flipperzero-firmware
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flipperdevices
PRNG error making Emulated NFC tags unreadable
Describe the bug.
while trying to debug a failing NFC emulation i came accross a small behavior i would like to share, maybe it can help making the NFC emulation a little bit better.
I have an NXP MIFARE Classic 1k tag, i read it with the flipper and it succeed with all keys found and all sectors read. now when i emulate it on the reader it does not work.
so i decided to use a proxmark3 to see the difference between what the flipper emulates and whats the real tag is sending. and here is the results:
This is when i read the REAL TAG with proxmark3 :
UID : 5a 2f 1c 93
ATQA : 00 04
SAK : 08 [2]
TYPE : NXP MIFARE CLASSIC 1k | Plus 2k SL1
proprietary non iso14443-4 card found, RATS not supported
No chinese magic backdoor command detected
Prng detection: WEAK
Valid ISO14443A Tag Found - Quiting Search
proxmark3>
And this is what proxmark3 sees when i emulate with the flipper:
UID : 5a 2f 1c 93
ATQA : 00 04
SAK : 08 [2]
TYPE : NXP MIFARE CLASSIC 1k | Plus 2k SL1
proprietary non iso14443-4 card found, RATS not supported
No chinese magic backdoor command detected
PRNG error: selecting tag failed, can't detect prng.
Prng detection error.
Valid ISO14443A Tag Found - Quiting Search
proxmark3>
we can notice that there is no difference except for the PRNG error , it says PRNG detection errors, and for now i can't say why we have this difference , is it a normal thing when emulating ? i think the PRNG error is causing the emulation to fail on some readers.
Reproduction
1 . Read a TAG with the Flipper and make sure you have all keys and sectors 2 . Read the same TAG with proxmark, and save the output (foucs on the PRNG part) 3 . Emulate the same TAG with the flipper on the proxmark reader and save the output (foucs on the PRNG part) 4 . You should notice that the emulated TAG with the Flipper results in a PRNG error while the Real TAG is not.
Target
No response
Logs
No response
Anything else?
No response
Hi, thanks for your feedback! Can you please provide the trace files of both reading attemps? They can be saved by running trace save -f <filename> right after the search command.
Sure, here is the Two trace files where :
nfctag-1 is the trace of the NFC tag flipper-1 is the trace of the flipper emulation
note sure if it can help, thank you for the effort :)
FYI, for this one i think i used another MIFARE CLASSIC 1k, so the UID is different from the one in bug description*
Hello @shelld0n ! Could you please specify proxmark firmware version that you use
