merkletreejs
Advanced tools
The merkletreejs package is a JavaScript library for constructing and verifying Merkle Trees. Merkle Trees are a fundamental component in blockchain technology and cryptographic applications, providing a way to efficiently and securely verify the integrity of data. This package allows you to create Merkle Trees, generate proofs, and verify proofs.
Creating a Merkle Tree
This feature allows you to create a Merkle Tree from an array of data. The example uses the keccak256 hashing algorithm to hash the data and then constructs the tree. The root of the tree is then printed.
const { MerkleTree } = require('merkletreejs');
const keccak256 = require('keccak256');
const leaves = ['a', 'b', 'c'].map(x => keccak256(x));
const tree = new MerkleTree(leaves, keccak256, { sortPairs: true });
const root = tree.getRoot().toString('hex');
console.log(root);Generating a Proof
This feature allows you to generate a proof for a specific leaf in the Merkle Tree. The proof can be used to verify that the leaf is part of the tree.
const leaf = keccak256('a');
const proof = tree.getProof(leaf);
console.log(proof);Verifying a Proof
This feature allows you to verify a proof against the root of the Merkle Tree. It checks if the provided leaf and proof match the root, ensuring the integrity of the data.
const isValid = tree.verify(proof, leaf, root);
console.log(isValid);The merkletree package is another library for creating and verifying Merkle Trees. It offers similar functionalities to merkletreejs but may have different API conventions and additional features.
The merkle-tools package provides tools for creating and managing Merkle Trees. It includes functionalities for creating trees, generating proofs, and verifying proofs, similar to merkletreejs. It also offers additional utilities for working with Merkle Trees.
The merkle-lib package is a lightweight library for creating and verifying Merkle Trees. It focuses on simplicity and ease of use, providing core functionalities similar to merkletreejs.
Construct Merkle Trees and verify proofs in JavaScript.
From NPM:
npm install merkletreejs
Available on jsDelivr CDN:
<script src="https://cdn.jsdelivr.net/npm/merkletreejs@latest/merkletree.js"></script>
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:
MerkleTree.print(tree)
Output
└─ 311d2e46f49b15fff8b746b74ad57f2cc9e0d9939fda94387141a2d3fdf187ae
├─ 176f0f307632fdd5831875eb709e2f68d770b102262998b214ddeb3f04164ae1
│ ├─ 3ac225168df54212a25c1c01fd35bebfea408fdac2e31ddd6f80a4bbf9a5f1cb
│ └─ b5553de315e0edf504d9150af82dafa5c4667fa618ed0a6f19c69b41166c5510
└─ 0b42b6393c1f53060fe3ddbfcd7aadcca894465a5a438f69c87d790b2299b9b2
└─ 0b42b6393c1f53060fe3ddbfcd7aadcca894465a5a438f69c87d790b2299b9b2
▾ Visualization of Merkle Tree
▾ Visualization of Merkle Tree Proof
▾ Visualization of Invalid Merkle Tree Proofs
▾ Visualization of Bitcoin Merkle Tree
Class reprensenting a Merkle Tree
namespace MerkleTree
+ new MerkleTree(leaves: any[], hashAlgorithm: any, options: Options): MerkleTree
desc Constructs a Merkle Tree.
All nodes and leaves are stored as Buffers.
Lonely leaf nodes are promoted to the next level up without being hashed again.
example
const MerkleTree = require('merkletreejs')
const crypto = require('crypto')
function sha256(data) {
// returns Buffer
return crypto.createHash('sha256').update(data).digest()
}
const leaves = ['a', 'b', 'c'].map(x => keccak(x))
const tree = new MerkleTree(leaves, sha256)
Parameters:
| Name | Type | Default | Description |
|---|---|---|---|
leaves | any[] | - | Array of hashed leaves. Each leaf must be a Buffer. |
hashAlgorithm | any | SHA256 | Algorithm used for hashing leaves and nodes |
options | Options | {} | Additional options |
Returns: MerkleTree
▸ bufferToHex(value: Buffer): string
bufferToHex
desc Returns a hex string with 0x prefix for given buffer.
example
const hexStr = tree.bufferToHex(Buffer.from('A'))
Parameters:
| Name | Type |
|---|---|
value | Buffer |
Returns: string
▸ bufferify(value: any): Buffer
bufferify
desc Returns a buffer type for the given value.
example
const buf = tree.bufferify('0x1234')
Parameters:
| Name | Type |
|---|---|
value | any |
Returns: Buffer
▸ getDepth(): number
getDepth
desc Returns the tree depth (number of layers)
example
const depth = tree.getDepth()
Returns: number
▸ getHexLayers(): string[]
getHexLayers
desc Returns multi-dimensional array of all layers of Merkle Tree, including leaves and root as hex strings.
example
const layers = tree.getHexLayers()
Returns: string[]
▸ getHexLayersFlat(): string[]
getHexLayersFlat
desc Returns single flat array of all layers of Merkle Tree, including leaves and root as hex string.
example
const layers = tree.getHexLayersFlat()
Returns: string[]
▸ getHexLeaves(): string[]
getHexLeaves
desc Returns array of leaves of Merkle Tree as hex strings.
example
const leaves = tree.getHexLeaves()
Returns: string[]
▸ getHexMultiProof(tree: Buffer[], indices: number[]): string[]
getHexMultiProof
desc Returns the multiproof for given tree indices as hex strings.
example
const indices = [2, 5, 6]
const proof = tree.getHexMultiProof(indices)
Parameters:
| Name | Type | Description |
|---|---|---|
tree | Buffer[] | - |
indices | number[] | Tree indices. |
Returns: string[]
▸ getHexProof(leaf: Buffer, index?: number): string[]
getHexProof
desc Returns the proof for a target leaf as hex strings.
example
const proof = tree.getHexProof(leaves[2])
Parameters:
| Name | Type | Description |
|---|---|---|
leaf | Buffer | Target leaf |
index? | number | - |
Returns: string[]
▸ getPositionalHexProof(leaf: Buffer, index?: number): (string | number)[][]
getPositionalHexProof
desc Returns the proof for a target leaf as hex strings and corresponding position as binary.
example
const proof = tree.getPositionalHexProof(leaves[2])
Parameters:
| Name | Type | Description |
|---|---|---|
leaf | Buffer | Target leaf |
index? | number | - |
Returns: (string | number)[][]
▸ getHexRoot(): string
getHexRoot
desc Returns the Merkle root hash as a hex string.
example
const root = tree.getHexRoot()
Returns: string
▸ getLayers(): Buffer[]
getLayers
desc Returns multi-dimensional array of all layers of Merkle Tree, including leaves and root.
example
const layers = tree.getLayers()
Returns: Buffer[]
▸ getLayersAsObject(): any
getLayersAsObject
desc Returns the layers as nested objects instead of an array.
example
const layersObj = tree.getLayersAsObject()
Returns: any
▸ getLayersFlat(): Buffer[]
getLayersFlat
desc Returns single flat array of all layers of Merkle Tree, including leaves and root.
example
const layers = tree.getLayersFlat()
Returns: Buffer[]
▸ getLeaves(values?: any[]): Buffer[]
getLeaves
desc Returns array of leaves of Merkle Tree.
example
const leaves = tree.getLeaves()
Parameters:
| Name | Type |
|---|---|
values? | any[] |
Returns: Buffer[]
▸ getMultiProof(tree?: any[], indices?: any[]): Buffer[]
getMultiProof
desc Returns the multiproof for given tree indices.
example
const indices = [2, 5, 6]
const proof = tree.getMultiProof(indices)
Parameters:
| Name | Type | Description |
|---|---|---|
tree? | any[] | - |
indices? | any[] | Tree indices. |
Returns: Buffer[]
▸ getProof(leaf: Buffer, index?: number): any[]
getProof
desc Returns the proof for a target leaf.
example
const proof = tree.getProof(leaves[2])
example
const leaves = ['a', 'b', 'a'].map(x => keccak(x))
const tree = new MerkleTree(leaves, keccak)
const proof = tree.getProof(leaves[2], 2)
Parameters:
| Name | Type | Description |
|---|---|---|
leaf | Buffer | Target leaf |
index? | number | - |
Returns: any[]
▸ getProofFlags(leaves: Buffer[], proofs: Buffer[]): boolean[]
getProofFlags
desc Returns list of booleans where proofs should be used instead of hashing.
Proof flags are used in the Solidity multiproof verifiers.
example
const indices = [2, 5, 6]
const proof = tree.getMultiProof(indices)
const proofFlags = tree.getProofFlags(leaves, proof)
Parameters:
| Name | Type |
|---|---|
leaves | Buffer[] |
proofs | Buffer[] |
Returns: boolean[]
▸ getProofIndices(treeIndices: number[], depth: number): number[]
getProofIndices
desc Returns the proof indices for given tree indices.
example
const proofIndices = tree.getProofIndices([2,5,6], 4)
console.log(proofIndices) // [ 23, 20, 19, 8, 3 ]
Parameters:
| Name | Type | Description |
|---|---|---|
treeIndices | number[] | Tree indices |
depth | number | Tree depth; number of layers. |
Returns: number[]
▸ getRoot(): Buffer
getRoot
desc Returns the Merkle root hash as a Buffer.
example
const root = tree.getRoot()
Returns: Buffer
▸ print(): void
desc Prints out a visual representation of the merkle tree.
example
tree.print()
Returns: void
▸ toJSON(): void
Returns: void
▸ toString(): string
toString
desc Returns a visual representation of the merkle tree as a string.
example
console.log(tree.toString())
Returns: string
▸ verify(proof: any[], targetNode: Buffer, root: Buffer): boolean
verify
desc Returns true if the proof path (array of hashes) can connect the target node
to the Merkle root.
example
const root = tree.getRoot()
const proof = tree.getProof(leaves[2])
const verified = tree.verify(proof, leaves[2], root)
Parameters:
| Name | Type | Description |
|---|---|---|
proof | any[] | Array of proof objects that should connect target node to Merkle root. |
targetNode | Buffer | Target node Buffer |
root | Buffer | Merkle root Buffer |
Returns: boolean
▸ verifyMultiProof(root: Buffer, indices: number[], leaves: Buffer[], depth: number, proof: Buffer[]): boolean
verifyMultiProof
desc Returns true if the multiproofs can connect the leaves to the Merkle root.
example
const root = tree.getRoot()
const treeFlat = tree.getLayersFlat()
const depth = tree.getDepth()
const indices = [2, 5, 6]
const proofLeaves = indices.map(i => leaves[i])
const proof = tree.getMultiProof(treeFlat, indices)
const verified = tree.verifyMultiProof(root, indices, proofLeaves, depth, proof)
Parameters:
| Name | Type | Description |
|---|---|---|
root | Buffer | Merkle tree root |
indices | number[] | Leave indices |
leaves | Buffer[] | Leaf values at indices. |
depth | number | Tree depth |
proof | Buffer[] | Multiproofs given indices |
Returns: boolean
Static bufferToHex▸ bufferToHex(value: Buffer): string
bufferToHex
desc Returns a hex string with 0x prefix for given buffer.
example
const hexStr = MerkleTree.bufferToHex(Buffer.from('A'))
Parameters:
| Name | Type |
|---|---|
value | Buffer |
Returns: string
Static bufferify▸ bufferify(value: any): Buffer
bufferify
desc Returns a buffer type for the given value.
example
const buf = MerkleTree.bufferify('0x1234')
Parameters:
| Name | Type |
|---|---|
value | any |
Returns: Buffer
Static getMultiProof▸ getMultiProof(tree: Buffer[], indices: number[]): Buffer[]
getMultiProof
desc Returns the multiproof for given tree indices.
example
const flatTree = tree.getLayersFlat()
const indices = [2, 5, 6]
const proof = MerkleTree.getMultiProof(flatTree, indices)
Parameters:
| Name | Type | Description |
|---|---|---|
tree | Buffer[] | Tree as a flat array. |
indices | number[] | Tree indices. |
Returns: Buffer[]
Static isHexString▸ isHexString(v: string): boolean
isHexString
desc Returns true if value is a hex string.
example
console.log(MerkleTree.isHexString('0x1234'))
Parameters:
| Name | Type |
|---|---|
v | string |
Returns: boolean
Static marshalLeaves▸ marshalLeaves(leaves: any[]): string
marshalLeaves
desc Returns array of leaves of Merkle Tree as a JSON string.
example
const jsonStr = MerkleTree.marshalLeaves(leaves)
Parameters:
| Name | Type |
|---|---|
leaves | any[] |
Returns: string
Static marshalProof▸ marshalProof(proof: any[]): string
marshalProof
desc Returns proof array as JSON string.
example
const jsonStr = MerkleTree.marshalProof(proof)
Parameters:
| Name | Type | Description |
|---|---|---|
proof | any[] | Merkle tree proof array |
Returns: string
Static print▸ print(tree: any): void
desc Prints out a visual representation of the given merkle tree.
example
MerkleTree.print(tree)
Parameters:
| Name | Type | Description |
|---|---|---|
tree | any | Merkle tree instance. |
Returns: void
Static unmarshalLeaves▸ unmarshalLeaves(jsonStr: string | object): Buffer[]
unmarshalLeaves
desc Returns array of leaves of Merkle Tree as a Buffers.
example
const leaves = MerkleTree.unmarshalLeaves(jsonStr)
Parameters:
| Name | Type |
|---|---|
jsonStr | string | object |
Returns: Buffer[]
Static unmarshalProof▸ unmarshalProof(jsonStr: string | object): any[]
unmarshalProof
desc Returns the proof for a target leaf as a list of Buffers.
example
const proof = MerkleTree.unmarshalProof(jsonStr)
Parameters:
| Name | Type |
|---|---|
jsonStr | string | object |
Returns: any[]
Optional duplicateOdd• duplicateOdd? : boolean
If set to true, an odd node will be duplicated and combined to make a pair to generate the layer hash.
Optional hashLeaves• hashLeaves? : boolean
If set to true, the leaves will hashed using the set hashing algorithms.
Optional isBitcoinTree• isBitcoinTree? : boolean
If set to true, constructs the Merkle Tree using the Bitcoin Merkle Tree implementation. Enable it when you need to replicate Bitcoin constructed Merkle Trees. In Bitcoin Merkle Trees, single nodes are combined with themselves, and each output hash is hashed again.
Optional sort• sort? : boolean
If set to true, the leaves and hashing pairs will be sorted.
Optional sortLeaves• sortLeaves? : boolean
If set to true, the leaves will be sorted.
Optional sortPairs• sortPairs? : boolean
If set to true, the hashing pairs will be sorted.
npm test
Q: How do you verify merkle proofs in Solidity?
Q: How do you verify merkle multiproofs in Solidity?
As is, this implemenation is vulnerable to a second pre-image attack. Use a difference hashing algorithm 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.
Bitcoin mining the hard way: the algorithms, protocols, and bytes
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?
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.
FAQs
Construct Merkle Trees and verify proofs
The npm package merkletreejs receives a total of 54,090 weekly downloads. As such, merkletreejs popularity was classified as popular.
We found that merkletreejs demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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