Optional Properties Anonymity Both Alice and Bob should have the option to remain anonymous in relation to the payment. Furthermore, at the second level, they should have the option to remain completely invisible to the mere existence of a payment on their behalf.
Anonymity ensures the privacy of a transaction on multiple levels.
Beyond encryption, this optional untraceability feature of digital cash promises to be one of the major points of competition as well as controversy between the various providers. Transactional privacy will also be at the heart of the government's attack on digital cash because it is that feature which will most likely render current legal tender irrelevant. If digital currency were fully untraceable, it would open up opportunities for abuse that are not available to criminals now. In the physical world, money is bulky. In the physical world, it is possible to follow people, so a kidnaper can potentially be caught if the currency is marked, if the money was being observed on location, or if the serial numbers were recorded.