this post was submitted on 20 May 2024
380 points (98.2% liked)
Technology
59192 readers
2513 users here now
This is a most excellent place for technology news and articles.
Our Rules
- Follow the lemmy.world rules.
- Only tech related content.
- Be excellent to each another!
- Mod approved content bots can post up to 10 articles per day.
- Threads asking for personal tech support may be deleted.
- Politics threads may be removed.
- No memes allowed as posts, OK to post as comments.
- Only approved bots from the list below, to ask if your bot can be added please contact us.
- Check for duplicates before posting, duplicates may be removed
Approved Bots
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
If there's no central control or ledger, couldn't you just rewrite the card with the original values and the machines wouldn't know any difference?
you could add a random number to the encrypted data on the card and require it to always be the same or larger than the last time that card was seen, and then increment it every time the card is used.
The problem with that is that if the machines don't talk to one another then there's no way to make that system work across machines. I guess if each machine enforced it then you would eventually run out of machines that work for your hacked card.
You could store a counter for every machine used on the card, realistically, given few Laundromats would have over 50 or so machines. That'd mean that as you say, restoring the cards initial state would break it for every machine you previously used.
Going way too far now for what would make sense for a Laundromat, but just to entertain the idea...
You could also use an OTP encryption scheme on the card, where the exchange encryption key is based on the laundry machine ID, card ID, and a current timestamp, and thus changes every time the card is used. It would then be quite hard to "restore" the initial state of the card without having the laundry machine's hidden ID. Everything you read off the card would be useless a second later.
Oh yeah, that's true, so you wouldn't have destroyed the card, but it's not a useful hack if they've done even the most basic security measures.
That said, I would be fascinated to know what was on that card. I'd give it pretty good odds of having absolutely no security measures whatsoever.