一種隱藏式附加日期的電子現金付款機制

A Veiled Date-Attachment e-Cash Scheme

隨著電子商務的盛行，電子付款系統在電子商務上的需求也越來越受到重視。在眾多的線上電子付款系統中，電子現金付款系統是最為消費者喜愛與注意的，原因是它像紙鈔現金一樣，是一種無具名且可自由轉移的電子支付工具。目前電子現金的實作系統多是根據David Chaum的「盲目數位簽章」 ( Blind Digital Signature) 理論實作而成的。然而，Chaum所提出的方法中並無附加日期資訊，因此可能會讓使用者有重複消費，以及商家無從了解銀行是否正確計息等問題。為此，Chang等人提出一種在電子現金中附加日期資訊的方法來處理電子現金有效日期問題，然而他們的方法卻會產生日期資訊外曝的缺點。此一缺點將可能造成電子現金使用者的損失，例如，顧客向銀行提取電子現金時，此時若日期外曝的話，惡意人士若蓄意收集某銀行跟企業客戶電子現金提取交易的日期，而在企業客戶交易最頻繁的日期傳送大量封包使其交易產生延遲或中斷。另外，銀行體系也可能因本身之利益而利用電子現金日期資訊私下控制利息之高低，這也會影嚮到顧客的利益。所以，在本論文中我們進一步改善Chang等人的方法，提出一種將消費日期隱藏在電子現金中的方法，可決解日期外曝的缺點。

With the boom of electronic commerce (EC), the needs of a safe and convenient electronic payment scheme have gained more and more respect by EC users. Many electronic payment schemes have been proposed up to date. Among them, electronic cash (e-cash) is one of the most popular schemes that support users on line payment. The implements of e-cash are always based on that of David Chaum blind digital signature theory. Unfortunately, Chaum method lacks date information. This will cause user double spends his e-cash, and the merchant will be unable to check whether its e-cash is properly interested or not. Recently, Chang et al. proposed a flexible date-attachment scheme to solve the mentioned problems. However, Chang et al. method still has some drawbacks. One of them is the date information in e-cash that is easily explored to the public. Internet malicious users can use the date information to blockade the payment translation. It will cause both merchant and user serious loss. In this paper, we proposed a veiled date-attachment electronic cash scheme that effectively improves Chang et al. method drawbacks.