Efficient generic constructions of timed-release encryption with pre-open capability

Abstract

Timed-release encryption with pre-open capability (TRE-PC), introduced by Hwang et al. in 2005, is a cryptosystem with which a sender can make a ciphertext so that a receiver can decrypt it by using a timed-release key provided from a trusted time-server, or by using a special information called pre-open key provided from the sender before the release-time, and thus adds flexibility to ordinary TRE schemes in many practical situations. Recently, Nakai et al. proposed a generic construction of a TRE-PC scheme from a public-key encryption scheme, an identity-based encryption scheme (with some special property), and a signature scheme. Concrete TRE-PC schemes derived via their generic construction are, however, not so practical because of the used building block primitives. Motivated by this situation, in this paper we propose two new generic constructions of TRE-PC schemes. Both of our constructions follow the basic idea behind the generic construction by Nakai et al. but overcome its inefficiency without losing " generality" for the used building block primitives. Concrete TRE-PC schemes derived from our generic constructions are comparable to or more efficient than the currently known TRE-PC schemes in terms of ciphertext overhead size and computation costs. © 2010 Springer-Verlag Berlin Heidelberg.