ABSTRACT

The threat of key exposure becoming more acute as cryptographic computations are performed more frequently on poorly protected devices (smart-cards, mobile phones, even PCs), new techniques are needed to deal with this concern. One promising approach which we focus on here is to construct forward secure cryptosystems. The existence of non-trivial, forward-secure public-key encryption (PKE) schemes,however, has been open .Forward-secure PKE has the obvious practical advantage that a compromise of the system does not compromise the secrecy of previously-encrypted information; it is thus appropriate for devices operating in insecure environments. Furthermore, using such a scheme enables some measure of security against adaptive adversaries who may choose which parties to corrupt based on information learned in the course of a given protocol. We presented in this paper variant of scheme with better complexity; in particular, the public-key size and the key-generation/key-update times are independent of N. We suggested a method to achieve chosen ciphertext security for HIBE schemes using the CHK transformation . The resulting schemes are selective-ID chosen-ciphertext secure without random oracles, based on the BTE .