FAQ

Which algorithms are supported?

HS256/384/512, RS256/384/512, PS256/384/512, ES256/384/512, EdDSA, and the unsigned none algorithm. For JWE, jwt-hack handles dir, RSA-OAEP, ECDH-ES, and AES key-wrap variants with A128GCM or A256GCM content encryption. The full list is on the introduction page.

Can crack recover an RS256 or ES256 secret?

No, and nothing can. RS/ES/PS/EdDSA tokens are signed with a private key, not a shared secret, so there is no secret to guess. crack only works on HMAC tokens (HS256/384/512). If you point it at an asymmetric token it tells you so and stops.

What you can do to an RS256 token is test for algorithm confusion, where the server verifies an attacker-supplied HS256 token using the RSA public key as the HMAC secret. See payload --target alg_confusion.

Why does verify exit with code 0 even when the token is invalid?

A bad signature is a valid, expected result, not a tool error. verify prints ✓ Token is valid. or ✗ Token is invalid. and exits 0 in both cases. Parse the stdout line, or use --json and read the valid field. Exit code 1 is reserved for real failures like an unreadable key file.

Does scan find the secret for me?

It runs a quick weak-secret check against a short built-in list, enough to catch secret, password, and friends. For a real wordlist, run crack directly, or pass scan -w <wordlist>.

How do I use jwt-hack in a script?

Add --json to any command for stable machine-readable output. See Scripting & Automation for field names and exit-code behavior.

Where does jwt-hack store its config and cache?

Under $XDG_CONFIG_HOME/jwt-hack when XDG_CONFIG_HOME is an absolute path, otherwise the platform config directory (~/.config/jwt-hack on Linux, ~/Library/Application Support/jwt-hack on macOS). Downloaded wordlist presets and the shell history file live there too. See Configuration and Environment Variables.

Is this legal to use?

jwt-hack is a testing tool. Only run it against tokens and systems you own or have written permission to test. See SECURITY.md.

Something isn't covered here

Open an issue on GitHub.