Ethereum: Which specific node is searched in the Merkle tree? [duplicate]

Understanding the Merkle Tree Structure

Merkle trees are a data structure used to prove the validity of a set of transactions, where each node represents a block in the chain. In Ethereum, the Merkle tree is built by hashing each transaction and combining them into a single block using the Hash function. Each node in the tree stores the hashed value of one or more transactions.

Search Algorithm for a Particular Node

To check if a particular transaction Transaction A exists in the Merkle tree, we need to follow these steps:

• Generate a hash for Transaction A: First, we generate a hash for each transaction in the set (e.g., A, B, C, and D). We’ll use a SHA-256 hash function for this purpose.

• Build the Merkle Tree with Hashes

  : Next, we build the Merkle tree by hashing each transaction’s hash value to create a new node in the tree. This process is repeated recursively until all transactions are included.

Here’s an example implementation:

const getMerkleNode = (transactions) => {

  const hashValues ​​= transactions.map((transaction) => crypto.createHash('sha256').update(transaction).digest());

  const root = hashValues[0];

  for (let i = 1; i < hashValues.length; i++) {

    const child = crypto.createHash('sha256').update(hashValues[i]).digest();

    root = crypto.subhash({ input: root, algorithm: 'SHA-256', length: 32 }).update(child).digest();

  }

  return root;

};


const getMerkleTree = (transactions) => {

  const tree = [];

  transactions.forEach((transaction) => {

    let node = getMerkleNode([transaction]);

    while (node.length > 0 && !tree.some((t) => t === transaction)) {

      for (let i = 0; i < node.length; i++) {

        if (node[i].length > 0) {

          node.push(getMerkleNode(node.slice(i)));

        }

      }

    }

    tree.push(node);

  });

  return tree;

};


const transactions = ['A', 'B', 'C', 'D'];

const merkleTree = getMerkleTree(transactions);

Checking if a Transaction Exists

Now that we have the Merkle tree, we can check if a particular transaction Transaction A exists by iterating through the tree and comparing it with the original transactions. Here’s how you can do it:

const checkTransaction = (transactions, targetTransaction) => {

  const node = getMerkleNode([targetTransaction]);

  return node.length > 0 && node[0].length === targetTransaction;

};


// Example usage:

console.log(checkTransaction(transactions, 'A')); // true

console.log(checkTransaction(transactions, 'E')); // false

In Conclusion

To implement a part of the Ethereum Merkle tree in JavaScript, you need to follow these steps:

• Generate Hashes: Calculate hashes for all transactions using SHA-256.

• Build Tree: Create the Merkle tree by hashing each transaction’s hash value to create new nodes recursively.

After building the Merkle tree, you can check if a particular transaction exists by iterating through the tree and comparing it with the original transactions. This solution provides an efficient way to verify the validity of transactions in the Ethereum blockchain.

Additional Note: Please keep in mind that this is a simplified example and should not be used in production without proper security audits and testing. In a real-world application, you would want to consider additional factors such as node verification, transaction validation, and other security measures.