[Globalplatform-developers] R: [EXT] Re: Card Challenge generation on SCP93

[Sette A. <ago...@te...>]

Hi Karsten,

I am sorry but I forgot one point which could be useful to better explain my problem:
I would like to ask you, because it is not clear to us, if the card challenge is generated randomly or in a deterministic way with the AES128-CMAC.
Thanks once again

Kind Regards

Agostino Sette


Da: Sette Agostino
Inviato: martedì 1 dicembre 2020 09:43
A: 'Karsten Ohme' <wid...@t-...>; glo...@li...
Oggetto: R: [EXT] Re: [Globalplatform-developers] Card Challenge generation on SCP93

Hi Karsten,

First of all thank you for the reply.
I answer to your questions inline in your email.
Kind Regards

Agostino Sette

Da: Karsten Ohme <wid...@t-...<mailto:wid...@t-...>>
Inviato: lunedì 30 novembre 2020 23:05
A: glo...@li...<mailto:glo...@li...>
Oggetto: [EXT] Re: [Globalplatform-developers] Card Challenge generation on SCP93


Hi,



The test vector from the SCP03 test should be OK.

[Agostino] Yes, it is.

Could you describe your problem?

[Agostino] I would like to understand how you obtain the card challenge, what parameters are used and if what I make to generate it is correct, in a very easy way.

You are not able to replicate the result from the test with your own code?

[Agostino] No, I am not able to replicate the result from the test with my own code. I try to clarify: if I use the host challenge and the card challenge derived from scp03Test.c, from that point on in the mutual authentication phase looks good. A part from host challenge, I would like to understand the card challenge generation, that's all.

A step-by-step debugging of the scp03Test in e.g. Eclipse C/C++ IDE should give you all the intermediate steps so that you can compare the libraries and your result.

[Agostino] I will try again but I haven't found a .project file for eclipse. Furthermore I am not using libraries at the moment.

What is the goal? Implement the server side on a smart card?

[Agostino] The goal is to implement both the server and the smart card side.

Add support for a different programming language?

[Agostino] The used programming language is C

I think there are already OS projects for Java, Python and C.

[Agostino] I will appreciate if you could suggest me OS projects for C.



Karsten
On 30/11/2020 15:21, Sette Agostino via Globalplatform-developers wrote:
Hi,

I am trying to develop my own SCP03 protocol and for this reason I cloned this

git clone https://git.code.sf.net/p/globalplatform/git globalplatform-git

as a starting point, first to understand how to proceed and then to check if what I did was correct.
I verified almost everything except the Card Challenge, to be clear I would like to know how it is generated.
As far a I know it should be generated as follows:

Card challenge (8 bytes) (with PRNG):

AES-CMAC (Key-ENC , 0x00 00 00 00 00 00 00 00 00 00 00 02 00 00 40 01 || context)

"context": concat. of sequence counter (3 bytes) and AID of the application invoking the SecureChannel (5 to 16 bytes).

Starting from the information on the file

globalplatform/git/ci/master/tree/globalplatform/src/scp03Test.c

I assumed that:

  1.  Key-ENC = {0xF9, 0x95, 0xD0, 0xA0, 0x69, 0x33, 0x5C, 0x7D, 0xF4, 0x2E, 0x59, 0x03, 0x17, 0xFF, 0xEA, 0x6D};
  2.  Sequence counter = {0x00, 0x00, 0x15};
  3.  AID = {0xA0, 0x01, 0x00, 0x01, 0x51, 0x41, 0x43, 0x4C};

The result card challenge, present on the same file into the  "initializeUpdateResponse" is

Card Challenge = {0xC4, 0x09, 0x32, 0xA6, 0xFE, 0xFE, 0xAE, 0xB2};

First of all, is all this correct?

If yes,
                                                                        | context
(00000000000000000000000200004001000015A00100015141434C)

And the Key-ENC is

(F995D0A069335C7DF42E590317FFEA6D)

Where I am wrong or what I have forgot?
Any help would be appreciated.

Thanks in advance

Kind Regards
Agostino Sette





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