Issue with writing data to DESFire EV1 & EV2

[sbse]

Hi Guys

We have built a DESFire reader / writer based on a CLRC663+ with a credit card sized antenna.
The system allows us to authenticate with AES and read data from 32 byte files in encrypted mode.
We can also write data into the same files in encrypted mode but not the full 32 bytes of data.

Having tested with both DESFire EV1 and EV2 cards we do not end up with same result:

On EV1 cards we can write 22 bytes successfully, but trying to write more than 22 bytes of data results in _no_ response from the card.
On EV2 cards we can write 12 bytes successfully, but trying to write more than 12 bytes of data results in _no_ response from the card.

The cards may not come from the same manufacturer, but I would have expected this to be the reverse as the EV2 cards have a better read range.

All cards that we have tested are also checked using the TagInfo app on a Samsung S10.

The timeout for the transaction is set to max to ensure ample time for the write sequence to complete.
I have checked the power supply levels around the CLRC663+ chip to see if the supply voltage is dropping during a write but that does not seem to be the case.

Any suggestions or pointers would be much appreciate


Regards

Søren Bang

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[TapLinx Support]

Hi Søren,

I assume, the issue is in your reader. Generally, you can read any size of data block from the card. Here you must take attention, the reader buffer is limited. First, there is a reader buffer in card, and also buffer in the transport chain. But if you use larger blocks, automatically read extension will be used. This is not efficient, therefore I would not read more than 64 bytes in one chunk. 32 bytes data blocks should not be a problem.

Is it possible for you, to verify your software with a different approach? I mean you can check your software with a simple PC/SC USB reader and a desktop software. Or, if possible, with a simple Android app and TapLinx SDK. There is no GUI required, only the NFC communication and log output is needed to verify your reader implementation.

The TapLinx team

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[sbse]

Hi Team

Thank You for your reply - I'll take another look at our antenna matching as that could limited the power delivery to the transponder.

One other question : Does the DESFire EV2 chip require more power to work than the EV1 ?


Regards

Søren

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[TapLinx Support]

Hi Søren,

The field strength requirement of the MIFARE DESFire EV2 is <1.5A/m. This is quite lower as from ISO/IEC required. The EV2 need less energy in boot process and therefore it is slightly faster. The most commands for security requires the same energy as for the EV1 (more or less).

The TapLinx team

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