Signcryption Research Based On Certificateless Cryptosystem

Signcryption is a combination of signature and encryption.Compared with the traditional signature-first encryption,signcryption has great advantages in computational efficiency and communication overhead.Certificateless cryptosystem has been suffering from attention for a long time due to its neither has the key escrow problem nor the certificate management problem in traditional.Therefore,certificateless signcryption has become a research hotspot.However,Partial certificateless signcryption scheme has security problem and problem that messages can only be taken from a certain set.The main contributions in this thesis are listed as follow:(1)Aiming at the problem that Partial certificateless signcryption scheme is proved completely insecure about confidentiality and unforgeability,a new CLS scheme without pairings is proposed in this thesis which can resist the public key attack and internal attack in former schemes.Simulation results show that,It is provably secure in the Random Oracle Model and is more efficient than the existing schemes.Since only four point multiplications and two point multiplications are need in signcryption and unsigncryption separately.(2)Aiming at the problem that messages can only be taken from a certain set in traditional signcryption scheme and the group manager has oversize privilege in group signature scheme,an efficient hybrid ring signcryption scheme is proposed under certificateless signcryption cryptosystem.The new scheme combines the advantages of hybrid signcryption and ring signcryption,using the KEM-DEM mechanism to generate symmetric keys and encapsulate the messages that need to be transmitted,so as to achieve unrestricted transmission of message.Verify the message will not be exposed to the actual sender's information,to achieve an unconditional anonymous.Compared with the existing scheme,the new scheme has better computation efficiency and Communication overhead.Based on discrete logarithm problem and computational Diffie-Hellman problem,the new scheme is proved to be unforgeable and confidential under the random oracle model.