Electronic money (or digital money) refers to cash and transactions over computer networks such as the Internet and also a collective term for financial cryptography technologies enabling it.
While this has been an interesting problem for cryptography (see e.g. David Chaum's work), the use of digital cash so far has been relatively low.
Electronic Money, or E-Money, and Digital Cash (http://www.ex.ac.uk/~RDavies/arian/emoney.html) - a large collection of links
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