[Event registration] Expiring check in qr codes

[jucktnich]

See #442 and #413

Current Implementation

In version 2.0 a feature will be integrated to check in to events. It can't be prevented, that users "false check ins" (See Luca app). Although doing this on CWA is harder than on Luca and not so harmful, it is an issue tough.

Suggested Enhancement

Use expiring qr codes to prevent people from checking in to locations they aren't via over social media shared codes. To prevent this hosts are reminded to change they're codes ones a day, when they aren't open. Changing these codes while they're open would break tracing. The qr code should be displayed on f.e. a tv screen, to let it change ever f.e. 5 min.

This can be done in two ways I think:

• Use signing technologies like on the web, with a CWA server as a CA.

• Or use a concept like the one described below: (Information about the graphic: Generation of the keys should be done on the host device, and only the public key should be sent to the server (sorry, the website I was using was closed, so I wasn't able to change it); the authentication process is needed to prevent user from just changing the timestamps)

Expected Benefits

Prevent false check ins while making it possible (with more adjustments) to create bigger events.

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Internal Tracking ID: EXPOSUREAPP-6087

[dsarkar]

@jucktnich Thanks for contributing here. What is the difference to #413?

[dsarkar]

Internal Tracking ID: EXPOSUREAPP-6087

[jucktnich]

I think the difference is, that in this solution there is the same ID every time used, with a time stamp and the other issue uses, if I got it right every time another ID.

Here's the message on the right place