Tom McCurdy

Does anyone know what you would build that would prevent someone using a gargage door hacker from opening your garage door, but still allow you to open your garage door. I was thinking it would be something that scans for people submiting multiple codes somehow and then locks up the garage door code or something... actually i have no Idea, but i figured someone here would.

__________________
Physics-Electronics-

zachtheterrible

yeah, ur idea would work, or u could just use a non-standard frequency cuz the hacker will only work on one frequency

__________________
I'm no electronics god, i just talk too much.

Tom McCurdy

how would you do both suggestions u suggested?

how would I build something
and how would I get something that was off frequencey
also is there a way to build a hacker that could get these off frequency codes for a truely universal garage door hacker/>

__________________
Physics-Electronics-

panic mode

one way to do it is to ignore ANY code for a while if there was invalid code (let's say two monutes). this doesn't prevent brute force attack but it will dramatically slow down attackers progress. this also means that any neighbour using his garage door will actually lock your garage :-)
you can try to send the code twice or combined with reset code etc but all this does is making key code longer. if i was doing it, i would sit down and think hard before comitting to any work. for example, i would definitelly like to make comunication bidirectional. so for example every time you want to open garage door, door opener would send you a random key. you would have to decode it and send it back. this makes things more complicated but it's just an idea. comercial product seam to use similar approach where both sender and receiver generate own cyclic codes so they need to be synchronized before they work.

TheOne

One popular method is to use "rolling code" or "code hopping"

http://www.edn.com/index.asp?layout=...=2814&nid=2036

http://www.amourelle.co.uk/sentry-ch1.htm

ante

Hi Tom,

If it is a short distance why not use an IR transmitter to “start up” the RF receiver which then enables you to open. This will reduce the risk of unauthorized opening

dingo

Panic Mode has the idea, you need a two way connection encrypted.

With a radio reciever someone could wait until you came home and record your transmition when you open the door then play the recording back on the same frequency.

If you just want an increase in security remove any brand name from the door. Depending on the design of the circuit you could shift the frequency off the standard. There are stardard freq for remotes used by different countries 304mz 433mz to name two. This will make things a lot harder for someone to crack as they have to find the right freq first.

ante

I think it would be very hard to intercept and decode an IR signal as well as the radio signal code. You have to placed in the range between the IR transmitter and receiver to steal this code. But sure, the two way code is another possible way to go.

dingo

Using IR will be very short range, more so if the sun is shining on you. Half the time you will need to get out of the car to get close enough to the reciever. Plus unless it is 2 way it can still be hacked by just trying combinations until the door opens.

Your idea has merit though in so far as a lockout device. What about placing an LDR in the door so it picks up the head lights of the car? This way you need to have your head lights on while in the driveway shining at the door for the remote to work. A hacker will not think of that fast.

ante

Yes a short distance but with a fast coded IR signal to enable the system it would be fairly safe. A simple TV remote works fine in sunlight at 10feet or more so I don’t think you have to leave the car to open. BTW I have heard about a hole in the ozone down under, would this interfere whit the IR maybe? 8)

Just kidding Mate!

WilliamN

Or you could use some sort of power disruption ladder of some kind. I used this method to trigger relays remotely in the past. Have a bunch of relays in serries, say 5. Each relay driver needs a specific freq to "turn on" Becasue of the ladder method the relays have to turn on in sequence or it wont turn on your (insert protected cirucit here). which is good. Pick frequencies all over the spectrum for each relay driver. This might be too oldschool.