Proxmark3 community

tck

Member

Registered: 2011-04-06

Posts: 7

Strange LF Tag (What's that?)

Hi all,

i'm currently working with lf tags and it's still new and a little bit challenging for me. So a few days ago i've got an lf tag for a public car garage in my hometown. You can store an small amount of money on the tag and pay your parking fee from that credit without consulting the cashing machine. The tag is in classic credit card size with a nice logo on its front and a short number (324) on the back. With hw tune i could check that the tag must be lf.

So i did: lf read, data samples 4000, data plot  and then i've got that:

From my view askdemod or fskdemod does not make any sense. So, has anyone seen something similar before? Somewhere? I would be very glad for any type of hint, cause i'm very curious in what type of tag this is and what type data structure is on the tag? Just an UID ...

Cheers
TcK

tck

Member

Registered: 2011-04-06

Posts: 7

Re: Strange LF Tag (What's that?)

More info ... if you do an "data autocorr" on the sample, you get an flat line.

When i put the card on my lf antenna i get that:

proxmark3> hw tune
#db# Measuring antenna characteristics, please wait.                 
         
         
# LF antenna: 12.08 V @   125.00 kHz         
# LF antenna: 23.50 V @   134.00 kHz         
# LF optimal: 24.57 V @   134.83 kHz         
# HF antenna:  0.13 V @    13.56 MHz         
# Your HF antenna is unusable.         
proxmark3> hw tune
#db# Measuring antenna characteristics, please wait.                 
         
         
# LF antenna:  4.57 V @   125.00 kHz         
# LF antenna:  4.70 V @   134.00 kHz         
# LF optimal:  7.92 V @   169.01 kHz         
# HF antenna:  0.13 V @    13.56 MHz         
# Your LF antenna is marginal.         
# Your HF antenna is unusable.

Never saw such an voltage drop on any other card!!!

Doing the same with my hf antenna, it looks like this (just for the sake of completeness):

proxmark3> hw tune
#db# Measuring antenna characteristics, please wait.                 
         
         
# LF antenna:  0.13 V @   125.00 kHz         
# LF antenna:  0.13 V @   134.00 kHz         
# LF optimal:  0.40 V @   480.00 kHz         
# HF antenna:  8.93 V @    13.56 MHz         
# Your LF antenna is unusable.         
proxmark3> hw tune
#db# Measuring antenna characteristics, please wait.                 
         
         
# LF antenna:  0.13 V @   125.00 kHz         
# LF antenna:  0.00 V @   134.00 kHz         
# LF optimal:  0.40 V @   230.77 kHz         
# HF antenna: 11.21 V @    13.56 MHz         
# Your LF antenna is unusable.         

First "hw tune" is without the card in the field.  Any clues, hints or ideas??? If so, pleeeeease let me know!