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Author: Admin | 2025-04-28
Challenge-response protocol, these two pieces will be different. Thusthe Bank will be able to identify her as the multiple spender. Since onlyshe can dispense identifying information, we know that her coin was not copiedand re-spent by someone else.PROTOCOL 5: Off-line cash.Withdrawal: Alice creates an electronic coin, includingidentifying information. Alice blinds the coin. Alice sends the blinded coin to the Bank with a withdrawalrequest. Bank verifies that the identifying information is present. Bank digitally signs the blinded coin. Bank sends the signed blinded coin to Alice and debitsher account. Alice unblinds the signed coin.Payment: Alice gives Bob the coin. Bob verifies the Bank's digital signature. Bob sends Alice a challenge. Alice sends Bob a response (revealing one piece ofidentifying info). Bob verifies the response. Bob gives Alice the merchandise.Deposit: Bob sends coin, challenge, and response to the Bank. Bank verifies the Bank's digital signature. Bank verifies that coin has not already been spent. Bank enters coin, challenge, and response in spent-coindatabase. Bank credits Bob's account.Note that, in this protocol, Bob must verify the Bank's signature beforegiving Alice the merchandise. In this way, Bob can be sure that either hewill be paid or he will learn Alice's identity as a multiple spender. 3. PROPOSED OFF-LINE IMPLEMENTATIONS Having described electronic cash in a high-level way, we now wish to describethe specific implementations that have been proposed in the literature. Suchimplementations are for the off-line case; the on-line protocols are justsimplifications of them. The first step is to discuss the various implementationsof the public-key
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