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My cards can work with wrong GP keys, why?

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Tazmania09
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Joined: Mon Nov 30, 2015 3:40 am
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My cards can work with wrong GP keys, why?

Post by Tazmania09 » Mon Dec 07, 2015 5:33 am

As we all know, GP keys offcard should be the same as the keys on card. Otherwise, you can't do any operation on your card.

But I came across a strange thing. I used pyApdutool to operate my java card.

And, my card's GP keys are as follows:
S-ENC: 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
C-MAC: 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
DEK: 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F

In pyApdutool, I set the GP key as:
S-ENC: 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4E
C-MAC: 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
DEK: 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F

Though S-ENC key offcard is different with the key oncard, I can also upload and install applet successfully. It works fine with two different keys.
How strange it is! Could anyone tell me why this happened? Is this a bug in my card?

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mabel
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Re: My cards can work with wrong GP keys, why?

Post by mabel » Fri Dec 11, 2015 3:07 am

You only changed the parity bit which is not used by the card. So no matter how you change this parity bit, it doesn't influence the outcome of cipher computation.

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