- phone displays the generated ticket to the ticket scanner in the bus. - the scanner connects to the backend to verify the ticket.

this way the phone can remain offline after registration, and only need to get online to send money for your account.

i see no way for possible fraud as in fact all the ticket is doing in that case is to verify your identity to the server.

now how can we do the same thing but without revealing your identity, but just verifying that you paid?