Your next communication protocol is sound. Sounds about right.
Whisper
Idea
Workshops that we instruct are jam-packed with students. It is tough to mark the attendance of each and every student. Whisper can be set up on a kiosk for all rollcall purposes. Not to mention: leaving attendees in a state of absolute awe.
Your kiosk is in for a renovation.
Whisper is an attendance-managing app which exchanges secure tokens via sound.
A server is planted on a table which listens for Whispers from devices of attendees, employees and volunteers. Whenever a device throws in a Whisper; the data (token) is decoded into a byte array and the hash of the token is generated and sent back to the user device, again, through a Whisper. This hash is compared with a local hash generated by the device. If the two hashes equate, the device is marked present.
Demo