Matt Blaze1d ago

Physical security and cryptography can learn from each other, part 11367:

Hotels wisely don't put the room number on guest keycards so if someone finds your card, they'd have to exhaustively search the hotel to find the room it opens.

Some hotels now have elevators programmed to only let you call the floor for which your keycard is coded, preventing guests from wandering to other floors.

But it also means the elevator can be used as an efficient oracle to determine the floor of a found key.

Show threadMatt Blaze1d ago
In other words, restricting the elevator in this way is a bad tradeoff. It makes it harder for guests to visit their friends on other floors, but it reduces the complexity for an outsider burglar from O(|rooms|) to O(|floors|) + O(|rooms_per_floor|), a much more feasible search space.
Show threadTrammell Hudson18h ago
@mattblaze I've also seen some hotel elevators where you swipe your keycard and it selects the correct floor for you, removing the O(floors) component.
Show threadAriadne Conill 🐰18h ago
@th @mattblaze yeah i encountered that recently in germany and was just like ????????????? why
Show threadEnola Knezevic17h ago
@ariadne @th @mattblaze What if you wanted to have a drink at the rooftop bar before going to your room?
Show threadVelocipede Rider15h ago

@rhelune Also annoying if you are staying at a hotel with a group of friends (e.g. for an event). Then you cannot easily go to their floor and have to always meet in the lobby.

@ariadne @th

EDIT: OK I am an idiot, @mattblaze already covered this exact point! 🤪

>… harder for guests to visit their friends on other floors…

Show threadWellsiteGeo14h ago
@ruari @rhelune @ariadne @th @mattblaze
Hotels don't want guests visiting each other's rooms. They want guests meeting each other profitably in the bar. (Also make it easier to charge the prostitutes their ground rent.)
Show thread1000millimeter
@WellsiteGeo @ruari @rhelune @ariadne @th @mattblaze Ground rent?
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