Cryptanalysis of Two Ring Signcryption Schemes

Ring signcryption scheme is an important cryptographic primitive that can be used to protect privacy and authenticity of a collection of users who are connected through an ad-hoc network, such as Bluetooth. In this paper,we analyze two ring signcryption schemes:Wang-Zhang-Ma's scheme (2007) and Zhu-Zhang-Wang's scheme (2008). We give different attack methods to the above two ring signcryption schemes. There exist Malicious KGC attack and Non-repudiation attack on Wang-Zhang-Ma's scheme (2007). There exist anonymity attack and existential unforgeability attack on Zhu-Zhang-Wang's scheme.