Unformatted text preview: operties 1 through 6 as well, but the data requirement for a single purchase is approximately 200 megabytes. Another off-line divisible coin system is described in . The digital cash scheme proposed in , by the same authors, satisfies properties 1 through 6, without the enormous data requirements. The total data transfer for a payment is about 20 kilobytes, and the protocol can be completed in several seconds. The authors consider this the first ideal untraceable electronic cash system. Anonymous Credit Cards
This protocol  uses several different banks to protect the identity of the customer. Each customer has an account at two different banks. The first bank knows the person’s identity and is willing to extend him credit. The second bank knows the customer only under a pseudonym (similar to a numbered Swiss bank account). The customer can withdraw funds from the second bank by proving that the account is his. However, the bank does not know the person and is unwilling to extend him credit. The first bank knows the customer and transfers funds to the second bank—without knowing the pseudonym. The customer then spends these funds anonymously. At the end of the month, the second bank gives the first bank a bill, which it trusts the bank to pay. The first bank passes the bill on to the customer, which it trusts the customer to pay. When the customer pays, the first bank transfers additional funds to the second bank. All transactions are handled through an intermediary, which acts sort of like an electronic Federal Reserve: settling accounts among banks, logging messages, and creating an audit trail. Exchanges between the customer, merchant, and various banks are outlined in . Unless everyone colludes against the customer, his anonymity is assured. However, this is not digital cash; it is easy for the bank to cheat. The protocol allows customers to keep the advantages of credit cards without giving up their privacy. Previous Table of Contents Next Products | Contact Us...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips