Creating a Decryption Proof Verifier for the Estonian Internet Voting System

This paper describes the efforts made for and lessons learnt from creating a decryption proof verifier for the Estonian IVXV Internet voting system. Our main conclusion is that cryptographic protocols aiming at providing transparency through verifiability should also take into account a non-functional requirement of low implementation complexity. We identify several steps of the verification protocol that could be made easier to implement without sacrificing security. A side-product of our effort is a fully functional IVXV decryption proof verifier written in Go that we used during the latest Estonian parliamentary elections of March 2023.