| Abstract: | 隨著ID-based密碼系統的興起，擴大了雙線性配對密碼系統的應用層面，使得植基於雙線性配對(例如: Weil & Tate pairing)的密碼系統設計在近代密碼學佔有一席之地，而利用雙線性配對建構的密碼學相關應用有：加密系統、認證式金鑰協定、數位簽章等等。時至今日，這些相關應用更在近代密碼學研究上扮演一個重要的角色。 然而，ID-based密碼系統卻有一個非常大的缺點，因為在這種系統中的金鑰產生中心擁有系統主密鑰，因此金鑰產生中心可以得知所有使用者的私密金鑰，所以惡意的金鑰產生中心可以偽造任意使用者的數位簽章而不被發現。這會導致我們無法維持這種系統的機密性與不可否認性，而這兩個特性是密碼系統中相當重要且需要極力維護的要點。為了要解決這個缺點，學者Al-Riyami與Paterson提出免憑證公開金鑰密碼系統(CL-PKC)的概念，這個系統更兼具了傳統公開金鑰密碼系統與ID-based密碼系統兩者的優點。 在CL-PKC中，使用者的公開金鑰與私密金鑰之建置，均須由使用者與金鑰產生中心共同完成，所以這種系統排除了傳統的憑證而具有自我憑證的概念。也因如此CL-PKC引起學界的討論熱潮，也有許多研究論文探討相關的方法與安全模式。而早年學者Girault對公開金鑰系統信任層級所做的定義，也重新引起學界廣泛的討論，學者Hu等人更針對ID-based密碼系統與CL-PKC提出相關分析與評定，並建立完成安全層級Level 3的相關理論與安全模式，因此學界對於能達到Level 3安全性能的方法有著迫切的需求。 在2009年時，學者Du與Wen提出一種較之前作法更有效率的CL-PKC，但是這個方法也達不到最高Level 3的信任層級。因此有學者針對他們的方法提出一個改善且能達到Level 3的信任層級的最新作法。可惜的是，這個改善方案並未提出一個能被學界接受的安全模式與證明。因此本計劃的主要目的就是研究出如何限縮金鑰產生中心之權限，以達到信任層級Level 3並且具有可證明式安全的方法，這個研究將可拓展Pairing-based密碼系統的應用領域，並且對我國的CL-PKC相關研究做出貢獻。
The rise of ID-based cryptography has led to extensive use of bilinear pairings such as Weil pairing and Tate pairing. Since then, the design of Pairing-based cryptosystems has been an important issue in the cryptography, such as, encryption system, key-agreement protocol, signature scheme and so on. Henceforth, applications utilizing these pairings have played an important role in modern cryptography. However, the ID-based cryptosystem have a disadvantage, that is, the Key Generation Center (KGC) can perform public key cryptographic operations as any users. Therefore, confidentiality and non-repudiation cannot be satisfied by such systems perfectly. To solve such drawback of ID-based cryptosystems Al-Riyami and Paterson proposed a Certificate-Less Public Key Cryptosystem (CL-PKC), which has the advantages of public key infrastructure and ID-based cryptosystems. In CL-PKC, self-certified keys enable the use of public key cryptography without traditional certificates. That is, the private key needs to be chosen before the public key generated, therefore, KGC cannot generate the user’s complete private keys along. Many CL-PKC schemes and security models have been recounted by the researchers. Girault showed the trusted levels for conventional public key systems, and Hu et al. also presented that trusted levels for ID-based cryptosystems and CL-PKC. CL-PKC with Girault’s level 3 security is urgently required since the improved generic model introduced by Hu et al. has already included the security property. In 2009, Du and Wen proposed a more efficient CL-PKC scheme than the previous ones, but it is not enough secure to achieve Girault’s level 3 security. As a result, the goal of this project is to study the Girault’s security level, and will propose a provable secure and efficient level 3 scheme. It is helpful to the research in applications of Pairing-based cryptosystem, and plays an important role for the CL-PKC in our country. |
