Android中，重新打开应用程序后尝试解密时，cipher.doFinal会出现BadPaddingException异常。

Question

问题可能很长，但我会尽量详细地描述它。

这里有一个类似我的问题的演示。

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。只有当指纹已经注册并且指纹有效时，才能使用指纹验证方式来获取这些密码。

存储时： 1. 用户输入密码。 2. 使用由AndroidKeyStore生成的SecretKey创建加密模式密码器。

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);
    }
}

指纹管理器验证密码（Cipher A），并获取真正的加密密码（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();

使用由FingerprintManager支持的密码加密算法（Cipher B）加密密码， 并将加密后的密码和加密向量（cipher iv）存储在SharedPreferences中。

//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. 读取密钥IV并创建解密模式加密(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);
    }
}

有效的指纹并获取真正的解密密码（密码 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();

阅读加密密码并使用真正的解密密码（Cipher D）进行解密。

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);
    }
}

如果不关闭应用程序，一切都没问题！！！

但是，当我杀死进程并重新启动它时，在decryptPin()方法中执行cipher.doFinal()时，我会得到BadPaddingException异常。

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

有人能帮我解决这个问题吗？是由于SecretKey引起的吗？谢谢！！！

- lovefish

---

“if not closing app”意味着你忘记保存某些东西（例如Keystore）。日志中的KeyStoreException是与BadPaddingException相关的吗？请不要将日志粘贴为图像。许多人使用日志来搜索问题源等。 - Toris

我已将日志粘贴为测试。@Toris - lovefish

Answer 1

我已经找到了问题所在。是因为我在init()方法中生成了相同别名的密钥导致的错误。我通过添加判断条件来解决这个问题。

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

- lovefish