Cryptocurrency has been one of the sectors which arguably saw the biggest technological innovation in the past decade. The technology behind this new revolution is called blockchain and it has the potential to innovate other sectors too. Its core concepts of decentralization, immutability and anonymity are traits that can revolutionize any sector if implemented properly. In this work, we investigate how blockchain technology can be beneficial for the used vehicle market without intervention of any third party. Currently, most people cannot get basic information of the used vehicle they are buying and even when they do they cannot verify most of them. Thus various companies proposed solutions centered around vehicle passport. Staying true to its name, a vehicle passport contains all the relevant information of the vehicle which will help both the buyer and seller. The buyer will have a detailed report on any vehicle he is potentially buying and will have more chance of safeguarding himself against any kind of fraud. On the other hand, the seller will be able to sell his vehicle for the correct valuation because he has proof of the vehicle condition. The goal of this work is to provide a better solution where blockchain-based decentralized data sharing of vehicle passports prevents any centralized authority from possessing all the power. By using smart contract of blockchain we provided fair exchange. This removes the necessity of having an entity overseeing the transaction because no transaction will take place unless all parties are guaranteed service/payment. One of the main requirements is proving the authenticity of the vehicle passport before the transaction takes place. Accordingly, we design a zero-knowledge proof system that verifies the consistency of encrypted data against its publicly committed value. The verification is done onchain. After all the requirements for the transaction are met, fair exchange takes place where the buyer receives the vehicle passport encrypted with their public key and service providers receive their payments. / Graduate

雙方相等性驗證即是在不洩漏任何自身私密資訊的情況下，進行秘密計算來了解彼此的資訊是否相等。然而在大多數的現有協議之中，多數為不公平的協定，也就是說其中的一方(被告知方)只能相信另一方(告知方)所告知的比較結果，而無從驗證。雖然邱等學者在2011 年提出的〝具隱私保護功能之兩方相等性驗證機制之提案〞已經提供了具雙方驗證的協定，但此方案因為在加密演算法上的限制導致實作較為困難。因此，在本論文中，將利用ElGamal 的加密機制，提出了一套新的雙方相等性驗證的協議，具備相同的雙方相等性驗證的功能，但對加密演算法的限制較少，實作及運算也較為有效率。另外，搭配模糊傳輸的協定，讓使用者藉由本研究所提出的協定跟伺服器端溝通，來獲得所欲取得的資料，並同時保障使用者以及伺服器端的隱私。同時除了理論的證明安全性及正確性之外，也撰寫程式模擬並證實協定的正確性及討論其效能。 / Two-party equality testing protocol allows two entities to compare their secrete information without leaking any information except the comparison result. In previous works, the comparison result can only be obtained by one entity (ie. informer) and then the entity informs the result to the other entity (ie. receiver). The receiver has to accept the received result since he has no way to verify its correctness. Ciou et al. in 2011 first mentioned this problem and proposed a new protocol to solve the aforementioned problem. However, their protocol has some specific restrictions which making it unpractical. In this paper, based on the ElGamal encryption, we propose a new two-party equality testing protocol. Our protocol has the same feature (ie. allows the two entries to test the correctness of the comparison result) as Ciou et al.’s protocol but is more efficient and practical than theirs. On the other hand, combining our protocol with an oblivious transfer protocol can let users communicate with servers and to get the data in a private way. It is useful on the issue of privacy protection. Finally, the security and correctness are discussed and proved. The efficiency of the protocol is also provided.