MerkleTree.js

Construct Merkle Trees and verify proofs in JavaScript.

Install
Example
Getting started
Diagrams
Documentation
Test
FAQ
Notes
Resources
Contributing
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:

MerkleTree.print(tree)

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

Class: MerkleTree

Class reprensenting a Merkle Tree

namespace MerkleTree

Hierarchy

MerkleTree

Index

Constructors

constructor

Methods

Constructors

constructor

+ new MerkleTree(leaves: any[], hashFn: 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.
`hashFn`	any	SHA256	Hash function to use for hashing leaves and nodes
`options`	Options	{}	Additional options

Returns: MerkleTree

Methods

bufferToHex

▸ 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

▸ 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

▸ getDepth(): number

getDepth

desc Returns the tree depth (number of layers)

example

const depth = tree.getDepth()

Returns: number

getHexLayers

▸ 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

▸ 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

▸ getHexLeaves(): string[]

getHexLeaves

desc Returns array of leaves of Merkle Tree as hex strings.

example

const leaves = tree.getHexLeaves()

Returns: string[]

getHexMultiProof

▸ 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[]

Multiproofs as hex strings.

getHexProof

▸ 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[]

Proof array as hex strings.

getPositionalHexProof

▸ 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)[][]

Proof array as hex strings with position.

getHexRoot

▸ getHexRoot(): string

getHexRoot

desc Returns the Merkle root hash as a hex string.

example

const root = tree.getHexRoot()

Returns: string

getLayers

▸ 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

▸ getLayersAsObject(): any

getLayersAsObject

desc Returns the layers as nested objects instead of an array.

example

const layersObj = tree.getLayersAsObject()

Returns: any

getLayersFlat

▸ 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

▸ 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

▸ 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[]

Multiproofs

getProof

▸ 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[]

Array of objects containing a position property of type string with values of 'left' or 'right' and a data property of type Buffer.

getProofFlags

▸ 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[]

Boolean flags

getProofIndices

▸ 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[]

Proof indices

getRoot

▸ getRoot(): Buffer

getRoot

desc Returns the Merkle root hash as a Buffer.

example

const root = tree.getRoot()

Returns: Buffer

print

▸ print(): void

desc Prints out a visual representation of the merkle tree.

example

tree.print()

Returns: void

toJSON

▸ toJSON(): void

Returns: void

toString

▸ toString(): string

toString

desc Returns a visual representation of the merkle tree as a string.

example

console.log(tree.toString())

Returns: string

verify

▸ 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

▸ 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[]

Multiproofs

`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

List of leaves as JSON 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

Proof array as JSON 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[]

Unmarshalled list of leaves

`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[]

Marshalled proof

Interface: Options

Hierarchy

Options

Index

Properties

`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 functions.

`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.

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.

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

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.

License

MIT

MerkleTree.js

Contents

Install

CDN

Example

Getting started

Diagrams

Documentation

Class: MerkleTree

Hierarchy

Index

Constructors

Methods

Constructors

constructor

Methods

bufferToHex

bufferify

getDepth

getHexLayers

getHexLayersFlat

getHexLeaves

getHexMultiProof

getHexProof

getPositionalHexProof

getHexRoot

getLayers

getLayersAsObject

getLayersFlat

getLeaves

getMultiProof

getProof

getProofFlags

getProofIndices

getRoot

print

toJSON

toString

verify

verifyMultiProof

Static bufferToHex

Static bufferify

Static getMultiProof

Static isHexString

Static marshalLeaves

Static marshalProof

Static print

Static unmarshalLeaves

Static unmarshalProof

Interface: Options

Hierarchy

Index

Properties

Properties

Optional duplicateOdd

Optional hashLeaves

Optional isBitcoinTree

Optional sort

Optional sortLeaves

Optional sortPairs

Test

FAQ

Notes

Resources

Contributing

License

About

Languages

`Static` bufferToHex

`Static` bufferify

`Static` getMultiProof

`Static` isHexString

`Static` marshalLeaves

`Static` marshalProof

`Static` print

`Static` unmarshalLeaves

`Static` unmarshalProof

`Optional` duplicateOdd

`Optional` hashLeaves

`Optional` isBitcoinTree

`Optional` sort

`Optional` sortLeaves

`Optional` sortPairs