(data)K = Encrypt data using CAST 128 CBC with key = K
The Key is generated with a Diffie-Hellman key exchange as follows:
Ma - first message = g^Ra mod p (sent by the Client to the Server)
Mb - second message = g^Rb mod p (sent by the Server to the Cleint)
K - Key = Mb^Ra mod p = Ma^Rb mod p
We are using CAST 128, (the implementation from SSLeay) in CBC mode with the IV in the second message being the bytestring "CJalbert" and the IV in the third message being the bytestring "LWallace".
