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Help Is my phone behaving similar to proximity cards?

jstuardo

jstuardo

Lurker
Hello,

I need to understand this in order to use it in my work.

I work with access control systems. One of the hardware I use is proximity card readers, which read both 13,56 MHz and 125 kHz cards.

Accidentally I put my Samsung S20 phone near the reader and my surprise was that the reader did some readings.

Then I have opened Notepad and put the phone near the reader again and I saw that reader have read several numbers. For example, I have just put my phone in the reader and this was read:

4029234184
3629474568
1516677640
3332058120
2247351560
1729290504
0046941192
0967781384

It was like I have placed 8 proximity cards but in this case, all are contained inside my phone.

Can anybody explain me how this is happening? Is there an application that is allowing the phone to act as proximity cards? numbers read are always different every time.

The number of cards read depends on how long I keep the phone near the reader.

Thanks in advance,

Jaime
 
Looks like your phone's NFC is interacting with these whatever it is "proximity cards". What those number mean, no idea. Access control systems and pass-cards can use NFC technology.

FYI some public transports, like subways and buses, use contactless fare-cards that work via NFC. And sometimes they have a payment app, so you can use your phone's NFC instead of swiping a card at the turnstiles and gates.
 
Thanks for your reply, but I need to know how the phone behaves like that. Is there an app that generates random numbers continually and if I place the phone near a reader, those random numbers are read? Can I disable that random numbers generation (without disabling NFC)?

I am a developer who has a system that uses proximity cards to recognize people belonging to a company. If I can develop an app that sends, via NFC, always the same number (for example, the person's DNI number) I could allow the customers to use their own phones instead of purchasing proximity cards for all staff, which is worth a high price.

Regards
Jaime
 
Not a developer so I have no idea how they work. Maybe if you want we can get a mod to move this to the developer forum. I would also re-word your op for this thread mentioning that you are a developer.
 
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ocnbrze said:
Not a developer so I have no idea how they work. Maybe if you want we can get a mod to move this to the developer forum. I would also re-word your op for this thread mentioning that you are a developer.
Click to expand...

Hello.... it could be, however, question is not directly related to development. The question is for understanding how the phone works.

I have purchased a Samsung S20 phone. I have not installed any NFC app however, for some reason, phone is generating random numbers and send them through NFC interface. I need to disable that behavour, or if it is there any application that does that, I need to know how to discover which app is doing that.

After all that is understood and solved, I could post a question in the development forum if i got problems with NFC interface programming.

Regards
Jaime
 
ocnbrze said:
well i think most folks here would not know the science behind how NFC works. i have no idea how it works.

i did find this:https://squareup.com/us/en/townsquare/nfc

in the article nfc uses encryption to communicate, so those numbers you see are part of the encryption and who knows what they represent.
Click to expand...

Hello, never mind. I have asked in other Samsung forum also. I know how NFC actually works. The question is really why the phone is generating those numbers without my permission.

If I finally develop an application to send person's DNI, phone will also send those random number, which of course will affect my application.

Regards
Jaime
 
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