MerkleTree.js

Construct Merkle Trees and verify proofs in JavaScript.

Contents

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

Install

From NPM:

npm install merkletreejs

CDN

Available on jsDelivr CDN:

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

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 = tree.getProof(badLeaf)
console.log(tree.verify(badProof, leaf, 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: Is there a CLI version of this library?

  • Yes, see merkletreejs-cli.

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.

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

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.

Tip Jar

3KdMW53vUMLPEC33xhHAUx4EFtvmXQF8Kf

0x9ed3D6793a6b74d8c9A998f5C4b50a25947D53aF

Thank you for tips! 🙏

License

Released under the MIT license.

© Miguel Mota