Studies On Proxy Re-encryption Schemes

In Eurocrypt’98, Blaze, Bleumer and Strauss introduced the concept of Proxy Re-Encryption (PRE). In a PRE system, the proxy is given a re-encryption key so thatit is able to transform a ciphertext under the public key of delegator into a ciphertextwhich is forwarded to another user. However, this proxy acquires no knowledge ofthese two ciphertexts both of which are encryptions of the same plaintext. There aremany practical applications of PRE in real life, such as digital rights management,distributed fle systems, outsourced fltering of encrypted spam, and cloud computing.In this paper, we study on proxy re-encryption schemes, and achieve the followingresults:1. Traditional PRE enables the proxy to convert all of delegator’s ciphertexts, with-out any discrimination, so it can not implement fne-grained delegation of de-cryption rights. To address this issue, Jian Weng and others introduced the no-tion of conditional proxy re-encryption (C-PRE), in such systems, ciphertextsare generated with respect to a certain condition, and the proxy can translate aciphertext only if the associated condition is satifed. In this paper we reformal-ize more rigorous defnition and security notions for C-PRE, and then propose amore efcient C-PRE scheme. Our scheme is, in the random oracle model, prov-able secure. Furthermore, the scheme has obvious advantages in communicationoverhead and computational cost.2. The existing conditions proxy re-encryption research is mostly limited to the en-vironment of a public key infrastructure.In this paper, we discuss how to con-structidentity-basedconditionalproxyre-encryption(IBCPRE)scheme, formal-ize the formal defnition and security model of identity-based conditional proxyre-encryptionandsecuritymodel, andthenproposetwoIBCPREschemes:oneis selective-ID security without random oracle model, and the other is adaptive-IDsecurity without random oracle model.3. Although, lots of PRE schemes have been proposed, the majority of them arebased on either traditional public key encryption (PKE) or identity-based en-cryption (IBE). However, it is well known that traditional PKE sufers from theproblems of certifcate management, like revocation, and IBE has inherent keyescrowproblem(forexample, theKeyGenerationCenter(KGC)candecryptanyciphertext in an IBE scheme). In this paper, we reformalize more rigorous secu-rity notions for certifcateless proxy re-encryption (CL-PRE), and then proposeCL-PRE scheme. Our scheme is, in the random oracle, provable secure.