Publication of proof of cryptographic protocol

Publication of proof of cryptographic protocol 22.03.18

Swiss Post is publishing documents concerning the cryptographic protocol for its system. Specialists from the ETH Zurich have verified that the mathematical proofs contained in the protocol are correct and conform to the Swiss regulation. The cryptographic protocol sets out the encryption methods used.

Any e-voting system must meet the strict security requirements of the Swiss Confederation before it can be used in a Swiss electoral contest. The system and the way in which it is operated must be examined in detail based on various criteria, including the cryptographic protocol. This is a complex mathematical document which describes the various encryption methods used.

The exact verification criteria for an e-voting encryption protocol can be found under section 5.1 of the appendix to OEV. The cryptographic protocol proof must be provided or verified by highly specialized institutions. The choice of organization must be approved by the Federal Chancellery in advance.

A team of experts of the ETH has examined the cryptographic protocol according to the criteria of the Confederation. These experts concluded that the proof provided is correct and that the protocol satisfies federal legal requirements.

Two documents relating to the Scytl system were used by the team of experts of the ETH as the basis for examining the cryptographic protocol. These can both can be viewed on the Swiss Post website:

  1. “Swiss Online Voting System – Cryptographic proof of Individual Verifiability”
    (a description of the protocol for the e-voting system used in Switzerland for up to 50% of the cantonal electorate)
  2. “Analysis of Cast-as-Intended Verifiability and Ballot Privacy Properties for Scytl’s Swiss Online Voting Protocol using ProVerif”
    (a report on the automatic proof of individual verifiability and voting secrecy for the protocol using ProVerif)

The Swiss Post e-voting solution is based on a state-of-the-art system developed by the company Scytl. Scytl defined the cryptographic protocol for the system used for 50% of the electorate in a canton in conjunction with two renowned universities in this field (the University of Birmingham and Lorraine research laboratory in computer science and its applications).

Once the Swiss Post system is used for 100% of the electorate in a canton, further requirements will need to be met and corresponding proof will need to be provided (universal verifiability).