Construct merkle trees with MerkleTree.js and verify merkle proofs in Solidity.
pragma solidity ^0.5.2; contract MerkleProof { function verify( bytes32 root, bytes32 leaf, bytes32[] memory proof ) public pure returns (bool) { bytes32 computedHash = leaf; for (uint256 i = 0; i < proof.length; i++) { bytes32 proofElement = proof[i]; if (computedHash <= proofElement) { // Hash(current computed hash + current element of the proof) computedHash = keccak256(abi.encodePacked(computedHash, proofElement)); } else { // Hash(current element of the proof + current computed hash) computedHash = keccak256(abi.encodePacked(proofElement, computedHash)); } } // Check if the computed hash (root) is equal to the provided root return computedHash == root; } }const MerkleProof = artifacts.require('MerkleProof') const MerkleTree = require('merkletreejs') const keccak256 = require('keccak256') const contract = await MerkleProof.new() const leaves = ['a', 'b', 'c', 'd'].map(v => keccak256(v)) const tree = new MerkleTree(leaves, keccak256, { sort: true }) const root = tree.getHexRoot() const leaf = keccak256('a') const proof = tree.getHexProof(leaf) console.log(await contract.verify.call(root, leaf, proof)) // true const badLeaves = ['a', 'b', 'x', 'd'].map(v => keccak256(v)) const badTree = new MerkleTree(badLeaves, keccak256, { sort: true }) const badProof = badTree.getHexProof(leaf) console.log(await contract.verify.call(root, leaf, badProof)) // falsemake testMIT