Tools and Development

Keccak

What is Keccak-256

Keccak-256 is a cryptographic hash function that produces a fixed 256-bit output, similar to SHA-256, but it follows a different internal process. It's the basis of the SHA-3 standard (Secure Hash Algorithm 3) and is widely used in blockchain platforms like Ethereum, where it's called keccak256.

1. Overview

Keccak-256 is a member of the Keccak family of cryptographic hash functions, which won the NIST (National Institute of Standards and Technology) competition to become the SHA-3 standard in 2015. It takes an arbitrary amount of input data and generates a 256-bit (32-byte) fixed-length output, known as a hash or digest. The key property of Keccak-256, like other hash functions, is that even the slightest change in input will produce a vastly different hash output (avalanche effect), making it useful for data integrity and security.

2. Properties of Keccak-256

  • Fixed-Length Output: Regardless of the size of the input, Keccak-256 always produces a 256-bit (32-byte) hash.
  • Pre-image Resistance: It is computationally infeasible to reverse the process and retrieve the original input from the hash.
  • Collision Resistance: Finding two different inputs that produce the same hash (collision) is highly improbable due to the large output space.
  • Avalanche Effect: A tiny change in the input (even a single bit) drastically changes the output hash.

3. Keccak-256 vs SHA-256

  • Different Standards: Keccak-256 is the basis of SHA-3, while SHA-256 is part of SHA-2.
  • Internal Mechanisms: Keccak-256 uses a sponge construction (absorption and squeezing), while SHA-256 follows the Merkle-Damgård construction (based on iterative hashing).
  • Block Size: Keccak-256 uses larger internal states (1600 bits) compared to SHA-256’s smaller internal state (512 bits).

4. Keccak-256 in Ethereum

In the Ethereum blockchain, keccak256 is the default hash function. It’s used for multiple purposes, including:

  • Hashing transactions and blocks.
  • Generating unique addresses.
  • Storing data efficiently.

Smart contracts in Ethereum use the keccak256 function to verify integrity, create signatures, and much more.

Summary

Keccak-256 is a powerful cryptographic hash function that plays a major role in Ethereum and other blockchain technologies. It operates using a sponge construction that absorbs the input data, performs several permutations, and squeezes out a 256-bit output. It’s different from SHA-256 in terms of internal workings and design but is just as secure. Ethereum developers often rely on keccak256 for creating hashes and ensuring data integrity within the blockchain.