| 摘要: | 近年來，由於網路的大量使用，創造了無限商機。因此，有許多傳統的交易方式漸漸朝向電子化轉型，這樣的變化便利了人們的生活。所以電子現金系統變得越來越受人注意。 雖然匿名的電子現金系統可以保障顧客的匿名性，然而這種特性卻有可能被惡意的顧客所濫用。因此，可以對付費做追蹤的這種機制不管對政府或是銀行都是很需要的。然而，那些可以匿名測銷的電子現金系統卻非常沒有效率，所以如何建構出一個有效率的可匿名撤銷的電子現金系統變成是一個很重要的目標。 為了能有效率地將顧客的身份與電子現金綁在一起，我們改進部份盲簽章而提出一個新的盲簽章。而且，我們還利用新的盲簽章建構出具有匿名撤銷及偵測雙重付費兩種防禦機制的一個電子現金系統。除此之外，我們使用批次技術的概念，使得顧客可以在一次提款中提領很多電子現金，而且商家和銀行也可以對這些電子現金只做一次的驗證動作。這樣的設計大大地分攤了在提領現電子現金時所需的計算成本。 此外，Moses Liskov和Silvio Micali使用了Markle hash tree的架構使顧客可以一次向銀行提領很多電子現金，雖然這樣的設計分攤了顧客產生電子現金時的計算成本，但卻增加了在每一次交易所需花費的計算成本。而且，在這個系統中如果顧客不誠實的輸入他的身份，將會迫使偵測雙重付費的機制失效。為了改善這個問題，我們提出一個新的電子現金系統。因為TTP的牽涉和批次技術的取代，使得改進後的系統不但額外提供追蹤機制去防範犯罪，而且還降低了在每次交易時顧客所需花費的計算成本。除此之外，由於改進後的系統不需要使用零知識證明，這大大減低了通訊成本及計算成本。因此，改進後的系統是比原來的系統來得更有效率。 In recent years, due to the tremendous development of the Internet, a great deal of business opportunities are created. Therefore, many traditional business transactions are approached in an electronic form so that this is convenient for people. For this reason, electronic cash systems become more and more interesting. Although the property of anonymity can protect customers' privacy, this property may be misused by malicious customers. Therefore, tracing of payments is a desired property for governments and banks. However, those anonymous electronic cash systems with anonymity revocation must pay a great sacrifice in efficiency. As a result, two efficient revocable anonymity electronic cash systems are proposed in this thesis. In order to correctly embed customers' identity into the electronic coin in an efficient manner, we propose a new blind signature improving partially blind signature. Furthermore, we utilize this blind signature to construct an anonymous electronic cash system which provides two protection mechanisms to resist double spending, blackmailing, and money laundering: double-sending detection and tracing. Moreover, due to the involvement of registration protocol, the employment of zero-knowledge proofs is extremely reduced. In addition, we take advantage of the concern of batch cryptography to enable the customer to withdraw many coins once with the bank during a single withdrawal, and enable the merchant and the bank to validate these coins once. This amortizes computation cost through many coins. Additionally, Liskov-Micali scheme uses the structure of Merkle hash tree to enable customers withdraw many coins once. Although this amortizes computation cost, it increases customers' computation cost during each payment. Moreover, if customers dishonestly embed identity in Liskov-Micali scheme, double-spending detection becomes abnormal. Therefore, we propose an improved electronic cash system improving Liskov-Micali scheme. Due to the involvement of TTP and the replacement of batch cryptography, the improved system not only additionally provides tracing capability but also decreases customers' computation cost during each payment. In addition, because the employment of zero-knowledge proofs is not necessary in the improved system, this reduces computation and communication costs. Therefore, the improved system is more efficient than Liskov-Micali scheme. |
