MerkleTree.js Solidity example

Construct merkle trees with MerkleTree.js and verify merkle proofs in Solidity.

Example

contracts/MerkleProof.sol

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;
  }
}

test/merkleproof.js

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)) // false

Test

make test

License

MIT