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Sparse Merkle tree

Sparse Merkle tree implementation in TypeScript.

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A sparse Merkle tree is a data structure useful for storing a key/value map where every leaf node of the tree contains the cryptographic hash of a key/value pair and every non leaf node contains the concatenated hashes of its child nodes. Sparse Merkle trees provides a secure and efficient verification of large data sets and they are often used in peer-to-peer technologies. This implementation is an optimized version of the traditional sparse Merkle tree and it is based on the concepts expressed in the papers and resources below.

Notice: this library is still not stable and therefore it must be used with care.


  1. Rasmus Dahlberg, Tobias Pulls and Roel Peeters. Efficient Sparse Merkle Trees: Caching Strategies and Secure (Non-)Membership Proofs. Cryptology ePrint Archive: Report 2016/683, 2016. https://eprint.iacr.org/2016/683.
  2. Faraz Haider. Compact sparse merkle trees. Cryptology ePrint Archive: Report 2018/955, 2018. https://eprint.iacr.org/2018/955.
  3. Jordi Baylina and Marta Bellés. Sparse Merkle Trees. https://docs.iden3.io/publications/pdfs/Merkle-Tree.pdf.
  4. Vitalik Buterin Fichter. Optimizing sparse Merkle trees. https://ethresear.ch/t/optimizing-sparse-merkle-trees/3751.


npm or yarn

You can install @zk-kit/sparse-merkle-tree package with npm:

npm i @zk-kit/sparse-merkle-tree --save

or yarn:

yarn add @zk-kit/sparse-merkle-tree


You can also load it using a script tag using unpkg:

<script src="https://unpkg.com/@zk-kit/sparse-merkle-tree/"></script>

or JSDelivr:

<script src="https://cdn.jsdelivr.net/npm/@zk-kit/sparse-merkle-tree/"></script>

📜 Usage

# new SparseMerkleTree(hash: HashFunction, bigNumbers?: boolean): SparseMerkleTree

import { SparseMerkleTree } from "@zk-kit/sparse-merkle-tree"
import { sha256 } from "js-sha256"
import { poseidon } from "circomlibjs"

// Hexadecimal hashes.
const hash = (childNodes: ChildNodes) => sha256(childNodes.join(""))
const tree = new SparseMerkleTree(hash)

// Big number hashes.
const hash2 = (childNodes: ChildNodes) => poseidon(childNodes)
const tree2 = new SparseMerkleTree(hash2, true)

console.log(tree.root) // 0
console.log(tree2.root) // 0n

# add(key: string | number, value: string | number): void

tree.add("2b", "44") // Hexadecimal key/value.
tree.add("16", "78")
tree.add("d", "e7")
tree.add("10", "141")
tree.add("20", "340")

console.log(tree.root) // 31ee2a59741c9c32a32d8c7fafe461cca1ccaf5986c2d592586e3e6482a48645

# get(key: string | number): undefined | string

const value = tree.get("16")

console.log(value) // 78

# update(key: string | number, value: string | number): void

tree.update("16", "79")

const value = tree.get("16")

console.log(value) // 79

# delete(key: string | number): void


const value = tree.get("16")

console.log(value) // undefined

# createProof(key: string | number): Proof

const membershipProof = tree.createProof("2b")
const nonMembershipProof = tree.createProof("16") // This key has been deleted.

    entry: [ '2b', '44', '1' ],
    matchingEntry: undefined,
    siblings: [
    root: 'c3c023c84afc0a7bab1dbebcef5f7beaf3d6af4af98e8f481620dec052be7d0d',
    membership: true

    entry: [ '16' ],
    matchingEntry: undefined,
    siblings: [
    root: 'c3c023c84afc0a7bab1dbebcef5f7beaf3d6af4af98e8f481620dec052be7d0d',
    membership: false

# verifyProof(proof: Proof): boolean

console.log(tree.verifyProof(membershipProof)) // true
console.log(tree.verifyProof(nonMembershipProof)) // true



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