code: public String produce(String state, long time) {
          Nonce nonce = new Nonce(INSTANCE, time > 0 ? time : TTL, SIZE, _random);
          _map.put(state + ':' + nonce.value, nonce);
          return nonce.value;
      }
docs: Produces a nonce that is associated with the given state and is to be proved within a time limit.
  
  @param state an arbitrary state to be associated with the new nonce.
  @param time the TTL of the new nonce, in milliseconds. If this parameter is 0 or negative, the default TTL is used instead.
  @return the new nonce as a hexadecimal string