Coercion-freeness in e-voting via multi-party designated verifier schemes

In this paper we present how multi-party designated verifier signatures can be used as generic solution to provide coercion-freeness in electronic voting schemes. We illustrate the concept of multi-party designated verifier signatures with an enhanced version of Ghodosi and Pieprzyk [GP06]'s threshold signature scheme. The proposed scheme is efficient, secure, allows distributed computations of the signature on the ballot receipt, and can be parameterized to set a threshold on the number of required signers. The security of the designated verifier property is evaluated using the simulation paradigm [Gol00] based on the security analysis of [GHKR08]. Unlike previously provable schemes, ours is ideal, i.e. the bit-length of each secret key share is bounded by the bit-length of the RSA modulus.