http://groups.csail.mit.edu/mac/classes/6.805/articles/money/nsamint/nsamint.htmThe entire paper is interesting but look at the references:
11. Tatsuaki Okamoto, An Efficient Divisible Electronic Cash Scheme, Advances in Cryptology - CRYPTO '95, Springer-Verlag, pp. 438-451.
12. Tatsuaki Okamoto and Kazuo Ohta, Universal Electronic Cash, Advances in Cryptology - CRYPTO '91, Springer-Verlag, pp. 324-337.
