A Modular Scripting Language for Secure Multi-Party Computation

安全多方計算的研究主要是針對在分散環境下的兩造(或多方)之間，如何在不透露彼此私有的資料的情況下，計算一個約定函數的問題，並要確保除了計算結果及其可能推導出的資訊，不會洩漏額外的私有資料。依此要求設計出來的函數算法，稱為安全的多方計算協定。 本研究室曾根據一套基於向量內積運算發展出的多方安全計算方法，設計了一個分散式系統框架與符合安全需求的函式庫。其後再以自動化使用這套函式庫的動機出發，開發出多方安全計算語言 smcSL (secure multiparty computation Scripting Language)。然此套語言目前尚缺作為使用者表述與解決問題重要工具的自定函式功能，以及模組化相關功能。本研究即於現有 smcSL 的基礎，在安全性受到保證的情況下，允許使用者於程式中自定函式與模組，使編寫更複雜且實際的應用成為可能，並在設計上希望能達到下列四點目標 一、 保持原有smcSL之安全特性:包括對於各變數存取權限的檢查，以及相應產生程式碼在防止資訊洩漏上的安全考量。 二、 函式導向的語言設計原則：引入函式的同時，也代表引入所謂的變數作用區域，以及相應的特性。因此像變數遮蔽（Variable Shadowing）、全域變數、區域變數、傳值或傳參等議題，皆是設計上的要點。 三、 相容現有成果：在smcSL語言正在持續發展的階段，維持執行環境的相容是必要的。最理想的情況是不修改而只是增加原有執行環境的功能，就可以使新特色運作順暢。 四、 擴充與靈活性：在smcSL持續發展的情況下，有必要為了可預見的需求留下設計擴充的餘地。因此在實作與設計上，帶有新特色的smcSL語言編譯器，以及其他組件，都會遵循此原則進行。Recently, language-based tools are emerging to better support the systematic development of secure multiparty computation (SMC) protocols. In particular, our colleagues had developed a scripting language for automating the development of complex protocols for a commodity-based approach to SMC. The implementation of the language consists of two parts, namely a distributed runtime environment and library of SMC protocols in the Ruby language and a compiler to translate a SMC script to executable Ruby code exploiting the distributed SMC runtime environment. The basic constructs of our scripting languages are pretty common, such as variables, data types, expressions, assignment statements and for-loops. The salient features of our language are a symmetric view of all participating parties and a three-level data security attributes, namely public, private, and shared, that users can employ to express their security requirements by associating variables with these attributes in a declarative manner. Furthermore, these security attributes also direct how our compiler should perform security check as well as code generation. However, currently the scripting language lacks of modular constructs such as functions and modules found in most programming languages, thus making it difficult for developers to compose large programs without redundant code. To make our language more flexible and practical, this thesis presents an enhancement of smcSL with functions and a basic module facility, and discusses how and why their design and implementation can still follows the security requirements, which ensures our new features not only make developers apt to construct large programs, but also keep them secure