Paper 2022/373

Blind accumulators for e-voting

Abstract

We present a novel cryptographic primitive, blind accumulator, aimed at constructing e-voting systems. Blind accumulators collect private keys of eligible voters in a decentralized manner not getting information about the keys. Once the accumulation is complete, a voter processes the resulting accumulator and derives a public key which refers to a private key previously added by this voter. Public keys are derived deterministically and can therefore stand as fixed voter pseudonyms. The voter can prove that the derived key refers to some accumulated private key without revealing neither that key nor the voter itself. The voter uses the accumulated private key to sign a ballot. The corresponding public key is used to verify the signature. Since the public key is fixed, it is easy to achieve verifiability, to protect against multiple submissions of ballots by the same voter or, conversely, to allow multiple submissions but count only the last one. We suggest a syntax of blind accumulators and security requirements for them. We embed blind accumulators in the Pseudonymous Key Generation (PKG) protocol which details the use of accumulators in practical settings close to e-voting. We propose an instantiation of the blind accumulator scheme whose main computations resemble the Diffie-Hellman protocol. We justify the security of the proposed instantiation.

Note: Made the text more rigorous, added an appendix on contexts.