report on the use of trapdoor commitments in the SwissPost / Scytl e-voting system

https://people.eng.unimelb.edu.au/vjteague/UniversalVerifiabilitySwissPost.pdf

https://people.eng.unimelb.edu.au/vjteague/HowNotToProveElectionOutcome.pdf

https://people.eng.unimelb.edu.au/vjteague/HowNotToProveElectionOutcomeAddendum.pdf

March 12, 2019

The implementation of the commitment scheme in the SwissPost-Scytl mixnet uses a trapdoor commitment scheme, which allows an authority who knows the trapdoor values to generate a shuffle proof transcript that passes verification but actually alters votes. We give two examples of details of how this could be used. The first example allows the first mix to use the trapdoors to substitute votes for which it knows the randomness used to generate the encrypted vote. The second example does not even require knowledge of the random factors used to generate the votes, and could be used by the last mix in the sequence.

Any anon able to attach the PDFs? Not able atm.