以立體圖及資訊隱藏技術做秘密通訊

Abstract

本論文研究提出三種自動產生不同立體圖的技術，及利用它們與資訊隱藏 方法做秘密傳輸的技術。針對這三種立體圖的特性，我們提出的資訊隱藏技術分 別是「利用替換LSB 技術建立灰階隨機點立體圖」，「利用降低失真之區塊編碼技 術建立黑白桌布立體圖」，及「利用隨機樣式區塊編碼技術建立黑白隨機點影像 序列立體圖」。第一種秘密傳輸方法  利用替換LSB 技術建立灰階隨機點立體 圖  需兩個遮罩,一個是隱蔽遮罩，另一個是秘密遮罩或文字。當用隱蔽遮罩 建立隱蔽灰階隨機點立體圖後,秘密訊息將會被嵌入至隱蔽立體圖中而產生偽裝 立體圖。第二種秘密傳輸方法  利用降低失真之區塊編碼技術建立黑白桌布立 體圖  提出2x2 區塊編碼資訊隱藏方法將秘密訊息藏在立體圖中。最後一種秘 密通訊方法  利用隨機樣式區塊編碼技術建立黑白隨機點影像序列立體圖  與產生單張立體圖相似，只是將秘密訊息換成多個畫格序列。上述方法都是為了 讓秘密傳輸的過程不要洩密，因此利用不同的立體圖及其特性提出對應的資訊隱 藏技術。最後我們提出相關的實驗結果證明所提方法之可行性。

In this study, three kinds of autostereogram images together with different data hiding techniques are proposed for the purpose of covert communication  grayscale random dot autostereogram with the LSB replacement technique, black and white wallpaper autostereogram with the distortion-reducing block coding technique, and black-and-white random dot image sequence autostereogram with random-pattern block coding technique. The proposed covert communication method via grayscale random dot autostereograms requires two masks, one being a cover mask and the other a secret mask or text. After a grayscale random dot cover autostereogram is created with the cover mask, the message is then converted into a bit string, which along with a key is then embedded into the cover autostereogram by LSB replacement, yielding a stego-autostereogram. With the same key, the hiding process can be reversed to recover the secret autostereogram composed with the secret mask. Wallpaper autostereogram generation is almost the same as autostereogram generation but the proposed covert communication method via them adopts a different information hiding technique. In additional to the mask images and the key required, a black and white pattern is necessary for the creation of the autostereogram and the hiding task is implemented while creating the autostereogram. The encryption of a secret message uses a specific 22 block pattern that represents different bit strings of the message. Such encryption is done in the vertical stripe pattern before completing the background, so it can be hidden in the blind spot of the autostereogram. The pattern with the encrypted data is then used to create the stego-autostereogram. Subsequently, the process can be reverted to get the hidden secret autostereogram produced with the secret message embedded. The last proposed method of covert communication is implemented on a sequence of black-and-white random dot autostereograms. The generation of each autostereogram image in the sequence is similar to that of a single autostereogram except that instead of using single cover and secret masks, sequences of multiple frames are processed. However, the employed technique is random-pattern block coding, which uses sixteen patterns to match sixteen different bit strings of the message. Moreover, all the data hiding techniques implement special features of the generation processes of the respective types of autostereograms to conduct data encryption. Different types of backgrounds are developed in these techniques due to the necessity of not attracting much attention from hackers and not exposing the secret message hidden. The hiding techniques are just simply complementing the types of backgrounds produced. Good experimental results are also presented, which show the feasibility and practicality of the proposed methods for covert communication via autostereograms.