带充气城堡的 256 位 AES/CBC/PKCS5Padding

2022-01-10 00:00:00 cryptography aes bouncycastle java

我在将以下 JDK JCE 加密代码映射到 Bouncy Castles 轻量级 API 时遇到问题:

I am having trouble mapping the following JDK JCE encryption code to Bouncy Castles Light-weight API:

public String dec(String password, String salt, String encString) throws Throwable {
    // AES algorithm with CBC cipher and PKCS5 padding
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding", "BC");

    // Construct AES key from salt and 50 iterations 
    PBEKeySpec pbeEKeySpec = new PBEKeySpec(password.toCharArray(), toByte(salt), 50, 256);
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithSHA256And256BitAES-CBC-BC");
    SecretKeySpec secretKey = new SecretKeySpec(keyFactory.generateSecret(pbeEKeySpec).getEncoded(), "AES");

    // IV seed for first block taken from first 32 bytes
    byte[] ivData = toByte(encString.substring(0, 32));
    // AES encrypted data
    byte[] encData = toByte(encString.substring(32));

    cipher.init( Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec( ivData ) );

    return new String( cipher.doFinal( encData ) );
}

上述方法效果很好，但由于 Oracle 对加密强度的限制，移植性不太好.我曾多次尝试移植到 Bouncy Castles 轻量级 API，但均未成功.

The above works great, but is not very portable due to Oracle's restriction on encryption strengths. I've made several attempts at porting to Bouncy Castles Light-weight API but without success. 

public String decrypt1(String password, String salt, String encString) throws Exception {

    byte[] ivData = toByte(encString.substring(0, 32));
    byte[] encData = toByte(encString.substring(32));

    PKCS12ParametersGenerator gen = new PKCS12ParametersGenerator(new SHA256Digest());
    gen.init(password.getBytes(), toByte(salt), 50);
    CBCBlockCipher cbcBlockcipher = new CBCBlockCipher(new RijndaelEngine(256));
    CipherParameters params = gen.generateDerivedParameters(256, 256);

    cbcBlockcipher.init(false, params);

    PaddedBufferedBlockCipher aesCipher = new PaddedBufferedBlockCipher(cbcBlockcipher, new PKCS7Padding());
    byte[] plainTemp = new byte[aesCipher.getOutputSize(encData.length)];
    int offset = aesCipher.processBytes(encData, 0, encData.length, plainTemp, 0);
    int last = aesCipher.doFinal(plainTemp, offset);
    byte[] plain = new byte[offset + last];
    System.arraycopy(plainTemp, 0, plain, 0, plain.length);
    return new String(plain);
}

上述尝试导致 org.bouncycastle.crypto.DataLengthException: last block complete in decryption.

The above attempt results in a org.bouncycastle.crypto.DataLengthException: last block incomplete in decryption.

我已经在网上搜索了示例，但是没有很多示例可以使用 PKCS5/PKCS7 作为填充，为 256 位 AES 和 CBC 提供您自己的 IV 数据.

I have searched for examples online, but there isn't many examples of providing your own IV data for 256bit AES with CBC using PKCS5/PKCS7 as padding.

注意:toByte 函数使用 base64 或类似方法将字符串转换为字节数组.

NB: The toByte function converts a String into a byte array using base64 or similar.

推荐答案

这应该适合你:

public String dec(String password, String salt, String encString)
        throws Exception {

    byte[] ivData = toByte(encString.substring(0, 32));
    byte[] encData = toByte(encString.substring(32));

    // get raw key from password and salt
    PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray(),
            toByte(salt), 50, 256);
    SecretKeyFactory keyFactory = SecretKeyFactory
            .getInstance("PBEWithSHA256And256BitAES-CBC-BC");
    SecretKeySpec secretKey = new SecretKeySpec(keyFactory.generateSecret(
            pbeKeySpec).getEncoded(), "AES");
    byte[] key = secretKey.getEncoded();

    // setup cipher parameters with key and IV
    KeyParameter keyParam = new KeyParameter(key);
    CipherParameters params = new ParametersWithIV(keyParam, ivData);

    // setup AES cipher in CBC mode with PKCS7 padding
    BlockCipherPadding padding = new PKCS7Padding();
    BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(
            new CBCBlockCipher(new AESEngine()), padding);
    cipher.reset();
    cipher.init(false, params);

    // create a temporary buffer to decode into (it'll include padding)
    byte[] buf = new byte[cipher.getOutputSize(encData.length)];
    int len = cipher.processBytes(encData, 0, encData.length, buf, 0);
    len += cipher.doFinal(buf, len);

    // remove padding
    byte[] out = new byte[len];
    System.arraycopy(buf, 0, out, 0, len);

    // return string representation of decoded bytes
    return new String(out, "UTF-8");
}

我假设您实际上是在为 toByte() 进行十六进制编码，因为您的代码为 IV 使用了 32 个字符(它提供了必要的 16 个字节).虽然我没有您用来进行加密的代码，但我确实验证了此代码将提供与您的代码相同的解密输出.

I assume that you're actually doing hex encoding for toByte() since your code uses 32 characters for the IV (which provides the necessary 16 bytes). While I don't have the code you used to do the encryption, I did verify that this code will give the same decrypted output as your code.

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