Product keys that are easy to type
License keys are usually typed in by hand from an email or a printed card, so they need a format that is hard to get wrong. The default is 5 groups of 5 characters from A-Z and 2-9, leaving out I, O, 0 and 1. That gives 125 bits of entropy, so valid keys cannot be guessed.
Generate a batch, store them in your licensing database and assign one to each customer.
Random keys and signed keys
Random keys like these have to be checked against your server or database, which is simple and lets you revoke keys. If your software must validate keys offline, you need signed license keys, where the key carries data signed with a private key and the app checks it with an embedded public key. The ECDSA and Ed25519 generators create signing keys for that.
Frequently asked questions
Can people guess valid license keys?
Not when the keys are random and long enough. With 125 bits, guessing is hopeless. Attacks on license systems usually target the software’s checking code instead.
Can I change the format?
Yes. Set the number of groups, characters per group, the character set and the separator in the options.