Bcrypt & Argon2 Hash Generator

Hash a password with bcrypt or Argon2id, or switch to verify mode to check whether a password matches a hash you already have. Useful for seeding a user row by hand, or for working out why a login is being rejected.

Nothing you type is stored, logged or reused — the hash is computed in memory and returned.

How it works

A password hash is not encryption. There is no key and no way back: the only way to check a password is to hash the attempt and compare. What separates a good password hash from a bad one is how slow it is. MD5 and SHA-256 were designed to be fast, which is exactly wrong here — a modern GPU computes billions of them per second, so a stolen database of SHA-256 passwords is largely readable within hours.

bcrypt solves this with a cost factor. The cost is an exponent: raising it by one doubles the work. At cost 10 a single hash takes roughly 50–100 ms on a typical server; at cost 12, four times that. Legitimate logins happen once and can absorb a tenth of a second, while an attacker grinding through a wordlist pays that cost on every guess. The cost is stored in the hash itself, which is why old hashes keep verifying after you raise the default — and why you can rehash a user's password at the new cost the next time they log in successfully.

Argon2id is the newer answer and the one the Password Hashing Competition selected. Besides time, it deliberately consumes memory, which blunts the advantage of GPUs and custom hardware — those can parallelise arithmetic cheaply but not RAM. If your platform supports it and you are choosing today, Argon2id is the better default. bcrypt remains entirely respectable and is far more widely supported.

One bcrypt quirk worth knowing: it silently truncates input beyond 72 bytes. A passphrase longer than that is no stronger than its first 72 bytes, and because UTF-8 multibyte characters cost more than one byte each, the limit arrives sooner than the character count suggests. Argon2 has no such limit.

Finally, the $2y$ prefix you see is PHP's identifier for bcrypt. $2a$ and $2b$ appear in hashes from other languages and verify identically in PHP; the prefixes record which implementation minted the hash, not a different algorithm.

Frequently asked questions