Help with MSE:SET command for ECDSA signing with non-repudiation key

[Mamisoa Andriantafika]

I'm trying to implement digital signature using the Belgian eID card's non-repudiation key. I've successfully:
1. Selected the Belpic applet (AID: A0 00 00 00 30 29 05 70 00 AD 13 10 01 01 FF)
2. Selected the non-repudiation key file (path: 3F 00 DF 00 50 38)

However, I'm getting stuck at the MSE:SET command. Here's my current workflow:

1. Select non-repudiation key file:
   ```
   Command:  00 A4 08 0C 06 3F 00 DF 00 50 38
   Response: SW1=0x90, SW2=0x00 (Success)
   ```

2. Set up security environment with MSE:SET:
   ```
   Command:  00 22 41 B6 06 80 01 40 84 01 83
   Response: SW1=0x67, SW2=0x00 (Wrong length)
   ```

The MSE:SET command data consists of:
- Algorithm reference (80 01 40): ECDSA mechanism
- Key reference (84 01 83): Non-repudiation key

I've tried several variations:
- Different algorithm references (01 for SHA-256, 40 for ECDSA)
- Different key references (82, 83)
- Different command structures (with/without algorithm reference)

But I keep getting SW1=0x67, SW2=0x00 (Wrong length) for all attempts.

Questions:
1. What is the correct MSE:SET command structure for ECDSA signing with the non-repudiation key?
2. Should the algorithm reference (tag 0x80) specify ECDSA or SHA-256 or both?
3. Is there a specific order or format required for the TLV data?

Environment:
- Belgian eID card (latest)
- Linux 6.8.0-51-generic
- Python with pyscard

I feel my difficulties come from the understanding of MSE:SET command:
Data: Length of following data =’04’ ||
Tag for Algorithm reference =’80’ ||
Algorithm reference (refer to Table 14) ||
Tag for private key reference =’84’ ||
Private key reference (refer to Table 16) = ‘82’, ‘83’

--> can you give me an example ? What means "length of following data" ?

Any help or pointers to documentation would be greatly appreciated.

[Frederik Vernelen]

Hello,

The key and algo references are both only 1 byte long.
So the LC byte (Length of subsequent data field) is '05'
"0x04 as Length of following data" means 4 bytes will follow

You can find a good example in the minidriver here:
https://github.com/Fedict/eid-mw/blob/master/cardcomm/minidriver/src/SmartCard.c#L755C7-L755C14

 /* Prepare SET COMMAND before a VERIFY PIN */
   Cmd [0] = 0x00;
   Cmd [1] = 0x22;   /* MSE: SET COMMAND */
   Cmd [2] = 0x41;
   Cmd [3] = 0xB6;
   Cmd [4] = 0x05;
   Cmd [5] = 0x04;   /* Length of following data      */
   Cmd [6] = 0x80;   /* ALGO Rreference               */
   Cmd [7] = bAlgo;//0x01;   /* RSA PKCS#1                    */
   Cmd [8] = 0x84;   /* TAG for private key reference */
   Cmd [9] = bKey; /*0x82 for AUTH, 0x83 for NONREP*/
   
Wkr,
 Frederik

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[Mamisoa Andriantafika]

Thanks a lot for your help !