The web is a very rich source of information relating to electronic cash. There is a large literature both from providers of such facilities, academics studying the issues surrounding electronic cash, and various groups that are opposed to the current proposals for electronic cash. Here are some good starting points:
Here is a requirements document for an unrelated system used in the course a few years ago, to give you an idea of what a requirements document might look like for a system larger than those treated in the lectures. Note that this example is much longer than the requirements document I expect you to produce!
Browsable documentation on the Moscow ML Library is here and a 2-up postscript version of the same thing is here.