Updatable threshold encryption from isogenies

Abstract. In this paper, we propose a new primitive called updatable threshold encryption (UTE) which is motivated by real-world applications. Namely one would like to encrypt extremely sensitive data, handle post-compromise and forward security and distribute trust amongst many parties for decryption. As one is interested in long-term security we also would like the scheme to be quantum-resistant.
UTE can be seen as a variant of updatable encryption (UE) with certain threshold properties. We introduce algorithms and security definitions for UTE and provide an instantiation with cryptographic group actions. In order to handle shares being revoked and new parties being added we introduce the first post-quantum dynamic secret sharing scheme based on group actions.