Construct Merkle Trees and verify proofs in JavaScript.
From NPM:
npm install merkletreejs
Available on jsDelivr CDN:
<script src="https://cdn.jsdelivr.net/npm/merkletreejs@latest/merkletree.js"></script>
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
▾ Visualization of Merkle Tree
▾ Visualization of Merkle Tree Proof
▾ Visualization of Invalid Merkle Tree Proofs
▾ Visualization of Bitcoin Merkle Tree
Class reprensenting a Merkle Tree
namespace
MerkleTree
- MerkleTree
- getDepth
- getHexLayers
- getHexLayersFlat
- getHexLeaves
- getHexMultiProof
- getHexProof
- getHexRoot
- getLayers
- getLayersAsObject
- getLayersFlat
- getLeaves
- getMultiProof
- getProof
- getProofFlags
- getProofIndices
- getRoot
- toString
- verify
- verifyMultiProof
- bufferify
- getMultiProof
- isHexString
+ 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
▸ getDepth(): number
getDepth
desc
Returns the tree depth (number of layers)
example
const depth = tree.getDepth()
Returns: number
▸ 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(): 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(): string[]
getHexLeaves
desc
Returns array of leaves of Merkle Tree as hex strings.
example
const leaves = tree.getHexLeaves()
Returns: string[]
▸ 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(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(): string
getHexRoot
desc
Returns the Merkle root hash as a hex string.
example
const root = tree.getHexRoot()
Returns: string
▸ 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(): any
getLayersAsObject
desc
Returns the layers as nested objects instead of an array.
example
const layersObj = tree.getLayersAsObject()
Returns: any
▸ 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(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(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(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(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(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(): 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
▸ toString(): string
toString
desc
Returns a visual representation of the merkle tree as a string.
example
console.log(tree.toString())
Returns: string
▸ 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(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
▸ 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
▸ 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
▸ 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
▸ 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
- Options
• duplicateOdd? : boolean
If set to true
, an odd node will be duplicated and combined to make a pair to generate the layer hash.
• hashLeaves? : boolean
If set to true
, the leaves will hashed using the set hashing algorithms.
• 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.
• sort? : boolean
If set to true
, the leaves and hashing pairs will be sorted.
• sortLeaves? : boolean
If set to true
, the leaves will be sorted.
• sortPairs? : boolean
If set to true
, the hashing pairs will be sorted.
npm test
-
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.
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.
-
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?
Pull requests are welcome!
For contributions please create a new branch and submit a pull request for review.