eip: <to be assigned>
title: Practical Randomness via Dual Contract
author: Yao-Chieh Hu (@yhuag) <yhuag@connect.ust.hk>, Ting-Ting Lee (@tina1998612) <tleeae@connect.ust.hk>
status: Draft
type: Standards Track
category: ERC
created: 2019-02-17

Simple Summary

A proposal for achieving "nearly" non-predictable randomness via two smart contracts.

Abstract

There are two smart contracts: Main.sol and Randomness.sol.

Main.sol generates a random number by submitting a main_seed to Randomness.sol, which is derived from msg.data, msg.sender, and an arbitrary number salt. Randomness.sol takes in main_seed to mix with its rand_seed inside a random function that is embedded with a func_seed. During each round of the random number generation, the rand_seed is updated according to main_seed.

Correctness

Since that we only expose the Main.sol code, the Randomness.sol code remains invisible. The security level escalates from known-plaintext attack to ciphertext-only attack. Any attempt towards the Randomeness.col can only change the state of it without making it a feasible "key-value" pair in any time of future.

Though we are free to get the private rand_seed in the Randomness.sol (I wrote a tutorial for that if interested), it could be hard to retrieve the func_seed inside the random function.

The Randomness.sol's random function has been made as owner only via OpenZeppelin's Ownable.sol, so it makes it harder for submitting an external attempt for trials.

Disclaimer

Please think twice before using it on some profitable projects. I am really looking forward to any comment and suggestion. Thanks. :)

Specification

Main.sol

pragma solidity ^0.4.25;

import { Ownable } from "./openzeppelin-solidity/contracts/ownership/Ownable.sol";
import { Randomness } from "./Randomness.sol";

contract Main is Ownable {

  Randomness randomnessContract;

  // ... SOME CRAZY LOGICS

  // Random Function (free to use it any where)
  function _random(uint256 _salt) internal returns (uint256) {
    return uint256(randomnessContract.rand(
      keccak256(
        abi.encodePacked(
          msg.data,
          msg.sender,
          _salt
        )
      )
    ));
  }
}

Randomness.sol

THIS SHOULD BE HIDDEN FROM THE PUBLIC

pragma solidity ^0.4.25;

import { Ownable } from "./openzeppelin-solidity/contracts/ownership/Ownable.sol";

contract Randomness is Ownable {

  bytes32 private rand_seed = "hحَi";

  function rand(bytes32 key) public onlyOwner returns (bytes32) {
    rand_seed ^= key;
    // That super wierd string below is the func_seed
    return keccak256(abi.encodePacked(key, rand_seed, "台灣きन्दी한حَNo.1 :) "));
  }
}

Copyright

Copyright and related rights waived via MIT.