Tree-Homomorphic Encryption and Scalable Hierarchical Secret-Ballot Elections

In this work we present a new paradigm for trust and work distribution in a hierarchy of servers that aims to achieve scalability of work and trust simultaneously. The paradigm is implemented with a decryption capability which is distributed and forces a workflow along a tree structure, enforcing distribution of the workload as well as fairness and partial disclosure (privacy) properties. We call the method “tree-homomorphic” since it extends traditional homomorphic encryption and we exemplify its usage within a large scale election scheme, showing how it contributes to the properties that such a scheme needs. We note that existing design models over which e-voting schemes have been designed for, do not adapt to scale with respect to a combination of privacy and trust (fairness); thus we present a model emphasizing the scaling of privacy and fairness in parallel to the growth and distribution of the election structure. We present two instantiations of e-voting schemes that are robust, publicly verifiable, and support multiple candidate ballot casting employing tree-homomorphic encryption schemes. We extend the scheme to allow the voters in a smallest administrated election unit to employ a security mechanism that protects their privacy even if all authorities are corrupt.