1. Data Hiding in a Kind of PDF Texts for Secret Communication Authors : S.P. Zhong, X.Q. Cheng, and T.R. Chen Source : International Journal of Network Security, vol. 4, no. 1, pp. 17-26, 2007 Presenter : Ping-Kun Hsu( 許鈵昆 ) Date : 2011/01/21 1

2. Outline  Introduction  TJ Operator  Logistic Chaotic Map  The Proposed Scheme  Experiment Result  Analysis  Conclusion  Comment 2

3. Introduction  Goal  Hiding secret data in PDF file to achieve the undetectability, perceptual transparency, and capacity.  Related Works  TJ Operator  Logical Chaotic Map 3

4. TJ Operator 2D vector-graph positioning model 4

5. Logistic Chaotic Map X n+1 = r × X n × (1-X n ) 0 ≦ X n ≦ 1, 0 ≦ r ≦ 4 If 3.57 ≦ r ≦ 4, the iteration values are random 5

6. The Proposed Scheme(1/5) Secret dataKey Logistic chaotic map Map 1Map 2 Start point Num1Num2 0101|1010 5 | 10 SHA-1 01011011 91 mod 16 11 FlagStr2 IND 6 SHA-1 01011010 90 mod 16 10 FlagStr1 Transformed data FlagStr2

7. The Proposed Scheme(2/5) [ 4 -2 20 15 ]TJ If the absolute value of the integer numeral is in [1,16] If the Num2 is bigger than φ Replace the integer numeral by the numeral in IND 10,11,12 Replace the integer numeral by the numeral transformed from Num1 yesno yes Keep the integer numeral constant no [ 10 11 20 12 ]TJ IND 7

8. The Proposed Scheme(3/5) Key SHA-1 01011011 91 mod 16 11 FlagStr Map 2 Start point Num2 8 Logistic chaotic map

9. The Proposed Scheme(4/5) If the absolute value of the integer numeral is in [1,16] If the Num2 is bigger than φ Extract the integer numeral and check the next integer numeral Check the next integer numeral yesno yes no [ 10 11 20 12 ]TJ 9

10. The Proposed Scheme(5/5) CheckStrEmbedded DataFlagStr2 SHA-1 compare Data have been extracted successfully Data may have been tampered noyes 10

11. Experiment Result 11

12. Analysis 12

13. Conclusion  The proposed scheme is secure, and the embedded capacity is high. 13

14. Comment  How to calculate integer numeral by the numeral transformed from Num1 14