Cryptographic Voting Protocols: A Systems Perspective

Cryptographic voting protocols offer the promise of verifiable voting without needing to trust the integrity of any software in the system. However, these cryptographic protocols are only one part of a larger system composed of voting machines, software implementations, and election procedures, and we must analyze their security by considering the system in its entirety. In this paper, we analyze the security properties of two different cryptographic protocols, one proposed by Andrew Neff and another by David Chaum. We discovered several potential weaknesses in these voting protocols which only became apparent when considered in the context of an entire voting system. These weaknesses include: subliminal channels in the encrypted ballots, problems resulting from human unreliability in cryptographic protocols, and denial of service. These attacks could compromise election integrity, erode voter privacy, and enable vote coercion. Whether our attacks succeed or not will depend on how these ambiguities are resolved in a full implementation of a voting system, but we expect that a well designed implementation and deployment may be able to mitigate or even eliminate the impact of these weaknesses. However, these protocols must be analyzed in the context of a complete specification of the system and surrounding procedures before they are deployed in any large-scale public election.