storing credit card information

Discussion in 'Computer Security' started by yawnmoth, Jul 2, 2008.

  1. yawnmoth

    yawnmoth Guest

    My first question is... does the PCI require retail stores store
    credit card numbers? <
    doc_id=135602> suggests that they are. If so, what does the PCI say
    about storing them encrypted vs. storing them unencrypted?

    I can see virtue to both, actually.

    If you store credit card numbers encrypted or hashed, it's a lot
    harder for the database administrator to get ahold of every customers
    credit card.

    The problem with with encryption / hashing is that... say a customer
    wanted to search for invoices by their credit card number. If the
    credit cards were stored unencrypted, a customer could give just the
    last four digits of the credit card number out and with them, a search
    could be made. Just do something like...

    SELECT * FROM invoices WHERE credit_card_num LIKE '%xxxx';

    The point-of-sale system could do that, via SSL/TLS, and get the
    invoices without ever disclosing the full credit card number to the
    phone receptionist or cashier or whomever (although I imagine a
    cashier would probably be swiping the physical card in some sort of
    magnetic strip reader).

    If credit card numbers, in contrast, were stored encrypted or hashed,
    that probably wouldn't work. If you were using a block cipher with a
    block size of 4 and were in ECB mode, you could do the search (just
    encrypt the last four digits with the key and plug the result into the
    LIKE query), but if the block size wasn't 4 or if you were in CBC
    mode... at that point, you'd be out-of-luck.

    So it does seem that both techniques have their virtues.

    Of course, it seems to me that the virtue of encrypting far outweighs
    the virtue of not encrypting. A single database administrator having
    access to everything can do a ton more damage than a phone
    receptionist who's just been given a single credit card number
    (assuming you even have phone receptions).
    yawnmoth, Jul 2, 2008
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