Before revision: Techniques Common PRNG (pseudorandom number generator) — preferably cryptographically secure — in both transmitter and receiver Transmitter sends 'next' code in sequence Receiver compares 'next' to its calculated 'next' code.
After revision: Rolling codes were introduced around the year 2001Techniques Common PRNG (pseudorandom number generator) — preferably cryptographically secure — in both transmitter and receiver Transmitter sends 'next' code in sequence Receiver compares 'next' to its calculated 'next' code.