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Commutative Encryption and Watermarking in Video Compression

交換式加密及浮水印法應用在視頻壓縮IEEE Transactions on Circuits and Systems for Video Technology, VOL. 17, NO. 6, June 2007

Author ： Shiguo Lian, Zhongxuan Liu, Zhen Ren,Haila Wang

Adviser ：鄭錦楸 ,郭文中 教授 Reporter ：林彥宏

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Outline

Introduction

Research Method • Watermarking and Encryption Scheme • Proposed Encryption Process • Proposed Watermarking Process • Watermark Extraction

Performance Analysis • Security • Robustness and Imperceptibility • Commutation

Conclusions

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Introduction(1/6)

H.264/AVC(Advanced Video Coding) • Intra-Prediction mode (IPM) I-frame (Intra) P-frame (Unidirectional Predication) B-frame (Bidirectional Predication)

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Introduction(2/6)

intra_4x4

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Introduction(3/6)

intra_16x16

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Introduction(4/6)

• Inter-Prediction mode

block size selection={16×16, 8×16, 16×8, 8×8, 4×8, 8×4,

4×4}

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Introduction(5/6)

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Introduction(6/6)

Motion Vector Difference (MVD)Temporal RedundancySpatial Redundancy

Residue Data

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Research Method

Proposed watermarking and encryption scheme based on H.264/AVC

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Watermarking and Encryption Scheme

be composed of two independent parameters and

encrypted copy of watermarked copy of watermark key encryption key encryption algorithm watermark algorithm

w

e

Z,B,KZ

Y,KY

W

E

Y Z

eKwK

YZ

Y ZX

E

W

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Proposed Encryption Process

MVD Encryption ： Signs of MVD are encrypted

Exp-Golomb code (2M+1) 0 → 1 → 1

1 → 10 → 010 2 → 11 → 011 3 → 100 → 00100 4 → 101 → 00101 5 → 110 → 00110 …..

yx,

yy

xx

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Proposed Encryption Process

IPM Encryption ： EX ： 0001011

Residue Encryption ： • each non-zero residue macroblock DCT coefficients

are encrypted partially • first 8 coefficients’ signs in each 4×4 DCT block are encrypted

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Proposed Watermarking Process

watermark embedding is composed of three steps ： • Block Selection ： 1) residue block is nonzero

2) for I/P-frame, residue DCT block is composed of

only ac

3) for B-frame, residue DCT block is composed of

either dc or ac

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Proposed Watermarking Process

• Coefficient Selection ： coefficient in middle frequency are preferred • Watermark Embedding ： if

is watermark is original coefficient is quantization step

1w

02 % / if , .Sign 1 /

12 % / if ,

qzzqqz

qzzz

wzq

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Proposed Watermarking Process

if otherwise

ex：

qzzq

qand zqzzqqz

qzz

z

- if , Sign2

- 1%2 / if , Sign 1-/

02 % / if ,

w

-2)Sign(12 -

1q , -1 , 0

zzqz

zw

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Proposed Watermarking Process

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Watermark Extraction

Watermark Extraction：

1 2 % / if 1,

0 2 % / if 0,

qz

qzw

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Performance Analysis

Security： 128-bit AES (Advanced Encryption Standard )

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Robustness and Imperceptibility

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Commutation

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Commutation

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Conclusions

The modified watermarking algorithm makes the watermarking operation and encryption operation commutative.

The scheme keeps secure against present attacks, is efficient in implementation, keeps imperceptible, and is robust against recompression in some extent.