Security Analysis of Offline E-cash Systems with Malicious Insider

When we build electronic cash systems, the main focus of the design is usually on preventing customers’ malicious actions. However, since authorities such as banks and certificate authorities may have important secret data of customers, the insiders in the potentially untrusted authorities can become threats to electronic cash systems. Miyazaki and Sakurai [2] first systematically analyzed security of offline anonymous electronic cash systems by considering the insider threats from untrusted authorities. They investigated 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 and investigate the possible effective countermeasures against malicious insiders.