Generate salted bcrypt hashes for passwords and verify plaintext against an existing hash, all in your browser.
Generate salted bcrypt hashes for passwords and verify plaintext against an existing hash, all in your browser. Generate salted bcrypt hashes for passwords and verify plaintext against an existing hash, all in your browser.
bcrypt is an adaptive password hashing function designed by Niels Provos and David Mazieres in 1999. Unlike fast digests such as MD5 or SHA-256, bcrypt deliberately costs CPU time: each hash runs the Blowfish cipher through a configurable number of rounds, and the work doubles with every increment of the cost factor. This slowdown is what makes offline dictionary and brute-force attacks expensive. A correct bcrypt implementation also embeds a random 128-bit salt inside the output string, so two hashes of the same password are always different and rainbow tables are useless against it.
A bcrypt hash looks like $2b$12$e0.6kJ8a5X8u5Yp3qR5E0e9dF4z3W2c1v0b9n8m7l6k5j4h3g2f1. The
parts after the leading dollar signs carry the algorithm version, the cost,
and the salt:
$2b$ -- the algorithm revision. $2a$ and $2y$ are older variants with
subtle handling differences for the 8-bit sign bug; $2b$ is the current
recommendation and what bcryptjs emits.12 -- the cost factor. 2^12 = 4096 rounds of the key schedule. Each +1
doubles the time; 10-12 is a reasonable default for interactive login,
while 12-14 suits stored credentials.Type a password into the input, pick a cost factor, and press Hash. The generated hash appears in the output box and is also placed into the verify field. To check an existing hash, paste it into the verify field and type the candidate password in the input: the page compares immediately and shows a green check or a red cross. Because the comparison is done with bcrypt.compareSync, it never reveals how close a wrong guess was -- every attempt is hashed in full before the result is decided.
bcrypt truncates input to 72 bytes: longer passwords are silently cut, so two passwords sharing the first 72 bytes compare equal. If you need longer inputs, pre-hash with SHA-256 (hex-encoded) and bcrypt that digest instead. Bcrypt is a deliberate memory-light algorithm -- it resists GPU arrays less well than memory-hard designs such as Argon2 or scrypt, but its 4 KB table and 64-byte state still make cheap ASIC cracking unattractive. For brand-new systems Argon2id is often a better choice; bcrypt remains an excellent, widely supported option for legacy compatibility and for cases where the runtime cannot provide Argon2. This page runs entirely in your browser: the password and the hash never leave your device, and you can inspect the code path (MIT/BSD bcryptjs) bundled in public/assets.