Hash Generator

What a hash guarantees, and what it does not

A cryptographic hash promises three things: the same input always gives the same digest, a digest reveals nothing about its input, and finding two inputs with the same digest is computationally infeasible. That third promise is the one that breaks first, and it is what "broken" means when applied to MD5 and SHA-1 — collisions can be constructed deliberately, and have been, including for real certificate and document formats. Note what does not break: verifying a download against a checksum published alongside it by the same party still works, because an attacker who could replace the file could equally replace the checksum, so the digest was never the security boundary in that scenario. The distinction is why these algorithms are simultaneously unsuitable for signatures and perfectly reasonable for the checksum on an old release page.

Why passwords need more than a hash

Hashing a password before storing it stops a database leak handing over plaintext, but only just. Fast hashes are fast for attackers too: a modern GPU computes billions of SHA-256 digests per second, so the entire space of common passwords falls in minutes, and identical passwords produce identical digests, which reveals who shares one. Salting — mixing a unique random value into each password before hashing — fixes the second problem and defeats precomputed lookup tables. The first problem needs a hash designed to be slow and memory-hungry, which is what bcrypt, scrypt and Argon2 are for. None of that is what this tool does; it computes general-purpose digests. If you are storing passwords, reach for a password-hashing function, not SHA-256.