The ARCFour keystream is implemented in the
class ARCFour, which defines the following additional constant:
ARCFour. The value mapped must be a byte array of the secret
key, which can be up to 256 bytes long.
Also note that using the ARCFour PRNG as a stream cipher is as simple as:
IRandom arcfour; // initialized elsewhere. byte in, out; out = in ^ arcfour.next();