A Study On Certificate-Based Encryption, Identity-Based Encryption And Proxy Cryptosystem

Identity-based public key cryptography(IB-PKC)obtains user's public key from the identity information directly.It doesn't need certificates for certificating the public key of users,avoiding the cost of certificate management.Certificate-based public key cryptography(CB-PKC)overcomes the certificate management problem in traditional public key system and the key escrow problem in the IB-PKC,which is the best public key cryptography at present.A proxy cryptosystem(PC)can delegates the right of decryption to the proxy decryptor,thereby alleviating the burden of original decryptor and have widely application prospects.This paper mainly studies the relationship among certificate-based encryption(CBE),identity-based encryption(IBE)and PC.1.The generic transforming method between CBE and proxy-protected anonymous proxy decryption(PPAPD)were proposed with a proof of its security under the form model.Then we draw a conclusion that CBE and PPAPD were equivalent.Therefore any secure PPAPD scheme can be transformed into CBE scheme and vice versa.By this way,the research achievements of CBE and PPAPD were greatly enriched.We also provided the examples of transforming one existing cryptosystem to another new cryptosystem in the paper.2.The generic transforming method between IBE and time segmentation based proxy cryptosystem(PCBTS)were proposed with a proof of its security under the form model.Then we draw a conclusion that IBE and PCBTS equivalent was obtained.Therefore any secure PCBTS scheme can be transformed into IBE scheme and vice versa.By this way,the research achievements of IBE and PCBTS were greatly enriched.We also provided the examples of transforming one existing cryptosystem to another new cryptosystem in the paper.3.Combining the merits of CB-PKC and authorization-limited transformation-free proxy cryptosystem(AL-TFP),the definition and secure model of certificate-based and authorization-limited proxy cryptography(Certificate-Based AL-TFP)were proposed.And aconcrete scheme was also proposed in the paper.Compared with the existing certificate-based proxy cryptography,the scheme has lower computing cost and shorter proxy ciphertext length.