A new encryption algorithm over elliptic curve

Various public key encryption systems have been proposed in modern information technology. Some of them have also been used in various applications, such as e-commerce and mobile database. This paper proposes two secure receiptor-oriented encryption systems. The decryptioner´s private keys could be changed with the different time periods. This case would be very useful in some practical scenarios, for instance, in a mobile database environment. Besides the semantic security, the proposed schemes have the backward-and-future security, a new security requirement for semantically secure encryption schemes. In terms of construction, the two schemes are based on the pairings over elliptic curves. Also, this paper provides a heuristic security analysis for the underlying system.