Researches On Certificateless Proxy Re-encryption

Proxy re-encryption (PRE) has recently become a hot topic in cryptography research field,and it has found many practical applications such as digital right protection, encrypted emailforwarding, cloud computing，etc. PRE allows a proxy to transform a ciphertext generated byAlice’s public key into one that can be opened by Bob’s secret key.Most of PRE schemes are constructed in traditional public key inrfastructure (PKI), oridentity-based setting. However, cryptosystems in PKI involve additional works for certificatemanagement, while cryptosystems in identity-based setting suffer rfom the key escrow problem.To solve the problems，Sur et al. introduced a new primitive notion named certificatelessProxy re-encryption(CL-PRE), which enjoys the advantages of certificateless public key cryp?tography while providing the functionalities of proxy re-encryption. But it is regrettable thatwe found out secure problem in their scheme. Their articles are still constructive and bring usan question about how to construct a CL-PRE scheme in the random oracle model with cho?sen ciphertext secure. We have work to solve this issue. Our contributions are summarized asfollows:Firstly, we proposed a generic construction method of certificateless proxy re-encryptionscheme. It combines by identity based schemes with ordinary public key cryptosystems addingproxy re-encryption factor and satisfies the chosen ciphertext security. It could be used to ex?amine existing PRE scheme security.Secondly，we employ generic construction method to inspect Sur et al’.s CL-PRE schemeand conifrmed its insecurity.Then, we propose an improvement for this scheme which provablyIND-CCA secure in the stronger security model.Thirdly, we construct a new detail CL-PRE scheme (NewCL-PRE) rfom Identity-BasedProxy re-encryption and Public Key Proxy re-encryption according to our generic constructionmethod. Atfer that we analyze the effectiveness and correctness for the NewCL-PRE schemeand prove that it is secure against chosen ciphertext attack. This scheme is the first one withIND-CCA secure propetry up to now. This paper also analyses the NewCL-PRE scheme’s per?formance and features.Finally, based on the research of proxy re-encryption factor, we check on K.Emura et al’.s IB-PRE scheme，then present an attack to break it and proposes an improvement scheme. Weprove that our improvement is secure against chosen ciphertext attack with source hiding prop?erty in the random oracle model. The article emphasizes the principle of the first level ciphertextcan be publicly verified by proxy is important for Proxy Re-Encryption schemes.