Earticle

E-cash enables consumers to spend e-coin anonymously in information system, but unconditional anonymity of E-cash may be misused by malicious user, therefore fair E-cash was put forward. In fair E-cash system, the anonymity of customer can be revoked when e-coins are involved in crimes, and e-coin can be traced also. However, it is challenging work that providing a practical and complete tracing E-cash scheme. After pointing out some unpractical or incomplete designs in existing schemes, we present a practical scheme with complete tracing, including trusted authority’s unconditional tracing, bank’s repeat-spending tracing and loss-coin tracing which is neglected in prior schemes. Moreover, for resolving efficiency problem of complete fair tracing, we design a nested structure of signature of knowledge in payment protocol, which has an obvious efficiency advantage comparing with conventional signature of knowledge. Then we provide proofs of all security attributes of our E-cash system, and compare our scheme with some current schemes in efficiency. Our original design of nested structure of knowledge proof will also make other applications of knowledge-controllable-leak more efficient.