AES 使用相同的 IV 进行加密和解密

Question

我的代码存在一些问题，因此我没有使用相同的 IV 进行加密和解密。我知道为了正确执行此操作，我必须在数据之前将 IV 写入我的输出文件，但是我正在努力实现这一点。谁能帮我解决这个问题？

再次编辑代码以显示完整范围

public class TestFileEncryption {
    private static void mainCrypto(int cipherMode, File inputFile, File outputFile) throws Exception{
        //Let the user enter the key they wish to use
        Key secretKey = new SecretKeySpec(UITest.getStoreKey().getBytes(), UITest.getSendAlg()); //Generates a key based on the default keysize for the specified algorithm

        //Generate an Initialization Vector (IV)
        final int ALG_KEYLENGTH = UITest.getStoreKey().length(); //Change this as desired for the security level you want
        byte[] iv = new byte[ALG_KEYLENGTH]; //Save the IV bytes or send it in plaintext with the encrypted data so you can decrypt the data later
        SecureRandom prng = new SecureRandom(); //Use SecureRandom to generate random bits. The size of the IV matches the blocksize of the cipher
        prng.nextBytes(iv); //Construct the appropriate IvParameterSpec object for the data to pass to Cipher's init() method

        //Create a Cipher by specifying the following parameters: Alg name, Mode (CBC), Padding (PKC7/PKCS5)
        Cipher cipherForEncryption = Cipher.getInstance(UITest.getSendAlg() + "/CBC/PKCS5PADDING"); // Must specify the mode explicitly as most JCE providers default to ECB mode

        //Initialize the Cipher for Encryption
        cipherForEncryption.init(cipherMode, secretKey, new IvParameterSpec(iv));

        //Declare / Initialize the Data, Convert the Input to Bytes and encrypt or decrypt using doFinal.
        FileInputStream inputStream = new FileInputStream(inputFile);
        byte[] inputBytes = new byte[(int) inputFile.length() - ALG_KEYLENGTH];
        inputStream.read(iv);
        inputStream.read(inputBytes);
        byte[] outputBytes = cipherForEncryption.doFinal(inputBytes);
        FileOutputStream outputStream = new FileOutputStream(outputFile);
        outputStream.write(iv);
        outputStream.write(outputBytes);
        inputStream.close();
        outputStream.close();
    }

    public static void encrypt(File inputFile, File outputFile) throws Exception {
        mainCrypto(Cipher.ENCRYPT_MODE, inputFile, outputFile); //ENC_MODE = Constant used to initialize cipher to encryption mode.
    }

    public static void decrypt(File inputFile, File outputFile) throws Exception {
        mainCrypto(Cipher.DECRYPT_MODE, inputFile, outputFile); //ENC_MODE = Constant used to initialize cipher to encryption mode.
    }

    public static void main(String[] args) {}
}

Answer 1

你只需要在密文之前写IV：

outputStream.write(iv);
outputStream.write(outputBytes);

然后，解密时，读取IV和密文：

byte[] iv = new byte[ALG_BLOCKSIZE];
byte[] inputBytes = new byte[(int) inputFile.length() - ALG_BLOCKSIZE];
inputStream.read(iv);
inputStream.read(inputBytes);

这里 ALG_BLOCKSIZE 对于 AES-CBC 需要为 16。

Answer 2

只是扩展@Javier 的答案。

您似乎希望使用相同的方法进行加密和解密（取决于模式），但是在处理 IV 方面存在差异。

您生成了一个随机 IV，然后用（普通）输入的输入覆盖它，最后将它写入输出（不管它是解密）。

所以你要区分模式是否是

• 加密 - IV 在密文之前生成并写入输出
• 解密 - IV 从输入读取并用于解密，但不写入输出

类似的东西：

private void encrypt(File inputFile, File outputFile)  {
    //Declare / Initialize the Data, Convert the Input to Bytes and encrypt or decrypt using doFinal.
    FileInputStream inputStream = new FileInputStream(inputFile);
    byte[] inputBytes = new byte[(int) inputFile.length()];
    byte[] iv = new byte[16]; // 16 for AES-CBC
    SecureRandom prng = new SecureRandom(); //Use SecureRandom to generate random bits. The size of the IV matches the blocksize of the cipher
    prng.nextBytes(iv); //Construct the appropriate IvParameterSpec object for the data to pass to Cipher's init() method

    //Create a Cipher by specifying the following parameters: Alg name, Mode (CBC), Padding (PKC7/PKCS5)
    Cipher cipherForEncryption = Cipher.getInstance(UITest.getSendAlg() + "/CBC/PKCS5PADDING"); // Must specify the mode explicitly as most JCE providers default to ECB mode

    //Initialize the Cipher for Encryption
    cipherForEncryption.init(cipherMode, secretKey, new IvParameterSpec(iv));      
        inputStream.read(inputBytes);
        byte[] outputBytes = cipherForEncryption.doFinal(inputBytes);
        FileOutputStream outputStream = new FileOutputStream(outputFile);
        outputStream.write(iv);
        outputStream.write(outputBytes);
        outputStream.flush();
        inputStream.close();
        outputStream.close();
    }
}

private void decrypt(File inputFile, File outputFile) {
    //Declare / Initialize the Data, Convert the Input to Bytes and encrypt or decrypt using doFinal.
    FileInputStream inputStream = new FileInputStream(inputFile);
    byte[] inputBytes = new byte[(int) inputFile.length()-16];
    byte[] iv = new byte[16]; // 16 for AES-CBC

    //Create a Cipher by specifying the following parameters: Alg name, Mode (CBC), Padding (PKC7/PKCS5)
    Cipher cipherForEncryption = Cipher.getInstance(UITest.getSendAlg() + "/CBC/PKCS5PADDING"); // Must specify the mode explicitly as most JCE providers default to ECB mode

    //Initialize the Cipher for Encryption
    cipherForEncryption.init(cipherMode, secretKey, new IvParameterSpec(iv));      
    inputStream.read(iv);
    inputStream.read(inputBytes);
    byte[] outputBytes = cipherForEncryption.doFinal(inputBytes);
    FileOutputStream outputStream = new FileOutputStream(outputFile);
    outputStream.write(outputBytes);
    outputStream.flush();
    inputStream.close();
    outputStream.close();
}

为了省略一些细节，也许你可以直接使用 Java CipherOutputStream 和 CiptherInputStream 并且实现会为你处理这些细节（如果你不关心确切的格式）。

接下来你缺少的是一个身份验证标签，至少是明文的哈希，以确保密文的完整性。 （称为认证加密）