'Returns a Deferred that gets a callback if it is a valid key, or
an errback if not.
@type hostKey: L{bytes}
@param hostKey: The host key to verify.
@type fingerprint: L{bytes}
@param fingerprint: The fingerprint of the key.
@return: A deferred firing with C{True} if the key is valid.'

def verifyHostKey(self, hostKey, fingerprint):

    return defer.fail(NotImplementedError())
