# MerkleTree.js > Construct [Merkle Trees](https://en.wikipedia.org/wiki/Merkle_tree) and verify proofs in JavaScript. [](https://raw.githubusercontent.com/miguelmota/merkletreejs/master/LICENSE) [](https://github.com/miguelmota/merkletreejs/tree/master/docs) [](https://travis-ci.org/miguelmota/merkletreejs) [](https://david-dm.org/miguelmota/merkletreejs) [](http://badge.fury.io/js/merkletreejs) [](#contributing) ## Contents - [Install](#install) - [Example](#example) - [Getting started](#Getting-started) - [Diagrams](#diagrams) - [Documentation](#documentation) - [Test](#test) - [FAQ](#faq) - [Notes](#notes) - [Resources](#resources) - [Contributing](#contributing) - [License](#license) ## Install From [NPM](https://www.npmjs.com/package/merkletreejs): ```bash npm install merkletreejs ``` ### CDN Available on [jsDelivr](https://www.jsdelivr.com/) CDN: ```html ``` ## Example [https://lab.miguelmota.com/merkletreejs](https://lab.miguelmota.com/merkletreejs) ## Getting started Construct tree, generate proof, and verify proof: ```js 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: ```js console.log(tree.toString()) ``` Output: ```bash └─ 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](docs/classes/_src_merkletree_.merkletree.md) (under [docs/](docs/)) ## Test ```bash npm test ``` ## FAQ - Q: How do you verify merkle proofs in Solidity? - A: Check out the example repo [merkletreejs-solidity](https://github.com/miguelmota/merkletreejs-solidity) on how to generate merkle proofs with this library and verify them in Solidity. - Q: How do you verify merkle [multiproofs](https://github.com/ethereum/eth2.0-specs/blob/dev/ssz/merkle-proofs.md#merkle-multiproofs) in Solidity? - A: Check out the example repo [merkletreejs-multiproof-solidity](https://github.com/miguelmota/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](https://github.com/miguelmota/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](https://github.com/miguelmota/merkletreejs-cli). - Q: Is there a way to visualize the merkle trees in the browser? - Yes, see [merkletree-viz](https://github.com/miguelmota/merkletree-viz). ## Notes As is, this implemenation is vulnerable to a [second pre-image attack](https://en.wikipedia.org/wiki/Merkle_tree#Second_preimage_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](https://bitcointalk.org/?topic=102395). ## Resources - [Bitcoin mining the hard way: the algorithms, protocols, and bytes](http://www.righto.com/2014/02/bitcoin-mining-hard-way-algorithms.html) - [Bitcoin Talk - Merkle Trees](https://bitcointalk.org/index.php?topic=403231.msg9054025#msg9054025) - [How Log Proofs Work](https://www.certificate-transparency.org/log-proofs-work) - [Raiden Merkle Tree Implemenation](https://github.com/raiden-network/raiden/blob/f9cf12571891cdf54feb4667cd2fffcb3d5daa89/raiden/mtree.py) - [Why aren't Solidity sha3 hashes not matching what other sha3 libraries produce?](https://ethereum.stackexchange.com/questions/559/why-arent-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?](https://crypto.stackexchange.com/questions/2106/what-is-the-purpose-of-using-different-hash-functions-for-the-leaves-and-interna) - [Why is the full Merkle path needed to verify a transaction?](https://bitcoin.stackexchange.com/questions/50674/why-is-the-full-merkle-path-needed-to-verify-a-transaction) - [Where is Double hashing performed in Bitcoin?](https://bitcoin.stackexchange.com/questions/8443/where-is-double-hashing-performed-in-bitcoin) - [Compact Merkle Multiproofs](https://arxiv.org/pdf/2002.07648.pdf) - [Eth 2.0 specs - Merkle Multiproofs](https://github.com/ethereum/eth2.0-specs/blob/dev/ssz/merkle-proofs.md#merkle-multiproofs) - [What is complete binary tree?](https://xlinux.nist.gov/dads/HTML/completeBinaryTree.html) - [What is perfect binary tree?](https://xlinux.nist.gov/dads/HTML/perfectBinaryTree.html) ## 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](https://github.com/miguelmota/merkletreejs/graphs/contributors) that made this library better._ ## License Released under the [MIT](./LICENSE) license. © [Miguel Mota](https://github.com/miguelmota)