def auth(message)
      authenticator = Util.zeros(tag_bytes)
      message = message.to_str
      compute_authenticator(authenticator, message)
      authenticator
    end
def auth(message)
      authenticator = Util.zeros(tag_bytes)
      message = message.to_str
      compute_authenticator(authenticator, message)
      authenticator
    end
Compute authenticator for message

 @param [#to_str] message the message to authenticate

 @return [String] the authenticator as raw bytes