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EM cards used in access control systems have a Unique Identification Number (UID) which can be read with a card reader.
To make "unique" cards som suppliers manipulate the number read from the cards, recalculates a new number, and print that number on the cards - so that the new number may be entered into systems where the cards will be used.
I need help to reverse engineer the numbers on some cards, to establish how the printed numbers on those cards have been calculated from the original UID.
I have made an Excel sheet where the UID for 10 cards have been read, of which 5 specify the recalculated number.