Need ideas for a secure short range (3m) wireless system.

[bobleny]

So, I am working on an alarm system for my bike. As apart of that system, I would absolutely love to have it recognize me from a short distance, say 1 to 2 meters away, and deactivate the alarm and turn the accessories on. For that to work, I would obviously have to keep something on me that could either be read by the bike or something that could send a signal to the bike.

My current thought is to use a micro controller to create a public private key pair. It would of course transmit the public key that the device I have on me will use to encrypt a secret password known only to device on me and the bike.

How can I do something like this?
Can anyone think of a way of doing this with out having to carry around a brick sized device? It would really be nice to just shove something in my wallet.
Does anyone have any other ideas on how to something similar?

Thanks!

 

[pebe1]

You could use a micro to send 3 bytes of data every 5 seconds via a small Tx like those from RF Solutions. That would give you almost 17million combinations of code. By the time you got on to your bike the Rx would have received the code and disarmed the bike. If it received no further codes in, say, 10secs the bike would be re-armed.