Timed-release encryption revisited

Abstract

Timed-release encryption (TRE) is a two-factor encryption scheme combining public key encryption and time-dependent encryption - decryption requires a trapdoor which is kept confidential by a time-server until at an appointed time. This paper revisits two recent results. In ESORICS 2007, Chalkias et al. proposed an efficient anonymous TRE scheme. Unfortunately, we show the security threats of their scheme in the presence of a curious time-server and an impatient recipient. Recently, Chow et al. proposed an encryption scheme in the standard model which can be used as TRE. Nevertheless, only confidentiality is guaranteed. We demonstrate how to support pre-open capability, which is often desirable in applications of TRE. Our extension also enables only the recipient to know the release-time from the ciphertext. This feature is not considered in previous notion of release-time confidentiality. © 2008 Springer Berlin Heidelberg.