It was weird but I thought it might be fun to read.
I was discussing an issue on GitHub, regarding NFC app’s supported cards plugin: my card was supported, but plugin wasn’t working correctly. After developer’s response I found out that there was another set of MFC keys and that is why the plugin can’t detect the card properly. Fortunately, I had a veeeery old, almost unusable NFC tablet with android and MCT which had required keys (I don’t use it anymore, instead I have a phone for Android’s nfc-related tasks). Dev asked for a dump in FFF format and I agreed to send it.
I’ve checked 10 cards to see if keys are the same, created a new MCT’s .keys file to transfer it to the PC and then - to the Flipper’s user dict. And here starts the fun😁
My tablet is super-slow, it is impossible to run browser or even email client. Custom firmware it is on, is broken in so many ways, that there is no way to access internal memory from outside or send a file via Bluetooth. To be honest - NFC is the only function that works correctly. It doesn’t have SD-card slot either,so… How to move ~70 keys in hex format to the PC?
After copying around 7 keys by reading them from tablet’s screen and typing them on PC I thought “this isn’t a way”. So I took my flipper, created an empty MIFARE Classic 4k tag (~70keys were 800-something bytes, so 1K isn’t enough) and started emulation. On the tablet I formatted the tag as NDEF-formatted and wrote the keys as a plaintext. Then I read emulated tag on my phone, got keys, and added them to user’s dict. Voila! I used Mifare classic as an actual memory card!
1 Like
Sounds familiar, like a Nexus7 2012 …
I loved this tablet, but the hardware bug is so annoying. I would try to install the original Android 4.4 in your situation. I can tell no CM, LOS or other customs will work.
1 Like
You’ve guessed it! 
It is a Nexus 7 2012, my first nfc device. I updated to custom FW because was unable to install some app on 4.0.4, but now can’t roll back because too much data there can’t be transferred. That’s why it lies dormant in the shelf, keepeng the keys of old and no more existent systems