Tool · SHA-256

The hash avalanche.

A good hash function turns a one-character change into a completely different output: about half of the 256 bits flip, unpredictably. That property is why hash-based signatures can be trusted. Try it.

Input A

Input B

Bits that differ (each square is one of 256 bits)

0of 256 bits (0%)

Why this matters

Winternitz signatures, and the SLH-DSA, XMSS and LMS standards built on them, rely on two things being infeasible: running the hash backwards, and finding two inputs with the same output. The avalanche effect is the visible side of that: if similar inputs produced similar outputs, an attacker could search their way toward a match. See how the signatures work →