An Efficient Identity-Based Online/Offline Encryption Scheme

In this paper, we present an efficient Identity-based Online / Offline Encryption (IBOOE) scheme. An IBOOE scheme allows one to split the encryption into two phases. In the offline phase, most heavy computations such as exponentiation or pairing, if any, are done in this phase. Yet it does not require the knowledge of the plaintext or the receiver’s identity. This nice property allows it can be executed ‘offline’, or inside some powerful device. The next phase is called the online phase, where only light computations such as integer addition, multiplication or hashing are needed, together with the plaintext and the receiver’s identity. This can be executed inside some embedded device such as smart card or wireless sensor where the computation power is very limited. We propose an efficient IBOOE scheme, with great improvement in the computation requirement of both the offline, online encryption phase and decryption phase, together with much shorten ciphertext over previous schemes. Our scheme can be proven secure in the random oracle model.