Ethereum: How are transaction hashes calculated?

Ethereum Transaction Hash Calculation

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Calculating the hash of Ethereum transactions can be a bit tricky, especially for those new to Ethereum. In this article, we’ll explore how Ethereum calculates transaction hashes and provide examples to help you understand the process.

Understanding Ethereum Transactions

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In Ethereum, each block contains multiple transactions, known as “messages”. Each message is a sequence of inputs (called “data”) followed by a signature (known as a “block hash”). The block hash is calculated using a complex algorithm that takes into account the data and previous hashes.

Transaction Hash Calculation Algorithm

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Ethereum’s transaction hash calculation algorithm is based on the following steps:

• Hash functions: Ethereum uses two types of hash functions:

* Keccak-256: A 256-bit hash function designed to be computationally fast.

* BLAKE2b: A 256-bit hash function designed to be memory-safe and fast.

• Message normalization

  

  : Each transaction is normalized into a byte array, which represents the input data.

• Block hash calculation: The block hash is calculated by concatenating the previous block hash, the message header (a 4-byte signature of the block), and the normalized input data.

Example: Calculating the Hash of a Single Transaction

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Let’s say we have a transaction with the following inputs:

transaction_id: 0x1234567890abcdef

from: 0x9876543210fedcba

to: 0x876543210fedcba

value: 0x1234567890abcdef

The input data would be:

[0x1234567890abcdef, 0x9876543210fedcba, 0x876543210fedcba]

Next, we concatenate the block hash (using Keccak-256) with the message header (a signature) and normalized input data:

block_hash = Keccak-256(0x1234567890abcdef + 0x9876543210fedcba + 0x876543210fedcba)

message_header = 0x67454bbf

normalized_input_data = [0x1234567890abcdef, 0x9876543210fedcba, 0x876543210fedcba]

Then, we concatenate the concatenated block hash with the normalized input data to form the transaction hash:

transaction_hash = Keccak-256(block_hash + message_header + normalized_input_data)

Using a Tool or Library

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To calculate the transaction hash, you’ll need a tool or library that supports Ethereum’s hash functions. Some popular options include:

• ethhash: A Python library that calculates Ethereum hashes.

• blockchain (a Node.js library): Provides a convenient API for working with Ethereum data structures.

In summary, Ethereum calculates transaction hashes by concatenating the previous block hash, message header (a signature), and normalized input data. The resulting hash is then calculated using two hash functions: Keccak-256 and BLAKE2b. By following these steps and using a tool or library to assist, you should be able to calculate the hash of any Ethereum transaction.

Note that this is just an introduction to the process. For more advanced topics, such as smart contracts and blockchain programming, please consult official resources and documentation from Ethereum developers.