TecmagDiams, on 11 October 2012 - 04:26 PM, said:
I guess to explain my point I'll give a quick example:
Want to make store credit with the cards? Awesome, perfect use of Mag Cards! Person has card with 10 units of money on it. They swipe the card and the machine reads the 10 units, they buy something for 2, and then must swipe the card again to pay (As the card must now be written as 10-2, aka 8) and get their item. Everything is fine up to this last step... If they say, had, a second card and swiped THIS card at this point, they now have 10 units of money on their original card, and 8 on their new card. They bought something and earned 8. There is NO way to protect this either, because you write blindly to the next inserted card, you can't read it and check, because it always blindly waits to write... I think it would be nice if it worked similar to the RFID writer, you would slip the card in it, and it would suck the card in, and when it was done it would spit it out after any reading/writing it wanted to do.
The solution to this is to store account numbers on the cards, then keep the amount of credit in a database of account numbers. User swipes card with his account number, database reads 10 credit from card, updates to 8 units, all in one swipe. Even with the read and write in one operation, they could still just make as many copies of the card with 10 units on it as they want.
I'm not denying that this feature could be useful for other things