Security of Offline Anonymous Electronic Cash Systems against Insider Attacks by Untrusted Authorities Revisited

In the design of electronic cash systems, we usually focus on preventing customers' malicious behaviors. However, since authorities such as banks and certificate authorities may have important secret data of customers, the insider attacks by the untrusted authorities also need to be handled carefully. Miyazaki and Sakurai \cite{MS99} first evaluated security of offline anonymous electronic cash systems against the insider attacks by untrusted authorities. They analyzed the security of the existing electronic cash systems and categorized the systems into four types. In this paper, we reconsider the security of offline anonymous electronic cash systems including more recent systems based on the classification of Miyazaki and Sakurai.