用java解密AES加密文件

发布于 2024-12-28 18:12:35 字数 333 浏览 0 评论 0原文

我有一个使用 AES 使用 java 应用程序加密的文件。我还有一个加密的密钥文件。但我不明白如何使用密钥来解密文件。大多数教程和示例都会在一个地方创建临时随机密钥、加密文件和解密。所以，问题是如何指定必须用于解密的密钥？

编辑：我发现的示例使用以下代码来生成密钥。我不知道在哪里可以使用我的钥匙。

KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
SecretKey key = kgen.generateKey();

原文

I have a file encrypted with java application using AES. I also have a key file was encrypted with. But i can't understand how to use the key to decrypt file. Most tutorials and examples create temporary random key, encrypt file and decrypt it in one place.
So, question is how to specify a key which have to be used for decryption?

EDIT:
Samples i found use following code to generate key. I have no idea where i can use my key here.

KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
SecretKey key = kgen.generateKey();

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坚持沉默 2025-01-04 18:12:35

只是总结我对路西法答案的评论。

如果您不知道使用什么填充来加密，请使用“无填充”集进行解密。这将解密所有内容，包括填充，并且不会因为填充不匹配而引发错误。
解密密文后，查看输出的最后一个块并查看使用了哪些填充。不同的填充会留下不同的字节模式，因此通常很容易辨别。
将您的解密方法设置为期望正确的填充类型，系统会自动为您删除它。

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聚集的泪 2025-01-04 18:12:35

答案可能只是将密钥数据作为字节放入 SecretKeySpec 中，如下所示：

SecretKeySpec aesKey = new SecretKeySpec(myKeyData, "AES");

请注意 SecretKeySpec 实现了 Key 接口，因此您可以直接在 Cipher.init() 方法中使用它。因此不需要 SecretKeyFactory，否则您将使用它。

The answer could be simply to put the key data as bytes into a SecretKeySpec like this:

SecretKeySpec aesKey = new SecretKeySpec(myKeyData, "AES");

Note that SecretKeySpec implements the Key interface, so you can use it directly in a Cipher.init() method. So there is no SecretKeyFactory needed, which you would use otherwise.

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触ぅ动初心 2025-01-04 18:12:35

如果对您有帮助，请尝试以下方法。

private static byte[] cipherData(PaddedBufferedBlockCipher cipher, byte[] data)
        throws Exception
{
    int minSize = cipher.getOutputSize(data.length);
    byte[] outBuf = new byte[minSize];
    int length1 = cipher.processBytes(data, 0, data.length, outBuf, 0);
    int length2 = cipher.doFinal(outBuf, length1);
    int actualLength = length1 + length2;
    byte[] result = new byte[actualLength];
    System.arraycopy(outBuf, 0, result, 0, result.length);
    return result;
}

private static byte[] decrypt(byte[] cipher, byte[] key, byte[] iv) throws Exception
{
    PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(
            new AESEngine()));
    CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
    aes.init(false, ivAndKey);
    return cipherData(aes, cipher);
}

private static byte[] encrypt(byte[] plain, byte[] key, byte[] iv) throws Exception
{
    PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(
            new AESEngine()));
    CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
    aes.init(true, ivAndKey);
    return cipherData(aes, plain);
}

Please try following methods, if might helpful for you.

private static byte[] cipherData(PaddedBufferedBlockCipher cipher, byte[] data)
        throws Exception
{
    int minSize = cipher.getOutputSize(data.length);
    byte[] outBuf = new byte[minSize];
    int length1 = cipher.processBytes(data, 0, data.length, outBuf, 0);
    int length2 = cipher.doFinal(outBuf, length1);
    int actualLength = length1 + length2;
    byte[] result = new byte[actualLength];
    System.arraycopy(outBuf, 0, result, 0, result.length);
    return result;
}

private static byte[] decrypt(byte[] cipher, byte[] key, byte[] iv) throws Exception
{
    PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(
            new AESEngine()));
    CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
    aes.init(false, ivAndKey);
    return cipherData(aes, cipher);
}

private static byte[] encrypt(byte[] plain, byte[] key, byte[] iv) throws Exception
{
    PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(
            new AESEngine()));
    CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
    aes.init(true, ivAndKey);
    return cipherData(aes, plain);
}

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