Question

For certain reasons I need to implement Rijndael de/compression with a blocksize of 256 bits instead of AES which uses a block size of 128 bits (reason: data is encrypted in PHP using Rijndael…).

How can I change the block-size for a cipher?

If i just get a cipher with "RIJNDAEL/CFB/PKCS5Padding" and try to initialize a IV with 256 bits I get an exception, because the block-size is only 128 bits.

Answer 1

There is no support in any of the Sun JCE providers for anything other than Rijndael with the 128-bit blocksize: this is the AES algorithm. To get rijndael with the 256-bit blocksize you will have to go somewhere else. I suggest the Bouncycastle java library. The RijndaelEngine class has a constructor that accepts a block size in bits. Most people find the PaddedBufferedBlockCipher class to be more convenient when used with suitable padding, e.g.

PaddedBufferedBlockCipher c = new PaddedBufferedBlockCipher(new RijndaelEngine(256), new PKCS7Padding());