On The Strongly Unforgeable Digital Signatures In The Standard Model

Digital signature is analogous to the traditional handwriting signature.Since it guarantees identity authentication,data integrity and non-repudiation,digital signature is one of the core technology of computer information security,and it plays an important role in E-commerce and E-government.In the standard model,a digital signature is said to be secure if it is existentially unforgeable under an adaptive chosen-message attack.For a variety of applications such as group signatures,however,a stronger security property called strong unforgeability is required.The main work of this thesis falls into two parts,one focuses on a concrete signature,the other focuses on a general formalization signature.Motivated by certificateless signatures and a strongly unforgeable ID-based signature,namely SOO signature scheme,a strongly unforgeable certificateless signature is constructed in Section 3.The security of the signature is also proved in Theorem 3.1 and Theorem 3.2.Moreover,the Verify Phase of SOO signature is improved. Motivated by algorithms of generic transformation from existentially unforgeable signature to strongly unforgeable signature in the literature such as BSW algorithm,a new algorithm which transforms from existentially unforgeable signature∑to strongly unforgeable signature∑_new is constructed in Section 4.The security of∑_new is proved in Theorem 4.1,and the efficience of new algorithm is same as BSW algorithm,but BSW algorithm requires existentially unforgeable signatures meet partitioned property.There is no such requirement for the new algorithm.