MerkleTree.js
Construct Merkle Trees and verify proofs in JavaScript.
Contents
Install
From NPM:
npm install merkletreejs
CDN
Available on jsDelivr CDN:
<script src="https://cdn.jsdelivr.net/npm/merkletreejs@latest/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))
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))
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
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) {
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
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:
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[]
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[]
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)
Parameters:
Name | Type | Description |
---|
treeIndices | number[] | Tree indices |
depth | number | Tree depth; number of layers. |
Returns: number[]
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
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
bufferify
▸ bufferify(value
: any): Buffer
bufferify
desc
Returns a buffer type for the given value.
example
const buf = MerkleTree.bufferify('0x1234')
Parameters:
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:
Returns: boolean
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
Interface: Options
Hierarchy
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
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