support separate encryption/lockscreen passwords

This adds the necessary infrastructure for allowing users to opt-in to a
distinct device encryption passphrase. The passwords are still tied
together by default. This makes it possible to use a complex encryption
passphrase without losing the convenience of a very simple lockscreen
pin.

This feature can be combined with a forced reboot after a chosen number
of failed unlocking attempts to prevent brute-forcing by requiring the
entry of the encryption password instead.

3 files changed, 77 insertions, 3 deletions

diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 3ab16fe..e6f1f4a 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -4926,6 +4926,13 @@ public final class Settings {
                 "lock_screen_allow_private_notifications";
 
         /**
+         * Separate password for encryption and the lockscreen.
+         * @hide
+         */
+        public static final String LOCK_SEPARATE_ENCRYPTION_PASSWORD =
+                "lock_separate_encryption_password";
+
+        /**
          * Set by the system to track if the user needs to see the call to action for
          * the lockscreen notification policy.
          * @hide
diff --git a/core/java/com/android/internal/widget/LockPatternUtils.java b/core/java/com/android/internal/widget/LockPatternUtils.java
index 5dc91d2..92f520b 100644
--- a/core/java/com/android/internal/widget/LockPatternUtils.java
+++ b/core/java/com/android/internal/widget/LockPatternUtils.java
@@ -462,7 +462,8 @@ public class LockPatternUtils {
             // well, we tried...
         }
 
-        if (userHandle == UserHandle.USER_OWNER) {
+        if (userHandle == UserHandle.USER_OWNER
+                && !isSeparateEncryptionPasswordEnabled()) {
             // Set the encryption password to default.
             updateEncryptionPassword(StorageManager.CRYPT_TYPE_DEFAULT, null);
         }
@@ -523,7 +524,8 @@ public class LockPatternUtils {
 
             // Update the device encryption password.
             if (userId == UserHandle.USER_OWNER
-                    && LockPatternUtils.isDeviceEncryptionEnabled()) {
+                    && LockPatternUtils.isDeviceEncryptionEnabled()
+                    && !isSeparateEncryptionPasswordEnabled()) {
                 if (!shouldEncryptWithCredentials(true)) {
                     clearEncryptionPassword();
                 } else {
@@ -732,7 +734,8 @@ public class LockPatternUtils {
 
             // Update the device encryption password.
             if (userHandle == UserHandle.USER_OWNER
-                    && LockPatternUtils.isDeviceEncryptionEnabled()) {
+                    && LockPatternUtils.isDeviceEncryptionEnabled()
+                    && !isSeparateEncryptionPasswordEnabled()) {
                 if (!shouldEncryptWithCredentials(true)) {
                     clearEncryptionPassword();
                 } else {
@@ -1089,6 +1092,69 @@ public class LockPatternUtils {
         }
     }
 
+    private void updateEncryptionPasswordFromPassword(String password) {
+        if (!TextUtils.isEmpty(password)) {
+            int computedQuality = computePasswordQuality(password);
+            boolean numeric = computedQuality
+                == DevicePolicyManager.PASSWORD_QUALITY_NUMERIC;
+            boolean numericComplex = computedQuality
+                == DevicePolicyManager.PASSWORD_QUALITY_NUMERIC_COMPLEX;
+            int type = numeric || numericComplex ? StorageManager.CRYPT_TYPE_PIN
+                : StorageManager.CRYPT_TYPE_PASSWORD;
+            updateEncryptionPassword(type, password);
+        } else {
+            clearEncryptionPassword();
+        }
+    }
+
+    /**
+     * Set the encryption password separately from the lockscreen password.
+     *
+     * @param password The password to save
+     */
+    public void setSeparateEncryptionPassword(String password) {
+        updateEncryptionPasswordFromPassword(password);
+        setSeparateEncryptionPasswordEnabled(true);
+    }
+
+    /**
+     * Replace the separate encryption password by tying it to the lockscreen
+     * password. No change will occur if the provided lockscreen password is
+     * incorrect.
+     *
+     * @param password The current lockscreen password
+     * @return Whether the lockscreen password was correct.
+     */
+    public void replaceSeparateEncryptionPassword(String password) {
+        updateEncryptionPasswordFromPassword(password);
+        setSeparateEncryptionPasswordEnabled(false);
+    }
+
+    /**
+     * Replace the separate encryption password by tying it to the lockscreen
+     * pattern. No change will occur if the provided lockscreen password is
+     * incorrect.
+     *
+     * @param pattern The current lockscreen pattern
+     * @return Whether the lockscreen pattern was correct.
+     */
+    public void replaceSeparateEncryptionPasswordWithPattern(List<LockPatternView.Cell> pattern) {
+        String stringPattern = patternToString(pattern);
+        updateEncryptionPassword(StorageManager.CRYPT_TYPE_PATTERN, stringPattern);
+        setSeparateEncryptionPasswordEnabled(false);
+    }
+
+    /**
+     * @return Whether the encryption password is separate from the lockscreen password.
+     */
+    public boolean isSeparateEncryptionPasswordEnabled() {
+        return getBoolean(Settings.Secure.LOCK_SEPARATE_ENCRYPTION_PASSWORD, false, UserHandle.USER_OWNER);
+    }
+
+    private void setSeparateEncryptionPasswordEnabled(boolean enabled) {
+        setBoolean(Settings.Secure.LOCK_SEPARATE_ENCRYPTION_PASSWORD, enabled, UserHandle.USER_OWNER);
+    }
+
     /**
      * @return Whether tactile feedback for the pattern is enabled.
      */
diff --git a/services/core/java/com/android/server/LockSettingsService.java b/services/core/java/com/android/server/LockSettingsService.java
index 10b0bdd..81cbc19 100644
--- a/services/core/java/com/android/server/LockSettingsService.java
+++ b/services/core/java/com/android/server/LockSettingsService.java
@@ -839,6 +839,7 @@ public class LockSettingsService extends ILockSettings.Stub {
         Secure.LOCK_PATTERN_SIZE,
         Secure.LOCK_DOTS_VISIBLE,
         Secure.LOCK_SHOW_ERROR_PATH,
+        Secure.LOCK_SEPARATE_ENCRYPTION_PASSWORD
     };
 
     // Reading these settings needs the contacts permission