At risk of irritating some folks who already saw this, a crosspost:
Medvinsky, Gennady and B. Clifford Neuman. "NetCash: A Design for Practical Electronic Currency on the Internet" Proceedings of the First ACM Conference on Computer Communications Security (November 1993) [available via anonymous FTP, <URL=ftp://prospero.isi.edu/pub/papers/security/netcash-cccs93.ps.Z>]. Addressing the pressing problem of how to conduct fiduciary business on the Internet, Medvinsky and Neuman describe a system that allows clients, merchants, and currency servers to interact in a secure fashion over an insecure medium. The framework presented here addresses, to varying degrees, the following issues: security, anonymity, scalability, acceptability, off-line operation, transferability, and hardware independence. The authors readily admit that this scheme does not solve all of these problems perfectly, but it does allow for the integration of other protocols when utmost anonymity and offline capabilities are required. - DR