Double Size UIDs


  • 13. July 2015 at 13:46
    DESFire double size UIDs appear to take the form:

    04 XX XX XX XX XX 80

    I understand that UID0 is the code for the manufacturer (04=NXP) but I am wondering what the significance of UID6 being 0x80 is?

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    Re: Double Size UIDs

    13. July 2015 at 19:39
    Hey Christopher,
    The 80h represents BCC = Block Check Character, which is calculated as Exclusive OR over the last 4 bytes.

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    Re: Double Size UIDs

    29. December 2015 at 20:12
    Christopher isn't asking about BCC1, he is asking about UID6.
    In almost every MIFARE tag with a double size UID, UID6 is 0x80 (even in the examples provided in various MIFARE documents). I have seen a few with 0x81 or 0x84, but most are 0x80. Is UID6 used as a bit mask or something?
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