EVM

Switchboard Randomness for EVM applications

Prerequisites

• Basic understanding of Ethereum and smart contracts.

• Familiarity with common smart contract development tools (e.g., Hardhat, Foundry).

• A development environment set up and ready to go.

Installation

1. Solidity SDK:

   npm install @switchboard-xyz/on-demand-solidity
   

2. TypeScript SDK: (For off-chain randomness resolution)

   npm install @switchboard-xyz/on-demand
   

3. Forge (If applicable): Add the following lines to your remappings.txt file:

   @switchboard-xyz/on-demand-solidity/=node_modules/@switchboard-xyz/on-demand-solidity
   

Step 1: EVM Contract Setup (Solidity)

1. Import Switchboard Interfaces:

   import {Structs} from "@switchboard-xyz/on-demand-solidity/structs/Structs.sol";
   import {ISwitchboard} from "@switchboard-xyz/on-demand-solidity/ISwitchboard.sol";
   

2. Implementation:

   // Address of the Switchboard contract
   address private immutable _switchboard;
   
   // Random Number to receive Switchboard Randomness
   uint256 public randomNumber;
   
   // Reference to the Switchboard contract
   ISwitchboard switchboard;
   
   // Queue IDs
   bytes32 constant MAINNET_QUEUE = 0x86807068432f186a147cf0b13a30067d386204ea9d6c8b04743ac2ef010b0752;
   bytes32 constant TESTNET_QUEUE = 0xd9cd6a04191d6cd559a5276e69a79cc6f95555deeae498c3a2f8b3ee670287d1;
   
   // Choose chain-appropriate queue
   bytes32 public queue;
   
   constructor(address switchboardAddress, bool isMainnet) {
      _switchboard = switchboardAddress;
      switchboard = ISwitchboard(switchboardAddress);
   
      // setup the chain selection for mainnet or testnet
      if(isMainnet){
          queue = MAINNET_QUEUE;
      } else {
          queue = TESTNET_QUEUE;
      }
   }
   
   // Unique identifier for each randomness request
   bytes32 public randomnessId;
   

Note that one has to inject the address of the Switchboard contract on deployment and select the appropriate network for the queue. For reference, the latest deployments can be found here. https://docs.switchboard.xyz/product-documentation/data-feeds/evm#deployments

1. Request Randomness: Call the requestRandomness function within your smart contract. The randomness is needed.

function roll() external {
    ...
    // Make it unique and random
    randomnessId = keccak256(abi.encodePacked(msg.sender, block.timestamp));

    // Invoke the on-demand contract reference
    switchboard.requestRandomness(
         randomnessId,            // randomnessId (bytes32): Unique ID for the request.
         address(this),            // authority (address):  Authority to re-roll the request.
         queue,                    // queueId (bytes32 ): Chain selection for requesting randomness.
         30                         // minSettlementDelay (uint16): Minimum seconds to settle the request.
     );
 }

randomnessId has to be unique for tracking your request. Then inject it into your chain-appropriate queue using the deployed Switchboard's address and requestRandomness function.

IMPORTANT: ensure sufficient delay time for randomness to be resolved by oracles! You will be able to save on costs.

1. Setup update feed handler

   // Function for resolving randomness within the same contract.
   function resolve(bytes[] calldata switchboardUpdateFeeds) external {
          // invoke
          switchboard.updateFeeds(switchboardUpdateFeeds);
   
          // store value for later use
          Structs.RandomnessResult memory randomness = switchboard.getRandomness(randomnessId).result;
          require(randomness.settledAt != 0, "Randomness failed to Settle");
   
          // update the number for state changes
          randomNumber = randomness.value;
    }
   

   Given all the correct parameters, you are now able to call into the Switchboard oracle to resolve your randomness.

Step 2: Resolve Randomness Off-Chain (TypeScript)

1. Fetch Randomness:

   import { CrossbarClient } from "@switchboard-xyz/on-demand";
   
   const crossbar = new CrossbarClient("https://crossbar.switchboard.xyz");
   
   const { encoded } = await crossbar.resolveEVMRandomness({
     chainId: 1115, // Chain ID for Core Testnet.  Example:  Morph Holesky/Testnet is (1115).
     randomnessId: "0xYOUR_RANDOMNESS_ID", //  ID from your Solidity contract
   });
   

2. Submit to Contract: Use a library like ethers.js or web3.js to submit the encoded data to your smart contract. Using ethers.js, it would look similar to:

   import { ethers } from "ethers";
   
   const exampleAddress = "0xYOUR_CONTRACT_ADDRESS";  //  contract Address
   const abi = ["function resolve(bytes[] calldata updates)"]; //  copy the function signature
   
   const provider = new ethers.providers.JsonRpcProvider(process.env.RPC_URL);
   const signer = new ethers.Wallet(process.env.PRIVATE_KEY, provider);
   const yourContract = new ethers.Contract(exampleAddress, abi, signer);
   
   const tx = await yourContract.resolve(encoded);
   await tx.wait();
   
   console.log("Randomness resolved in transaction:", tx.hash);
   

In Summary

Integrate Switchboard randomness to get solidity randomness. Once the ID is given to the oracle, you can then use it on-chain for the randomness function. It would also be more efficient if the settlement of randoms is delayed until it gets resolved.

You've now implemented a secure and verifiable way to get randomness in your EVM smart contracts!