1. 1 A Combined Approach to Integrity Protection and Verification of Palette Images Using Fragile Watermarks and Digital Signatures Source: IEICE TRANS. On FUNDAMENTALS, vol. E87-A, no. 6, pp. 1612- 1619, Jun. 2004 Author: Chih-Hsuan Tzeng and Wen-Hsiang Tsai Speaker: Na-I Wu ( 吳男益 ) Data: 2004/09/16

2. 2 Outline Introduction The proposed method (1) Fragile watermarking embedding (2) Generate “digital signatures” Experimental results

3. 3 Introduction An indexed image consists of data matrix, X, and a colormap matrix, map. Size: 129 x 126 Ex: 256 色 Indices: form 1 to 256 File Size: Color map: 129 x 126 x 8 Indices: 256 x 3 x 8 6.19k bytes

4. 4 Introduction

5. 5 The proposed method Fragile watermarking embedding To classify pixels into embeddable and non-embeddable ones. Embed authentication signals Generate Digital signature

6. 6 Fragile watermarking embedding Raster Scanning Manner : to find “embeddable”, and “non-embeddable” 256 200154123200154 256 200155132200155 256 200156133200156 200 16350200163 256 200154123200154 256 200155132200155 256 200156133200156 200 16350200163 8x8 Raster Scanning Manner : to find “embeddable”, and “non-embeddable”

7. 7 Raster Scanning Manner : to find “embeddable”, and “non-embeddable” P1(i-1, j-1)P2(i, j-1)P3(I+1, j-1) P4(i-1, j)X(i,j) Raster Scanning Fragile watermarking embedding α: the number of distinct colors of pixels in Prec(X) β: The maximum color distance d max (X, Prec(X))

8. 8 How to compute α, β values 12 60α = 1 12 16 10 α = 3 Fragile watermarking embedding 12  (50, 60, 70)  轉成 L, a, b 顏色模式  (69, 10, 5) 10  (90, 10, 60)  轉成 L, a, b 顏色模式  (10, 7, 6) 兩者的距離 =[(69-10) 2 +(10-7) 2 +(5-6) 2 ] 1/2 L: luminance a: green to red B: blue to yellow

9. 9 Fragile watermarking embedding The values of T c and T d be set by user EX1: T c =2, T d =10 12 α = 0, β = 0 12 60 α = 1, β = 48 “non-embeddable”

10. 10 The values of T c and T d be selected by user EX2: T c =2, T d =10 “embeddable” 12 16 10 α = 3, β = 6 121617 1018 α = 4, β = 8 Fragile watermarking embedding

11. 11 Palette Mapping Function M Fragile watermarking embedding 1(120,50,30) 2(111,51,21) 3(112,52,32) 4(123,13,33) 5(134,4,34) 6(25,55,35) Color palette 重排列 f(u)=2 16 xr +2 8 xg +b 換算權重值 1 7877150 2 7287573 3 7353376 4 8064289 5 8782882 6 1652515 5 8782882 4 8064289 1 7877150 3 7353376 2 7287573 6 1652515

12. 12 Palette Mapping Function M Fragile watermarking embedding 5 8782882 4 8064289 1 7877150 3 7353376 2 7287573 61652515 K: secret key Generate a random bit stream 1 1 0 0 1 1 若為 n 色，則產生 n bits. 5 1 4 1 1 0 3 0 2 1 61

13. 13 Fragile watermarking embedding Palette Mapping Function M 1(120,50,30) 1 2(111,51,21) 1 3(112,52,32) 0 4(123,13,33) 0 5(134,4,34) 1 6(25,55,35) 1 attack 1(120,50,30) 1 3(112,52,32) 1 2(111,51,21) 0 4(123,13,33) 0 5(134,4,34) 1 6(25,55,35) 1 將 pixel 值 2 變 3 ， 3 變 2

14. 14 EX2: T c =2, T d =10 ， and want to hide “0” 12 16 10 α = 3, β = 6 Fragile watermarking embedding 12345678 910111213141516 10110101 00101011 K: secret key No modify Authentication Data: 010101011 K: secret key

15. 15 EX2: T c =2, T d =10 ， and want to hide “1” 12 16 10 α = 3, β = 6 Fragile watermarking embedding 12345678 910111213141516 10110101 00101011 K: secret key (1) 去找週遭 4 個的 Lab 顏色 模式，其差最小的那一個 and (2) M(i)==secret data 修改完之必需符合 “Embeddable pixels” 的規定 α > T c and T d < β 16

16. The proposed method Generate “digital signatures” 12345678 910111213141516 10110101 00101011 EX1: T c =2, T d =10 12 α = 0, β = 0 “non-embeddable” 0 Authentication Data: 010101011 K: secret key XOR operator 0 Generate “digital signatures”

17. 17 The proposed method 每個 8x8 區塊的 “ digital signatures ” 的長度不一樣， 故每個 簽章的前面先放 ceil(nxn) bits ，用來 記錄每個 小區塊的 簽章的長度。 將每個小區塊的簽章的長度，合併起來來， 最後放在檔頭。

18. 18 The Authentication Process EX2: T c =2, T d =10 12 16 10 α = 3, β = 4 16 12345678 910111213141516 10110101 00101011 K: secret key K: Authentication Data secret data “1” temper 12 16 10 α = 3, β = 4 12

19. 19 The Authentication Process EX1: T c =2, T d =10 12 α = 0, β = 0 “non-embeddable” 12345678 910111213141516 K: secret key K: Authentication Data 010101011 “digital signatures” 0 10110101 00101011 XOR operator temper 12 1013 α = 1, β = 1 1

20. 20 Experimental Results Block size = 8 × 8 T c = 2, T d = 15 Size: 560 × 504 256 palette colors Digital signatures: 7938bytes The degrees of average distortion in the embeddable pixels of a block: ADEPB(max): 8.25

21. 21 Experimental Results Size: 488 × 672 64 palette colores Digital signatures: 11907bytes ADEPB(max): 9.76