Question

I am trying to decrypt data that is encrypted using the Bouncy Castle library in Java with a C#. The data that is encrypted in Java (again with the Bouncy Castle Libraries) can be decrypted with Java. I am using the same keys and parameters but when I reach DoFinal I get the error “pad block corrupted”.

Here is the Java:

KeyParameter keyParam = new KeyParameter(key);
CipherParameters param = new ParametersWithIV(keyParam, initVector);

BlockCipherPadding padding = new PKCS7Padding();
BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new CBCBlockCipher(new AESEngine()), padding);
cipher.reset();
cipher.init(true, param);

byte[] fileBytes = Base64.decodeBase64(decryptedStringData);
byte[] encrypted = new byte[cipher.getOutputSize(fileBytes.length)];
int l = cipher.processBytes(fileBytes, 0, fileBytes.length, encrypted, 0);
l += cipher.doFinal(encrypted, l);

return (Base64.encodeBase64String(encrypted));

Here is the C#:

KeyParameter keyParam = new KeyParameter(key);
ICipherParameters param = new ParametersWithIV(keyParam, initVector);

IBlockCipherPadding padding = new Pkcs7Padding();
BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new CbcBlockCipher(new AesEngine()), padding);
cipher.Reset();
cipher.Init(false, param);

byte[] fileBytes = Convert.FromBase64String(encryptedDataString);
byte[] decrypted = new byte[cipher.GetOutputSize(fileBytes.Length)];
int l = cipher.ProcessBytes(fileBytes, 0, fileBytes.Length, decrypted, 0);
l += cipher.DoFinal(decrypted, l);

return(Convert.ToBase64String(decrypted));

I am generating a 32 byte PBK for the key based on a hash that has been buffered… however, we checked the key generated between Java and C# and they are the same.

Answer 1

It turns out that the data provided for encryption and decryption were encoded in different formats. I was pulling in UTF-8 encoded strings to decrypt and they needed to be made into Base64 strings first. Thanks for all of the help provided.