Generating Random Numbers in Solidity

This recipe explores generating a random number on SKALE without the use of a 3rd-party provider like Chainlink and without callbacks. The actual random value is generating from the signature of the block signature which is randomized depending on which entities active in validation of the chain sign the actual block.

Using RNG

@dirtroad/skale-rng (recommended)
Direct Precompile Call (0x18)

Using SKALE RNG Library

The easiest way is to use the SKALE RNG library:

Step 1: Install Library

npm install @dirtroad/skale-rng

Step 2: Import and Use

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "@dirtroad/skale-rng/contracts/RNG.sol";

contract MyRandomContract is RNG {

    /**
    * Generate a random number between 0 and 2^256-1
    */
    function generateRandom() external view returns (uint256) {
        return getRandomNumber();
    }
    
    /*
    * Generate a random number between min and max
    */
    function generateRandomInRange(uint256 min, uint256 max) external view returns (uint256) {
        return getNextRandomRange(min, max);
    }
}

Direct Precompiled Contract Call

Use inline assembly to call the precompiled contract at address 0x18:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

contract GetRandomNumber {
    function getRandom() public view returns (bytes32) {
        bytes32 randomValue;
        assembly {
            let freemem := mload(0x40)
            let start_addr := add(freemem, 0)
            if iszero(staticcall(gas(), 0x18, 0, 0, start_addr, 32)) {
                invalid()
            }
            randomValue := mload(freemem)
        }
        return randomValue;
    }
    
    function getRandomUint256() public view returns (uint256) {
        return uint256(getRandom());
    }
}

Coin Flip Implementation

A coin flip randomly selects between two outcomes:

Heads (true or 1)
Tails (false or 0)

SKALE RNG Library
Direct Precompile Call (0x18)

Step 1: Install Library

npm install @dirtroad/skale-rng

Basic Coin Flip

Using the SKALE RNG library makes it simpler:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "@dirtroad/skale-rng/contracts/RNG.sol";

contract CoinFlipWithLibrary is RNG {
    enum CoinSide { Heads, Tails }
    
    event CoinFlipped(address indexed player, CoinSide result);
    
    function flip() public returns (CoinSide) {
        uint256 random = getRandomNumber();
        CoinSide result = (random % 2 == 0) ? CoinSide.Heads : CoinSide.Tails;
        
        emit CoinFlipped(msg.sender, result);
        return result;
    }
}

Basic Coin Flip

Here’s a simple coin flip contract using inline assembly to call the RNG precompile:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

contract CoinFlip {
    enum CoinSide { Heads, Tails }
    
    event CoinFlipped(address indexed player, CoinSide result);
    
    function flip() public returns (CoinSide) {
        uint256 random = getRandomNumber();
        CoinSide result = (random % 2 == 0) ? CoinSide.Heads : CoinSide.Tails;
        
        emit CoinFlipped(msg.sender, result);
        return result;
    }
    
    function getRandomNumber() private view returns (uint256) {
        bytes32 randomBytes;
        assembly {
            let freemem := mload(0x40)
            if iszero(staticcall(gas(), 0x18, 0, 0, freemem, 32)) {
                invalid()
            }
            randomBytes := mload(freemem)
        }
        return uint256(randomBytes);
    }
}

RNG is native to SKALE and relies on SKALE’s Consensus. In local testing or on other chains, this will always return 0.

Random numbers are generated per block. Multiple calls in the same block will return the same value unless manipulated through bitwise or other mathemtical operations.

Resources

SKALE RNG Library

Deployment

Smart Contracts

Privacy

x402

MPP

Facilitators

AI Agents

Native Features

Generating Random Numbers in Solidity

Using RNG

Using SKALE RNG Library

Step 1: Install Library

Step 2: Import and Use

Direct Precompiled Contract Call

Coin Flip Implementation

Step 1: Install Library

Basic Coin Flip

Basic Coin Flip

Resources

​Using RNG

​Using SKALE RNG Library

​Step 1: Install Library

​Step 2: Import and Use

​Direct Precompiled Contract Call

​Coin Flip Implementation

​Step 1: Install Library

​Basic Coin Flip

​Basic Coin Flip

​Resources

Using RNG

Using SKALE RNG Library

Step 1: Install Library

Step 2: Import and Use

Direct Precompiled Contract Call

Coin Flip Implementation

Step 1: Install Library

Basic Coin Flip

Basic Coin Flip

Resources