Merkle Tree Implementation

Overview

A production-ready Merkle Tree implementation in Java, designed for efficient data integrity verification. Merkle trees are fundamental to blockchain technology, enabling quick verification of large datasets.

What is a Merkle Tree?

A Merkle tree is a binary tree where:

• Leaf nodes contain hashes of data blocks
• Non-leaf nodes contain hashes of their children
• The root hash represents the entire dataset

Key Features

• Proof Generation: Create compact proofs for any element
• Proof Verification: Verify inclusion without full dataset
• Tree Construction: Efficient bottom-up building
• Multiple Hash Algorithms: Support for SHA-256, Keccak, etc.

Implementation

Node Structure

public class MerkleNode {
    private final byte[] hash;
    private final MerkleNode left;
    private final MerkleNode right;

    public static MerkleNode createLeaf(byte[] data) {
        return new MerkleNode(
            HashUtils.sha256(data),
            null,
            null
        );
    }

    public static MerkleNode createParent(MerkleNode left, MerkleNode right) {
        byte[] combined = ByteUtils.concat(left.hash, right.hash);
        return new MerkleNode(
            HashUtils.sha256(combined),
            left,
            right
        );
    }
}

Proof Generation

public List<ProofElement> generateProof(int index) {
    List<ProofElement> proof = new ArrayList<>();
    // Traverse from leaf to root, collecting sibling hashes
    // Each element includes the sibling hash and position (left/right)
    return proof;
}

Use Cases

1. Blockchain: Transaction verification in Bitcoin/Ethereum
2. Git: File integrity verification
3. Distributed Databases: Synchronization protocols
4. Certificate Transparency: Audit logs

Performance

• Construction: O(n) time complexity
• Proof Generation: O(log n)
• Verification: O(log n)
• Space: O(n) for tree, O(log n) for proofs

Applications in My Work

This implementation has been used in:

• Cryptocurrency exchange proof of reserves
• Distributed system state synchronization
• Data integrity verification systems