設計一個分派秘密的協定

Abstract

本篇論文定義了一個題目，某一祕密的擁有者欲將N 個秘密值分派給N 個 分享者，但須滿足下列兩條件：(1) 任兩個分享者不得拿到相同的秘密值 。(2) 秘密擁有者不知道任一分享者分得何秘密值，任一分享者也無法得 知他人分得何秘密值。本文所提出的協定，有許多實際的應用面，例如： 電腦網路的匿名投票，發票中心依此協定將投票代碼發給投票者，投票者 以此代碼驗證選舉結果的正確性。此外，會議金匙的分派也是一種應用。 在文章中，我們先對秘密分享的相關文獻作一回顧，然後提出一個秘密分 派的協定。我們會討論使用的加解密方法與秘密分派的流程，其次分析分 派程序所需的傳遞次數與加解密次數，最後討論本協定的安全性與可能的 聯合攻擊的威脅。 Secret sharing has been a popular research topic in the field of cryptography, and many schemes have been proposed to solve the problem. This thesis defines a new problem which could be considered belonging to the domain of secret sharing. Imaging the following scenario, a person wants to distribute N secrets to N subscribers, but no two subscribers get the same secret value. Moreover, each subscriber only knows what secret value he acquires, but has no idea of the relationship between other secrets and who has acquired which secret. The target of this thesis is to propose a protocol for distributing secrets. Hierarchical structure and blind signature are two important concepts used in designing this protocol. The thesis also analyzes the computational comple- xity in respect of transmission times and encryption/decryp- tion times. Last, the security of this protocol and possible cooperative attack are discussed.