Merkle Airdrop

included in CS

2025-03-26 212 words One minute

Contents

How to play?

Airdrop a bunch of ERC20 tokens to users
Deploy a smart contract
Send an email with wallet address, token amount and proof to each user
The user claims their tokens from the smart contract

Build a merkle tree

import { MerkleTree } from 'merkletreejs';
import keccak256 from 'keccak256';
import { solidityPacked } from 'ethers';

function main() {
  const whitelist = [
    { address: '0x2173dEd80D3c17D2f349234a31ab8789D28Dd333', amount: 100 },
    { address: '0x2AFAF65965e08DBd0e0aD7a5594E6b5BE398CBd6', amount: 200 },
    { address: '0xfbc89Db3927bCCda61F550d3d9f3998750b7b93f', amount: 300 },
  ];

  const leaves = whitelist.map((x) => keccak256(solidityPacked(['address', 'uint256'], [x.address, x.amount])));
  const tree = new MerkleTree(leaves, keccak256, { sortPairs: true });
  const merkleRoot = tree.getRoot().toString('hex');

  console.log('Merkle Root:', '0x' + merkleRoot);
  console.log('Merkle Tree:\n', tree.toString());

  for (let i = 0; i < leaves.length; i++) {
    const proof = tree.getHexProof(leaves[i], i);
    console.log(`Proof for ${whitelist[i].address}: [${proof}]`);
  }
}

main();

Deploy a contract

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.26;

import "@openzeppelin/contracts/utils/cryptography/MerkleProof.sol";

contract MerkleAirdrop {
    bytes32 public merkleRoot;
    mapping(address => bool) public claimed;

    constructor(bytes32 _merkleRoot) {
        merkleRoot = _merkleRoot;
    }

    function claim(address user, uint256 amount, bytes32[] calldata proof) external {
        require(!claimed[user], "Already claimed");

        bytes32 leaf = keccak256(abi.encodePacked(user, amount));
        bool isValid = MerkleProof.verify(proof, merkleRoot, leaf);
        require(isValid, "Invalid proof");

        claimed[user] = true;

        // the logic of minting NFT
        // ...
    }
}

See the depolyed MerkleAirdrop on Holesky Testnet