MerkleTree.js

Construct Merkle Trees and verify proofs in JavaScript.

Contents

• Install
• Example
• Getting started
• Diagrams
• Documentation
• Test
• FAQ
• Notes
• Resources
• Contributing
• License

Install

From NPM:

npm install merkletreejs

Import as ES6 module

import { MerkleTree } from 'merkletreejs'

Import as CommonJs

const { MerkleTree } = require('merkletreejs')

CDN

Available on jsDelivr CDN:

<script src="https://cdn.jsdelivr.net/npm/merkletreejs@latest/merkletree.js"></script>

The exported classes will be available on window object, e.g. window.MerkleTree

Example

https://lab.miguelmota.com/merkletreejs

Getting started

Construct tree, generate proof, and verify proof:

const { MerkleTree } = require('merkletreejs')
const SHA256 = require('crypto-js/sha256')

const leaves = ['a', 'b', 'c'].map(x => SHA256(x))
const tree = new MerkleTree(leaves, SHA256)
const root = tree.getRoot().toString('hex')
const leaf = SHA256('a')
const proof = tree.getProof(leaf)
console.log(tree.verify(proof, leaf, root)) // true


const badLeaves = ['a', 'x', 'c'].map(x => SHA256(x))
const badTree = new MerkleTree(badLeaves, SHA256)
const badLeaf = SHA256('x')
const badProof = badTree.getProof(badLeaf)
console.log(badTree.verify(badProof, badLeaf, root)) // false

Print tree to console:

console.log(tree.toString())

Output:

└─ 7075152d03a5cd92104887b476862778ec0c87be5c2fa1c0a90f87c49fad6eff
   ├─ e5a01fee14e0ed5c48714f22180f25ad8365b53f9779f79dc4a3d7e93963f94a
   │  ├─ ca978112ca1bbdcafac231b39a23dc4da786eff8147c4e72b9807785afee48bb
   │  └─ 3e23e8160039594a33894f6564e1b1348bbd7a0088d42c4acb73eeaed59c009d
   └─ 2e7d2c03a9507ae265ecf5b5356885a53393a2029d241394997265a1a25aefc6
      └─ 2e7d2c03a9507ae265ecf5b5356885a53393a2029d241394997265a1a25aefc6

Diagrams

▾ Visualization of Merkle Tree

▾ Visualization of Merkle Tree Proof

▾ Visualization of Invalid Merkle Tree Proofs

▾ Visualization of Bitcoin Merkle Tree

Documentation

See documentation (under docs/)

Test

npm test

FAQ

• Q: How do you verify merkle proofs in Solidity?

  • A: Check out the example repo merkletreejs-solidity on how to generate merkle proofs with this library and verify them in Solidity.

• Q: How do you verify merkle multiproofs in Solidity?

  • A: Check out the example repo merkletreejs-multiproof-solidity on how to generate merkle multiproofs with this library and verify them in Solidity.

• Q: Is there an NFT whitelist example in Solidity?

  • A: Check out the example repo merkletreejs-nft-whitelist on how to generate merkle root of whitelisted accounts and merkle proofs with this library and verify them in Solidity.

• Q: What other types of merkle trees are supported?

  • Besides standard MerkleTree, there's also MerkleMountainRange, MerkleSumTree, IncrementalMerkleTree, and MerkleRadixTree implemenation classes available. For Merkle Patricia Tree, see @ethereumjs/trie.

• Q: How do I hash a JSON object?

• See https://www.npmjs.com/package/json-stable-stringify for deterministic stringifying of JSON objects.

• Q: Is there a CLI version of this library?

  • Yes, see merkletreejs-cli.

• Q: Is there a way to visualize the merkle trees in the browser?

  • Yes, see example ui and merkletree-viz.

Notes

As is, this implemenation is vulnerable to a second pre-image attack. Use a difference hashing function for leaves and nodes, so that H(x) != H'(x).

Also, as is, this implementation is vulnerable to a forgery attack for an unbalanced tree, where the last leaf node can be duplicated to create an artificial balanced tree, resulting in the same Merkle root hash. Do not accept unbalanced tree to prevent this. More info here.

Please use the library @openzeppelin/merkle-tree if you're integrating with OpenZeppelin contracts or using multiproofs. There are known issues with the current multiproof implementation as pointed out in issues.

Disclaimer

This library was created for my own purposes and is provided as-is. Use at your own risk.

Resources

• Bitcoin mining the hard way: the algorithms, protocols, and bytes

• Bitcoin Talk - Merkle Trees

• How Log Proofs Work

• Raiden Merkle Tree Implemenation

• Why aren't Solidity sha3 hashes not matching what other sha3 libraries produce?

• What is the purpose of using different hash functions for the leaves and internals of a hash tree?

• Why is the full Merkle path needed to verify a transaction?

• Where is Double hashing performed in Bitcoin?

• Compact Merkle Multiproofs

• Eth 2.0 specs - Merkle Multiproofs

• What is complete binary tree?

• What is perfect binary tree?

Contributing

Pull requests are welcome!

For contributions please create a new branch and submit a pull request for review.

Many thanks to all the contributors that made this library better.

License

Released under the MIT license.

© Miguel Mota