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Cryptanalysis of Correlation-Based Watermarking Utilizing a Single Watermarked Copy

This paper discusses cryptanalysis methods targeting correlation-based digital watermarking schemes using a single watermarked copy. The authors, Tanmoy Kanti Das and Subhamoy Maitra, detail how attackers can exploit correlations between watermark data and attacked copies to execute successful cryptanalytic attacks. The effectiveness of these attacks is demonstrated through statistical methods and experimental results, revealing vulnerabilities in existing watermarking techniques. Conclusions drawn emphasize the theoretical foundations and statistical criteria that support the proposed cryptanalysis approach.

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Cryptanalysis of Correlation-Based Watermarking Utilizing a Single Watermarked Copy

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  1. Cryptanalysis of Correlation-Based Watermarking Schemes Using Single Watermarked Copy Author: Tanmoy Kanti Das and Subhamoy Maitra From IEEE SIGNAL PEOCESSING LETTERS, April 2004 Presented by 詹益誌 6/8/2004

  2. Outline • Introduction • How to Get Convinced That the Attack is Successful. • Exact Cryptoanalytic Attack. • Experimental results. • Conclusions

  3. Introduction • Most of the existing digital watermarking techniques are based on correlation between “some information stored in the watermarked copy” and “related information retrieved from attacked watermarked copy”. • They show how to remove this correlation to mount a cipher text-only cryptanalytic attack on these watermarking schemes.

  4. How to Get Convinced That the Attack is Successful • Theorem 1: consider two datasets v1,…,vt and u1,…,ut that are uncorrelated.The mean and standard deviation of the dataset are approximately and

  5. How to Get Convinced That the Attack is Successful • Corollary 1: consider two datasets v1,…,vt and u1,…,ut selected at random from a standard normal distribution. The mean and standard deviation of the data u1-v1,…,ut-vt are approximately

  6. How to Get Convinced That the Attack is Successful • Neither Id nor s(i) is known to the attacker, but some knowledge about statistical distribution of s(i) is known.

  7. Exact Cryptoanalytic Attack • A single watermarked copy I(i) is available. Push I(i) in a stack ST of image. • Take the topmost image from the stack ST and consider it as I#. • The maximum t values of Id# are identified. DCT polynomial are formed. • The coefficients of the DCT polynomial are changed in a small range to create a population of several DCT polynomials and respective images are considered.

  8. Exact Cryptoanalytic Attack 5.From the population, images are selected which are visually indistinguishable from I(i). Moreover, we analyze s(i,#) as mentioned above. If the mean and standard deviation of s(I,#) is close to 0.1 and , respectively, then we select Id# as an attacked one. 6.If required number of images are available, the terminate; otherwise go to step 2.

  9. Experimental results • <image name, count of image, mean, std of the data s(I,#), PSNR(w,a)> • <Lena , 7200, 0.16, 0.69, 33.88> • <Pentagon, 8400, 0.193, 1.71, 32.7> • <Peppers , 6000, 0.081, 1.84, 31.93>

  10. Experimental results • <image name, PSNR(o,w), PSNR(o,a), correlation, similarity factor> • <Lena, 36.77, 33.02, 0.178, 1.08> • <Pentagon, 42.3, 32.1, 0.169, 1.91> • <Peppers, 36.94, 30.78, 0.181, 2.01>

  11. Conclusions • Support the theoretical concepts based on statistical criteria.

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