[Cryptography] How to crypto secure speed limit signs

[Henry Baker]

At 07:26 AM 3/25/2015, Natanael wrote:
>Den 25 mar 2015 14:59 skrev "Henry Baker" <hbaker1 at pipeline.com>:
>>
>> FYI -- In order to keep these Fords from being spoofed, we would need to "secure" each speed limit sign with a crypto signature.  Presumably, this could be done with a QR code.
>>
>> But how to avoid a "replay" attack -- i.e., cloning an existing sign & installing it somewhere else?  Should the QR code crypto sign the sign's GPS coordinates?  Wouldn't that make speed limit signs pretty expensive to manufacture & install?
>>
>> Ditto with all kinds of other street signs.
>
>The only thing that makes sense IMHO is a good GPS and signed official map data kept frequently updated. (yes, GPS spoofing then becomes the new issue...) 
>
>You could however let the signs double as radio beacons - your vehicle can ignore any obviously wrong signals, while also letting the beacons assist positioning. If you keep them online (mesh radio, or listening to broadcasts?) they can also broadcast their own ID + position + current time + given speed limit. 
>
>Secure positioning is a whole other matter. one potential solution that have been considered is letting the client devices compare measured noise with the servers (or beacons) to verify proximity.
>
>Also plain challenge-response with timing - any relay must inherently add latency, therefore you know the beacon isn't actually as close as it appears.

You bring up excellent points.

I understand that certain high-end German cars can already read & interpret various road signs ("TSR"/"ADAS"), so it should be possible to "spoof" these cars already.  I wonder if anyone has already done such a thing ?

http://en.wikipedia.org/wiki/Traffic_sign_recognition

Fake street signs aren't new; an artist even put up a fake freeway sign on one of the Los Angeles interstate highways, and this particular sign remained for a number of years.

http://magazine.good.is/articles/the-fake-freeway-sign-that-became-a-real-public-service

http://www.ankrom.org/freeway_signs.html

Fake roadway signs were used during WWII to sabotage troop & tank movements; one scene in the 1970 movie "Patton" shows the results of such a sabotage.