Sparse Merkle tree
Sparse Merkle tree implementation in TypeScript.
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.
## References
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.
---
## Install
### npm or yarn
You can install `@zk-kit/smt` package with npm:
```bash
npm i @zk-kit/smt --save
```
or yarn:
```bash
yarn add @zk-kit/smt
```
### CDN
You can also load it using a `script` tag using [unpkg](https://unpkg.com/):
```html
```
or [JSDelivr](https://www.jsdelivr.com/):
```html
```
## 📜 Usage
```typescript
import { ChildNodes, SMT } from "@zk-kit/smt"
import sha256 from "crypto-js/sha256"
import { poseidon2, poseidon3 } from "poseidon-lite"
// Hexadecimal hashes.
const hash = (childNodes: ChildNodes) => sha256(childNodes.join("")).toString()
// Create the SMT with an Hexadecimal (SHA256) hash.
const tree = new SMT(hash)
// 0
console.log(tree.root)
// Big number hashes.
const hash2 = (childNodes) => (childNodes.length === 2 ? poseidon2(childNodes) : poseidon3(childNodes))
// Create the SMT with a BigNumber (Poseidon) hash.
const tree2 = new SMT(hash2, true)
// 0n
console.log(tree2.root)
// Add nodes to the SMT.
tree.add("2b", "44")
tree.add("16", "78")
tree.add("d", "e7")
tree.add("10", "141")
tree.add("20", "340")
// 31ee2a59741c9c32a32d8c7fafe461cca1ccaf5986c2d592586e3e6482a48645
console.log(tree.root)
// Get the value of the leaf.
const value = tree.get("16")
// 78
console.log(value)
// Update the value of the leaf.
tree.update("16", "79")
// 79
console.log(tree.get("16"))
// Delete the leaf.
tree.delete("16")
// undefined
console.log(tree.get("16"))
// Compute the proof of membership for the leaf.
const membershipProof = tree.createProof("2b")
// Compute the proof of membership for a previously deleted leaf.
const nonMembershipProof = tree.createProof("16") // This key has been deleted.
/*
{
entry: [ '2b', '44', '1' ],
matchingEntry: undefined,
siblings: [
'006a0ab15a212e0e0126b81e056b11576628b1ad80792403dbb3a90be2e71d64',
'f786ce5a843614d7da216d95c0087c1eb29244927feeeeeb658aa60cf124cd5e'
],
root: 'c3c023c84afc0a7bab1dbebcef5f7beaf3d6af4af98e8f481620dec052be7d0d',
membership: true
}
*/
console.log(membershipProof)
/*
{
entry: [ '16' ],
matchingEntry: undefined,
siblings: [
'960f23d9fbb44241be53efb7c4d69ac129bb1cb9482dcb6789d3cc7e6de2de2b',
'2a1aef839e68d1bdf43c1b3b1ed9ef16c27162e8a175898c9ac64a679b0fc825'
],
root: 'c3c023c84afc0a7bab1dbebcef5f7beaf3d6af4af98e8f481620dec052be7d0d',
membership: false
}
*/
console.log(nonMembershipProof)
// Verify the proofs.
console.log(tree.verifyProof(membershipProof)) // true
console.log(tree.verifyProof(nonMembershipProof)) // true
```