code: public String produce(int size) {
          byte bytes[] = new byte[size];
          _random.nextBytes(bytes);
          return Strings.toHexString(bytes);
      }
docs: Produces a nonce of an arbitrary size in bytes, which is not to be proved later.
  
  @param size the size of the nonce in bytes
  @return the new nonce as a hexadecimal string