8086's are very cheap these days. They have enough computing power to run something like IDEA, albeit very slowly. I'd use a challenge/response method with something like this, because you have to keep in mind that encrypted signals can just as easily be captured. You'd need a clock on the garage controller. CMOS clock chips anyone? It doesn't have to be acurate to the second, but certainly to the minute, and have date, month and year available to it. The garage opener would receive a signal from the remote, issue a challenge code based on a hash of the time/date + some random numbers. The remote would encrypt this hash with the owner's IDEA key and send back the response. Both units would need some sort of keypad to program the codes into them. A backup batery for both sides is also important along with a warning that the main battery has failed. You wouldn't want to lose access to your garage. I suppose some backup entry system would also help... a two key system (using physical keys with high security mushroom pin locks, etc.) Remember that should the remote opener fail, the driver would be damned pissed at crypto and we want him very happy.