mjso7660 / Merkle-Tree

Simple merkle tree implementation - Rajatree is a implementation of a merkle tree and Hash_node is each node resulted from hashing child nodes.

Merkle Tree

A simple implementation of merkle tree data structure.

Explanation

We have two classes: Hash_node and Rajatree. Rajatree is a implementation of a merkle tree and Hash_node is each node resulted from hashing child nodes. Each Hash_node has four attributes: (1) parent_hash, (2) data, (3) left_child and (4) right_child.

1. How a node’s parent node is accessed from a child node

A child node’s pointer to its parent node should be a hash pointer, meaning if anything changes in the parent node, its child nodes should not point to the parent node anymore. We achieve this by not having child nodes directly point to their parent node but to have them store the hash of the actual parent node and search (_search) for a node that has the parent_hash value.

2. How parent nodes are created

RajaTree’s _hash_transaction method and _process_level method hashes transactions and then creates parents method for every two hashed transactions.

3. Verification

_verify_list sends string data to peer/server and retrieve a list of hashes to hash with for verification of validity. Then verify_membership function and verify_nonmember uses _verify_list function to check membership of a node. Verify_nonmember basically implements verify_membership methods a couple of times to check nonmembership.

4. Traverse

Searches for the specific transactions from the transaction list and follows its parent_node until it reaches the root.

Tests

Creating a tree

    transactions = ['a','b','c','d','e','f','g']
    merkle_tree = RajaTree(transactions)
    merkle_tree.create_tree()

Testing traversal

    merkle_tree.traverse('a')
    print('-----')
    merkle_tree.traverse('b')
    print('-----')
    merkle_tree.transactions = ['a','b','c','d','e','f','0']
    merkle_tree.traverse('h')

Testing hash pointer

    transactions = ['a','b','c','d','e','f','g']
    merkle_tree.list_represent[-2].data = 'k'
    merkle_tree.traverse('g')
    print('-----')
    transactions = ['a','b','c','d','e','f','g']
    parent_of_g = merkle_tree.list_represent[-8]
    merkle_tree.list_represent[-8].data = 'something'
    merkle_tree.traverse('g')

Testing Membership and nonmembership of a string

    peer = merkle_tree
    merkle_tree.verify_membership('a' , peer)
    merkle_tree.verify_membership('0' , peer)
    merkle_tree.verify_nonmember('b', peer)
    merkle_tree.verify_nonmember('0', peer)

Prerequisites

hashlib for hashing with SHA256 function

pip install hashlib

Authors

• Min Joon So - mjso7660
• Shailesh Patro - ortap