Image Steganography and Reversible Data Embedding Techniques 影像偽裝與可逆式資訊隱藏技術 Advisor: Prof. Chin-Chen Chang (張真誠 教授) Student: Wei-Liang Tai (戴維良) Department of Computer Science and Information Engineering, National Chung Cheng University

Outline Part I: Image Steganography Part II: Reversible Data Embedding covert (undetectable) communication slight modification Part II: Reversible Data Embedding lossless (reversibility) original image

Image Steganography Escape Alice Bob Warden

Steganography for VQ Compressed Images Using Hamming Codes and Declustering

Vector Quantization (VQ)

LSB Embedding Codebook Y of size m : Arrange Codebook : such that are similar Cover compression codes : {3, 6, 5, 0} = {011, 110, 101, 000}2 Secret message bits : (0, 0, 1, 1) Stego compression codes : {010, 110, 101, 001}2 = {2, 6, 5, 1} Embedding efficiency =

Single-Error-Correcting Codes Send 1101 1 1 1 1 Finally send 1101010

Single-Error-Correcting Codes (Cont.) Receive 1101000 1 Binary (7, 4) Hamming Code

Single-Error-Correcting Codes (Cont.) Receive w=1101010 s=HwT= Receive w=1101000 s=HwT= HwT ≠ 0, 1-error occurred Corrected x = w - el(HwT) = (1101000) – (0000010) = (1011010)

Proposed Method Apply binary (7, 4) Hamming Code Codebook Y of size m : Arrange Codebook : such that are similar Two sub-codebooks: Apply binary (7, 4) Hamming Code 7 Cover compression codes : {3, 7, 4, 1, 2, 6, 4} 7-bit Cover vector: w=(1101000) 3-bit Message m=(011)

Embedding and Extraction s=HwT= HxT = 0 HxT = m HxT = HwT – HwT + m HxT = HwT – (HwT – m) HxT = H(w - el(HwT - m)) x = w - el(HwT - m) HwT – m = (010)-(011) = (001) Stego vector x = w – el(001) =(1101000)-(0000001) =(1101001) 7 Stego codes = {3, 7, 4, 1, 2, 6, 5} Extract : m = HxT=(011) Embedding efficiency =

q-ary Hamming Codes Apply 3-ary (4, 2) Hamming Code Codebook q -1 … Y0 Y1 Yq -1 Similar Apply 3-ary (4, 2) Hamming Code 4 Cover vector: w=(1021) 2 Message m=(21)3 s=HwT= HwT – m = (02)-(21) = (11) Stego vector x = w – el(11) =(1021)-(0010) =(1011) Extract : m = HxT=(21) Embedding efficiency =

Analysis Use the q-ary Hamming codes to convey r q-ary symbols in Embedding efficiency = > 2 = LSB embedding Use the q-ary Hamming codes by performing at most one embedding change. indices to convey r q-ary symbols in

VQ compressed image (PSNR = 31.26 dB) Visual Quality VQ compressed image (PSNR = 31.26 dB) LSB embedding (PSNR = 29.92 dB) Proposed scheme (PSNR = 30.97 dB)

Reversible Data Embedding Marked image Authentication code Original cover image Cover image = authentic Extracted auth. code Auth. code

Reversible Data Hiding Based on Histogram Modification of Pixel Differences

Z. Ni, Y. Q. Shi, N. Ansari, and W. Su, “Reversible data hiding,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 16, no. 3, pp. 354-362, Mar. 2006. Original image peak point zero point 2 5 3 1 4 2 6 4 1 5 3 2 6 3 1 5 Marked image Messages: 11001101

Histogram Modification Marked image 2 6 4 1 5 3 a=3 b=6 2 6 4 1 5 3 Extracted bits =11001101 extract 2 6 4 1 5 3 2 5 3 1 4 recover Original cover image

Proposed Method

Proposed Method Peak point P=1 Cover image 155 156 158 159 160 153 157 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 xi 155 156 158 159 160 157 153 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 di 155 Peak point P=1

Shift xi by 1 units: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 xi 155 156 158 159 160 157 153 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 di 155 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 yi 155 159 158 157 152

Let m be the secret data to be embedded m={0 ,1}. P = 1, message to be embedded: 011001 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 xi 155 156 158 159 160 157 153 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 di 155 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 yi 155 156 154 159 158 160 157 152

Extraction and Recovery 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 yi 155 156 154 159 158 160 157 152 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 xi 155 156 158 159 160 157 153 P=1, extracted message m= 011001

Experimental Results In the worse case, all pixel values will be increased or decreased by 1 but the first pixel. That is, the mean squared error (MSE) is (N-1)/N . The lower bound of PSNR: Original Lena 48.32 dB embedded with 0.0854 bpp

Performance Comparison

Future Works Image Steganography Reversible Data Embedding spatial domain, JPEG, JPEG2000, etc. combine other codes Reversible Data Embedding higher hiding capacity with lower distortion. transform domains such as wavelet