QR code validation app

We want a server back end that will initially be on a hosted platform but eventually sit on a local server which we will set up. It will:
1) Creates the unique bar codes with an encrypted key (maybe 30 alpha numeric) this code being held as a listing on the server
2) Ability to print QR codes of the encrypted key to printer within a custom created document.
3) a database of people that have their own unique ID code, email and phone fields.
4) Ability to print ID cards for each user with a QR code of their ID code.

Then we need an App for Ios, Android, windows, Mac and Linux. The App will
1) Scan the encrypted key QR code that has been printed
2) Scan the QR code of the person sending or receiving the printed encrypted key
3) Send this information to the Server
4) Allow for multiple QR codes to be scanned offline and then send them to the server when online.

The program on the server will then match a chain of events and validate that the QR code has not been passed to 2 different people.
Then send a validation back to the App validating each or all of the keys.

A bit more is to explain but this is essentially how it works.