Research On Certificateless Digital Signcryption Schemes

With the rapid development of the information technology and the widely use of network technology, the security of information has become more and more important, and it has been focused by either domestic or aboard academic scientists. The core technic of the information security is cryptology.In 1997, professor Zheng proposed a new crypto primitive called signcryption, which fulfills the confidentiality and authentication of the message in one logical algorithm and has lower cost on computational complexity and communication complexity than those of traditional ways, that is, "signature then encryption". Signcryption has been proven to be a much better way to implement the confidentiality and authentication of the information at the same time. Currently, digital signcryption has been widely used in many areas such as e-cash, key agreemen and so on.This thesis focuses on the design of the certificateless digital signcryption schemes and their provably security. The main contributions of the thesis are as follows:1. Presented an introduction and a hensive analysis of certificateless public key crypto systems, signature schemes and signcryption schemes. Then, we have made a brief analysis and summary about the efficiency and the security of several famous schemes. Besides, we have given a detail analysis and summary of the security model of the certificateless signcryption.2. Proposed a certificateless signature scheme (LH) from bilinear pairings, then, on the basis of the LH, we designed a certificateless signcryption scheme (LHL). By precomputing one bilinear pairing in the setup phase, LHL scheme has greatly improved the computation efficiency which only needs two bilinear pairings in the signcrypt and designcrypt phases. At last, we gave a security analysis of our scheme under the discrete logarithm problem (DLP) assumption and computational Diffie-Hellman promble (CDHP) assumption based on the security model proposed by Riyami and Paterson.3. Designed a provably secure certificateless signcryption scheme (LHLL) in the random oracle model. The scheme just needs two bilinear pairings in the designcrypt phase and doesn't need any bilinear pairing at all in the signcrypt phase. Besides, LHLL scheme's ciphertext size is shorter than those of other certificateless signcryption schemes. So our scheme is more efficient than other schemes. In addition, we have formally proved the security of our scheme in the random oracle model. 4. Implemented the LHL scheme with C++ and MIRACL lib. The results of our experiment show that LHL scheme is correct, feasible and efficient.