非權限發授式多中心時間發布加密法和其實現

Abstract

「將訊息送至未來」這個題目自1990年代為因應現代的應用需求被提出，例如:電子投票、電子商務投標等具有時間機密特性之應用，這些應用都需要有延後解密特性的加密法才可完善運作。時間釋放加密法(Timed-Release Encryption)在90年代後持續發展至今。 目前，現有的時間釋放加密法大多藉由兩種之一的機制確保資料可以被延後解密，其一，第三方伺服器負責定期釋放時間點鑰匙，即藉由第三方認定的某時間點已到，所有被加密至此時間之前的資料都允許被解密，其二，用一個極為耗時的時間謎題加密資料，藉此保證使用者需要花費足夠多的時間才可以解密。 在本篇碩士論文中，我們提出一個分散式中心的時間釋放加密法以解決單點失敗而導致的系統癱瘓問題，另外我們使用密文策略屬性加密法作為比較時間的核心技術，藉由設計策略的演算法，簡短時間的描述長度並增加計算的速度。

The idea of "sending messages into the future" was proposed in 1993 for some modern applications that require time-delayed decryption of data; i.e. e-voting, business sealed-bid commitments, or time-sensitive confidential applications. Timed-release encryption (TRE) is a solution to the above applications being developed in the last decade. There are mainly two approaches in most TRE schemes. One approach that time-lock puzzles to guarantee data be revealed after certain period of time, which depends on machine efficiency. In the other approach, a trusted central time server is required to generate and broadcast time-bound keys over time for users to decrypt the data. This may possibly suffer from single point failure. In addition, time-bound keys should be stored permanently by servers for decryption of data encrypted for every possible time instant in the past. Our contribution in this paper is decentralized timed-release encryption with dealerless distribute key generation. Our system is based on comparison encryption constructed by cipher-policy attribute-based encryption (CPABE) along with privacy-preserving encoding.