Rolling code

A rolling code or hopping code is often used in radio-based vehicle opening systems or entrance control systems such as B. Garage door openers used to wirelessly authenticate a legitimate user . Based on a shared secret between sender and recipient (“symmetrical key”) and a suitable cryptographic algorithm , the sender transmits a continuously changing so-called next code to the recipient for verification ( verification ). The next code is never directly repeated by the sender in order to make replay attacks more difficult, but it is still an element of a predefined, suitably long, cyclically iterated list (hence the term rolling code ). A well-known, widely used rolling code is, for example, the Keeloq algorithm.