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Key-derivation functions

How to identify and crack a bcrypt hash

Identify a bcrypt hash and crack it with ready-to-run hashcat and John the Ripper commands. Slow by design.

hashcat mode -m 3200John format bcrypt

bcrypt is a key-derivation hash type. It uses a deliberately slow, salted key-derivation scheme, so only weak or short passwords are realistically recoverable. This page shows how to recognise it and the exact commands to attack it.

All identification runs locally in WebAssembly. The commands below write the hash to a local file on your machine — nothing is sent to this site.

Identifying the hash

The hash identifier on the home page detects bcrypt entirely in your browser — your hash is never uploaded. A typical example looks like this:

$2a$12$R9h/cIPz0gi.URNNX3kh2OPST9/PgBkqquzi.Ss7KIUgO2t0jWMUW

Cracking bcrypt with hashcat

Save the hash to a file and run hashcat in mode -m 3200. Expect this to be slow — use a focused wordlist. Start with a wordlist such as rockyou.txt:

echo '$2a$12$R9h/cIPz0gi.URNNX3kh2OPST9/PgBkqquzi.Ss7KIUgO2t0jWMUW' > hash.txt && hashcat -m 3200 hash.txt /usr/share/wordlists/rockyou.txt

Add a rule set to mutate dictionary words (capitalisation, leetspeak, appended digits) and dramatically widen coverage:

echo '$2a$12$R9h/cIPz0gi.URNNX3kh2OPST9/PgBkqquzi.Ss7KIUgO2t0jWMUW' > hash.txt && hashcat -m 3200 hash.txt /usr/share/wordlists/rockyou.txt -r /usr/share/hashcat/rules/best64.rule

Cracking bcrypt with John the Ripper

John the Ripper can attack the same hash with the bcrypt format:

echo '$2a$12$R9h/cIPz0gi.URNNX3kh2OPST9/PgBkqquzi.Ss7KIUgO2t0jWMUW' > hash.txt && john --format=bcrypt --wordlist=/usr/share/wordlists/rockyou.txt hash.txt