Talk about applied math!  Here’s a little trick that can open all 5-key keyless vehicles in 3129 key strokes (usually less).  Neat stuff…if you don’t own a vehicle with keyless entry.  One more reason to love my mid-90’s Jeep, if only I could stop the driver’s side door from rusting off…

The easy way for car-makers to make this a non-issue is to require an action (another key press like ‘Enter’ or attempting to open the door) in order for the combination to be accepted and simultaneously reset the keys.  That would significantly increase the time it takes to run through all the combinations and defeat the economies the system gains with each sequence building one number at a time from the previous sequence.

(H/T Bruce Schneier)