C'punks, On Tue, 26 Jul 1994, Arsen Ray Arachelian wrote:
You'd need a clock on the garage controller....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.
Am I missing something here? Why would you need a clock? What I had in mind was something like: 1--The owner presses the "open" button on the remote. 2--The remote sends an "ask me" signal to the door unit. 3--The door unit transmits a random number in the clear. 4--The remote encrypts and signs the random number using its unique private key. 5--The door unit decrypts and compares the numbers, using the remotes public key. 6--If the numbers match, the door opens. QED. Adjusting my flame retardant underwear, S a n d y P.S. For most car and garage doors, relatively short (32 bit?) keys should be more than sufficient, I would think.