Android cipher.doFinal 在重新打开应用程序后尝试解密时出现 BadPaddingException

Question

问题可能很长，但我会尽量详细描述。

这是一个demo有像我这样的问题。

我有一个 android 应用程序，我想添加一个功能，允许用户在 SharedPreferences 中加密和保存他们的密码，并从 SharedPreferences 中读取和解密它们。仅当指纹已登记且指纹有效可作为获取这些密码的验证方式时才可用。

存储时间:

1. user input password
2. create encrpty mode cipher by SecretKey generated by AndroidKeyStore

public Cipher getEncryptCipher() {
    try {
        Cipher cipher = Cipher.getInstance(KeyProperties.KEY_ALGORITHM_AES + "/"
                + KeyProperties.BLOCK_MODE_CBC + "/"
                + KeyProperties.ENCRYPTION_PADDING_PKCS7);
        mKeyStore.load(null);
        SecretKey key = (SecretKey) mKeyStore.getKey(KEY_NAME, null);
        cipher.init(Cipher.ENCRYPT_MODE, key);
        return cipher;
    } catch (Exception e) {
        throw new RuntimeException("Failed to encrypt pin ", e);
    }
}

3. FingerprintManager valid the cipher(Cipher A) and get real encrpty cipher (Cipher B)

//mCryptoObject is generated by cipher in step 2
mFingerprintManager.authenticate(mCryptoObject, mCancellationSignal, 0 /* flags */, FingerprintManager.AuthenticationCallback, null);


//in FingerprintManager.AuthenticationCallback
javax.crypto.Cipher cipher = result.getCryptoObject().getCipher();

4. encrpty password by the cipher(Cipher B) supported from FingerprintManager
5. store encrypted password and cipher iv in SharedPreferences

//In my app, we have many device, every could have one password. Pin is password.
public void encryptPin(String deviceId, String pin, javax.crypto.Cipher cipher) {
    try {
        if (cipher == null) return;
        byte[] encryptedBytes = cipher.doFinal(pin.getBytes("utf-8"));
        byte[] cipherIv = cipher.getIV();
        String encodedPin = Base64.encodeToString(encryptedBytes, Base64.DEFAULT);
        String encodeCipherIv = Base64.encodeToString(cipherIv, Base64.DEFAULT);
        SharedPreferences.Editor editor = mSharedPreferences.edit();
        editor.putString(createPinKey(deviceId), encodedPin);
        editor.putString(createIvKey(deviceId), encodeCipherIv);
        editor.apply();
    } catch (IOException | IllegalBlockSizeException | BadPaddingException e) {
        throw new RuntimeException("Failed to encrypt pin ", e);
    }
}

阅读时:

1. read cipher iv and create decrpty mode cipher(Cipher C)

public Cipher getDecryptCipher(String deviceId) {
    try {
        String encodedIv = mSharedPreferences.getString(createIvKey(deviceId), "");
        byte[] cipherIv = Base64.decode(encodedIv, Base64.DEFAULT);
        Cipher cipher = Cipher.getInstance(KeyProperties.KEY_ALGORITHM_AES + "/"
                + KeyProperties.BLOCK_MODE_CBC + "/"
                + KeyProperties.ENCRYPTION_PADDING_PKCS7);
        mKeyStore.load(null);
        SecretKey key = (SecretKey) mKeyStore.getKey(KEY_NAME, null);
        cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(cipherIv));
        return cipher;
    } catch (Exception e) {
        throw new RuntimeException("Failed to encrypt pin ", e);
    }
}

2. valid fingerprint and get the real decrypt cipher(Cipher D)

//mCryptoObject is generated by cipher in step 1
mFingerprintManager.authenticate(mCryptoObject, mCancellationSignal, 0 /* flags */, FingerprintManager.AuthenticationCallback, null);


//in FingerprintManager.AuthenticationCallback
javax.crypto.Cipher cipher = result.getCryptoObject().getCipher();

3. read encrypted password and decrypt it by the real decrypt cipher(Cipher D)

public String decryptPin(String deviceId, javax.crypto.Cipher cipher) {
    String encryptedPin = mSharedPreferences.getString(createPinKey(deviceId), "");
    if (TextUtils.isEmpty(encryptedPin)) {
        return "";
    }
    try {
        if (cipher == null) return "";
        byte[] decodedBytes = Base64.decode(encryptedPin, Base64.DEFAULT);
        //BadPaddingException in this line 
        byte[] decryptBytes = cipher.doFinal(decodedBytes);
        return new String(decryptBytes, Charset.forName("UTF8"));
    } catch (Exception e) {
        MyLog.d(TAG, "Failed to decrypt the data with the generated key." + e.getMessage());
        e.printStackTrace();
        return "";
    }
}

我的初始化方法:

private void init() {
    try {
        mKeyStore = KeyStore.getInstance("AndroidKeyStore");
        mKeyStore.load(null);
        KeyGenParameterSpec.Builder builder = new KeyGenParameterSpec.Builder(KEY_NAME,
                KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
                .setBlockModes(KeyProperties.BLOCK_MODE_CBC)
                .setUserAuthenticationRequired(true)
                .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_PKCS7);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            builder.setInvalidatedByBiometricEnrollment(true);
        }


        KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
        keyGenerator.init(
                    builder.build());
        keyGenerator.generateKey();


    } catch (Exception e) {
        throw new RuntimeException("Fail to init:" + e);
    }
}

不关闭应用一切正常!!!

然而，当我终止进程并重新启动它时，我在执行 cipher.doFinal() 时在 decryptPin() 方法中得到 BadPaddingException。

System.err: javax.crypto.BadPaddingException
at android.security.keystore.AndroidKeyStoreCipherSpiBase.engineDoFinal(AndroidKeyStoreCipherSpiBase.java:482)
at javax.crypto.Cipher.doFinal(Cipher.java:1502)
at com.xiaomi.smarthome.framework.page.verify.DeviceVerifyConfigCache.decryptPin(DeviceVerifyConfigCache.java:156)
at com.xiaomi.smarthome.framework.page.verify.VerifyManager.decryptPin(VerifyManager.java:173)
at com.xiaomi.smarthome.framework.page.verify.FingerPrintVerifyActivity$1.onAuthenticated(FingerPrintVerifyActivity.java:62)
at com.xiaomi.smarthome.framework.page.verify.view.FingerPrintOpenVerifyDialog.onAuthenticationSucceeded(FingerPrintOpenVerifyDialog.java:136)
at android.hardware.fingerprint.FingerprintManager$MyHandler.sendAuthenticatedSucceeded(FingerprintManager.java:805)
at android.hardware.fingerprint.FingerprintManager$MyHandler.handleMessage(FingerprintManager.java:757)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5458)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
Caused by: android.security.KeyStoreException: Invalid argument
at android.security.KeyStore.getKeyStoreException(KeyStore.java:632)
at android.security.keystore.KeyStoreCryptoOperationChunkedStreamer.doFinal(KeyStoreCryptoOperationChunkedStreamer.java:224)
at android.security.keystore.AndroidKeyStoreCipherSpiBase.engineDoFinal(AndroidKeyStoreCipherSpiBase.java:473)
... 13 more

有谁能帮我解决这个问题吗？是不是SecretKey引起的？谢谢!!!

Answer 1

我发现了我的问题。在我的 init() 方法中生成具有相同别名的 Key 是我的错误。我通过添加判断条件来解决问题。

        if (!mKeyStore.containsAlias(KEY_NAME)) {
            KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
            keyGenerator.init(
                    builder.build());
            keyGenerator.generateKey();
        }