Abstract
To provide universal verifiability, cryptographic voting protocols often require a broadcast channel to spread the election data to the public. The basic requirements on such a broadcast channel are similar for most protocols, for example that the channel maintains a memory of all broadcast messages and that nothing can be deleted from the channel’s memory. In this paper, we provide a formal definition for such broadcast channels with memory and describe their properties. We also analyze the significance of a broadcast channel with memory in cryptographic voting protocols and propose that such a channel is provided in form of a service that we call bulletin board. Based on this service, we analyze some real-world problems that cryptographic voting protocols might have and provide possible solutions. For this we define a generic interface for the main board functionalities, which offers a flexible way of extending the basic properties of a bulletin board to comply with all sorts of additional requirements.
Highlights
The concept of a bulletin board (BB) is an important building block to achieve universal verifiability in cryptographic voting protocols
From a conceptual point of view, a BB is often regarded as a broadcast channel with memory (BCM), which is a theoretical model of an ideal channel with very specific properties (Cramer, Gennaro, and Schoenmakers 1997a; Peters 2005)
We introduced a formal model for a broadcast channel with memory and defined its ideal functionality
Summary
The concept of a bulletin board (BB) is an important building block to achieve universal verifiability in cryptographic voting protocols. A common approach is to substitute the broadcast channel with memory by one or multiple additional parties participating in the protocol These parties provide the service of accepting and memorizing the messages transmitted over the broadcast channel during the protocol execution. There are numerous operational problems, for example, separating the election data when multiple elections run in parallel, opening and closing the electronic ballot box, archiving the election data when the protocol terminates, or ensuring consistent views for all users reading data from the board. This leads to highly specific implementations of bulletin boards, essentially one for each voting system. The security of the cryptographic protocol gets undermined by an insecure BB implementation
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