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資訊安全期末 Paper 報告. Data Hiding on 3D Triangle Meshes François Cayre and Benoît Macq , Senior Member, IEEE. 89321018 藺心皓. 1. Introduction. 近年來由於電腦硬體的發達,間接促成3 D 技術的普及,因此有人開始將3 D 圖形的特性應用到 Steganography 之中。 TSPS – Triangle Strip Peeling Sequence

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Paper

資訊安全期末Paper報告

Data Hiding on 3D Triangle Meshes

François Cayre and Benoît Macq, Senior Member, IEEE

89321018 藺心皓


1 introduction
1.Introduction

  • 近年來由於電腦硬體的發達,間接促成3D技術的普及,因此有人開始將3D圖形的特性應用到Steganography之中。

  • TSPS – Triangle Strip Peeling Sequence

    最簡單將資訊加到3D mesh上的技術,但是因為此法採用“The modification of topology”,導致容易被attacker找出payload。


1 introduction cont
1.Introduction (Cont.)

  • 因此本篇paper主要提出一種簡易且提高安全性的TSPS修改版


2 background
2.Background

  • cover- media : 用來遮掩plaintext的東西,在本篇中即為 Triangle-Meshes

  • Payload : 其實就是 plaintext

  • 本篇paper所使用的加密方法 : substitutive

    Blind scheme in the spatial domain.


2 background cont
2.Background(cont.)

此為一般加解密的動作,在此就不加以贅述


3 presentation of the proposed algorithm
3. PRESENTATION OF THE PROPOSED ALGORITHM

  • TSPS basic idea :

每個三角形分為Entry edge以及兩個exit edges

要包含payload的三角型以帶狀散佈在model上


3 presentation of the proposed algorithm cont
3. PRESENTATION OF THE PROPOSED ALGORITHM (cont.)

  • 基本的演算法,包含兩個步驟:

  • 1. 利用Secret Key 找出用來掩蓋payload的Triangle mesh

  • 2. 將payload 與 mesh結合,此步驟稱為

    macro embedding procedure (MEP)


3 presentation of the proposed algorithm cont1
3. PRESENTATION OF THE PROPOSED ALGORITHM (cont.)

  • Part1 : mesh strip的挑選取決於secret key


3 presentation of the proposed algorithm cont2
3. PRESENTATION OF THE PROPOSED ALGORITHM (cont.)

  • Part2.(MEP)

Define :

P 為在空間中垂直於line_AB的平面

比照secret Key & payload,若C已在該在的位置上,則不變動其位置,反之則調整C的位置


4 binary mep
4. Binary MEP

圖:將line_AB依n細分為許多格,當n越大,細分層級越小,則C會變動的距離越小。(But 處理時間會上升)


4 binary mep cont
4. Binary MEP  (cont.)

“入k” : C(原本Triangle兩個exit edge所夾的point) 到 P的距離


4 binary mep cont1
4. Binary MEP  (cont.)

當n = 2時,“入” 會比 n=1時更小,如此將比較不會破壞原本的model形狀


5 moving on the mesh
5.Moving on the Mesh

1. Avoiding Peeling

定義Triangle 以Entry edge為底時,右邊(exit edge)為1,左邊為0。

2. Admissibility and Upper Bound for Capacity

如果在找triangle時遇到重複的則跳過,繼續找下一個。

Data store upper bound = number of points inside the cover mesh


5 moving on the mesh cont
5.Moving on the Mesh(cont.)

  • Topological Boundaries: Initial and the Final Cells

    Initial Cells : 兩種方法,一是選擇具有某些特性的三角形(面積max or min, etc.),另一方法則是由Secret key決定。

    至於Initial edge則是選長度最大的作為Initial entry edge。

    Final Cells : 由secret key決定 (key的長度 = payload data 的長度)


5 moving on the mesh cont1
5.Moving on the Mesh(cont.)

  • Security

    Attacker需要解決的兩個首要的問題:

  • Find the initial Cells

  • Find the path over the meshes


6 results and future improvements
6. RESULTS AND FUTURE IMPROVEMENTS

Coding speed

&

Payload length


6 results and future improvements cont
6. RESULTS AND FUTURE IMPROVEMENTS(cont.)

Distortion

&

MEP order


6 results and future improvements cont1
6. RESULTS AND FUTURE IMPROVEMENTS (cont.)

Processing Time

&

Payload length


6 results and future improvements cont2
6. RESULTS AND FUTURE IMPROVEMENTS (cont.)

  • 兩個主要的缺點:

  • Model本身缺乏變化,亦即Attacker可以由原本的模型 & cover過的model下手攻擊。

  • 硬體精細度的限制,在Triangle極小的情形下可能出現錯誤。


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