• HakFoo@lemmy.sdf.org
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        3 days ago

        Standard compliance rules generally allow showing the first six and last four digits on a statement or receipt or whatever. That leaves 6 digits, and since you know it has to match the cksum, 1/100,000 odds on straight guess.

        You may be able to knock down two more digits if you know which bank and card type (debit, prepaid, etc) it is. The first 6 digits used to encapsulate that data but there’s a transition to 8 now.

        • JPAKx4@piefed.blahaj.zone
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          2 days ago

          Sure, but in this case we have a credit card number summed with a 3-4 digit number (which you don’t have to guess the length bc of the first digits of the processor identificatoon). You can try every permutation of 3-4 digit number taken out, and eliminate all the ones that don’t have a valid checksum