AES 128 DOT NET and Java Compatibility

Question

We have been trying a prototype of a scheme where we encrypt decrypt data between two systems: One in .NET and the other in Java. We were going to use simple 128 bit AES Encryption.

The problem I am facing is trivial, but I cannot find a proper solution. Maybe my understanding of AES or Encryption in general is less.

Assuming we have a predefined key, represented by the following hex string: "9c361fec3ac1ebe7b540487c9c25e24e". This is a 16-byte key. The encryption part in Java would be

  final byte[] rawKey = hexStringToByteArray("9c361fec3ac1ebe7b540487c9c25e24e");
  final SecretKeySpec skeySpec = new SecretKeySpec(rawKey, "AES");
  // Instantiate the cipher
  final Cipher cipher = Cipher.getInstance("AES");
  cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

  final byte[] encrypted = cipher.doFinal(plainText.getBytes());

The 'hexStringToByteArray' function converts the hex string to a byte array. The problem is that in java, bytes are signed. So the value 9C is -100 and not 156 (as it would be in .NET).

In Java this becomes: -100,54,31,-20,58,-63,-21,-25,-75,64,72,124,-100,37,-30,78

In .NET however, this is: 156,54,31,236,58,193,235,231,181,64,72,124,156,37,226,78

Question: Given that the representation of the keys itself differs, would it affect the encryption process itself? This is simple encryption without CBC and PADDING.

Edit: Updated the code to look formatted.

Hi I'm suffered by the same issue. My java encrypted data is different from the .net encrypt data. I followed the same method that you followed. need your help. — Rajesh Rajaram

Jon Skeet Jon Skeet · Accepted Answer · 2010-11-23T17:47:35

I don't think that you've got a problem at all. You've got exactly the same data in both platforms. One version shows it as signed data, the other as unsigned... but the bits themselves are the same.

I wouldn't expect there to be any problem at all in using these keys for cryptography.

AES 128 DOT NET and Java Compatibility

1 Answers