core/java/com/android/internal/widget/LockPatternUtils.java

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.internal.widget;

import android.annotation.IntDef;
import android.app.admin.DevicePolicyManager;
import android.app.trust.IStrongAuthTracker;
import android.app.trust.TrustManager;
import android.content.ComponentName;
import android.content.ContentResolver;
import android.content.Context;
import android.content.pm.UserInfo;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.os.SystemClock;
import android.os.SystemProperties;
import android.os.UserHandle;
import android.os.UserManager;
import android.os.storage.IMountService;
import android.os.storage.StorageManager;
import android.provider.Settings;
import android.text.TextUtils;
import android.util.Log;
import android.util.SparseIntArray;

import com.google.android.collect.Lists;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import libcore.util.HexEncoding;

/**
 * Utilities for the lock pattern and its settings.
 */
public class LockPatternUtils {

    private static final String TAG = "LockPatternUtils";
    private static final boolean DEBUG = false;

    /**
     * The key to identify when the lock pattern enabled flag is being acccessed for legacy reasons.
     */
    public static final String LEGACY_LOCK_PATTERN_ENABLED = "legacy_lock_pattern_enabled";

    /**
     * The number of incorrect attempts before which we fall back on an alternative
     * method of verifying the user, and resetting their lock pattern.
     */
    public static final int FAILED_ATTEMPTS_BEFORE_RESET = 20;

    /**
     * The interval of the countdown for showing progress of the lockout.
     */
    public static final long FAILED_ATTEMPT_COUNTDOWN_INTERVAL_MS = 1000L;


    /**
     * This dictates when we start telling the user that continued failed attempts will wipe
     * their device.
     */
    public static final int FAILED_ATTEMPTS_BEFORE_WIPE_GRACE = 5;

    /**
     * The minimum number of dots in a valid pattern.
     */
    public static final int MIN_LOCK_PATTERN_SIZE = 4;

    /**
     * The minimum size of a valid password.
     */
    public static final int MIN_LOCK_PASSWORD_SIZE = 4;

    /**
     * The minimum number of dots the user must include in a wrong pattern
     * attempt for it to be counted against the counts that affect
     * {@link #FAILED_ATTEMPTS_BEFORE_TIMEOUT} and {@link #FAILED_ATTEMPTS_BEFORE_RESET}
     */
    public static final int MIN_PATTERN_REGISTER_FAIL = MIN_LOCK_PATTERN_SIZE;

    @Deprecated
    public final static String LOCKOUT_PERMANENT_KEY = "lockscreen.lockedoutpermanently";
    public final static String LOCKOUT_ATTEMPT_DEADLINE = "lockscreen.lockoutattemptdeadline";
    public final static String LOCKOUT_ATTEMPT_TIMEOUT_MS = "lockscreen.lockoutattempttimeoutmss";
    public final static String PATTERN_EVER_CHOSEN_KEY = "lockscreen.patterneverchosen";
    public final static String PASSWORD_TYPE_KEY = "lockscreen.password_type";
    @Deprecated
    public final static String PASSWORD_TYPE_ALTERNATE_KEY = "lockscreen.password_type_alternate";
    public final static String LOCK_PASSWORD_SALT_KEY = "lockscreen.password_salt";
    public final static String DISABLE_LOCKSCREEN_KEY = "lockscreen.disabled";
    public final static String LOCKSCREEN_OPTIONS = "lockscreen.options";
    @Deprecated
    public final static String LOCKSCREEN_BIOMETRIC_WEAK_FALLBACK
            = "lockscreen.biometric_weak_fallback";
    @Deprecated
    public final static String BIOMETRIC_WEAK_EVER_CHOSEN_KEY
            = "lockscreen.biometricweakeverchosen";
    public final static String LOCKSCREEN_POWER_BUTTON_INSTANTLY_LOCKS
            = "lockscreen.power_button_instantly_locks";
    @Deprecated
    public final static String LOCKSCREEN_WIDGETS_ENABLED = "lockscreen.widgets_enabled";

    public final static String PASSWORD_HISTORY_KEY = "lockscreen.passwordhistory";

    private static final String LOCK_SCREEN_OWNER_INFO = Settings.Secure.LOCK_SCREEN_OWNER_INFO;
    private static final String LOCK_SCREEN_OWNER_INFO_ENABLED =
            Settings.Secure.LOCK_SCREEN_OWNER_INFO_ENABLED;

    private static final String LOCK_SCREEN_DEVICE_OWNER_INFO = "lockscreen.device_owner_info";

    private static final String ENABLED_TRUST_AGENTS = "lockscreen.enabledtrustagents";
    private static final String IS_TRUST_USUALLY_MANAGED = "lockscreen.istrustusuallymanaged";

    private static final String SEPARATE_PROFILE_CHALLENGE_KEY = "lockscreen.profilechallenge";

    // Maximum allowed number of repeated or ordered characters in a sequence before we'll
    // consider it a complex PIN/password.
    public static final int MAX_ALLOWED_SEQUENCE = 3;

    private final Context mContext;
    private final ContentResolver mContentResolver;
    private DevicePolicyManager mDevicePolicyManager;
    private ILockSettings mLockSettingsService;
    private UserManager mUserManager;

    /**
     * Use {@link TrustManager#isTrustUsuallyManaged(int)}.
     *
     * This returns the lazily-peristed value and should only be used by TrustManagerService.
     */
    public boolean isTrustUsuallyManaged(int userId) {
        if (!(mLockSettingsService instanceof ILockSettings.Stub)) {
            throw new IllegalStateException("May only be called by TrustManagerService. "
                    + "Use TrustManager.isTrustUsuallyManaged()");
        }
        try {
            return getLockSettings().getBoolean(IS_TRUST_USUALLY_MANAGED, false, userId);
        } catch (RemoteException e) {
            return false;
        }
    }

    public void setTrustUsuallyManaged(boolean managed, int userId) {
        try {
            getLockSettings().setBoolean(IS_TRUST_USUALLY_MANAGED, managed, userId);
        } catch (RemoteException e) {
            // System dead.
        }
    }

    public static final class RequestThrottledException extends Exception {
        private int mTimeoutMs;
        public RequestThrottledException(int timeoutMs) {
            mTimeoutMs = timeoutMs;
        }

        /**
         * @return The amount of time in ms before another request may
         * be executed
         */
        public int getTimeoutMs() {
            return mTimeoutMs;
        }

    }

    public DevicePolicyManager getDevicePolicyManager() {
        if (mDevicePolicyManager == null) {
            mDevicePolicyManager =
                (DevicePolicyManager)mContext.getSystemService(Context.DEVICE_POLICY_SERVICE);
            if (mDevicePolicyManager == null) {
                Log.e(TAG, "Can't get DevicePolicyManagerService: is it running?",
                        new IllegalStateException("Stack trace:"));
            }
        }
        return mDevicePolicyManager;
    }

    private UserManager getUserManager() {
        if (mUserManager == null) {
            mUserManager = UserManager.get(mContext);
        }
        return mUserManager;
    }

    private TrustManager getTrustManager() {
        TrustManager trust = (TrustManager) mContext.getSystemService(Context.TRUST_SERVICE);
        if (trust == null) {
            Log.e(TAG, "Can't get TrustManagerService: is it running?",
                    new IllegalStateException("Stack trace:"));
        }
        return trust;
    }

    public LockPatternUtils(Context context) {
        mContext = context;
        mContentResolver = context.getContentResolver();
    }

    private ILockSettings getLockSettings() {
        if (mLockSettingsService == null) {
            ILockSettings service = ILockSettings.Stub.asInterface(
                    ServiceManager.getService("lock_settings"));
            mLockSettingsService = service;
        }
        return mLockSettingsService;
    }

    public int getRequestedMinimumPasswordLength(int userId) {
        return getDevicePolicyManager().getPasswordMinimumLength(null, userId);
    }

    /**
     * Gets the device policy password mode. If the mode is non-specific, returns
     * MODE_PATTERN which allows the user to choose anything.
     */
    public int getRequestedPasswordQuality(int userId) {
        return getDevicePolicyManager().getPasswordQuality(null, userId);
    }

    private int getRequestedPasswordHistoryLength(int userId) {
        return getDevicePolicyManager().getPasswordHistoryLength(null, userId);
    }

    public int getRequestedPasswordMinimumLetters(int userId) {
        return getDevicePolicyManager().getPasswordMinimumLetters(null, userId);
    }

    public int getRequestedPasswordMinimumUpperCase(int userId) {
        return getDevicePolicyManager().getPasswordMinimumUpperCase(null, userId);
    }

    public int getRequestedPasswordMinimumLowerCase(int userId) {
        return getDevicePolicyManager().getPasswordMinimumLowerCase(null, userId);
    }

    public int getRequestedPasswordMinimumNumeric(int userId) {
        return getDevicePolicyManager().getPasswordMinimumNumeric(null, userId);
    }

    public int getRequestedPasswordMinimumSymbols(int userId) {
        return getDevicePolicyManager().getPasswordMinimumSymbols(null, userId);
    }

    public int getRequestedPasswordMinimumNonLetter(int userId) {
        return getDevicePolicyManager().getPasswordMinimumNonLetter(null, userId);
    }

    public void reportFailedPasswordAttempt(int userId) {
        getDevicePolicyManager().reportFailedPasswordAttempt(userId);
        getTrustManager().reportUnlockAttempt(false /* authenticated */, userId);
        requireStrongAuth(StrongAuthTracker.SOME_AUTH_REQUIRED_AFTER_WRONG_CREDENTIAL, userId);
    }

    public void reportSuccessfulPasswordAttempt(int userId) {
        getDevicePolicyManager().reportSuccessfulPasswordAttempt(userId);
        getTrustManager().reportUnlockAttempt(true /* authenticated */, userId);
    }

    public int getCurrentFailedPasswordAttempts(int userId) {
        return getDevicePolicyManager().getCurrentFailedPasswordAttempts(userId);
    }

    public int getMaximumFailedPasswordsForWipe(int userId) {
        return getDevicePolicyManager().getMaximumFailedPasswordsForWipe(
                null /* componentName */, userId);
    }

    /**
     * Check to see if a pattern matches the saved pattern.
     * If pattern matches, return an opaque attestation that the challenge
     * was verified.
     *
     * @param pattern The pattern to check.
     * @param challenge The challenge to verify against the pattern
     * @return the attestation that the challenge was verified, or null.
     */
    public byte[] verifyPattern(List<LockPatternView.Cell> pattern, long challenge, int userId)
            throws RequestThrottledException {
        throwIfCalledOnMainThread();
        try {
            VerifyCredentialResponse response =
                getLockSettings().verifyPattern(patternToString(pattern), challenge, userId);
            if (response == null) {
                // Shouldn't happen
                return null;
            }

            if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_OK) {
                return response.getPayload();
            } else if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_RETRY) {
                throw new RequestThrottledException(response.getTimeout());
            } else {
                return null;
            }
        } catch (RemoteException re) {
            return null;
        }
    }

    /**
     * Check to see if a pattern matches the saved pattern.  If no pattern exists,
     * always returns true.
     * @param pattern The pattern to check.
     * @return Whether the pattern matches the stored one.
     */
    public boolean checkPattern(List<LockPatternView.Cell> pattern, int userId)
            throws RequestThrottledException {
        throwIfCalledOnMainThread();
        try {
            VerifyCredentialResponse response =
                    getLockSettings().checkPattern(patternToString(pattern), userId);

            if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_OK) {
                return true;
            } else if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_RETRY) {
                throw new RequestThrottledException(response.getTimeout());
            } else {
                return false;
            }
        } catch (RemoteException re) {
            return true;
        }
    }

    /**
     * Check to see if a password matches the saved password.
     * If password matches, return an opaque attestation that the challenge
     * was verified.
     *
     * @param password The password to check.
     * @param challenge The challenge to verify against the password
     * @return the attestation that the challenge was verified, or null.
     */
    public byte[] verifyPassword(String password, long challenge, int userId)
            throws RequestThrottledException {
        throwIfCalledOnMainThread();
        try {
            VerifyCredentialResponse response =
                    getLockSettings().verifyPassword(password, challenge, userId);

            if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_OK) {
                return response.getPayload();
            } else if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_RETRY) {
                throw new RequestThrottledException(response.getTimeout());
            } else {
                return null;
            }
        } catch (RemoteException re) {
            return null;
        }
    }

    /**
     * Check to see if a password matches the saved password.  If no password exists,
     * always returns true.
     * @param password The password to check.
     * @return Whether the password matches the stored one.
     */
    public boolean checkPassword(String password, int userId) throws RequestThrottledException {
        throwIfCalledOnMainThread();
        try {
            VerifyCredentialResponse response =
                    getLockSettings().checkPassword(password, userId);
            if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_OK) {
                return true;
            } else if (response.getResponseCode() == VerifyCredentialResponse.RESPONSE_RETRY) {
                throw new RequestThrottledException(response.getTimeout());
            } else {
                return false;
            }
        } catch (RemoteException re) {
            return true;
        }
    }

    /**
     * Check to see if vold already has the password.
     * Note that this also clears vold's copy of the password.
     * @return Whether the vold password matches or not.
     */
    public boolean checkVoldPassword(int userId) {
        try {
            return getLockSettings().checkVoldPassword(userId);
        } catch (RemoteException re) {
            return false;
        }
    }

    /**
     * Check to see if a password matches any of the passwords stored in the
     * password history.
     *
     * @param password The password to check.
     * @return Whether the password matches any in the history.
     */
    public boolean checkPasswordHistory(String password, int userId) {
        String passwordHashString = new String(
                passwordToHash(password, userId), StandardCharsets.UTF_8);
        String passwordHistory = getString(PASSWORD_HISTORY_KEY, userId);
        if (passwordHistory == null) {
            return false;
        }
        // Password History may be too long...
        int passwordHashLength = passwordHashString.length();
        int passwordHistoryLength = getRequestedPasswordHistoryLength(userId);
        if(passwordHistoryLength == 0) {
            return false;
        }
        int neededPasswordHistoryLength = passwordHashLength * passwordHistoryLength
                + passwordHistoryLength - 1;
        if (passwordHistory.length() > neededPasswordHistoryLength) {
            passwordHistory = passwordHistory.substring(0, neededPasswordHistoryLength);
        }
        return passwordHistory.contains(passwordHashString);
    }

    /**
     * Check to see if the user has stored a lock pattern.
     * @return Whether a saved pattern exists.
     */
    private boolean savedPatternExists(int userId) {
        try {
            return getLockSettings().havePattern(userId);
        } catch (RemoteException re) {
            return false;
        }
    }

    /**
     * Check to see if the user has stored a lock pattern.
     * @return Whether a saved pattern exists.
     */
    private boolean savedPasswordExists(int userId) {
        try {
            return getLockSettings().havePassword(userId);
        } catch (RemoteException re) {
            return false;
        }
    }

    /**
     * Return true if the user has ever chosen a pattern.  This is true even if the pattern is
     * currently cleared.
     *
     * @return True if the user has ever chosen a pattern.
     */
    public boolean isPatternEverChosen(int userId) {
        return getBoolean(PATTERN_EVER_CHOSEN_KEY, false, userId);
    }

    /**
     * Used by device policy manager to validate the current password
     * information it has.
     */
    public int getActivePasswordQuality(int userId) {
        int quality = getKeyguardStoredPasswordQuality(userId);

        if (isLockPasswordEnabled(quality, userId)) {
            // Quality is a password and a password exists. Return the quality.
            return quality;
        }

        if (isLockPatternEnabled(quality, userId)) {
            // Quality is a pattern and a pattern exists. Return the quality.
            return quality;
        }

        return DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED;
    }

    /**
     * Clear any lock pattern or password.
     */
    public void clearLock(int userHandle) {
        setLong(PASSWORD_TYPE_KEY, DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED, userHandle);

        try {
            getLockSettings().setLockPassword(null, null, userHandle);
            getLockSettings().setLockPattern(null, null, userHandle);
        } catch (RemoteException e) {
            // well, we tried...
        }

        if (userHandle == UserHandle.USER_SYSTEM) {
            // Set the encryption password to default.
            updateEncryptionPassword(StorageManager.CRYPT_TYPE_DEFAULT, null);
            setCredentialRequiredToDecrypt(false);
        }

        getDevicePolicyManager().setActivePasswordState(
                DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED, 0, 0, 0, 0, 0, 0, 0, userHandle);

        onAfterChangingPassword(userHandle);
    }

    /**
     * Disable showing lock screen at all for a given user.
     * This is only meaningful if pattern, pin or password are not set.
     *
     * @param disable Disables lock screen when true
     * @param userId User ID of the user this has effect on
     */
    public void setLockScreenDisabled(boolean disable, int userId) {
        setBoolean(DISABLE_LOCKSCREEN_KEY, disable, userId);
    }

    /**
     * Determine if LockScreen is disabled for the current user. This is used to decide whether
     * LockScreen is shown after reboot or after screen timeout / short press on power.
     *
     * @return true if lock screen is disabled
     */
    public boolean isLockScreenDisabled(int userId) {
        return !isSecure(userId) &&
                getBoolean(DISABLE_LOCKSCREEN_KEY, false, userId);
    }

    /**
     * Save a lock pattern.
     * @param pattern The new pattern to save.
     * @param userId the user whose pattern is to be saved.
     */
    public void saveLockPattern(List<LockPatternView.Cell> pattern, int userId) {
        this.saveLockPattern(pattern, null, userId);
    }
    /**
     * Save a lock pattern.
     * @param pattern The new pattern to save.
     * @param savedPattern The previously saved pattern, converted to String format
     * @param userId the user whose pattern is to be saved.
     */
    public void saveLockPattern(List<LockPatternView.Cell> pattern, String savedPattern, int userId) {
        try {
            if (pattern == null || pattern.size() < MIN_LOCK_PATTERN_SIZE) {
                throw new IllegalArgumentException("pattern must not be null and at least "
                        + MIN_LOCK_PATTERN_SIZE + " dots long.");
            }

            getLockSettings().setLockPattern(patternToString(pattern), savedPattern, userId);
            DevicePolicyManager dpm = getDevicePolicyManager();

            // Update the device encryption password.
            if (userId == UserHandle.USER_SYSTEM
                    && LockPatternUtils.isDeviceEncryptionEnabled()) {
                if (!shouldEncryptWithCredentials(true)) {
                    clearEncryptionPassword();
                } else {
                    String stringPattern = patternToString(pattern);
                    updateEncryptionPassword(StorageManager.CRYPT_TYPE_PATTERN, stringPattern);
                }
            }

            setBoolean(PATTERN_EVER_CHOSEN_KEY, true, userId);

            setLong(PASSWORD_TYPE_KEY, DevicePolicyManager.PASSWORD_QUALITY_SOMETHING, userId);
            dpm.setActivePasswordState(DevicePolicyManager.PASSWORD_QUALITY_SOMETHING,
                    pattern.size(), 0, 0, 0, 0, 0, 0, userId);
            onAfterChangingPassword(userId);
        } catch (RemoteException re) {
            Log.e(TAG, "Couldn't save lock pattern " + re);
        }
    }

    private void updateCryptoUserInfo(int userId) {
        if (userId != UserHandle.USER_SYSTEM) {
            return;
        }

        final String ownerInfo = isOwnerInfoEnabled(userId) ? getOwnerInfo(userId) : "";

        IBinder service = ServiceManager.getService("mount");
        if (service == null) {
            Log.e(TAG, "Could not find the mount service to update the user info");
            return;
        }

        IMountService mountService = IMountService.Stub.asInterface(service);
        try {
            Log.d(TAG, "Setting owner info");
            mountService.setField(StorageManager.OWNER_INFO_KEY, ownerInfo);
        } catch (RemoteException e) {
            Log.e(TAG, "Error changing user info", e);
        }
    }

    public void setOwnerInfo(String info, int userId) {
        setString(LOCK_SCREEN_OWNER_INFO, info, userId);
        updateCryptoUserInfo(userId);
    }

    public void setOwnerInfoEnabled(boolean enabled, int userId) {
        setBoolean(LOCK_SCREEN_OWNER_INFO_ENABLED, enabled, userId);
        updateCryptoUserInfo(userId);
    }

    public String getOwnerInfo(int userId) {
        return getString(LOCK_SCREEN_OWNER_INFO, userId);
    }

    public boolean isOwnerInfoEnabled(int userId) {
        return getBoolean(LOCK_SCREEN_OWNER_INFO_ENABLED, false, userId);
    }

    /**
     * Sets the device owner information. If the information is {@code null} or empty then the
     * device owner info is cleared.
     *
     * @param info Device owner information which will be displayed instead of the user
     * owner info.
     */
    public void setDeviceOwnerInfo(String info) {
        if (info != null && info.isEmpty()) {
            info = null;
        }

        setString(LOCK_SCREEN_DEVICE_OWNER_INFO, info, UserHandle.USER_SYSTEM);
    }

    public String getDeviceOwnerInfo() {
        return getString(LOCK_SCREEN_DEVICE_OWNER_INFO, UserHandle.USER_SYSTEM);
    }

    public boolean isDeviceOwnerInfoEnabled() {
        return getDeviceOwnerInfo() != null;
    }

    /**
     * Compute the password quality from the given password string.
     */
    static public int computePasswordQuality(String password) {
        boolean hasDigit = false;
        boolean hasNonDigit = false;
        final int len = password.length();
        for (int i = 0; i < len; i++) {
            if (Character.isDigit(password.charAt(i))) {
                hasDigit = true;
            } else {
                hasNonDigit = true;
            }
        }

        if (hasNonDigit && hasDigit) {
            return DevicePolicyManager.PASSWORD_QUALITY_ALPHANUMERIC;
        }
        if (hasNonDigit) {
            return DevicePolicyManager.PASSWORD_QUALITY_ALPHABETIC;
        }
        if (hasDigit) {
            return maxLengthSequence(password) > MAX_ALLOWED_SEQUENCE
                    ? DevicePolicyManager.PASSWORD_QUALITY_NUMERIC
                    : DevicePolicyManager.PASSWORD_QUALITY_NUMERIC_COMPLEX;
        }
        return DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED;
    }

    private static int categoryChar(char c) {
        if ('a' <= c && c <= 'z') return 0;
        if ('A' <= c && c <= 'Z') return 1;
        if ('0' <= c && c <= '9') return 2;
        return 3;
    }

    private static int maxDiffCategory(int category) {
        if (category == 0 || category == 1) return 1;
        else if (category == 2) return 10;
        return 0;
    }

    /*
     * Returns the maximum length of a sequential characters.  A sequence is defined as
     * monotonically increasing characters with a constant interval or the same character repeated.
     *
     * For example:
     * maxLengthSequence("1234") == 4
     * maxLengthSequence("1234abc") == 4
     * maxLengthSequence("aabc") == 3
     * maxLengthSequence("qwertyuio") == 1
     * maxLengthSequence("@ABC") == 3
     * maxLengthSequence(";;;;") == 4 (anything that repeats)
     * maxLengthSequence(":;<=>") == 1  (ordered, but not composed of alphas or digits)
     *
     * @param string the pass
     * @return the number of sequential letters or digits
     */
    public static int maxLengthSequence(String string) {
        if (string.length() == 0) return 0;
        char previousChar = string.charAt(0);
        int category = categoryChar(previousChar); //current category of the sequence
        int diff = 0; //difference between two consecutive characters
        boolean hasDiff = false; //if we are currently targeting a sequence
        int maxLength = 0; //maximum length of a sequence already found
        int startSequence = 0; //where the current sequence started
        for (int current = 1; current < string.length(); current++) {
            char currentChar = string.charAt(current);
            int categoryCurrent = categoryChar(currentChar);
            int currentDiff = (int) currentChar - (int) previousChar;
            if (categoryCurrent != category || Math.abs(currentDiff) > maxDiffCategory(category)) {
                maxLength = Math.max(maxLength, current - startSequence);
                startSequence = current;
                hasDiff = false;
                category = categoryCurrent;
            }
            else {
                if(hasDiff && currentDiff != diff) {
                    maxLength = Math.max(maxLength, current - startSequence);
                    startSequence = current - 1;
                }
                diff = currentDiff;
                hasDiff = true;
            }
            previousChar = currentChar;
        }
        maxLength = Math.max(maxLength, string.length() - startSequence);
        return maxLength;
    }

    /** Update the encryption password if it is enabled **/
    private void updateEncryptionPassword(final int type, final String password) {
        if (!isDeviceEncryptionEnabled()) {
            return;
        }
        final IBinder service = ServiceManager.getService("mount");
        if (service == null) {
            Log.e(TAG, "Could not find the mount service to update the encryption password");
            return;
        }

        new AsyncTask<Void, Void, Void>() {
            @Override
            protected Void doInBackground(Void... dummy) {
                IMountService mountService = IMountService.Stub.asInterface(service);
                try {
                    mountService.changeEncryptionPassword(type, password);
                } catch (RemoteException e) {
                    Log.e(TAG, "Error changing encryption password", e);
                }
                return null;
            }
        }.execute();
    }

    /**
     * Save a lock password.  Does not ensure that the password is as good
     * as the requested mode, but will adjust the mode to be as good as the
     * password.
     * @param password The password to save
     * @param savedPassword The previously saved lock password, or null if none
     * @param quality {@see DevicePolicyManager#getPasswordQuality(android.content.ComponentName)}
     * @param userHandle The userId of the user to change the password for
     */
    public void saveLockPassword(String password, String savedPassword, int quality,
            int userHandle) {
        try {
            DevicePolicyManager dpm = getDevicePolicyManager();
            if (password == null || password.length() < MIN_LOCK_PASSWORD_SIZE) {
                throw new IllegalArgumentException("password must not be null and at least "
                        + "of length " + MIN_LOCK_PASSWORD_SIZE);
            }

            getLockSettings().setLockPassword(password, savedPassword, userHandle);
            int computedQuality = computePasswordQuality(password);

            // Update the device encryption password.
            if (userHandle == UserHandle.USER_SYSTEM
                    && LockPatternUtils.isDeviceEncryptionEnabled()) {
                if (!shouldEncryptWithCredentials(true)) {
                    clearEncryptionPassword();
                } else {
                    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);
                }
            }

            setLong(PASSWORD_TYPE_KEY, Math.max(quality, computedQuality), userHandle);
            if (computedQuality != DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED) {
                int letters = 0;
                int uppercase = 0;
                int lowercase = 0;
                int numbers = 0;
                int symbols = 0;
                int nonletter = 0;
                for (int i = 0; i < password.length(); i++) {
                    char c = password.charAt(i);
                    if (c >= 'A' && c <= 'Z') {
                        letters++;
                        uppercase++;
                    } else if (c >= 'a' && c <= 'z') {
                        letters++;
                        lowercase++;
                    } else if (c >= '0' && c <= '9') {
                        numbers++;
                        nonletter++;
                    } else {
                        symbols++;
                        nonletter++;
                    }
                }
                dpm.setActivePasswordState(Math.max(quality, computedQuality),
                        password.length(), letters, uppercase, lowercase,
                        numbers, symbols, nonletter, userHandle);
            } else {
                // The password is not anything.
                dpm.setActivePasswordState(
                        DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED,
                        0, 0, 0, 0, 0, 0, 0, userHandle);
            }

            // Add the password to the password history. We assume all
            // password hashes have the same length for simplicity of implementation.
            String passwordHistory = getString(PASSWORD_HISTORY_KEY, userHandle);
            if (passwordHistory == null) {
                passwordHistory = "";
            }
            int passwordHistoryLength = getRequestedPasswordHistoryLength(userHandle);
            if (passwordHistoryLength == 0) {
                passwordHistory = "";
            } else {
                byte[] hash = passwordToHash(password, userHandle);
                passwordHistory = new String(hash, StandardCharsets.UTF_8) + "," + passwordHistory;
                // Cut it to contain passwordHistoryLength hashes
                // and passwordHistoryLength -1 commas.
                passwordHistory = passwordHistory.substring(0, Math.min(hash.length
                        * passwordHistoryLength + passwordHistoryLength - 1, passwordHistory
                        .length()));
            }
            setString(PASSWORD_HISTORY_KEY, passwordHistory, userHandle);
            onAfterChangingPassword(userHandle);
        } catch (RemoteException re) {
            // Cant do much
            Log.e(TAG, "Unable to save lock password " + re);
        }
    }

    /**
     * Gets whether the device is encrypted.
     *
     * @return Whether the device is encrypted.
     */
    public static boolean isDeviceEncrypted() {
        IMountService mountService = IMountService.Stub.asInterface(
                ServiceManager.getService("mount"));
        try {
            return mountService.getEncryptionState() != IMountService.ENCRYPTION_STATE_NONE
                    && mountService.getPasswordType() != StorageManager.CRYPT_TYPE_DEFAULT;
        } catch (RemoteException re) {
            Log.e(TAG, "Error getting encryption state", re);
        }
        return true;
    }

    /**
     * Determine if the device supports encryption, even if it's set to default. This
     * differs from isDeviceEncrypted() in that it returns true even if the device is
     * encrypted with the default password.
     * @return true if device encryption is enabled
     */
    public static boolean isDeviceEncryptionEnabled() {
        final String status = SystemProperties.get("ro.crypto.state", "unsupported");
        return "encrypted".equalsIgnoreCase(status);
    }

    /**
     * Determine if the device is file encrypted
     * @return true if device is file encrypted
     */
    public static boolean isFileEncryptionEnabled() {
        return StorageManager.isFileBasedEncryptionEnabled();
    }

    /**
     * Clears the encryption password.
     */
    public void clearEncryptionPassword() {
        updateEncryptionPassword(StorageManager.CRYPT_TYPE_DEFAULT, null);
    }

    /**
     * Retrieves the quality mode for {@param userHandle}.
     * {@see DevicePolicyManager#getPasswordQuality(android.content.ComponentName)}
     *
     * @return stored password quality
     */
    public int getKeyguardStoredPasswordQuality(int userHandle) {
        return (int) getLong(PASSWORD_TYPE_KEY,
                DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED, userHandle);
    }

    /**
     * Enables/disables the Separate Profile Challenge for this {@param userHandle}. This is a no-op
     * for user handles that do not belong to a managed profile.
     */
    public void setSeparateProfileChallengeEnabled(int userHandle, boolean enabled) {
        UserInfo info = getUserManager().getUserInfo(userHandle);
        if (info.isManagedProfile()) {
            setBoolean(SEPARATE_PROFILE_CHALLENGE_KEY, enabled, userHandle);
        }
    }

    /**
     * Retrieves whether the Separate Profile Challenge is enabled for this {@param userHandle}.
     */
    public boolean isSeparateProfileChallengeEnabled(int userHandle) {
        UserInfo info = getUserManager().getUserInfo(userHandle);
        if (info == null || !info.isManagedProfile()) {
            return false;
        }
        return getBoolean(SEPARATE_PROFILE_CHALLENGE_KEY, false, userHandle);
    }

    /**
     * Retrieves whether the current DPM allows use of the Profile Challenge.
     */
    public boolean isSeparateProfileChallengeAllowed(int userHandle) {
        UserInfo info = getUserManager().getUserInfo(userHandle);
        if (info == null || !info.isManagedProfile()) {
            return false;
        }
        return getDevicePolicyManager().isSeparateProfileChallengeAllowed(userHandle);
    }

    /**
     * Retrieves whether the current profile and device locks can be unified.
     */
    public boolean isSeparateProfileChallengeAllowedToUnify(int userHandle) {
        return getDevicePolicyManager().isProfileActivePasswordSufficientForParent(userHandle);
    }

    /**
     * Deserialize a pattern.
     * @param string The pattern serialized with {@link #patternToString}
     * @return The pattern.
     */
    public static List<LockPatternView.Cell> stringToPattern(String string) {
        if (string == null) {
            return null;
        }

        List<LockPatternView.Cell> result = Lists.newArrayList();

        final byte[] bytes = string.getBytes();
        for (int i = 0; i < bytes.length; i++) {
            byte b = (byte) (bytes[i] - '1');
            result.add(LockPatternView.Cell.of(b / 3, b % 3));
        }
        return result;
    }

    /**
     * Serialize a pattern.
     * @param pattern The pattern.
     * @return The pattern in string form.
     */
    public static String patternToString(List<LockPatternView.Cell> pattern) {
        if (pattern == null) {
            return "";
        }
        final int patternSize = pattern.size();

        byte[] res = new byte[patternSize];
        for (int i = 0; i < patternSize; i++) {
            LockPatternView.Cell cell = pattern.get(i);
            res[i] = (byte) (cell.getRow() * 3 + cell.getColumn() + '1');
        }
        return new String(res);
    }

    public static String patternStringToBaseZero(String pattern) {
        if (pattern == null) {
            return "";
        }
        final int patternSize = pattern.length();

        byte[] res = new byte[patternSize];
        final byte[] bytes = pattern.getBytes();
        for (int i = 0; i < patternSize; i++) {
            res[i] = (byte) (bytes[i] - '1');
        }
        return new String(res);
    }

    /*
     * Generate an SHA-1 hash for the pattern. Not the most secure, but it is
     * at least a second level of protection. First level is that the file
     * is in a location only readable by the system process.
     * @param pattern the gesture pattern.
     * @return the hash of the pattern in a byte array.
     */
    public static byte[] patternToHash(List<LockPatternView.Cell> pattern) {
        if (pattern == null) {
            return null;
        }

        final int patternSize = pattern.size();
        byte[] res = new byte[patternSize];
        for (int i = 0; i < patternSize; i++) {
            LockPatternView.Cell cell = pattern.get(i);
            res[i] = (byte) (cell.getRow() * 3 + cell.getColumn());
        }
        try {
            MessageDigest md = MessageDigest.getInstance("SHA-1");
            byte[] hash = md.digest(res);
            return hash;
        } catch (NoSuchAlgorithmException nsa) {
            return res;
        }
    }

    private String getSalt(int userId) {
        long salt = getLong(LOCK_PASSWORD_SALT_KEY, 0, userId);
        if (salt == 0) {
            try {
                salt = SecureRandom.getInstance("SHA1PRNG").nextLong();
                setLong(LOCK_PASSWORD_SALT_KEY, salt, userId);
                Log.v(TAG, "Initialized lock password salt for user: " + userId);
            } catch (NoSuchAlgorithmException e) {
                // Throw an exception rather than storing a password we'll never be able to recover
                throw new IllegalStateException("Couldn't get SecureRandom number", e);
            }
        }
        return Long.toHexString(salt);
    }

    /*
     * Generate a hash for the given password. To avoid brute force attacks, we use a salted hash.
     * Not the most secure, but it is at least a second level of protection. First level is that
     * the file is in a location only readable by the system process.
     *
     * @param password the gesture pattern.
     *
     * @return the hash of the pattern in a byte array.
     */
    public byte[] passwordToHash(String password, int userId) {
        if (password == null) {
            return null;
        }

        try {
            byte[] saltedPassword = (password + getSalt(userId)).getBytes();
            byte[] sha1 = MessageDigest.getInstance("SHA-1").digest(saltedPassword);
            byte[] md5 = MessageDigest.getInstance("MD5").digest(saltedPassword);

            byte[] combined = new byte[sha1.length + md5.length];
            System.arraycopy(sha1, 0, combined, 0, sha1.length);
            System.arraycopy(md5, 0, combined, sha1.length, md5.length);

            final char[] hexEncoded = HexEncoding.encode(combined);
            return new String(hexEncoded).getBytes(StandardCharsets.UTF_8);
        } catch (NoSuchAlgorithmException e) {
            throw new AssertionError("Missing digest algorithm: ", e);
        }
    }

    /**
     * @param userId the user for which to report the value
     * @return Whether the lock screen is secured.
     */
    public boolean isSecure(int userId) {
        int mode = getKeyguardStoredPasswordQuality(userId);
        return isLockPatternEnabled(mode, userId) || isLockPasswordEnabled(mode, userId);
    }

    public boolean isLockPasswordEnabled(int userId) {
        return isLockPasswordEnabled(getKeyguardStoredPasswordQuality(userId), userId);
    }

    private boolean isLockPasswordEnabled(int mode, int userId) {
        final boolean passwordEnabled = mode == DevicePolicyManager.PASSWORD_QUALITY_ALPHABETIC
                || mode == DevicePolicyManager.PASSWORD_QUALITY_NUMERIC
                || mode == DevicePolicyManager.PASSWORD_QUALITY_NUMERIC_COMPLEX
                || mode == DevicePolicyManager.PASSWORD_QUALITY_ALPHANUMERIC
                || mode == DevicePolicyManager.PASSWORD_QUALITY_COMPLEX;
        return passwordEnabled && savedPasswordExists(userId);
    }

    /**
     * @return Whether the lock pattern is enabled
     */
    public boolean isLockPatternEnabled(int userId) {
        return isLockPatternEnabled(getKeyguardStoredPasswordQuality(userId), userId);
    }

    @Deprecated
    public boolean isLegacyLockPatternEnabled(int userId) {
        // Note: this value should default to {@code true} to avoid any reset that might result.
        // We must use a special key to read this value, since it will by default return the value
        // based on the new logic.
        return getBoolean(LEGACY_LOCK_PATTERN_ENABLED, true, userId);
    }

    @Deprecated
    public void setLegacyLockPatternEnabled(int userId) {
        setBoolean(Settings.Secure.LOCK_PATTERN_ENABLED, true, userId);
    }

    private boolean isLockPatternEnabled(int mode, int userId) {
        return mode == DevicePolicyManager.PASSWORD_QUALITY_SOMETHING
                && savedPatternExists(userId);
    }

    /**
     * @return Whether the visible pattern is enabled.
     */
    public boolean isVisiblePatternEnabled(int userId) {
        return getBoolean(Settings.Secure.LOCK_PATTERN_VISIBLE, false, userId);
    }

    /**
     * Set whether the visible pattern is enabled.
     */
    public void setVisiblePatternEnabled(boolean enabled, int userId) {
        setBoolean(Settings.Secure.LOCK_PATTERN_VISIBLE, enabled, userId);

        // Update for crypto if owner
        if (userId != UserHandle.USER_SYSTEM) {
            return;
        }

        IBinder service = ServiceManager.getService("mount");
        if (service == null) {
            Log.e(TAG, "Could not find the mount service to update the user info");
            return;
        }

        IMountService mountService = IMountService.Stub.asInterface(service);
        try {
            mountService.setField(StorageManager.PATTERN_VISIBLE_KEY, enabled ? "1" : "0");
        } catch (RemoteException e) {
            Log.e(TAG, "Error changing pattern visible state", e);
        }
    }

    /**
     * Set whether the visible password is enabled for cryptkeeper screen.
     */
    public void setVisiblePasswordEnabled(boolean enabled, int userId) {
        // Update for crypto if owner
        if (userId != UserHandle.USER_SYSTEM) {
            return;
        }

        IBinder service = ServiceManager.getService("mount");
        if (service == null) {
            Log.e(TAG, "Could not find the mount service to update the user info");
            return;
        }

        IMountService mountService = IMountService.Stub.asInterface(service);
        try {
            mountService.setField(StorageManager.PASSWORD_VISIBLE_KEY, enabled ? "1" : "0");
        } catch (RemoteException e) {
            Log.e(TAG, "Error changing password visible state", e);
        }
    }

    /**
     * @return Whether tactile feedback for the pattern is enabled.
     */
    public boolean isTactileFeedbackEnabled() {
        return Settings.System.getIntForUser(mContentResolver,
                Settings.System.HAPTIC_FEEDBACK_ENABLED, 1, UserHandle.USER_CURRENT) != 0;
    }

    /**
     * Set and store the lockout deadline, meaning the user can't attempt his/her unlock
     * pattern until the deadline has passed.
     * @return the chosen deadline.
     */
    public long setLockoutAttemptDeadline(int userId, int timeoutMs) {
        final long deadline = SystemClock.elapsedRealtime() + timeoutMs;
        setLong(LOCKOUT_ATTEMPT_DEADLINE, deadline, userId);
        setLong(LOCKOUT_ATTEMPT_TIMEOUT_MS, timeoutMs, userId);
        return deadline;
    }

    /**
     * @return The elapsed time in millis in the future when the user is allowed to
     *   attempt to enter his/her lock pattern, or 0 if the user is welcome to
     *   enter a pattern.
     */
    public long getLockoutAttemptDeadline(int userId) {
        long deadline = getLong(LOCKOUT_ATTEMPT_DEADLINE, 0L, userId);
        final long timeoutMs = getLong(LOCKOUT_ATTEMPT_TIMEOUT_MS, 0L, userId);
        final long now = SystemClock.elapsedRealtime();
        if (deadline < now && deadline != 0) {
            // timeout expired
            setLong(LOCKOUT_ATTEMPT_DEADLINE, 0, userId);
            setLong(LOCKOUT_ATTEMPT_TIMEOUT_MS, 0, userId);
            return 0L;
        }

        if (deadline > (now + timeoutMs)) {
            // device was rebooted, set new deadline
            deadline = now + timeoutMs;
            setLong(LOCKOUT_ATTEMPT_DEADLINE, deadline, userId);
        }

        return deadline;
    }

    private boolean getBoolean(String secureSettingKey, boolean defaultValue, int userId) {
        try {
            return getLockSettings().getBoolean(secureSettingKey, defaultValue, userId);
        } catch (RemoteException re) {
            return defaultValue;
        }
    }

    private void setBoolean(String secureSettingKey, boolean enabled, int userId) {
        try {
            getLockSettings().setBoolean(secureSettingKey, enabled, userId);
        } catch (RemoteException re) {
            // What can we do?
            Log.e(TAG, "Couldn't write boolean " + secureSettingKey + re);
        }
    }

    private long getLong(String secureSettingKey, long defaultValue, int userHandle) {
        try {
            return getLockSettings().getLong(secureSettingKey, defaultValue, userHandle);
        } catch (RemoteException re) {
            return defaultValue;
        }
    }

    private void setLong(String secureSettingKey, long value, int userHandle) {
        try {
            getLockSettings().setLong(secureSettingKey, value, userHandle);
        } catch (RemoteException re) {
            // What can we do?
            Log.e(TAG, "Couldn't write long " + secureSettingKey + re);
        }
    }

    private String getString(String secureSettingKey, int userHandle) {
        try {
            return getLockSettings().getString(secureSettingKey, null, userHandle);
        } catch (RemoteException re) {
            return null;
        }
    }

    private void setString(String secureSettingKey, String value, int userHandle) {
        try {
            getLockSettings().setString(secureSettingKey, value, userHandle);
        } catch (RemoteException re) {
            // What can we do?
            Log.e(TAG, "Couldn't write string " + secureSettingKey + re);
        }
    }

    public void setPowerButtonInstantlyLocks(boolean enabled, int userId) {
        setBoolean(LOCKSCREEN_POWER_BUTTON_INSTANTLY_LOCKS, enabled, userId);
    }

    public boolean getPowerButtonInstantlyLocks(int userId) {
        return getBoolean(LOCKSCREEN_POWER_BUTTON_INSTANTLY_LOCKS, true, userId);
    }

    public void setEnabledTrustAgents(Collection<ComponentName> activeTrustAgents, int userId) {
        StringBuilder sb = new StringBuilder();
        for (ComponentName cn : activeTrustAgents) {
            if (sb.length() > 0) {
                sb.append(',');
            }
            sb.append(cn.flattenToShortString());
        }
        setString(ENABLED_TRUST_AGENTS, sb.toString(), userId);
        getTrustManager().reportEnabledTrustAgentsChanged(userId);
    }

    public List<ComponentName> getEnabledTrustAgents(int userId) {
        String serialized = getString(ENABLED_TRUST_AGENTS, userId);
        if (TextUtils.isEmpty(serialized)) {
            return null;
        }
        String[] split = serialized.split(",");
        ArrayList<ComponentName> activeTrustAgents = new ArrayList<ComponentName>(split.length);
        for (String s : split) {
            if (!TextUtils.isEmpty(s)) {
                activeTrustAgents.add(ComponentName.unflattenFromString(s));
            }
        }
        return activeTrustAgents;
    }

    /**
     * Disable trust until credentials have been entered for user {@param userId}.
     *
     * Requires the {@link android.Manifest.permission#ACCESS_KEYGUARD_SECURE_STORAGE} permission.
     *
     * @param userId either an explicit user id or {@link android.os.UserHandle#USER_ALL}
     */
    public void requireCredentialEntry(int userId) {
        requireStrongAuth(StrongAuthTracker.SOME_AUTH_REQUIRED_AFTER_USER_REQUEST, userId);
    }

    /**
     * Requests strong authentication for user {@param userId}.
     *
     * Requires the {@link android.Manifest.permission#ACCESS_KEYGUARD_SECURE_STORAGE} permission.
     *
     * @param strongAuthReason a combination of {@link StrongAuthTracker.StrongAuthFlags} indicating
     *                         the reason for and the strength of the requested authentication.
     * @param userId either an explicit user id or {@link android.os.UserHandle#USER_ALL}
     */
    public void requireStrongAuth(@StrongAuthTracker.StrongAuthFlags int strongAuthReason,
            int userId) {
        try {
            getLockSettings().requireStrongAuth(strongAuthReason, userId);
        } catch (RemoteException e) {
            Log.e(TAG, "Error while requesting strong auth: " + e);
        }
    }

    private void onAfterChangingPassword(int userHandle) {
        getTrustManager().reportEnabledTrustAgentsChanged(userHandle);
    }

    public boolean isCredentialRequiredToDecrypt(boolean defaultValue) {
        final int value = Settings.Global.getInt(mContentResolver,
                Settings.Global.REQUIRE_PASSWORD_TO_DECRYPT, -1);
        return value == -1 ? defaultValue : (value != 0);
    }

    public void setCredentialRequiredToDecrypt(boolean required) {
        if (!(getUserManager().isSystemUser() || getUserManager().isPrimaryUser())) {
            throw new IllegalStateException(
                    "Only the system or primary user may call setCredentialRequiredForDecrypt()");
        }

        if (isDeviceEncryptionEnabled()){
            Settings.Global.putInt(mContext.getContentResolver(),
               Settings.Global.REQUIRE_PASSWORD_TO_DECRYPT, required ? 1 : 0);
        }
    }

    private boolean isDoNotAskCredentialsOnBootSet() {
        return mDevicePolicyManager.getDoNotAskCredentialsOnBoot();
    }

    private boolean shouldEncryptWithCredentials(boolean defaultValue) {
        return isCredentialRequiredToDecrypt(defaultValue) && !isDoNotAskCredentialsOnBootSet();
    }

    private void throwIfCalledOnMainThread() {
        if (Looper.getMainLooper().isCurrentThread()) {
            throw new IllegalStateException("should not be called from the main thread.");
        }
    }

    public void registerStrongAuthTracker(final StrongAuthTracker strongAuthTracker) {
        try {
            getLockSettings().registerStrongAuthTracker(strongAuthTracker.mStub);
        } catch (RemoteException e) {
            throw new RuntimeException("Could not register StrongAuthTracker");
        }
    }

    public void unregisterStrongAuthTracker(final StrongAuthTracker strongAuthTracker) {
        try {
            getLockSettings().unregisterStrongAuthTracker(strongAuthTracker.mStub);
        } catch (RemoteException e) {
            Log.e(TAG, "Could not unregister StrongAuthTracker", e);
        }
    }

    /**
     * Tracks the global strong authentication state.
     */
    public static class StrongAuthTracker {

        @IntDef(flag = true,
                value = { STRONG_AUTH_NOT_REQUIRED,
                        STRONG_AUTH_REQUIRED_AFTER_BOOT,
                        STRONG_AUTH_REQUIRED_AFTER_DPM_LOCK_NOW,
                        SOME_AUTH_REQUIRED_AFTER_USER_REQUEST})
        @Retention(RetentionPolicy.SOURCE)
        public @interface StrongAuthFlags {}

        /**
         * Strong authentication is not required.
         */
        public static final int STRONG_AUTH_NOT_REQUIRED = 0x0;

        /**
         * Strong authentication is required because the user has not authenticated since boot.
         */
        public static final int STRONG_AUTH_REQUIRED_AFTER_BOOT = 0x1;

        /**
         * Strong authentication is required because a device admin has requested it.
         */
        public static final int STRONG_AUTH_REQUIRED_AFTER_DPM_LOCK_NOW = 0x2;

        /**
         * Some authentication is required because the user has temporarily disabled trust.
         */
        public static final int SOME_AUTH_REQUIRED_AFTER_USER_REQUEST = 0x4;

        /**
         * Strong authentication is required because the user has been locked out after too many
         * attempts.
         */
        public static final int STRONG_AUTH_REQUIRED_AFTER_LOCKOUT = 0x8;

        /**
         * Some authentication is required because the user has entered a wrong credential.
         */
        public static final int SOME_AUTH_REQUIRED_AFTER_WRONG_CREDENTIAL = 0x10;

        private static final int ALLOWING_FINGERPRINT = STRONG_AUTH_NOT_REQUIRED
                | SOME_AUTH_REQUIRED_AFTER_USER_REQUEST
                | SOME_AUTH_REQUIRED_AFTER_WRONG_CREDENTIAL;

        private final SparseIntArray mStrongAuthRequiredForUser = new SparseIntArray();
        private final H mHandler;
        private final int mDefaultStrongAuthFlags;

        public StrongAuthTracker(Context context) {
            this(context, Looper.myLooper());
        }

        /**
         * @param looper the looper on whose thread calls to {@link #onStrongAuthRequiredChanged}
         *               will be scheduled.
         * @param context the current {@link Context}
         */
        public StrongAuthTracker(Context context, Looper looper) {
            mHandler = new H(looper);
            mDefaultStrongAuthFlags = getDefaultFlags(context);
        }

        public static @StrongAuthFlags int getDefaultFlags(Context context) {
            boolean strongAuthRequired = context.getResources().getBoolean(
                    com.android.internal.R.bool.config_strongAuthRequiredOnBoot);
            return strongAuthRequired ? STRONG_AUTH_REQUIRED_AFTER_BOOT : STRONG_AUTH_NOT_REQUIRED;
        }

        /**
         * Returns {@link #STRONG_AUTH_NOT_REQUIRED} if strong authentication is not required,
         * otherwise returns a combination of {@link StrongAuthFlags} indicating why strong
         * authentication is required.
         *
         * @param userId the user for whom the state is queried.
         */
        public @StrongAuthFlags int getStrongAuthForUser(int userId) {
            return mStrongAuthRequiredForUser.get(userId, mDefaultStrongAuthFlags);
        }

        /**
         * @return true if unlocking with trust alone is allowed for {@param userId} by the current
         * strong authentication requirements.
         */
        public boolean isTrustAllowedForUser(int userId) {
            return getStrongAuthForUser(userId) == STRONG_AUTH_NOT_REQUIRED;
        }

        /**
         * @return true if unlocking with fingerprint alone is allowed for {@param userId} by the
         * current strong authentication requirements.
         */
        public boolean isFingerprintAllowedForUser(int userId) {
            return (getStrongAuthForUser(userId) & ~ALLOWING_FINGERPRINT) == 0;
        }

        /**
         * Called when the strong authentication requirements for {@param userId} changed.
         */
        public void onStrongAuthRequiredChanged(int userId) {
        }

        void handleStrongAuthRequiredChanged(@StrongAuthFlags int strongAuthFlags,
                int userId) {

            int oldValue = getStrongAuthForUser(userId);
            if (strongAuthFlags != oldValue) {
                if (strongAuthFlags == mDefaultStrongAuthFlags) {
                    mStrongAuthRequiredForUser.delete(userId);
                } else {
                    mStrongAuthRequiredForUser.put(userId, strongAuthFlags);
                }
                onStrongAuthRequiredChanged(userId);
            }
        }


        final IStrongAuthTracker.Stub mStub = new IStrongAuthTracker.Stub() {
            @Override
            public void onStrongAuthRequiredChanged(@StrongAuthFlags int strongAuthFlags,
                    int userId) {
                mHandler.obtainMessage(H.MSG_ON_STRONG_AUTH_REQUIRED_CHANGED,
                        strongAuthFlags, userId).sendToTarget();
            }
        };

        private class H extends Handler {
            static final int MSG_ON_STRONG_AUTH_REQUIRED_CHANGED = 1;

            public H(Looper looper) {
                super(looper);
            }

            @Override
            public void handleMessage(Message msg) {
                switch (msg.what) {
                    case MSG_ON_STRONG_AUTH_REQUIRED_CHANGED:
                        handleStrongAuthRequiredChanged(msg.arg1, msg.arg2);
                        break;
                }
            }
        };
    }
}