UID Changeable cards are used to duplicate Mifare Classic 4K access cards. Whilst generally it is best practice to use unique Mifare Classic 14443A cards for each user, there are some instances where you may wish to clone a card and have multiple cards with the same UID and data. For example access control with few users with no user having the ability to add new cards into the system. Or for access control that has a user limit which has been reached. All three types of cards can be programmed with the Proxmark3, ACR122U or ICopy-xs.
hf mf gen3uid --uid 11223344556677
Mifare Gen3 Proxmark Commands (Iceman Firmware)
# change just UID: hf mf gen3uid # write block0: hf mf gen3blk # lock (uid/block0?) forever: hf mf gen3freeze
script run hf_mf_gen3_writer -h
# change just UID: hf 14a raw -s -c -t 2000 90FBCCCC07 11223344556677 # read block0: hf 14a raw -s -c 3000 # write block0: hf 14a raw -s -c -t 2000 90F0CCCC10 041219c3219316984200e32000000000 # lock (uid/block0?) forever: hf 14a raw -s -c 90FD111100
By ACR122U (PCSC Mifare Secure)
The UID of MIFARE Classic® Compatible 4K UID Tags is comprised of two parts: the UID itself, and the BCC. The BCC is a checksum value calculated from the UID. If the BCC is incorrect, tag will be rejected by the reader.
Most RFID tools, such as the Proxmark, LibNFC, MCT etc automatically calculate the BCC when the UID is modified. If you are modifying the UID by hand, it is vital that the BCC is correctly calculated.
KSEC cannot provide support or refunds under any circumstances for cards that were ‘bricked’ due to incorrect UID/BCC configuration.