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How can I use MAC session key without card challenge value?

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Marshaldll
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How can I use MAC session key without card challenge value?

Post by Marshaldll » Fri Dec 11, 2015 2:08 am

As GP 2.2.1 described, the pseudo random is generated as follows:

- The AID of the Application requesting to open the Secure Channel is padded according to the
padding rules defined in appendix B.4 - DES Padding;
- A MAC is calculated across the padded data as defined in appendix B.1.2.2 - Single DES Plus
Final Triple DES MAC , using the C - MAC session key and an ICV of binary zeroes;
- The six leftmost bytes of the resultant MAC constitute the card challenge.

How can I use MAC session key without card challenge value? Could anyone help me out?

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horse dream
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Re: How can I use MAC session key without card challenge value?

Post by horse dream » Sun Dec 20, 2015 11:44 pm

As far as I know, MAC session keys are generated after receiving card challenge value!

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UNKNwYSHSA
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Re: How can I use MAC session key without card challenge value?

Post by UNKNwYSHSA » Mon Dec 21, 2015 4:50 am

Specification GlobalPlatform Card Specification 2.2.1 said:
Generating the Secure Channel C-MAC session keys using the Secure Channel base key or
MAC key (S-MAC) and the session keys derivation data with a constant of '0101';

Key Derivation data is consists with:

Code: Select all

Constant(2 bytes) + Sequence Coutner(2 bytes) + '00' Padding(12 bytes)

So, this type of Card Challenge (said as Pseudo-random number) can be generated without Card Challenge.
And, other type of Card Challenge is a random. It is generated without the C-MAC session key.
sense and simplicity

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