I have got a NFC key to enter in my room and i want to make a copy of this key in case of loss. I read the nfc tag key with my nexus 5 with Broadcom BCM20793M NFC controller. The phone reads the tag and retrivies all the infos but when i try to copy the tag it gives an "Error reading the tag" message. The tag is a NXP MIFARE Classic. I read that it is not compatible with the newest chips so i wanna buy an Arduino NFC reader to read and copy the tag.
Might it works?
Below all the infos retrieved from the nfc key: 
Answer
The info you you shown us here is just the basic data that a mifare tag gives out (the only relevant info is actually the serial number). But in a mifare tag, there is also an EEPROM zone (1kbytes) that can be configured with custom data, and the contents of this zone is not displayed here. This zone can also be configured with read and/or write protections with custom keys.
Now, the system you are trying to "hack" can work in two ways:
- Either the reader knows the serial number of all the cards it should accept, in which case the card itself is not configured with relevant data in the 1k zone. In this case, to copy a card, you only need to copy its serial number. However, serial numbers in mifare cards are set in the factory and cannot be overridden, so you're doomed.
- Or the reader reads a particular area in the 1k zone, which says if the door should open or not. In this case you need to copy the 1k area from a card to the other. The problem is: it seems the phone can't read this area, probably because read access has been protected by a custom key. So it seems you're doomed anyway.
Usually, smart cards are made to be not copyable.
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