Construct Merkle Trees and verify proofs in JavaScript.
Diagram of Merkle Tree
Diagram of Merkle Tree Proof
Diagram of Invalid Merkle Tree Proofs
Diagram of Bitcoin Merkle Tree
npm install merkletreejs
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
Class reprensenting a Merkle Tree
namespace: MerkleTree
MerkleTree
- createHashes
- getLayers
- getLayersAsObject
- getLeaves
- getProof
- getRoot
- toString
- toTreeString
- verify
- bufferify
β new MerkleTree(leaves: any
, hashAlgorithm: any
, options?: *Options
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 value | Description |
---|---|---|---|
leaves | any |
- | Array of hashed leaves. Each leaf must be a Buffer. |
hashAlgorithm | any |
- | Algorithm used for hashing leaves and nodes |
Default value options |
Options | {} as any | Additional options |
Returns: MerkleTree
β duplicateOdd: boolean
β hashAlgo: function
βΈ(value: any
): any
Parameters:
Name | Type |
---|---|
value | any |
Returns: any
β hashLeaves: boolean
β isBitcoinTree: boolean
β layers: any
[]
β leaves: any
[]
β sortLeaves: boolean
β sortPairs: boolean
βΈ createHashes(nodes: any
): void
Parameters:
Name | Type |
---|---|
nodes | any |
Returns: void
βΈ getLayers(): any
[]
getLayers
desc: Returns array of all layers of Merkle Tree, including leaves and root.
example:
const layers = tree.getLayers()
Returns: any
[]
βΈ getLayersAsObject(): any
Returns: any
βΈ getLeaves(): any
[]
getLeaves
desc: Returns array of leaves of Merkle Tree.
example:
const leaves = tree.getLeaves()
Returns: any
[]
βΈ getProof(leaf: any
, index?: any
): 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 | any |
Target leaf |
Optional 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.
βΈ getRoot(): any
getRoot
desc: Returns the Merkle root hash as a Buffer.
example:
const root = tree.getRoot()
Returns: any
βΈ print(): void
Returns: void
βΈ toString(): any
Returns: any
βΈ toTreeString(): any
Returns: any
βΈ verify(proof: any
, targetNode: any
, root: any
): 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 | any |
Target node Buffer |
root | any |
Merkle root Buffer |
Returns: boolean
βΈ bufferify(x: any
): any
Parameters:
Name | Type |
---|---|
x | any |
Returns: any
βΈ print(tree: any
): void
Parameters:
Name | Type |
---|---|
tree | any |
Returns: void
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.
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.