'Make the master key by (1) combining the credentials to create
a composite hash, (2) transforming the hash using the transform seed
for a specific number of rounds and (3) finally hashing the result in
combination with the master seed.'

def _make_master_key(self):

    super(KDB4File, self)._make_master_key()
    composite = sha256(''.join(self.keys))
    tkey = transform_key(composite, self.header.TransformSeed, self.header.TransformRounds)
    self.master_key = sha256((self.header.MasterSeed + tkey))
