java - 尝试解密指纹 API 密码时出现 BadPaddingException

Question

在我的应用中，当用户在初始设置 [指纹注册] 中扫描手指时，我会保存用户访问代码的加密版本。当用户稍后尝试解锁应用程序时，我将尝试使用指纹 API [指纹验证] 来解密此访问代码。

但是，Cipher.doFinal 在解密时抛出以下异常:

javax.crypto.BadPaddingException
 at android.security.keystore.AndroidKeyStoreCipherSpiBase.engineDoFinal(AndroidKeyStoreCipherSpiBase.java:482)
 at javax.crypto.Cipher.doFinal(Cipher.java:1502)
 (...)

Caused by: android.security.KeyStoreException: Invalid argument
         at android.security.KeyStore.getKeyStoreException(KeyStore.java:940)
         at android.security.keystore.KeyStoreCryptoOperationChunkedStreamer.doFinal(KeyStoreCryptoOperationChunkedStreamer.java:224)
         at android.security.keystore.AndroidKeyStoreCipherSpiBase.engineDoFinal(AndroidKeyStoreCipherSpiBase.java:473)
        ... 12 more

指纹扫描仪显示在 DialogFragment 中。无论指纹是否正在登记或验证，以下函数始终从构造函数中按顺序调用。

初始化 keystore :

private void initializeKeystore() {

    try {
        mKeyStore = KeyStore.getInstance(KEY_STORE_NAME); //AndroidKeyStore
    } catch (KeyStoreException e) {
        mKeyStore = null;
    }

    try {
        mKeyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, KEY_STORE_NAME);
    } catch (NoSuchAlgorithmException | NoSuchProviderException e) {
        mKeyGenerator = null;
    }
}

创建 key :

private void createKey() {
    if (mKeyGenerator != null) {
        try {
            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);

            mKeyGenerator.init(builder.build());
            mKeyGenerator.generateKey();
        } catch (NoSuchAlgorithmException | InvalidAlgorithmParameterException |
                CertificateException | IOException e) {
            mKeyGenerator = null;
        }
    }
}

创建密码对象:

private void createCipher() {
    try {
        mCipher = Cipher.getInstance(KeyProperties.KEY_ALGORITHM_AES + "/"
                + KeyProperties.BLOCK_MODE_CBC + "/"
                + KeyProperties.ENCRYPTION_PADDING_PKCS7);
    } catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
        mCipher = null;
    }
}

当指纹扫描仪API成功验证用户身份时，依次调用以下代码:

@Nullable Cipher getCipher(@NonNull final FingerprintStore ivStore) {
    if (mKeyStore != null && mKeyGenerator != null && mCipher != null) {
        try {
            mKeyStore.load(null);
            SecretKey key = (SecretKey)mKeyStore.getKey(KEY_NAME, null);

            switch (mEncryptionMode) {
                case MODE_ENCRYPT:
                    mCipher.init(Cipher.ENCRYPT_MODE, key);
                    ivStore.writeIv(mCipher.getParameters().getParameterSpec(IvParameterSpec.class).getIV());
                    break;
                case MODE_DECRYPT:
                    byte[] iv = ivStore.readIv();
                    mCipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
                    break;
            }
            return mCipher;
        } catch (KeyStoreException | CertificateException | UnrecoverableKeyException | IOException
                | NoSuchAlgorithmException | InvalidKeyException | InvalidAlgorithmParameterException
                | InvalidParameterSpecException | NullPointerException e) {
            return null;
        }
    }

    return null;
}

并且，使用刚刚从上一次调用返回的 Cipher 实例:

@Nullable byte[] encryptOrDecrypt(@NonNull Cipher cipher, @NonNull byte[] subject) {
    try {
        return cipher.doFinal(subject);
    } catch (BadPaddingException | IllegalBlockSizeException e) {
        e.printStackTrace();
        return null;
    }
}

对 doFinal 的调用在加密数据时工作正常，但在解密时抛出异常。我检查了初始化 vector 和加密数据的 byte[]，发现它们被存储到磁盘 (Base64) 并正确读回内存。

Answer 1

没关系，显然我忽略了 SecretKey 应该只在注册阶段生成的事实。因为在尝试解密数据时调用了 createKey，所以在调用 doFinal 之前它被新生成的 key 覆盖。该代码现在可以完美运行。