Traitor Tracing for Image Fingerprinting

隨著電腦與網路的普及，產生、修改與傳遞數位資料變得十分容易，如此一來，數位資料面臨被非法散佈的危險。數位指紋嵌入技術利用在資料中置入可茲辨識訊息，以便於使用者非法傳播所購得的版本時，協助追溯洩密來源。 在現存的影像指紋嵌入系統相關研究中，想要同時達到指紋碼短、可以服務的使用者人數多(碼的個數多)、能抵抗的共謀人數多這三個條件，實屬不易。因此衍生出兩個值得研究的方向：一、如何設計浮水印演算法，使得在加強共謀抵抗能力的前提下所造成的長度極長的指紋碼可以嵌入影像而不造成破壞？二、如何建造一個短的指紋碼卻能擁有好的共謀抵抗能力與較多的指紋碼個數。本論文即在影像指紋嵌入系統中作叛徒追蹤的研究上作相關討論，並且試圖解決前述兩個問題，包含：影像指紋嵌入問題上的浮水印技術以及抵抗共謀破壞之指紋碼的設計。 在指紋嵌入的浮水印技術上，我們提出了一種可隨著不同影像內容自動調適的浮水印嵌入演算法。先將影像切割成小區塊，根據影像內容的特性，可以利用纇神經網路自動決定出嵌入的強度，而不須費心設計人類視覺模式，並以最佳化能量函數的方法，選擇適合的遷入位置。即使嵌入的指紋碼很長，此方法也能夠維持影像品質與浮水印強度的平衡，更將抵抗共謀破壞納入最佳化過程的考量。 在共謀抵抗指紋碼的設計上，我們提出了一種串接式追溯碼的建造方法，除了理論分析，也提供實作數據。此法可利用外層碼的符號個數的增加來加強追溯能力，並利用二元內層碼來符合”嚴格標記假設”。我們更設計一種利用使用者群組方式的特性來建立追溯碼的方法，來大幅改善追溯能力。根據以上兩種概念，共提出三種追溯碼：群組導向追溯碼、階層式追溯碼以及成員互斥追溯碼。群組導向追溯碼分別利用外層碼與內層碼為群組與組員編碼；階層式追溯碼將指紋碼切割成幾個階層，以樹狀結構來設計碼，而每群分枝僅須一個較為簡單的碼；成員互斥追溯碼則最大化同一群組使用者的指紋碼最短距離。三種碼都能有效將對於碼長、追溯能力與服務人群數量的需求，分散到不同階層各個擊破。實驗結果顯示所提出的方法的確能有效縮短碼長、強化追溯能力、並增加服務人群數。 本論文所提出的指紋碼浮水印嵌入演算法與追溯碼的建造方法，與現存的研究相較，都更為可行而有效，這的確提供一個在影像指紋嵌入系統中作叛徒追溯的一個好的研究方法。The demand of digital data protection is getting stronger dramatically nowadays as more and more digital contents are used on computers and distributed via the Internet. Digital fingerprinting is a technology designed to help protect digital assets and identify security leak sources. This dissertation addresses the problem of traitor tracing for image fingerprinting, including two major issues: watermarking strategies for image fingerprinting and the design of collusion-secure fingerprinting codes. In the fingerprint-watermarking, we propose a content-adaptive watermarking strategy, which can adaptively decide watermarking strengths and select suitable embedding positions according to the content based on a neural network and an optimization procedure respectively. It maintains the equilibrium of the robustness and the imperceptibility when embedding long fingerprints without the effort to deal with human visual models. Besides, the collusion-resistance is considered to resist collusion attacks. Experimental results show the feasibility of the proposed watermarking algorithm. In the fingerprint-designing, we derive a code construction scheme which constructs fingerprint in a concatenated way based on a user grouping policy. The concatenated construction method is analyzed and proven to be efficient in collusion-secure traceability codes: the larger alphabet size of the outer code guarantees the higher tracing ability and the binary inner code makes the fingerprint satisfying the “Strict Marking Assumption”. The group-based fingerprinting scheme can further improve the tracing ability under the concatenated code construction. Based on these two ideas of the fingerprint designing, we propose three collusion-secure traceability codes: the group-oriented traceability code, the hierarchical traceability code, and the member-exclusive traceability code. All of them successfully disperse the decoding efforts over the outer code and the inner code by the grouping structure. Both theoretical analyses and the practical implementation show good performances of error rates and collusion-resiliency. To sum up, the watermarking and code construction schemes developed in this dissertation provide more flexibility and higher collusion-resiliency than existing solutions, and thus offer a better match for the challenges of the traitor tracing for image fingerprinting.Chapter 1 Introduction 1 1.1. Multimedia Security 1 1.2. Digital Watermarking 2 1.3. Digital Fingerprinting 4 1.4. Goals and Contributions 6 1.5. Structure of Thesis 8 Chapter 2 Watermarking Strategies for Image Fingerprinting 9 2.1. SOM architecture 11 2.2. Adaptive Watermark-Strength Decision 15 2.3. Selection Algorithm for Embedding-Positions 21 2.4. Sequential Detection for Traitor Tracing 25 2.5. The Simulation of the Proposed Watermarking Scheme 28 2.5.1. c-TA Code Construction 28 2.5.2. Experimental Results 33 2.6. Conclusions 41 Chapter 3 Collusion-Secure Codes 42 3.1. Introduction 42 3.2. Combinatorial-designed Codes 42 3.3. Codes with Large Minimum Distances 44 3.3.1. Error Correcting Codes with Larger Relative Minimum Distances 46 3.3.2. Orthogonal Signals 47 3.4. Comparisons of Existing Collusion-Secure Codes 48 Chapter 4 Concatenated Construction of Fingerprinting Codes 55 4.1. Introduction 55 4.2. Concatenated Construction Strategy of Traceability Codes 58 4.3. Analysis of Concatenated Collusion-secure Codes 59 4.3.1. Code-length 60 4.3.2. Type I Errors 60 4.3.3. Type II Errors 61 4.4. The Decoding Algorithm 64 4.5. Examples of Concatenated Traceability Codes 65 Chapter 5 Group-Based Fingerprinting 69 5.1. Scheme 1 - Group-Oriented Traceability Codes 70 5.1.1. The Tracing Algorithm 72 5.1.2. Analysis of Group-Oriented Traceability Codes 73 5.1.3. Experimental Results 74 5.2. Scheme 2 - Hierarchical Traceability Codes 78 5.2.1. Segment-codes 78 5.2.2. Group-codes 80 5.2.3. Constructing Tree-Structured Traceability Codes from Existing Collusion-Secure Codes 83 5.2.4. Experimental Results 85 5.3. Scheme 3 – member-exclusive Traceability Codes 91 5.3.1. The Construction of Member-exclusive Codes 91 5.3.2. Experimental Results 93 5.4. Conclusions 96 Chapter 6 Conclusions 97 Appendix A 100 Reference 10