Generic Construction of Certificate-Based Encryption from Certificateless Encryption Revisited

摘要

Certificateless public key encryption (CLE) and certificate-based encryption (CBE) are motivated to simultaneously solve the heavy certificate management problem inherent in the traditional public key encryption (PKE) and the key escrow problem inherent in the identity-based encryption (IBE). Al-Riyami and Paterson proposed a general conversion from CLE to CBE, which is neat and natural. Kang and Park pointed out a flaw in their security proof. Wu et al. proposed another generic conversion from CLE to CBE which additionally involves collision resistant hash functions. It remains an open problem whether the generic conversion due to Al-Riyami and Paterson is provably secure or not. We are motivated to solve this open problem. Our basic idea is to enhance Type Ⅱ adversary's power a little by allowing it to conditionally replace a user's public key. We first formalize a new security model of CLE in this way. Then, we succeed in proving that the Al-Riyami-Paterson generic conversion from CLE to CBE is secure, if the CLE scheme is secure in our new security model. Finally, a concrete provably secure CBE scheme is presented to demonstrate the applicability of our result.