SipHash-2-4 Calculator

About this calculator

SipHash-2-4 is a fast, keyed pseudorandom function designed by Jean-Philippe Aumasson and Daniel J. Bernstein specifically to defend hash tables against hash-flooding denial-of-service attacks — a technique where an attacker sends inputs deliberately chosen to collide in a hash table’s buckets, degrading lookups from O(1) to O(n) and stalling a server. The “2-4” refers to its round structure: 2 compression rounds per message block and 4 finalization rounds.

Given a 16-byte (128-bit) secret key and a message, it produces a 64-bit digest that’s cheap to compute but hard to predict without the key. This is why languages and systems including Python, Rust, Ruby and Redis use SipHash internally as the default hash function for strings and dictionary/hash-map keys. This calculator computes the SipHash-2-4 digest of any text under a given hex key, useful for developers verifying implementations or exploring how the algorithm behaves.