具密文與金鑰效率之公開式廣播加密系統之研究

Abstract

廣播加密是一種有效率的金鑰管理及訊息傳播機制。對於大量的使用者，管理中心 可以傳播訊息給任意指定(未被註銷)的使用者，指定的使用者收到訊息後，可以依表頭 的內容解開資訊；而被註銷的使用者，即使共謀也無法從中得到資訊。廣播加密在生活 上有很多應用，如STB 收視控制、pay-per-view 電視、線上影片等。 本研究計畫將研究公開式廣播加密系統，現今最好的公開式廣播加密系統的私密金 鑰大小、公開金鑰和傳輸量能無法和私密式的廣播系統相比，我們覺得可以使之達到更 佳的效率：分別為O(r), O(log n) 和O(1)，同時計算量也可控制在合理的範圍之內，不 像BGW 的方法需要O(n)。 最近研究的frame proof code 及traceability code 是為了在廣播加密系統中防止陷害 及追蹤背叛者所發展出來的編碼方法，大部分為探討combinatorial 特性，我們將往這個 方向探討。最後，我們將實做出此一系統來。

Broadcast encryption is a very useful key management scheme for broadcasting messages to a set of intended users such that only the intended receivers can use their keys to decrypt and obtain the messages. The other receivers cannot get information about the messages. We can see that this saves quite a lot of bandwidth compared to the multicasting method. Broadcast encryption is very useful in many applications, for example the access control in STB, pay-per-view cable TV system, on-line movies, etc. We have found their application in the DVD region control system. In this project we study the public-key broadcast encryption system, in which every one can broadcast to a set of intended users. To our best knowledge, the best public-key broadcast encryption system has less efficiency in the size of the header, public key and private key of users, compared to the secret-key broadcast encryption system. One of the goals of this research is to invent a public-key broadcast encryption of O(r) header, O(log n) private keys per user and O(1) public key. We shall also have pretty good efficiency in encryption and decryption cost. The frame proof and traceability codes are invented to deal with the framing and traitor tracing problems in broadcast encryption. Up to today, most study of these two codes focuses on their combinatorial properties. I shall study these two codes further to have good computational properties. We shall design and implement a public-key broadcast encryption that is suitable many situations.