UG4 - Disable Gen2 CUID until needed?

Support
1

Hello all, I was wondering if there’s a command that someone is aware of for the FlexUG4/my UG4 card to disable the Gen2 CUID functionality until it’s needed/wanted? I changed the Gen4 creds on the device to prevent tampering, but I’d like to disable the Gen2 CUID functionality so a reader wouldn’t theoretically be able to detect it. Note: I have a PM3 RDv4 that I use to work on the cards.

[usb] pm3 --> hf mf info

[=] --- ISO14443-a Information ---------------------
[+]  UID: aa bb cc dd 
[+] ATQA: 00 04
[+]  SAK: 18 [2]

[=] --- Keys Information
[+] loaded  2 user keys
[+] loaded 61 keys from hardcoded default array
[+] Sector 0 key A... FFFFFFFFFFFF
[+] Sector 0 key B... FFFFFFFFFFFF
[+] Sector 1 key A... FFFFFFFFFFFF
[+] Block 0.......... aa bb cc dd 1C 00 00 11 77 81 85 BA 18 00 00 00 

[=] --- Fingerprint

[=] --- Magic Tag Information

[+] Magic capabilities... Gen 2 / CUID   <- I want to toggle this at will.

[=] --- PRNG Information
2

I think you can disable block 0 direct write with the following command:
hf 14a raw -s -c -t 1000 CF<passwd>CF01

as outlined here:

01: Deactivate direct write to block 0 (Same behaviour of vanilla cards)

2 Likes
3

Awesome, thank you so much! I somehow missed that it applied to Magic Cards.

4

This generally won’t be an issue because it would require both sector keys and the willingness of the reader to attempt to write to sector 0 which is a potentially destructive operation. Gen1 back door checking is far more likely as it’s non-destructive and has no possible protections / keys needed.

Gen4 command checking is very likely to become the next phase of reader checks vs gen2 sector 0 attempted writes.

3 Likes
5

Good point.