MerkleTree.js

Construct Merkle Trees and verify proofs in JavaScript.

Contents

• Install
• Getting started
• Diagrams
• Documentation
• Test
• FAQ
• Notes
• Resources
• Contributing
• License

Install

npm install 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

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

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

• getDepth
• getHexLayers
• getHexLayersFlat
• getHexLeaves
• getHexMultiProof
• getHexProof
• getHexRoot
• getLayers
• getLayersAsObject
• getLayersFlat
• getLeaves
• getMultiProof
• getProof
• getProofFlags
• getProofIndices
• getRoot
• print
• toString
• verify
• verifyMultiProof
• bufferify
• getMultiProof
• isHexString
• print

Constructors

constructor

+ new MerkleTree(leaves: any, hashAlgorithm: any, options: Options): MerkleTree

Defined in index.ts:39

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

getDepth

▸ getDepth(): number

Defined in index.ts:665

getDepth

desc Returns the tree depth (number of layers)

example

const depth = tree.getDepth()

Returns: number

---

getHexLayers

▸ getHexLayers(): any

Defined in index.ts:211

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: any

---

getHexLayersFlat

▸ getHexLayersFlat(): any

Defined in index.ts:257

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: any

---

getHexLeaves

▸ getHexLeaves(): string[]

Defined in index.ts:185

getHexLeaves

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

example

const leaves = tree.getHexLeaves()

Returns: string[]

---

getHexMultiProof

▸ getHexMultiProof(tree: any, indices: any): string[]

Defined in index.ts:496

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	any	-
indices	any	Tree indices.

Returns: string[]

• Multiproofs as hex strings.

---

getHexProof

▸ getHexProof(leaf: any, index?: any): string[]

Defined in index.ts:379

getHexProof

desc Returns the proof for a target leaf as hex strings.

example

const proof = tree.getHexProof(leaves[2])

Parameters:

Name	Type	Description
leaf	any	Target leaf
index?	any	-

Returns: string[]

• Proof array as hex strings.

---

getHexRoot

▸ getHexRoot(): string

Defined in index.ts:283

getHexRoot

desc Returns the Merkle root hash as a hex string.

example

const root = tree.getHexRoot()

Returns: string

---

getLayers

▸ getLayers(): any[]

Defined in index.ts:198

getLayers

desc Returns multi-dimensional array of all layers of Merkle Tree, including leaves and root.

example

const layers = tree.getLayers()

Returns: any[]

---

getLayersAsObject

▸ getLayersAsObject(): any

Defined in index.ts:677

getLayersAsObject

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

example

const layersObj = tree.getLayersAsObject()

Returns: any

---

getLayersFlat

▸ getLayersFlat(): any

Defined in index.ts:232

getLayersFlat

desc Returns single flat array of all layers of Merkle Tree, including leaves and root.

example

const layers = tree.getLayersFlat()

Returns: any

---

getLeaves

▸ getLeaves(data?: any[]): any[]

Defined in index.ts:161

getLeaves

desc Returns array of leaves of Merkle Tree.

example

const leaves = tree.getLeaves()

Parameters:

Name	Type
data?	any[]

Returns: any[]

---

getMultiProof

▸ getMultiProof(tree: any, indices: any): any[]

Defined in index.ts:440

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: any[]

• Multiproofs

---

getProof

▸ getProof(leaf: any, index?: any): any[]

Defined in index.ts:307

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	any	Target leaf
index?	any	-

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(els: any, proofs: any): any[]

Defined in index.ts:513

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
els	any
proofs	any

Returns: any[]

• Boolean flags

---

getProofIndices

▸ getProofIndices(treeIndices: any, depth: any): any[]

Defined in index.ts:395

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	any	Tree indices
depth	any	Tree depth; number of layers.

Returns: any[]

• Proof indices

---

getRoot

▸ getRoot(): any

Defined in index.ts:270

getRoot

desc Returns the Merkle root hash as a Buffer.

example

const root = tree.getRoot()

Returns: any

---

print

▸ print(): void

Defined in index.ts:713

print

desc Prints out a visual representation of the merkle tree.

example

tree.print()

Returns: void

---

toString

▸ toString(): any

Defined in index.ts:739

toString

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

example

console.log(tree.toString())

Returns: any

---

verify

▸ verify(proof: any, targetNode: any, root: any): boolean

Defined in index.ts:556

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	any	Target node Buffer
root	any	Merkle root Buffer

Returns: boolean

---

verifyMultiProof

▸ verifyMultiProof(root: any, indices: any, leaves: any, depth: any, proof: any): any

Defined in index.ts:630

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	any	Merkle tree root
indices	any	Leave indices
leaves	any	Leaf values at indices.
depth	any	Tree depth
proof	any	Multiproofs given indices

Returns: any

---

Static bufferify

▸ bufferify(x: any): any

Defined in index.ts:817

bufferify

desc Returns a buffer type for the given value.

example

const buf = MerkleTree.bufferify('0x1234')

Parameters:

Name	Type
x	any

Returns: any

---

Static getMultiProof

▸ getMultiProof(tree: any, indices: any): any[]

Defined in index.ts:757

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	any	Tree as a flat array.
indices	any	Tree indices.

Returns: any[]

• Multiproofs

---

Static isHexString

▸ isHexString(v: any): boolean

Defined in index.ts:843

isHexString

desc Returns true if value is a hex string.

example

console.log(MerkleTree.isHexString('0x1234'))

Parameters:

Name	Type
v	any

Returns: boolean

---

Static print

▸ print(tree: any): void

Defined in index.ts:857

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

Interface: Options

Hierarchy

• Options

Index

Properties

• duplicateOdd
• hashLeaves
• isBitcoinTree
• sort
• sortLeaves
• sortPairs

Properties

Optional duplicateOdd

• duplicateOdd? : boolean

Defined in index.ts:8

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

Defined in index.ts:10

If set to true, the leaves will hashed using the set hashing algorithms.

---

Optional isBitcoinTree

• isBitcoinTree? : boolean

Defined in index.ts:12

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

Defined in index.ts:18

If set to true, the leaves and hashing pairs will be sorted.

---

Optional sortLeaves

• sortLeaves? : boolean

Defined in index.ts:14

If set to true, the leaves will be sorted.

---

Optional sortPairs

• sortPairs? : boolean

Defined in index.ts:16

If set to true, the hashing pairs will be sorted.

Module: "index"

Index

Classes

• MerkleTree

Interfaces

• Options

Type aliases

• THashAlgo
• TLayer
• TLeaf
• TValue

Type aliases

THashAlgo

Ƭ THashAlgo: any

Defined in index.ts:21

---

TLayer

Ƭ TLayer: any

Defined in index.ts:24

---

TLeaf

Ƭ TLeaf: any

Defined in index.ts:23

---

TValue

Ƭ TValue: any

Defined in index.ts:22

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 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

• Bitcoin mining the hard way: the algorithms, protocols, and bytes

• Bitcoin Talk - Merkle Trees

• How Log Proofs Work

• Raiden Merkle Tree Implemenation

• 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?

• Why is the full Merkle path needed to verify a transaction?

• Where is Double hashing performed in Bitcoin?

• Compact Merkle Multiproofs

• Eth 2.0 specs - Merkle Multiproofs

Contributing

Pull requests are welcome!

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

License

MIT