I live across the Carquinez Straites from 'everything' in the
SF Bay area. So I cross a toll bridge frequently.

In my car is a little microwave transponder that pays my bridge toll.

I drive through the lane, the system detects my car's presence,
emits a public key query pulse, my transponder responds,
it knows it's me, charges my credit card, flashes a "valid toll collection"
sign, and I'm on my way.

It works by public key cryptography. The base unit transmits a big number.

My transponder responds with another big number.

The relationship between two is easy to turn into a private number, so they
know it's me. To guess the relationship from listening to the call/response
pairs is most definitely not. Far easier to break into my car and steal my
transponder.

speaking of the stupidity of stealing transponders....

I used to work for a company that used automatic vehicle locator units.

My boss got invited to one of these secret hacker fest things, and
wasn't supposed to let anybody know where it was.

Well, he carefully kept it a secret where he was going as he loaded
various demo toys into his car and took off for this thing.

We, of course, just tracked the AVL unit.

Similar story. Some crook thought he'd made a slick getaway in LA
when he jumped into the arresting officer's patrol car and sped off.

LAPD units are tracked by GPS. They weren't happy.

--
Anniepoo
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