電子錢的可追蹤性與使用者隱私保護

Abstract

目前已發展的各種電子錢系統，有許多是可以使支付電子錢的人，在 購物時保持絕對的匿名性。可是這種系統，很容易被不法之徒利用來從事 非法行為。並且因為電子錢完全的匿名性，導致執法者在偵辦此類案件時 ，十分不易追查到犯罪者的身分。 因此，有學者提出解決方案，一方 面可以顧及電子錢使用者的隱私，一方面又可以兼顧執法者的辦案需求。 其方法是在電子錢中，加入可供執法者追蹤的個人身分資訊。此個人身分 資訊唯有一個稱為可信賴的第三者才能解讀其內容，以獲得電子錢使用者 的身分資訊。也只有在有犯罪疑慮時，才能由法院發出命令給可信賴的第 三者，執行追蹤的任務。故一般守法的使用者，仍可保有其購物的隱私。 本論文就是以上列問題為研究重點。先將目前已發表有關此類問題的重要 文章，作一個簡要的介紹。再來，作者嘗試發展一個貼附隱藏身分的電子 錢系統（Hidden-Identity-Attached Digital Money System, HIADMS） ，可以解決上述問題，而且在效率及實用性上，均可比美其它系統。更重 要的是本系統所使用的方法，僅套用已被電子商務廣泛使用的密碼工具， 比起其它系統使用十分複雜的數學方法或不常用的密碼方法，本系統更顯 得易懂易用。 Digital money is one of payment instruments invented for electronic commerce. One major advantage of using this instrument is that the privacy of users, who hold or pay digital money, can be well protected. Such strength of privacy protection may be abused by outlaws, however. In recent developments of digital money, there have been several efforts trying to protect users' privacy and , in the meantime, to provide necessary traceability for the purpose of law enforcement.In this thesis, the author offers a comprehensive survey of the stateof the art. He also offers the design of a new system, called Hidden-Identity-Attached Digital Money System(HIADMA), which hides theholder's identity in an attachment to the digital money. As other scheme, HIADMS depends on a law enforcement unit, that is a Trusted Third Party (TTY), to decipher the identity of a user when necessary. Without the intervention of the Trusted Third Party, the anonymity of users remains well protected. The intervention must be regulated by laws. Instead of using sophisticated mathematics as that in other schemes, HIADMS uses cryptographic primitives that have been known as international standards. The rapid development of electronic commerce has created strong demands of standardization of those of those cryptographic primitives. Because of this strategy, our approach wouldbe more intelligible to the general public and is feasible of implementation in the real world.