +86,6 @@ public class KeyStoreHelper {
         return new KeyPair(entry.getCertificate().getPublicKey(), entry.getPrivateKey());
     }
 
-    public static Key loadOrGenerateSymmetricKey(Context context, String alias)
-            throws GeneralSecurityException, IOException {
-        final KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
-        keyStore.load(null);
-
-        if (! keyStore.containsAlias(alias)) {
-            KeyGenerator gen = KeyGenerator.getInstance("AES", "AndroidKeyStore");
-
-            gen.init(generateAlgorithmSpec(context, alias));
-            gen.generateKey();
-        }
-
-        return keyStore.getKey(alias, null);
-    }
-
     /**
      * Load our symmetric secret key.
      * The symmetric secret key is stored securely on disk by wrapping

app/src/main/java/org/shadowice/flocke/andotp/Utilities/Settings.java

@@ -25,14 +25,19 @@ package org.shadowice.flocke.andotp.Utilities;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.preference.PreferenceManager;
+import android.util.Base64;
 
 import org.apache.commons.codec.binary.Hex;
 import org.apache.commons.codec.digest.DigestUtils;
 import org.shadowice.flocke.andotp.R;
 
+import java.nio.charset.StandardCharsets;
+import java.security.KeyPair;
 import java.util.Collections;
 import java.util.Set;
 
+import static org.shadowice.flocke.andotp.Preferences.PasswordEncryptedPreference.KEY_ALIAS;
+
 public class Settings {
     private Context context;
     private SharedPreferences settings;
@@ -70,6 +75,21 @@ public class Settings {
 
             remove(R.string.settings_key_auth_pin);
         }
+
+        if (settings.contains(getResString(R.string.settings_key_backup_password))) {
+            String plainPassword = getBackupPassword();
+
+            try {
+                KeyPair key = KeyStoreHelper.loadOrGenerateAsymmetricKeyPair(context, KEY_ALIAS);
+                byte[] encPassword = EncryptionHelper.encrypt(key.getPublic(), plainPassword.getBytes(StandardCharsets.UTF_8));
+
+                setString(R.string.settings_key_backup_password_enc, Base64.encodeToString(encPassword, Base64.URL_SAFE));
+
+                remove(R.string.settings_key_backup_password);
+            } catch (Exception e) {
+                e.printStackTrace();
+            }
+        }
     }
 
     private String getResString(int resId) {
@@ -195,6 +215,22 @@ public class Settings {
         return getString(R.string.settings_key_backup_password, "");
     }
 
+    public String getBackupPasswordEnc() {
+        String base64Password = getString(R.string.settings_key_backup_password_enc, "");
+        byte[] encPassword = Base64.decode(base64Password, Base64.URL_SAFE);
+
+        String password = "";
+
+        try {
+            KeyPair key = KeyStoreHelper.loadOrGenerateAsymmetricKeyPair(context, KEY_ALIAS);
+            password = new String(EncryptionHelper.decrypt(key.getPrivate(), encPassword), StandardCharsets.UTF_8);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+
+        return password;
+    }
+
     public String getOpenPGPProvider() {
         return getString(R.string.settings_key_openpgp_provider, "");
     }

app/src/main/res/values/settings.xml

@@ -15,6 +15,7 @@
     <string name="settings_key_label_size" translatable="false">pref_label_size</string>
 
     <string name="settings_key_backup_password" translatable="false">pref_backup_password</string>
+    <string name="settings_key_backup_password_enc" translatable="false">pref_backup_password_enc</string>
     <string name="settings_key_openpgp_provider" translatable="false">pref_openpgp_provider</string>
     <string name="settings_key_openpgp_keyid" translatable="false">pref_openpgp_keyid</string>
     <string name="settings_key_openpgp_sign" translatable="false">pref_openpgp_sign</string>

app/src/main/res/xml/preferences.xml

@@ -57,8 +57,8 @@
     <PreferenceCategory
         android:title="@string/settings_category_title_backup">
 
-        <org.shadowice.flocke.andotp.Preferences.PasswordPreference
+        <org.shadowice.flocke.andotp.Preferences.PasswordEncryptedPreference
-            android:key="@string/settings_key_backup_password"
+            android:key="@string/settings_key_backup_password_enc"
             android:title="@string/settings_title_backup_password"
             android:summary="@string/settings_desc_backup_password" />