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Unformatted text preview: h can wend its way through the economy; when it is finally deposited, the bank can examine the cash and determine who, if anyone, cheated. Digital cash protocols can also be divided along another line. Electronic coins have a fixed value; people using this system will need several coins in different denominations. Electronic checks can be used for any amount up to a maximum value and then returned for a refund of the unspent portion. Two excellent and completely different off-line electronic coin protocols are [225, 226, 227] and [563, 564, 565]. A system called NetCash, with weaker anonymity properties, has also been proposed [1048, 1049]. Another new system is . In , Tatsuaki Okamoto and Kazuo Ohta list six properties of an ideal digital cash system: 1. Independence. The security of the digital cash is not dependent on any physical location. The cash can be transferred through computer networks. 2. Security. The digital cash cannot be copied and reused. 3. Privacy (Untraceability). The privacy of the user is protected; no one can trace the relationship between the user and his purchases. 4. Off-line Payment. When a user pays for a purchase with electronic cash, the protocol between the user and the merchant is executed off-line. That is, the shop does not need to be linked to a host to process the user’s payment. 5. Transferability. The digital cash can be transferred to other users. 6. Divisibility. A piece of digital cash in a given amount can be subdivided into smaller pieces of cash in smaller amounts. (Of course, everything has to total up properly in the end.) The protocols previously discussed satisfy properties 1, 2, 3, and 4, but not 5 and 6. Some on-line digital cash systems satisfy all properties except 4 [318, 413, 1243]. The first off-line digital cash system that satisfies properties 1, 2, 3, and 4, similar to the one just discussed, was proposed in . Okamoto and Ohta proposed a system that satisfies properties 1 through 5 ; they also proposed a system that satisfies pr...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.
- Fall '10