Clear DefinitionsKeccak-256
1 min read
Pronunciation
[kech-ak too fif-tee siks]
Analogy
Keccak-256 is like a unique industrial blender that turns any ingredients (data) into a very specific smoothie pattern. No matter how many or few ingredients you put in, you always get exactly the same amount of smoothie (256 bits), but with a completely different color and texture pattern for even the slightest change in ingredients. Even more importantly, it's impossible to figure out what ingredients went in just by examining the smoothie.
Definition
A cryptographic hash function that produces a 256-bit output, serving as Ethereum's primary hashing algorithm. Keccak-256 is a variant of the Keccak algorithm, which was selected as the winner of the NIST SHA-3 competition, though Ethereum uses a slightly modified implementation.
Key Points Intro
Keccak-256 provides Ethereum's fundamental data fingerprinting mechanism.
Key Points
Transforms inputs of any size into a fixed 256-bit (32-byte) hash value.
Used extensively in Ethereum for transaction hashing, address generation, and smart contract operations.
Implements a different internal structure than SHA-256, providing algorithm diversity in the blockchain ecosystem.
Based on the 'sponge construction' with strong security properties.
Example
When creating an Ethereum address, the user's public key is passed through Keccak-256, and the last 20 bytes of the resulting hash are used as the address. This process creates a shorter, more manageable identifier while maintaining cryptographic security.
Technical Deep Dive
Keccak-256 differs fundamentally from SHA-2 algorithms in its internal structure, using a 'sponge construction' with two phases: 'absorbing' input data into an internal state and 'squeezing' output data from that state. The core operation is a permutation function called Keccak-f applied to a 1600-bit state represented as a 5×5×64 three-dimensional array of bits. Each round applies five operations (θ, ρ, π, χ, ι) that provide diffusion and nonlinearity. Importantly, Ethereum uses a slightly different implementation than the NIST-standardized SHA-3: Ethereum's Keccak-256 uses different padding rules (Keccak's original padding rather than NIST's modified padding), creating incompatibility with standard SHA-3-256. This difference means hash values for the same input will differ between Ethereum's implementation and standard SHA-3 libraries, which has occasionally caused confusion when integrating with Ethereum systems.
Security Warning
Caveat
The subtle difference between Ethereum's Keccak-256 implementation and the standardized SHA-3-256 has created compatibility challenges and occasional security issues when developers incorrectly assume they are identical. Always use Ethereum-specific libraries when calculating hashes for Ethereum applications.
Keccak-256 - Related Articles
No related articles for this term.