Timed-release computational secret sharing scheme and its applications

Abstract

A secret sharing scheme is an important cryptographic primitive. In this paper, we focus on a computational secret sharing (CSS) scheme, which is a practical, simple secret sharing scheme, with timedrelease functionality, which we call a timed-release computational secret sharing (TR-CSS) scheme. In TR-CSS, participants more than or equal to a threshold number can reconstruct a secret by using their shares only when the time specified by a dealer has come. Our TR-CSS can be regarded as a natural extension of Krawczyk’s CSS, and we finally succeed to add timed-release functionality to Krawczyk’s CSS with small overhead, which seems to be almost optimal. Moreover, we show our proposal of TR-CSS is important for constructing threshold encryption and multiple encryption with timed-release functionality in a generic and efficient way.