How does POLYAS rule out multiple votes?

POLYAS uses a so-called token (a random number generated by the system) which, while maintaining voting secrecy, prevents voters from voting multiple times. It works like this: When an eligible voter uses their access data to login to the Online Voting System, a temporary token is generated that anonymizes their identity. If the eligible voter submits a binding vote, the token is sent to the electoral roll, where the voter is deleted. Once a voter is crossed off the electoral roll, they are unable to log in again because the system has noted that this voter has already received and used a token. In this way, multiple votes can be prevented while at the same time maintaining voting secrecy. 

After the election, the voting token is deleted and the relevant voter ID is marked in the electoral roll database.