MerkleTree Class Documentation

A comprehensive implementation of a Merkle Tree data structure for creating tamper-proof data structures and generating cryptographic proofs. This is the core class of the merkletreejs library.

Features

• Standard Merkle Tree: Classic binary tree implementation
• Multiple Hash Functions: Support for SHA256, keccak256, and custom hash functions
• Proof Generation: Generate and verify inclusion proofs
• Multi-Proofs: Generate and verify proofs for multiple leaves simultaneously
• Bitcoin Compatibility: Support for Bitcoin-style Merkle trees
• Serialization: Marshal/unmarshal trees and proofs to/from JSON
• Flexible Options: Configurable sorting, duplicate handling, and tree completion
• Type Safety: Full TypeScript support with proper type definitions

Installation

npm install merkletreejs

Quick Start

import { MerkleTree } from 'merkletreejs'
import SHA256 from 'crypto-js/sha256'

// Create leaves (typically hashed data)
const leaves = ['a', 'b', 'c', 'd'].map(x => SHA256(x))

// Create tree
const tree = new MerkleTree(leaves, SHA256)

// Get root
const root = tree.getRoot()
const hexRoot = tree.getHexRoot()

// Generate proof
const leaf = SHA256('b')
const proof = tree.getProof(leaf)

// Verify proof
const verified = tree.verify(proof, leaf, root)
console.log('Proof verified:', verified) // true

Constructor

new MerkleTree(leaves, hashFunction?, options?)

Creates a new Merkle tree instance.

Parameters: - leaves (Buffer[]): Array of leaf nodes (should be pre-hashed) - hashFunction (Function): Hash function to use (defaults to SHA256) - options (Options): Configuration options

Example:

const tree = new MerkleTree(leaves, SHA256, {
  sortPairs: true,
  duplicateOdd: false
})

Options

interface Options {
  duplicateOdd?: boolean        // Duplicate odd nodes (default: false)
  hashLeaves?: boolean          // Hash leaves before adding (default: false)
  isBitcoinTree?: boolean       // Use Bitcoin-style tree (default: false)
  sortLeaves?: boolean          // Sort leaves (default: false)
  sortPairs?: boolean           // Sort pairs (default: false)
  sort?: boolean                // Sort leaves and pairs (default: false)
  fillDefaultHash?: Function    // Fill function for odd layers
  complete?: boolean            // Create complete tree (default: false)
  concatenator?: Function       // Custom concatenation function
}

Core Methods

Tree Information

getRoot()

Returns the Merkle root as a Buffer.

const root = tree.getRoot()

getHexRoot()

Returns the Merkle root as a hex string with '0x' prefix.

const hexRoot = tree.getHexRoot()

getLeaves(values?)

Returns array of leaves. Optionally filter by specific values.

const allLeaves = tree.getLeaves()
const filteredLeaves = tree.getLeaves([specificHash1, specificHash2])

getHexLeaves()

Returns array of leaves as hex strings.

const hexLeaves = tree.getHexLeaves()

getLeafCount()

Returns the total number of leaves.

const count = tree.getLeafCount()

getDepth()

Returns the tree depth (number of layers).

const depth = tree.getDepth()

Leaf Operations

getLeaf(index)

Gets a leaf by index.

const leaf = tree.getLeaf(0)

getHexLeaf(index)

Gets a leaf by index as hex string.

const hexLeaf = tree.getHexLeaf(0)

getLeafIndex(leaf)

Gets the index of a leaf (-1 if not found).

const index = tree.getLeafIndex(leafHash)

addLeaf(leaf, shouldHash?)

Adds a single leaf to the tree.

tree.addLeaf(newLeafHash)
tree.addLeaf('raw data', true) // Hash before adding

addLeaves(leaves, shouldHash?)

Adds multiple leaves to the tree.

tree.addLeaves([hash1, hash2, hash3])
tree.addLeaves(['data1', 'data2'], true) // Hash before adding

removeLeaf(index)

Removes a leaf by index.

const removedLeaf = tree.removeLeaf(2)

updateLeaf(index, value, shouldHash?)

Updates a leaf at specific index.

tree.updateLeaf(1, newHash)
tree.updateLeaf(1, 'new data', true) // Hash before updating

Proof Operations

getProof(leaf, index?)

Generates a proof for a leaf.

const proof = tree.getProof(leafHash)
// For duplicate leaves, specify index
const proof = tree.getProof(leafHash, 2)

getHexProof(leaf, index?)

Generates a proof as hex strings.

const hexProof = tree.getHexProof(leafHash)

getPositionalHexProof(leaf, index?)

Generates a proof with positional information.

const positionalProof = tree.getPositionalHexProof(leafHash)
// Returns: [[position, hash], [position, hash], ...]

verify(proof, targetNode, root)

Verifies a proof against a root.

const isValid = tree.verify(proof, leafHash, root)

getProofs()

Gets proofs for all leaves.

const allProofs = tree.getProofs()

getHexProofs()

Gets proofs for all leaves as hex strings.

const allHexProofs = tree.getHexProofs()

Multi-Proof Operations

getMultiProof(indices)

Generates a multi-proof for multiple leaves.

const multiProof = tree.getMultiProof([0, 2, 4])

getHexMultiProof(tree, indices)

Generates a multi-proof as hex strings.

const hexMultiProof = tree.getHexMultiProof(flatTree, [0, 2, 4])

verifyMultiProof(root, proofIndices, proofLeaves, leavesCount, proof)

Verifies a multi-proof.

const isValid = tree.verifyMultiProof(
  root, 
  [0, 2, 4], 
  [leaf0, leaf2, leaf4], 
  totalLeaves, 
  multiProof
)

getProofFlags(leaves, proofs)

Gets boolean flags for multi-proof verification.

const flags = tree.getProofFlags([leaf0, leaf2], multiProof)

Layer Operations

getLayers()

Gets all tree layers as 2D array of Buffers.

const layers = tree.getLayers()

getHexLayers()

Gets all tree layers as 2D array of hex strings.

const hexLayers = tree.getHexLayers()

getLayersFlat()

Gets all tree layers as flat array.

const flatLayers = tree.getLayersFlat()

getHexLayersFlat()

Gets all tree layers as flat array of hex strings.

const hexFlatLayers = tree.getHexLayersFlat()

Serialization

static marshalLeaves(leaves)

Converts leaves to JSON string.

const jsonLeaves = MerkleTree.marshalLeaves(leaves)

static unmarshalLeaves(jsonStr)

Converts JSON string back to leaves.

const leaves = MerkleTree.unmarshalLeaves(jsonLeaves)

static marshalProof(proof)

Converts proof to JSON string.

const jsonProof = MerkleTree.marshalProof(proof)

static unmarshalProof(jsonStr)

Converts JSON string back to proof.

const proof = MerkleTree.unmarshalProof(jsonProof)

static marshalTree(tree)

Converts entire tree to JSON string.

const jsonTree = MerkleTree.marshalTree(tree)

static unmarshalTree(jsonStr, hashFn?, options?)

Recreates tree from JSON string.

const tree = MerkleTree.unmarshalTree(jsonTree, SHA256)

Utility Methods

resetTree()

Clears all leaves and layers.

tree.resetTree()

toString()

Returns visual representation of the tree.

console.log(tree.toString())

getOptions()

Returns current tree options.

const options = tree.getOptions()

Static Methods

MerkleTree.verify(proof, targetNode, root, hashFn?, options?)

Static method to verify a proof without tree instance.

const isValid = MerkleTree.verify(proof, leaf, root, SHA256)

MerkleTree.getMultiProof(tree, indices)

Static method to generate multi-proof from flat tree.

const multiProof = MerkleTree.getMultiProof(flatTree, [0, 2, 4])

Examples

Basic Usage

import { MerkleTree } from 'merkletreejs'
import SHA256 from 'crypto-js/sha256'

// Prepare data
const leaves = ['alice', 'bob', 'charlie', 'dave'].map(x => SHA256(x))

// Create tree
const tree = new MerkleTree(leaves, SHA256)

// Get root
const root = tree.getHexRoot()
console.log('Root:', root)

// Generate and verify proof
const leaf = SHA256('bob')
const proof = tree.getProof(leaf)
const verified = tree.verify(proof, leaf, tree.getRoot())
console.log('Proof verified:', verified)

Bitcoin-Style Tree

const tree = new MerkleTree(leaves, SHA256, {
  isBitcoinTree: true
})

Sorted Tree (Recommended for Multi-Proofs)

const tree = new MerkleTree(leaves, SHA256, {
  sortPairs: true,
  sortLeaves: true
})

Complete Tree

const tree = new MerkleTree(leaves, SHA256, {
  complete: true // Creates a complete binary tree
})

Working with Raw Data

// Hash leaves automatically
const tree = new MerkleTree(['a', 'b', 'c'], SHA256, {
  hashLeaves: true
})

// Or hash manually
const leaves = ['a', 'b', 'c'].map(x => SHA256(x))
const tree = new MerkleTree(leaves, SHA256)

Multi-Proof Example

const tree = new MerkleTree(leaves, SHA256, { complete: true })
const indices = [0, 2, 4]
const multiProof = tree.getMultiProof(indices)
const proofLeaves = indices.map(i => leaves[i])

const verified = tree.verifyMultiProof(
  tree.getRoot(),
  indices,
  proofLeaves,
  leaves.length,
  multiProof
)

Serialization Example

// Serialize tree
const jsonTree = MerkleTree.marshalTree(tree)
localStorage.setItem('merkleTree', jsonTree)

// Deserialize tree
const savedTree = localStorage.getItem('merkleTree')
const restoredTree = MerkleTree.unmarshalTree(savedTree, SHA256)

Advanced Features

Custom Hash Functions

const customHash = (data) => {
  return crypto.createHash('sha1').update(data).digest()
}

const tree = new MerkleTree(leaves, customHash)

Custom Concatenator

const tree = new MerkleTree(leaves, SHA256, {
  concatenator: (buffers) => {
    // Custom way to combine buffers
    return Buffer.concat(buffers.reverse())
  }
})

Fill Default Hash

const tree = new MerkleTree(leaves, SHA256, {
  fillDefaultHash: (index, hashFn) => {
    return hashFn(`default-${index}`)
  }
})

Performance Considerations

• Use complete: true for better multi-proof performance
• Sort pairs and leaves for consistent tree structure
• Consider tree depth for large datasets
• Use static methods when you don't need tree instance

Security Notes

• Always hash your input data before creating leaves
• Use cryptographically secure hash functions
• Validate proofs on both client and server side
• Be aware of second preimage attacks with certain configurations

Browser Support

The MerkleTree class works in both Node.js and browser environments. For browser usage, ensure you have appropriate polyfills for Buffer operations.

TypeScript Support

Full TypeScript support with comprehensive type definitions for all methods and options.