Paper 2021/558

Verifiable Decryption in the Head

Kristian Gjøsteen and Thomas Haines and Johannes Müller and Peter Rønne and Tjerand Silde

Abstract

In this work we present a new approach to verifiable decryption which converts a 2-party passively secure distributed decryption protocol into a 1-party proof of correct decryption. To introduce our idea, we first present a toy example for an ElGamal distributed decryption protocol before applying our method to a lattice-based scheme. This leads to an efficient lattice-based verifiable decryption with only one server; it has lightweight computations as we reduce the need of zero-knowledge proofs. We believe the flexibility of the general technique is interesting and provides attractive trade-offs between complexity and security, in particular for the interactive variant where the online phase can be very efficient.