具偽裝效果及驗證功能之文字型文件資訊分享的研究

Abstract

秘密分享是一種資訊隱藏的技術，能將一份秘密資料轉換成多份分享並將之分發給參與者保管。之後，蒐集一定份數以上的分享可將原始秘密資料回復。偽裝學是另一種資訊隱藏技術，能將一份資料編譯或轉換成某種格式的檔案或檔案的一部分，達到保護一份資料的目的。而驗證則是保證資料完整性和真確性的資訊隱藏技術。本研究提出了一些具偽裝效果和驗證功能的文字型文件的資訊分享方法。首先提出的是，具偽裝效果和驗證功能的純文字文件之資訊分享方法，利用邏輯運算對秘密文件做秘密分享，並將分享轉換成利用有意義句子形成的英文文件，達到偽裝的目的。並且將驗證訊號藏入這些英文文件內，達到驗證的目的。接著提出一具偽裝效果的HTML文件秘密分享方法，將分享偽裝成一份HTML文件，並提出一個用來驗證這些偽裝成HTML的文件的新方法。這兩個方法合起來利用合作式分享運算對一份秘密HTML文件中的內容做分享，將分享偽裝成跟秘密文件具有相同格調的HTML文件，而內容部分則用另一份藏入分享資料和驗證訊號的內容來取代。最後針對電子郵件格式的文件，提出一具偽裝效果的階層式秘密分享的方法和一用來驗證電子郵件形式分享的方法。這些方法對一份秘密電子郵件文件中每一構成要素做秘密分享、偽裝和驗證，而保留了原秘密文件中構成要素的架構。這些方法根據不同格式內容的構成要素，將含有分享資料和驗證訊號藏在裡面的構成要素用來取代原來的構成要素，形成一份份的分享。實驗結果證明了這些方法的可行性。

Secret sharing is a kind of data hiding technique that transforms secret data into shares, which can be distributed to participants to keep and collected to recover the original secret. Steganography is another kind of data hiding technique that translates digital data into certain formats with difference appearances for protection of original data. And authentication is a technique for assuring the fidelity and integrity of protected digital data. In this study, secret sharing methods for text-type documents with steganography and authentication capabilities are proposed. A secret sharing method for pure texts with steganography and authentication capabilities is first proposed. The method shares a secret text by exclusive-OR operations. For steganographic effects, the shares are translated into meaningful sentences in which certain authentication signals using spaces are hidden for authentication. Next, a method for sharing HTML documents with steganographic effects is proposed, and a new authentication method for verifying HTML shares is described. The two methods together share the contents of a secret HTML by cooperative sharing operations, and retain the style of the secret HTML in the shares by replacing the contents of the secret HTML with fake contents imperceptibly containing share data and authentication signals. Finally, a hierarchical secret sharing method for e-mails and an authentication method for e-mail shares are proposed. The methods are applied to the components of a secret e-mail, and make the framework of the e-mail shares identical to that of the secret e-mail. The methods substitute fake components with share data for the original e-mail components to form shares. And depending on the content of each component, corresponding authentication signals are embedded and an appropriate authentication process conducted. Experimental results are also included, which show feasibility of all the proposed methods.