General Certificateless Encryption and Timed-Release Encryption


While recent timed-release encryption (TRE) schemes are
implicitly supported by a certificateless encryption (CLE) mechanism,
the security models of CLE and TRE differ and there is no generic trans-
formation from a CLE to a TRE. This paper gives a generalized model for
CLE that fulfills the requirements of TRE. This model is secure against
adversaries with adaptive trapdoor extraction capabilities for arbitrary
identifiers, decryption capabilities for arbitrary public keys, and partial
decryption capabilities. It also supports hierarchical identifiers. We pro-
pose a concrete scheme under our generalized model and prove it secure
without random oracles, yielding 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.