網際網路上的工程競標：應用密碼學理論建立一個安全且公平的商業機制

Abstract

密碼學是電子商務能否成功的一項關鍵技術，而工程競標亦是相當適合運 作於網際網路之上的一種商業活動。當我們想要隨著電子商務的腳步將競 標系統實作於網際網路上時，必須和電子商務一樣地運用基礎密碼學方法 及固有的密碼學協定來達成安全需求，如保持資料的秘密性、提供不可否 認性證明、保護資料的真確性等。除了安全性的保持之外，公平性也是工 程競標系統另一個必須達成的目標。我們在設計網際網路上的工程競標機 制時，必須要能防止主辦單位內部人員收賄，並阻止一些例如圍標的不法 行為，以維持工程競標的公平性。 本篇論文中，我們採用了多個密碼 學協定，他們分別是：(1)匿名化混亂器(Anonymous MIX)，(2)伺服器簽 章(Server-Support Signature)，(3)可檢驗身份的盲目簽章(Fair Blind Signature)，(4)可公開檢驗的秘密分享(Publicly Verifiable Secret Sharing)，(5)群體適用的加解密方法(Group-Oriented Cryptosystem)。 此一系統有著下列幾個特性：(1) 得標者的決定，是由一個決策群組所做 出的，沒有任何人可以任意單獨地進行決標 的程序；(2) 沒有人可以 偽造標單；(3) 可防止同一競標廠商重複投標；(4) 主辦單位會遵照先前 所訂定出的規則選出得標者；(5) 決策人員的選定可以到開標前才決定 ；(6) 競標廠商在開標前可取消先前投標。 在我們所設計的系統之內 有兩種角色：主辦單位以及競標廠商，作者對於他們的責任以及權力皆做 了清楚的定義。根據在此篇論文中所做的分析，這個工程競標系統是公平 地、安全地，並且適合應用在現實世界中。 Cryptography is a key technology to the success of electronic commerce(EC). Bidding through Internet, a potential activity of EC, must depend on cryptography too. Cryptographic primitives and their application protocols must be introduced into an Internet bidding system to protect information integrity, to keep data confidential, to offer non-repudiation proofs, and to provide other security services. Fairness is another essential goal that a bidding system must achieve. We must build into the system safeguards against corruption by officers and against illegal activities such as a monopoly by coercion. Several cryptographic protocols are adopted in the system presentedin this thesis. They are these: (1) Anonymous Mix, (2) Server-Supported Signature, (3) Fair Blind Signature, (4) Non-repudiation Proofs, and (5) Publicly Verifiable Secret Sharing. The system satisfies the following properties: (1) Deciding who is the winner is a group decision process and nobody can monopoly the process;(2) Nobody can forge a bid;(3) Double bidding will be detected;(4) The winner must be chosen according to the announced policy;(5) Officers for deciding who is winner can be appointed as late as possible; (6) A bidder can revoke his bid before the deadline. There are two types of participants in the system: the authorities and the bidders. The author has clearly defined the responsibilities and the rights for each type of participants. According to the analysis presented in this thesis, the system is fair, secure, and is feasible for implementation in the real world.