How to design your own map?

Question

Payment systems

Hello
There was a need to develop a system for working with the phone with "payment" cards
. There is no understanding of working with such things at all. I would like someone who has an understanding to give a tip how such tasks can be solved and where to dig.
1. It is necessary to develop a system in which there will be cards that contain a user ID. 2. The map will contain not only the identifier, but also the key. The amount of the operation is transferred to the card, the signing is performed on the card, and the terminal already transfers the signed operation by the card to the computer. (Not sure if this is the case) How do I program the card so that it can encrypt? How do you program cards? (I read only about JavaCard). Thanks in advance for your replies!
A balance in points is tied to this user, it doesn’t matter in rubles. At the time of payment, we check that the specified user has the amount and it can be debited. That is, the terminal reads the user ID and gives it to the computer, or does the terminal do all the work?
How to write this identifier to the card?
How to count and what will allow counting?

Answer 1

Judging by your description, you want to do something similar to Google Pay and Apple Pay
, here is a good article describing how everything works for them
https://habr.com/en/post/422551/
There are many references to ISO in the text standards, generally accepted protocols, etc.
Many of them are easy to google and read to learn even more details and wonder.
sim3x wrote everything to you correctly - without experience in this area, the chances are almost zero. Well, or you will be hacked right away.

Answer 2

Arduino or Raspberry + NFC module can help you to write / read from contactless media. And then it’s a matter of programming techniques and program interaction)