Store passwords encrypted

FAQ.md

@@ -702,10 +702,11 @@ Long version:
 <a name="faq37"></a>
 **(37) How are passwords stored?**
 
-Providers require passwords in plain text, so the background service that takes care of synchronizing messages needs to send passwords in plain text.
-Since encrypting passwords would require a secret and the background service needs to know this secret, this could only be done by storing that secret.
-Storing a secret together with encrypted passwords would not add anything, so passwords are stored in plain text in a safe, inaccessible place.
-Recent Android versions encrypt all user data anyway.
+On Android 6 Marshmallow and later passwords are stored encrypted in an app private database.
+Passwords are encrypted with the cipher AES/GCM/NoPadding
+and a generated secret key stored by the [Android keystore system](https://developer.android.com/training/articles/keystore).
+
+On earlier Android versions passwords are stored in plain text.
 
 <br />
 

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

@@ -3,6 +3,7 @@ package eu.faircode.email;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.database.Cursor;
+import android.os.Build;
 import android.preference.PreferenceManager;
 import android.text.TextUtils;
 
@@ -49,7 +50,7 @@ import io.requery.android.database.sqlite.RequerySQLiteOpenHelperFactory;
 // https://developer.android.com/topic/libraries/architecture/room.html
 
 @Database(
-        version = 52,
+        version = 53,
         entities = {
                 EntityIdentity.class,
                 EntityAccount.class,
@@ -560,6 +561,33 @@ public abstract class DB extends RoomDatabase {
                         db.execSQL("ALTER TABLE `folder` ADD COLUMN `total` INTEGER");
                     }
                 })
+                .addMigrations(new Migration(52, 53) {
+                    @Override
+                    public void migrate(SupportSQLiteDatabase db) {
+                        Log.i("DB migration from version " + startVersion + " to " + endVersion);
+                        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+                            Cursor cursor = db.query("SELECT id, password FROM account");
+                            while (cursor.moveToNext()) {
+                                long id = cursor.getLong(0);
+                                String plain = cursor.getString(1);
+                                db.execSQL("UPDATE account SET password = ? WHERE id = ?",
+                                        new Object[]{id, Helper.encryptPassword(plain)});
+                            }
+                            cursor.close();
+                        }
+
+                        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+                            Cursor cursor = db.query("SELECT id, password FROM identity");
+                            while (cursor.moveToNext()) {
+                                long id = cursor.getLong(0);
+                                String plain = cursor.getString(1);
+                                db.execSQL("UPDATE identity SET password = ? WHERE id = ?",
+                                        new Object[]{id, Helper.encryptPassword(plain)});
+                            }
+                            cursor.close();
+                        }
+                    }
+                })
                 .build();
     }
 

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

@@ -95,6 +95,20 @@ public class EntityAccount implements Serializable {
         return "imap" + (starttls ? "" : "s");
     }
 
+    String getPassword() {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M)
+            return this.password;
+        else
+            return Helper.decryptPassword(this.password);
+    }
+
+    void setPassword(String plain) {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M)
+            this.password = plain;
+        else
+            this.password = Helper.encryptPassword(plain);
+    }
+
     static String getNotificationChannelName(long account) {
         return "notification" + (account == 0 ? "" : "." + account);
     }
@@ -124,7 +138,7 @@ public class EntityAccount implements Serializable {
         json.put("insecure", insecure);
         json.put("port", port);
         json.put("user", user);
-        json.put("password", password);
+        json.put("password", getPassword());
         json.put("realm", realm);
 
         json.put("name", name);
@@ -156,7 +170,7 @@ public class EntityAccount implements Serializable {
         account.insecure = (json.has("insecure") && json.getBoolean("insecure"));
         account.port = json.getInt("port");
         account.user = json.getString("user");
-        account.password = json.getString("password");
+        account.setPassword(json.getString("password"));
         if (json.has("realm"))
             account.realm = json.getString("realm");
 
@@ -194,7 +208,7 @@ public class EntityAccount implements Serializable {
                     this.insecure == other.insecure &&
                     this.port.equals(other.port) &&
                     this.user.equals(other.user) &&
-                    this.password.equals(other.password) &&
+                    this.getPassword().equals(other.getPassword()) &&
                     Objects.equals(this.realm, other.realm) &&
                     Objects.equals(this.name, other.name) &&
                     Objects.equals(this.color, other.color) &&

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

@@ -19,6 +19,8 @@ package eu.faircode.email;
     Copyright 2018-2019 by Marcel Bokhorst (M66B)
 */
 
+import android.os.Build;
+
 import org.json.JSONException;
 import org.json.JSONObject;
 
@@ -99,6 +101,20 @@ public class EntityIdentity {
         return (starttls ? "smtp" : "smtps");
     }
 
+    String getPassword() {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M)
+            return this.password;
+        else
+            return Helper.decryptPassword(this.password);
+    }
+
+    void setPassword(String plain) {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M)
+            this.password = plain;
+        else
+            this.password = Helper.encryptPassword(plain);
+    }
+
     public JSONObject toJSON() throws JSONException {
         JSONObject json = new JSONObject();
         json.put("id", id);
@@ -116,7 +132,7 @@ public class EntityIdentity {
         json.put("insecure", insecure);
         json.put("port", port);
         json.put("user", user);
-        json.put("password", password);
+        json.put("password", getPassword());
         json.put("realm", realm);
         json.put("use_ip", use_ip);
 
@@ -154,7 +170,7 @@ public class EntityIdentity {
         identity.insecure = (json.has("insecure") && json.getBoolean("insecure"));
         identity.port = json.getInt("port");
         identity.user = json.getString("user");
-        identity.password = json.getString("password");
+        identity.setPassword(json.getString("password"));
         if (json.has("realm"))
             identity.realm = json.getString("realm");
         if (json.has("use_ip"))
@@ -199,7 +215,7 @@ public class EntityIdentity {
                     this.insecure.equals(other.insecure) &&
                     this.port.equals(other.port) &&
                     this.user.equals(other.user) &&
-                    this.password.equals(other.password) &&
+                    this.getPassword().equals(other.getPassword()) &&
                     Objects.equals(this.realm, other.realm) &&
                     this.use_ip == other.use_ip &&
                     this.synchronize.equals(other.synchronize) &&

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

@@ -845,7 +845,7 @@ public class FragmentAccount extends FragmentBase {
                 boolean check = (synchronize && (account == null ||
                         auth_type != account.auth_type ||
                         !host.equals(account.host) || Integer.parseInt(port) != account.port ||
-                        !user.equals(account.user) || !password.equals(account.password) ||
+                        !user.equals(account.user) || !password.equals(account.getPassword()) ||
                         !Objects.equals(realm, accountRealm)));
                 boolean reload = (check || account == null ||
                         !Objects.equals(account.prefix, prefix) ||
@@ -914,7 +914,7 @@ public class FragmentAccount extends FragmentBase {
                     account.insecure = insecure;
                     account.port = Integer.parseInt(port);
                     account.user = user;
-                    account.password = password;
+                    account.setPassword(password);
                     account.realm = realm;
 
                     account.name = name;
@@ -1135,7 +1135,7 @@ public class FragmentAccount extends FragmentBase {
 
                     etUser.setTag(account == null || auth_type == Helper.AUTH_TYPE_PASSWORD ? null : account.user);
                     etUser.setText(account == null ? null : account.user);
-                    tilPassword.getEditText().setText(account == null ? null : account.password);
+                    tilPassword.getEditText().setText(account == null ? null : account.getPassword());
                     etRealm.setText(account == null ? null : account.realm);
 
                     etName.setText(account == null ? null : account.name);

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

@@ -237,7 +237,7 @@ public class FragmentIdentity extends FragmentBase {
                 etEmail.setText(account.user);
                 etUser.setTag(auth_type == Helper.AUTH_TYPE_PASSWORD ? null : account.user);
                 etUser.setText(account.user);
-                tilPassword.getEditText().setText(account.password);
+                tilPassword.getEditText().setText(account.getPassword());
                 etRealm.setText(account.realm);
                 tilPassword.setEnabled(auth_type == Helper.AUTH_TYPE_PASSWORD);
                 etRealm.setEnabled(auth_type == Helper.AUTH_TYPE_PASSWORD);
@@ -589,7 +589,7 @@ public class FragmentIdentity extends FragmentBase {
                 boolean check = (synchronize && (identity == null ||
                         auth_type != identity.auth_type ||
                         !host.equals(identity.host) || Integer.parseInt(port) != identity.port ||
-                        !user.equals(identity.user) || !password.equals(identity.password) ||
+                        !user.equals(identity.user) || !password.equals(identity.getPassword()) ||
                         !Objects.equals(realm, identityRealm) ||
                         use_ip != identity.use_ip));
                 boolean reload = (identity == null || identity.synchronize != synchronize || check);
@@ -655,7 +655,7 @@ public class FragmentIdentity extends FragmentBase {
                     identity.insecure = insecure;
                     identity.port = Integer.parseInt(port);
                     identity.user = user;
-                    identity.password = password;
+                    identity.setPassword(password);
                     identity.realm = realm;
                     identity.use_ip = use_ip;
                     identity.synchronize = synchronize;
@@ -759,7 +759,7 @@ public class FragmentIdentity extends FragmentBase {
                     etPort.setText(identity == null ? null : Long.toString(identity.port));
                     etUser.setTag(identity == null || auth_type == Helper.AUTH_TYPE_PASSWORD ? null : identity.user);
                     etUser.setText(identity == null ? null : identity.user);
-                    tilPassword.getEditText().setText(identity == null ? null : identity.password);
+                    tilPassword.getEditText().setText(identity == null ? null : identity.getPassword());
                     etRealm.setText(identity == null ? null : identity.realm);
                     cbUseIp.setChecked(identity == null ? true : identity.use_ip);
                     cbSynchronize.setChecked(identity == null ? true : identity.synchronize);
@@ -864,7 +864,7 @@ public class FragmentIdentity extends FragmentBase {
                                     spAccount.setSelection(pos);
                                     // OAuth token could be updated
                                     if (pos > 0 && accounts.get(pos).auth_type != Helper.AUTH_TYPE_PASSWORD)
-                                        tilPassword.getEditText().setText(accounts.get(pos).password);
+                                        tilPassword.getEditText().setText(accounts.get(pos).getPassword());
                                     break;
                                 }
                             }

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

@@ -335,7 +335,7 @@ public class FragmentQuickSetup extends FragmentBase {
                     account.insecure = false;
                     account.port = provider.imap_port;
                     account.user = user;
-                    account.password = password;
+                    account.setPassword(password);
 
                     account.name = provider.name;
                     account.color = null;
@@ -389,7 +389,7 @@ public class FragmentQuickSetup extends FragmentBase {
                     identity.insecure = false;
                     identity.port = provider.smtp_port;
                     identity.user = user;
-                    identity.password = password;
+                    identity.setPassword(password);
                     identity.synchronize = true;
                     identity.primary = true;
 

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

@@ -42,7 +42,10 @@ import android.os.Build;
 import android.os.Bundle;
 import android.os.PowerManager;
 import android.preference.PreferenceManager;
+import android.security.keystore.KeyGenParameterSpec;
+import android.security.keystore.KeyProperties;
 import android.text.TextUtils;
+import android.util.Base64;
 import android.view.Menu;
 import android.view.View;
 import android.view.ViewGroup;
@@ -77,6 +80,8 @@ import java.io.UnsupportedEncodingException;
 import java.net.InetAddress;
 import java.net.URL;
 import java.net.UnknownHostException;
+import java.nio.charset.StandardCharsets;
+import java.security.KeyStore;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.text.DateFormat;
@@ -91,6 +96,10 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.ThreadFactory;
 
+import javax.crypto.Cipher;
+import javax.crypto.KeyGenerator;
+import javax.crypto.SecretKey;
+import javax.crypto.spec.GCMParameterSpec;
 import javax.mail.Address;
 import javax.mail.AuthenticationFailedException;
 import javax.mail.FolderClosedException;
@@ -100,6 +109,7 @@ import javax.mail.internet.InternetAddress;
 import javax.net.ssl.HttpsURLConnection;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
 import androidx.browser.customtabs.CustomTabsIntent;
 import androidx.core.content.ContextCompat;
 import androidx.lifecycle.Lifecycle;
@@ -809,12 +819,12 @@ public class Helper {
 
     static void connect(Context context, IMAPStore istore, EntityAccount account) throws MessagingException {
         try {
-            istore.connect(account.host, account.port, account.user, account.password);
+            istore.connect(account.host, account.port, account.user, account.getPassword());
         } catch (AuthenticationFailedException ex) {
             if (account.auth_type == AUTH_TYPE_GMAIL) {
-                account.password = refreshToken(context, "com.google", account.user, account.password);
+                account.setPassword(refreshToken(context, "com.google", account.user, account.getPassword()));
                 DB.getInstance(context).account().setAccountPassword(account.id, account.password);
-                istore.connect(account.host, account.port, account.user, account.password);
+                istore.connect(account.host, account.port, account.user, account.getPassword());
             } else
                 throw ex;
         }
@@ -1043,4 +1053,56 @@ public class Helper {
             return organization;
         }
     }
+
+    @RequiresApi(api = Build.VERSION_CODES.M)
+    private static SecretKey getSecretKey() throws Throwable {
+        final String alias = BuildConfig.APPLICATION_ID + ".key";
+
+        KeyStore store = KeyStore.getInstance("AndroidKeyStore");
+        store.load(null);
+
+        KeyStore.SecretKeyEntry entry = (KeyStore.SecretKeyEntry) store.getEntry(alias, null);
+        if (entry != null)
+            return entry.getSecretKey();
+
+        KeyGenerator generator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
+        KeyGenParameterSpec spec = new KeyGenParameterSpec.Builder(alias,
+                KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
+                .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
+                .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
+                .build();
+        generator.init(spec);
+        return generator.generateKey();
+    }
+
+    @RequiresApi(api = Build.VERSION_CODES.M)
+    static String decryptPassword(String secret) {
+        try {
+            int slash = secret.indexOf('/');
+            byte[] iv = Base64.decode(secret.substring(0, slash), Base64.URL_SAFE);
+            byte[] encrypted = Base64.decode(secret.substring(slash + 1), Base64.URL_SAFE);
+            Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
+            GCMParameterSpec spec = new GCMParameterSpec(128, iv);
+            cipher.init(Cipher.DECRYPT_MODE, getSecretKey(), spec);
+            byte[] decrypted = cipher.doFinal(encrypted);
+            return new String(decrypted, StandardCharsets.UTF_8);
+        } catch (Throwable ex) {
+            Log.e(ex);
+            return secret;
+        }
+    }
+
+    @RequiresApi(api = Build.VERSION_CODES.M)
+    static String encryptPassword(String plain) {
+        try {
+            Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
+            cipher.init(Cipher.ENCRYPT_MODE, getSecretKey());
+            byte[] iv = cipher.getIV();
+            byte[] encrypted = cipher.doFinal(plain.getBytes(StandardCharsets.UTF_8));
+            return Base64.encodeToString(iv, Base64.URL_SAFE) + "/" + Base64.encodeToString(encrypted, Base64.URL_SAFE);
+        } catch (Throwable ex) {
+            Log.e(ex);
+            return plain;
+        }
+    }
 }

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

@@ -294,13 +294,13 @@ public class ServiceSend extends LifecycleService {
             // Connect transport
             db.identity().setIdentityState(ident.id, "connecting");
             try {
-                itransport.connect(ident.host, ident.port, ident.user, ident.password);
+                itransport.connect(ident.host, ident.port, ident.user, ident.getPassword());
             } catch (AuthenticationFailedException ex) {
                 if (ident.auth_type == Helper.AUTH_TYPE_GMAIL) {
                     EntityAccount account = db.account().getAccount(ident.account);
-                    ident.password = Helper.refreshToken(this, "com.google", ident.user, account.password);
+                    ident.setPassword(Helper.refreshToken(this, "com.google", ident.user, account.getPassword()));
                     DB.getInstance(this).identity().setIdentityPassword(ident.id, ident.password);
-                    itransport.connect(ident.host, ident.port, ident.user, ident.password);
+                    itransport.connect(ident.host, ident.port, ident.user, ident.getPassword());
                 } else
                     throw ex;
             }