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#1 2018-09-27 18:06:46

JohnDoePM
Contributor
Registered: 2018-07-08
Posts: 3

Problem to decide if Mifare Classic 4k has 4 byte or 7 byte UID

Dear community,

my aim is to make a working clone of a Mifare classic 4k. The card belongs to a Salto 4XS system. This is the card:

proxmark3> hf search
          
 UID : ** ** ** **           
ATQA : 00 02          
 SAK : 18 [2]          
TYPE : NXP MIFARE Classic 4k | Plus 4k SL1          
proprietary non iso14443-4 card found, RATS not supported          
No chinese magic backdoor command detected          
Prng detection: HARDENED (hardnested)          

Valid ISO14443A Tag Found - Quiting Search
          
proxmark3> 

What I have done:
I bought a 4K Mifare UID Modifiable card from Lab401:

proxmark3> hf search
          
 UID : ** ** ** **           
ATQA : 00 02          
 SAK : 18 [2]          
TYPE : NXP MIFARE Classic 4k | Plus 4k SL1          
proprietary non iso14443-4 card found, RATS not supported          
Chinese magic backdoor command (GEN 1b) detected          
Prng detection: WEAK          

Valid ISO14443A Tag Found - Quiting Search
          
proxmark3> 

With the Mifare Classic Tool I read the complete card with all keys.
On the card I like to clone it says regarding generic tag info:

UID:
********(4 byte)
RF Technology:
ISO/IEC 14443, Type A
ATQA:
0002
SAK:
18
ATS:
-

Then I set blocks 0 to 3 of the UID modifiable card with a Proxmark 3 by

proxmark3> hf mf csetblk

After that, I assured that with a

proxmark3> hf mf rdbl 0 A A0A1A2A3A4A5

I can read block 0 (1,2) of the card with the (standard) keys I wrote to the trailer sector.

In addition, I wrote all the other sectors (except sector 0) from the card dump to the UID modifiable card. After that, again I read the now complete card with the MFC and assured that the content of the UID modifiable card is completely identical with the dump on my phone.

What 's my problem:
If I try the card on any doors, I get error code: Not an authorized Salto card format.
Explanation from here, page 2, last entry.

What 's my question:
Could it be possible that the card I try to clone has a 7 byte UID instead of the 4 byte of my modifiable card ? How can I distinguish that ? How can the reader interpret two cards with the same content in different ways ? How can I correct that ? Do I need 7 byte UID modifiable cards ?

What is more, I have a few other dumps of cards of that system on my phone. None of them have identical bytes at the beginning of block 0, sector 0. How could this come, as I tended to think that all cards from a manufacturer have identical bytes at the beginning of block 0 ?

Best regards,

JD.

Last edited by JohnDoePM (2018-09-27 18:24:14)

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#2 2018-10-03 18:57:40

ImSchatten360
Contributor
Registered: 2018-06-21
Posts: 4

Re: Problem to decide if Mifare Classic 4k has 4 byte or 7 byte UID

Hi JohnDoePM,

I probably cannot help you with your problem but I have a question regarding your description.
Do I understand correctly that all blocks on both cards are identical except block 0?
You only wrote the first 4 bytes of block 0 of your 4K Mifare UID Modifiable card?
How does the rest of block 0 look like? Are there any differences?

I ask because at the moment I have an issues with a copied card as well as it is not recognized. It is a different system and only a 1K Mifare card but that is why I ask if there are any differences in block 0 or if both your cards are fully identical.  I have heard that some readers can identify Chinese backdoor cards and do not accept them. Maybe this is the case with your Salto 4XS system and your GEN 1b card as well.

In another thread different kind of cards are discussed:

iceman wrote:

CUID
magic card, generation 2,   block0 writeable serveral times, with normal mifare commands.
Purpose:  to be used with any rfid reader/writer which supports mifare (like a smartphone)

FUID
unfused card, or write-once card.  Normal card but you can re-write UID once , with normal mifare commands.
Purpose:  parking/elevator system with "anti-clone" feature where it "re-writes" block 0, effectivly making sure your clone doesn't work.

UFUID
Magic card, generation 1a,  answers to backdoor commands

Some user later suggests that UFUID can be fused so that it does not answer to backdoor commands anymore.

If you cards are fully identical maybe the reader checks for backdoor commands and one of these more sophisticated special cards can get you around that additional check. But I do not even know if such cards exist for the 4K Mifare.

Cheers

ImSchatten360

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#3 2018-10-11 06:40:12

henc
Contributor
Registered: 2017-05-13
Posts: 8

Re: Problem to decide if Mifare Classic 4k has 4 byte or 7 byte UID

Have a look at sectors 35 to 39 - did you also change those? wink

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