To mark computer security pioneer Robert Morris' passing here is a puzzle he shared at his talk at Defcon some years ago
"This is a long term problem. If you work on it and make any progress against it, you'll find yourself much smarter at the far end, than you were at the near end.When I was in Norway about 5 years ago, I was there very close to the summer solstice. I was wandering around town at 2 o'clock in the morning and there was plenty of light out. You come to a sign that says New Minsk about 60 km and it points south.
And I ask the lady "what country is this?"
She scratched her head for a bit, and said "well I think its Norway"
I said "well who plows the roads?"
"well Norway does, but he have to pay them."
There is a triple boundary in this town that I was in between Norway, Finland and Russia.
But what I did there, was, I had a card about wallet size, I stuck it into a machine, I punched in four digits, and it gave me about 2,000 krone, whatever the hell that is.
Now there are a lot of participants in that transaction. When I put a card into that machine, punch in a pin, and it gurgles for awhile, and finally gives me, a fairly large amount of money. There are a lot of participants in that transaction. The bank that owned the machine that gave me the money, it gave some money away -- that bank wants it back. The pin is necessary to convince my own bank that I'm me. But I don't want my pin to be broadcast all over the world. My bank in the us, it hasn't really given out or taken in any money, really. But there is a lot of credits involved here. Somebody needs to charge somebody else for having more money available. Even though there was actually no cash transfer.
And the problem that I have in mind is
- who are all the participants in an ATM transaction?
- what do those participants need to satisfy their problems?
- how is that in fact done?
In a general way, does the atm system actually work in some reasonable sense? To which the answer is by the way: yes. The atm system damn well works. With extremely high reliability and accuracy. It surprises me. Its quite a bit different than voting machines.