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Two students find security bug that could let millions do laundry for free (www.theverge.com)

submitted 6 months ago by [email protected] to c/[email protected]

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[–] [email protected] 1 points 6 months ago (1 children)

Meaning I could either back up and rewrite a $20 card forever, or rewrite the balance to having FF credits or whatever.

As you can guess, checksum is stored somewhere. And that somewhere happens to be card that was just dumped.

[–] [email protected] 4 points 6 months ago* (last edited 6 months ago)

Yeah, but you'd need the algorithm. It could be a hash of some kind, and if you don't know what kind of algorithm they're using you can't replicate it.

EDIT: Oh, I see what you're saying. You mean you could simply rewrite the original card value back over it forever. That's actually quite clever, and it would work even in case the card was completely encrypted.

Actually that means this is trivial to beat I think.