屏幕锁定LockSettingsService服务

LockSettingsService服务的主要作用:保存图案密码,数字密码的数据,多用户管理等.系统非核心服务,初始化构造方式上说明了这一点.该服务在SystemServer中进行启动,内部包含了LockPatternUtils工具类和locksettings.db数据库.
1,服务的初始化:

        if (mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
            //if (!disableNonCoreServices) { // TODO: View depends on these; mock them?
            if (true) {
                try {
                    Slog.i(TAG, "Input Method Service");
                    imm = new InputMethodManagerService(context, wm);
                    ServiceManager.addService(Context.INPUT_METHOD_SERVICE, imm);
                } catch (Throwable e) {
                    reportWtf("starting Input Manager Service", e);
                }

                try {
                    Slog.i(TAG, "Accessibility Manager");
                    ServiceManager.addService(Context.ACCESSIBILITY_SERVICE,
                            new AccessibilityManagerService(context));
                } catch (Throwable e) {
                    reportWtf("starting Accessibility Manager", e);
                }
            }
        }

2,locksettings.db的位置.
在android系统中,应用的数据库文件在data/data//databases目录中.对于系统服务,其数据库源文件在/data/system目录内.具体详情可以参考ContextImpl.java的getDatabaseDir()方法.
ContextImpl.java

private File getDatabasesDir() {
        synchronized (mSync) {
            if (mDatabasesDir == null) {
                mDatabasesDir = new File(getDataDirFile(), "databases");
            }
            if (mDatabasesDir.getPath().equals("databases")) {
                mDatabasesDir = new File("/data/system");
            }
            return mDatabasesDir;
        }
    }

3,LockPatternUtils工具类常用的方法介绍:
3.1:isSecure():是否含有锁屏,图案,密码,复杂密码
3.2:getKeyguardStoredPasswordQuality();得到当前锁屏类型,其取值如下:

final boolean isPattern = mode == DevicePolicyManager.PASSWORD_QUALITY_SOMETHING; final boolean isPassword = mode == DevicePolicyManager.PASSWORD_QUALITY_NUMERIC || mode == DevicePolicyManager.PASSWORD_QUALITY_NUMERIC_COMPLEX || mode == DevicePolicyManager.PASSWORD_QUALITY_ALPHABETIC || mode == DevicePolicyManager.PASSWORD_QUALITY_ALPHANUMERIC || mode == DevicePolicyManager.PASSWORD_QUALITY_COMPLEX;

3.3:isDeviceEncryptionEnabled():设备是否加密

4,图案密码数据保存位置:
图案密码调用ＬockPatternUtils工具类的saveLockPattern进行存储.
最终图案数据会存储在/data /system /gesture.key文件中.该方式不是最安全的,但有两层防护,第一:数据经过了ＳＨＡ-1哈希转换.第二:数据文件只能系统进程能够读取.

  /*
     * 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;
        }
    }

5,数字密码数据保存位置:
数字密码调用ＬockPatternUtils工具类的saveLockPassword进行存储.
最终数字密码会存储在/data/system/password.key中,经过ＭＤ5加密.

public byte[] passwordToHash(String password, int userId) {
        if (password == null) {
            return null;
        }
        String algo = null;
        byte[] hashed = null;
        try {
            byte[] saltedPassword = (password + getSalt(userId)).getBytes();
            byte[] sha1 = MessageDigest.getInstance(algo = "SHA-1").digest(saltedPassword);
            byte[] md5 = MessageDigest.getInstance(algo = "MD5").digest(saltedPassword);
            hashed = (toHex(sha1) + toHex(md5)).getBytes();
        } catch (NoSuchAlgorithmException e) {
            Log.w(TAG, "Failed to encode string because of missing algorithm: " + algo);
        }
        return hashed;
    }