MIFARE DESFire Light Invalid Command String Error

[wilmer_suarez]

I am attempting to write to a MIFARE DESFire Light card using the Write Data command in ISO/IEC 7816 APDU Wrapping and native chaining. The card has a Standard File of size 256. I'm attempting to write exactly 256 bytes but I keep getting a response of "0x917E - Length of command string invalid". I've attempted to make the frame different sizes but that does not help. The datasheet says the card has a frame size of 128 bytes by default; but I still get the same error, so that cannot be the issue.

I tried writing just 7 bytes and that works, so the issue must be length parameter (3 bytes - little endian). If the file size is 256 I should be able to write 256 bytes, no? So, the length parameter should be 00 01 00.

Here's a byte view of the first frame that I'm sending to the card:

C-APDU --> 90 8D 00 00 71 00 00 00 00 00 01 00 |--- 87 bytes of data ---| 00

R-APDU <-- 91 7E

[Kan_Li]

Hi,

According to the data sheet, up to 248 bytes are allowed to write in one time. Please refer to the following for details.

Have a great day,
Kan

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[wilmer_suarez]

Yes, I have seen this. If 248 bytes are allowed then why wouldn't 87 bytes (+ the MAC) work? My reader's FIFO is limited to 128 bytes. My problem is that the tag isn't responding with an AF status to send the rest of the data. Right now I've forgone the chaining mechanism and I'm manually keeping track of the bytes to send and that seems to be working.

[Kan_Li]

That is because the comm mode is full and data filed includes secure messaging. Please refer to the following for details.

so due to the padding, you can only write 239 bytes in one command, and the same rule applies for the read operation.

Hope that makes sense,

Have a great day,
Kan

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[wilmer_suarez]

I'm attempting to do the same using RFIDDiscover; but I keep getting the error:

Recv from card: Error, Error: HAL,BUFFER_OVERFLOW
How do I change the buffer size?

[Kan_Li · Accepted solution]

I created a doc and video on that topic, please kindly refer to MIFARE DESFire Light read and write demonstration for details.

Hope that helps,

Have a great day,
Kan

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[wilmer_suarez]

Yes, thank you. This helped a lot.