1. Improvements of Image Sharing with Steganography and Authentication
Ching-Nung Yang, Tse-Shih Chen, Kun Hsuan Yu, Chung-Chun Wang
Journal of Systems and software, Vol. 80, Issue 7, pp , July, 2007
Reporter: 周美君

2. Outline Introduction Lin–Tsai scheme Proposed scheme
Experimental results
Conclusions

3. Introduction An example of Shamir's secret sharing
Ex: (2,3) threshold system (The secret key s =4)
F(x) = 4 + 2x
3 shares: (1,6), (5,14), (8,20) x y
F(x)
(1,6)
(5,14)
(8,20)
F(0)=4

4. Lin–Tsai scheme Using (2, 3)-threshold Watermark signal p=1
Parity Check
Secret image
Camouflage images 27 31 28 61 60 59 58
200
198
197 60
F(xi) = 60 + m1 × xi

5. 27 25 30 26 27 31 28 61 62 61 60 59 58
200
198
197
200
203
194
193
(∵ p=1, ∴parity check b=0) 27 27 25 30 26 01
110
010

6. 27 25 30 26 61 62 27 61
Check the Parity Check (p=1) is correct or not.
F(27) = s + m × 27 = = 114
F(61) = s + m × 27 = = 182 }
F(0) = s = 60 60

7. Improving Lin-Tsai scheme
Authentication
hash function with the secret key K
Quality of stego image
rearranging 17 bits
( 8 bit input xi + 8 bit output qi + 1 check bit Pi )
Non-lossless secret image
mod Galois Field GF(28)
g(x) = ( x8 + x4 + x3 + x + 1 )

8. Proposed scheme Camouflage images Secret image 23 20 15 11 27 31 28 6160 59 58 60
F(xi) = 60 + m1 × xi
F(23) = × 23 mod ( ) = 106
F(27) = × 27 mod ( ) = 114
F(61) = × 61 mod ( ) = 182

9. 21 18 14 10 23 20 15 11 25 27 28 30 27 31 28 62 59 53 58 61 60 59 58
F(23) = × 23 = 106 = 01
( illustration at next slide ) 21 18 14 10 11 10 10 10

10.
0001 0Pi10
106 =
Hk( || || || || Block ID || Image ID )= h
Pi = XOR h

11. Experimental Results Lin–Tsai scheme 38.54 38.49 38.31 Proposed scheme
Secret image
Experimental Results
Lin–Tsai scheme
38.54
38.49
38.31
Proposed scheme
41.02
41.08
40.59

14. Conclusions This paper improves Lin–Tsai scheme:
to strengthen authentication
to have batter quality of stego image
to have lossless recovery image.