Understanding Ethereum Transaction IDs

As a developer building a non-mainstream Ethereum client, you’re likely familiar with the concept of transaction IDs (TxIDs) on the Ethereum blockchain. In this article, we’ll delve into how these unique identifiers are generated and what happens to them after each block.

Transaction ID Generation

A transaction ID is an 18-byte hexadecimal string that represents a single Bitcoin transaction. The generation process involves several steps:

• Block Creation: A new block is created on the Ethereum network when a valid transaction is broadcast to the network.

• Transaction Hashing: Each transaction in the block is hashed using the sha256 algorithm with the block’s hash as input and the Merkle root of all transactions as an additional input.

• Transaction ID Generation: The transaction hash is then used to generate a unique, 18-byte hexadecimal string known as a Transaction ID (TxID).

The TxID is generated in two parts:

• Block Hash: This is the actual hash of the block, which is a combination of the block header and other metadata.

• Merkle Root: This is an additional input to the transaction hashing algorithm that helps to ensure uniqueness and integrity.

TxID Generation Algorithm

The Ethereum community has developed a consensus algorithm called “Keccak-256” for generating transaction IDs. The algorithm takes two inputs:

• Block Hash: This is the actual hash of the block.

• Merkle Root: This is an additional input to the Merkle root calculation.

The resulting TxID is generated using a combination of the block hash and the Merkle root, resulting in a 18-byte hexadecimal string.

When Does it Change?

After each block is created on the Ethereum network, the transaction ID for that block changes. This change occurs because every new block on the chain has its own unique transaction hash and Merkle root.

To illustrate this concept, consider the following example:

• Block 1: A new block is created with a specific block hash (e.g., 0x1234567890abcdef).

• Transaction Hashes: Each of the 10 transactions in Block 1 has its own unique transaction hash using Keccak-256.

• Merkle Roots: The Merkle root for each of these transactions is generated as well.

As a result, when we create new blocks on the Ethereum network, they will have their own unique block hashes and Merkle roots, leading to changes in the transaction IDs associated with those blocks.

Example Use Case:

To demonstrate how this works, let’s consider an example using Python:

import hashlib

import json


def generate_txid(block_hash):

    
Hashing function used for Keccak-256

    def hash_function(input_string):

        return hashlib.sha256(input_string.encode()).hexdigest()


    block_merkle_root = hash_function(str(block_hash))

    transaction_hashes = []

    for i in range(10):  
assuming 10 transactions

        txid = hash_function(json.dumps(i, sort_keys=True)) + block_merkle_root

        transaction_hashes.append(txid)


    return json.dumps(transaction_hashes), block_merkle_root


block_hash = "0x1234567890abcdef"

txids, merkle_root = generate_txid(block_hash)

print("Transaction Hashes:", txids)

print("Merkle Root:", merkle_root)

In this example, we create a new block hash using the hash_function function. We then use this block hash as input to the transaction hashing algorithm and store the resulting TxID along with the Merkle root.

This process ensures that each new block on the Ethereum network has its unique transaction ID and Merkle root, leading to changes in the transaction IDs associated with those blocks.

Conclusion

Understanding how transaction IDs are generated and changed is crucial for building a reliable and efficient non-mainstream Ethereum client.

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