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MerkleTree.js

Construct Merkle Trees and verify proofs in JavaScript.

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Contents

Install

From NPM:

npm install merkletreejs

CDN

Available on jsDelivr CDN:

<script src="https://cdn.jsdelivr.net/npm/[email protected]/merkletree.js"></script>

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

└─ 311d2e46f49b15fff8b746b74ad57f2cc9e0d9939fda94387141a2d3fdf187ae
   ├─ 176f0f307632fdd5831875eb709e2f68d770b102262998b214ddeb3f04164ae1
   │  ├─ 3ac225168df54212a25c1c01fd35bebfea408fdac2e31ddd6f80a4bbf9a5f1cb
   │  └─ b5553de315e0edf504d9150af82dafa5c4667fa618ed0a6f19c69b41166c5510
   └─ 0b42b6393c1f53060fe3ddbfcd7aadcca894465a5a438f69c87d790b2299b9b2
      └─ 0b42b6393c1f53060fe3ddbfcd7aadcca894465a5a438f69c87d790b2299b9b2

Diagrams

▾ Visualization of Merkle Tree

Merkle Tree

▾ Visualization of Merkle Tree Proof

Merkle Tree Proof

▾ Visualization of Invalid Merkle Tree Proofs

Merkle Tree Proof

▾ Visualization of Bitcoin Merkle Tree

Merkle Tree Proof

Documentation

Class: MerkleTree

Class reprensenting a Merkle Tree

namespace MerkleTree

Hierarchy

  • MerkleTree

Index

Constructors

Methods

Constructors

constructor

+ 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

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.

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

print

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

print

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

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 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.

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?

Notes

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.

Resources

Contributing

Pull requests are welcome!

For contributions please create a new branch and submit a pull request for review.

License

MIT


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