General Certificateless Encryption and Timed-Release Encryption.
Sherman S. M. Chow, Volker Röth, Eleanor Gilbert Rieffel · 2008
Abstract. Recent non-interactive timed-release encryption (TRE) schemes can be viewed as being supported by a certificateless encryption (CLE) mechanism. However, the security models of CLE and TRE differ and there is no generic transformation that turns a CLE into a TRE. In this paper, we give a generalized model for CLE that is also sufficient to fulfill the requirements of TRE. Our model is secure against an adversary with adaptive trapdoor extraction capabilities for arbitrary identifiers (instead of selective identifiers), decryption capabilities for arbitrary public keys (as considered in strongly-secure CLE) and partial decryption capabilities (as considered in security-mediated certificateless encryption, or SMCLE). Our model also supports hierarchical identities, which have not been considered formally in paradigms of TRE and CLE. We propose a concrete scheme under our generalized model and prove it secure without random oracles. Our proposal yields the first strongly-secure SMCLE and the first TRE in the standard model. In addition, our technique of partial decryption is different from the previous approach. Key words: security-mediated certificateless encryption, timed-release encryption