Linkability in Practical Electronic Cash Design

Abstract

Designing a practical and complete electronic cash scheme has proved difficult. Designs must seek to optimise often conflicting metrics such as efficiency, anonymity, the ability to make exact payments. Gains in one area often result in a loss in one or more other areas. Several schemes have accepted linkability of some payments as a concession to getting the balance right. A point that has not been highlighted is the problem of preventing linking between payments made with different linkable coins. This paper reviews several electronic cash schemes which have the linkability property and concludes that linking across coins is of significant practical concern. Design improvements are suggested along with observations regarding the user's active role in preserving anonymity.