Estimating the Secret Key of Spread Spectrum Watermarking Based on Equivalent Keys

Jinkun YOU, Yuan-Gen WANG, Guopu ZHU, Ligang WU, Hongli ZHANG, Sam KWONG

Research output: Journal PublicationsJournal Article (refereed)peer-review

1 Citation (Scopus)


The security of spread spectrum (SS) watermarking largely depends on the difficulty of estimating its secret key. Some estimators have been proposed to estimate the secret key in the known-message attack (KMA) scenario. However, the estimation accuracies of existing estimators are not satisfactory when the number of observations is not large enough. Currently, it is still a challenging and open problem to design more effective estimators. In this paper, we propose an equivalent keys (EK)-based estimator to estimate the secret key for both the traditional and more secure SS watermarking methods. Equivalent keys form an equivalent region, which is the intersection of a unit hypersphere and a hypercone. According to the Monte Carlo simulation, we find that the secret key can be estimated by adding up the equivalent keys uniformly sampled from the equivalent region. Thus, the proposed estimator selects equivalent keys from randomly-generated vectors by exploiting the pairs of watermarked signals and their embedded messages. A theoretical analysis is performed for the proposed estimator to evaluate the estimation accuracy. Experimental results verify the theoretical analysis and show the superiority of the proposed estimator over existing estimation methods. Furthermore, this paper also shows the insecurity of the more secure SS watermarking methods in the KMA scenario from a practical perspective for the first time.
Original languageEnglish
Pages (from-to)2459-2473
Number of pages15
JournalIEEE Transactions on Multimedia
Early online date1 Feb 2022
Publication statusPublished - 2023
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported in part by the National Key Research and Development Program of China under Grant 2020YFB1406902, in part by the National Natural Science Foundation of China under Grants 62172402, 62033005, 61872350, and 61872099, in part by the Natural Science Foundation of Heilongjiang Province under Grant ZD2021F001, in part by the Tip-top Scientific and Technical Innovative Youth Talents of Guangdong Special Support Program under Grant 2019TQ05X696, and in part by the Basic Research Program of Shenzhen under Grant JCYJ20170818163403748.

Publisher Copyright:
© 1999-2012 IEEE.


  • Equivalent keys
  • Monte Carlo simulation
  • secret key estimation
  • spread spectrum watermarking
  • watermarking security


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