Design And Analysis Of Signcryption Schemes

In 1997, Zheng proposed a novel cryptographic primitive called signcryption. Signcryption schemes can simultaneously provide digital signature and public key encryption functionalities in a valid single logic step, but require smaller computational overheads and lower communication costs than signature-and-then-encryption approach. As an ideal cryptographic primitive to realize privacy communication and message authentication synchronously, signcryption schemes have been widely used in network security engineerings, such as key management, e-cash payment, et al.The dissertation mainly focuses on the design of and the provable security for signcryption schemes. The contributions of the dissertation are outlined as follows:(1) A cryptanalysis of the signcryption scheme proposed by Li Fa-Gen et al. based on the bilinear pairings is provided. It is shown that the secret key of the private key generator (PKG) is hided in the signcryption process. Accordingly, a forgery attack is presented. The proposed forgery attack can successfully forge a signcryption passing the verification procedure. Furthermore, an improved scheme is proposed, which is immune from the proposed forgery attack. The improved scheme is proven to be existentially unforgeable under the adaptive chosen-message attack model and in the random oracle model. The improved proposal obtains a higher level security without compromise the performance of the original scheme.(2) A cryptanalysis of the verifiable certificateless ring signcrytion scheme proposed firstly by Wang Ling-Ling et al. based on bilinear pairings is provided. It is shown that the scheme is vulnerable to public key replacement attacks, and then we present a public key replacement attack. It is shown that an adversary who replaces the public key of a ring signcryptioner can forge valid ring signcryptions. So we draw the conclusion that Wang's scheme is not secure.