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
ββ 311d2e46f49b15fff8b746b74ad57f2cc9e0d9939fda94387141a2d3fdf187ae
ββ 176f0f307632fdd5831875eb709e2f68d770b102262998b214ddeb3f04164ae1
β ββ 3ac225168df54212a25c1c01fd35bebfea408fdac2e31ddd6f80a4bbf9a5f1cb
β ββ b5553de315e0edf504d9150af82dafa5c4667fa618ed0a6f19c69b41166c5510
ββ 0b42b6393c1f53060fe3ddbfcd7aadcca894465a5a438f69c87d790b2299b9b2
ββ 0b42b6393c1f53060fe3ddbfcd7aadcca894465a5a438f69c87d790b2299b9b2
βΎ Visualization of Merkle Tree
βΎ Visualization of Merkle Tree Proof
βΎ Visualization of Invalid Merkle Tree Proofs
βΎ Visualization of Bitcoin Merkle Tree
Class reprensenting a Merkle Tree
namespace
MerkleTree
- MerkleTree
- 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
+ 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
βΈ 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
βΈ 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
βΈ getDepth(): number
getDepth
desc
Returns the tree depth (number of layers)
example
const depth = tree.getDepth()
Returns: number
βΈ 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[]
βΈ 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[]
βΈ getHexLeaves(): string[]
getHexLeaves
desc
Returns array of leaves of Merkle Tree as hex strings.
example
const leaves = tree.getHexLeaves()
Returns: string[]
βΈ 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.
βΈ 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.
βΈ getPositionalHexProof(leaf
: Buffer, index?
: number): (string | number)[][]
getPositionalHexProof
desc
Returns the proof for a target leaf as hex strings and corresponding position as binary.
example
const proof = tree.getPositionalHexProof(leaves[2])
Parameters:
Name | Type | Description |
---|---|---|
leaf |
Buffer | Target leaf |
index? |
number | - |
Returns: (string | number)[][]
- Proof array as hex strings with position.
βΈ getHexRoot(): string
getHexRoot
desc
Returns the Merkle root hash as a hex string.
example
const root = tree.getHexRoot()
Returns: string
βΈ 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[]
βΈ getLayersAsObject(): any
getLayersAsObject
desc
Returns the layers as nested objects instead of an array.
example
const layersObj = tree.getLayersAsObject()
Returns: any
βΈ 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[]
βΈ 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[]
βΈ 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
βΈ 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.
βΈ 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
βΈ 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
βΈ getRoot(): Buffer
getRoot
desc
Returns the Merkle root hash as a Buffer.
example
const root = tree.getRoot()
Returns: Buffer
βΈ print(): void
desc
Prints out a visual representation of the merkle tree.
example
tree.print()
Returns: void
βΈ toJSON(): void
Returns: void
βΈ toString(): string
toString
desc
Returns a visual representation of the merkle tree as a string.
example
console.log(tree.toString())
Returns: string
βΈ 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
βΈ 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
βΈ 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
βΈ 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
βΈ 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
βΈ 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
βΈ 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
βΈ 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.
βΈ 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
βΈ 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
βΈ 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
- Options
β’ duplicateOdd? : boolean
If set to true
, an odd node will be duplicated and combined to make a pair to generate the layer hash.
β’ hashLeaves? : boolean
If set to true
, the leaves will hashed using the set hashing algorithms.
β’ 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.
β’ sort? : boolean
If set to true
, the leaves and hashing pairs will be sorted.
β’ sortLeaves? : boolean
If set to true
, the leaves will be sorted.
β’ 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.
Many thanks to all the contributors that made this library better.