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README.md
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)) // 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
Methods
- bufferToHex
- bufferify
- getDepth
- getHexLayers
- getHexLayersFlat
- getHexLeaves
- getHexMultiProof
- getHexProof
- getHexRoot
- getLayers
- getLayersAsObject
- getLayersFlat
- getLeaves
- getMultiProof
- getProof
- getProofFlags
- getProofIndices
- getRoot
- toJSON
- toString
- verify
- verifyMultiProof
- bufferToHex
- static:bufferify
- static:getMultiProof
- static:isHexString
- static:marshalLeaves
- static:marshalProof
- static:print
- static:unmarshalLeaves
- static:unmarshalProof
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(): 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
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?
- 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
-
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?
Contributing
Pull requests are welcome!
For contributions please create a new branch and submit a pull request for review.