# Distributed Ballot Based Protocol

This example protocol implements the task of Quantum E-voting. In this protocol, the election authority prepares and distributes to each voter a blank ballot, and gathers it back after all voters have cast their vote in order to compute the final outcome.

## Assumptions

• The tallier is assumed to be trusted to correctly prepare specific states.

## Outline

In the beginning, the election authority prepares an N-qudit ballot state where the kth qudit of the state corresponds to ${\displaystyle V_{k}}$’s blank ballot and sends the corresponding blank ballot to ${\displaystyle V_{k}}$ together with two option qudits, one for the “yes” and one for the “no” vote. then each voter decides on “yes” or “no” by appending the corresponding option qudit to the blank ballot and performing a 2-qudit measurement, then based on its result she performs a unitary correction and sends the 2-qudits ballot along with the measurement result back to the election authority. At the end of the election, the election authority applies a unitary operation on one of the qudits in the global state and another unitary operation on one of the qudits to find the number of yes votes.

## Notations

• ${\displaystyle V_{i}:i^{th}}$ voter
• c: number of possible candidates
• N: number of voters
• ${\displaystyle v_{i}}$: vote of ${\displaystyle i^{th}}$ voter
• T: election authority
• m: number of yes votes

## Requirements

• Quantum channel capable of sending qubits -> (qudit) between the election authority and voters
• Qudit Measurement Device for election authority and voters

## Properties

This protocol is vulnerable to double voting. Specifically, an adversary can mount a “d-transfer attack”, and transfer d votes for one option of the referendum election to the other.

## Further Information

*contributed by Sara Sarfaraz