2011

• Christian Hundt, Maciej Liskiewicz:
  New complexity bounds for image matching under rotation and scaling.
  Journal of Discrete Algorithms, 9:122–136, 2011.
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• Maciej Liskiewicz, Rüdiger Reischuk, Ulrich Wölfel:
  Grey-Box Steganography.
  Volume 6648 of Lecture Notes in Computer Science, pp. 390-402. Springer Verlag, Heidelberg, in Proceedings 8. TAMC, 2011.
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2009

• Maciej Liskiewicz, Rüdiger Reischuk, Ulrich Wölfel:
  Grey-Box Steganography.
  Technical report SIIM-TR-A-09-03, Schriftenreihe der Institute für Informatik/Mathematik der Universität zu Lübeck, 2009.
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  In Steganography secret messages are encoded into unsuspicious covertexts such that an adversary cannot distinguish the resulting stegotexts from original covertexts. To accomplish their respective tasks, encoder and adversary need information about the covertext distribution. In previous analyses, the knowledge about the covertext channel was unbalanced: while the adversary had full knowledge, the encoder could only query a black-box sampling oracle. In such a situation, the only general steganographic method known is rejection sampling, for which the sampling complexity has been shown to be exponential in the message length. To overcome this somewhat unrealistic scenario and to get finer-grained security analyses, we propose a new model, called grey-box steganography. Here, the encoder starts with at least some partial knowledge about the type of covertext channel. Using the sampling oracle, he first uses machine learning techniques to learn the covertext distribution and then tries to actively construct a suitable stegotext – either by modifying a covertext or by creating a new one. The efficiency of grey-box steganography depends on the learning complexity of the concept class for the covertext channel, the efficiency of membership tests, and the complexity of the modification procedure. We will give examples showing that this finer-grained distinction provides more insight and helps constructing efficient stegosystems that are provably secure against chosen hiddentext attacks. This way we can also easily model semantic steganography.
• Christian Hundt, Maciej Liskiewicz, Ragnar Nevries:
  A Combinatorial Geometric Approach to Two-dimensional Robustly Pattern Matching with Scaling and Rotation.
  Theoretical Computer Science, 51(410):5317-5333, 2009.
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• Christian Hundt, Maciej Liskiewicz:
  New Complexity Bounds for Image Matching under Rotation and Scaling.
  In Proceedings of Symposium on Combinatorial Pattern Matching (CPM), Volume 5577 of Lecture Notes in Computer Science, pp. 127-141. Springer, 2009.
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2008

• Christian Hundt, Maciej Liskiewicz:
  Combinatorial Bounds and Algorithmic Aspects of Image Matching under Projective Transformations.
  In Proceedings of the 33rd International Symposium on Mathematical Foundations of Computer Science (MFCS), Volume 5162 of Lecture Notes in Computer Science, pp. 395-406. Springer, 2008.
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• Christian Hundt, Maciej Liskiewicz:
  Two-dimensional Pattern Matching with Combined Scaling and Rotation.
  In Proceedings of the 19th Symposium on Combinatorial Pattern Matching (CPM), Volume 5029 of Lecture Notes in Computer Science, pp. 5-17. Springer, 2008.
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• Maciej Liskiewicz, Ulrich Wölfel:
  Computational Aspects of Digital Steganography.
  In Multimedia Forensics and Security, pp. 193-211. Information Science Reference, Hershey, New York, 2008.
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2007

• Christian Hundt, Maciej Liskiewicz:
  On the Complexity of Affine Image Matching.
  In Proceedings of the International Symposium on Theoretical Aspects of Computer Science (STACS 2007), Volume 4393 of Lecture Notes in Computer Science, pp. 284-295. Springer, 2007.
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2006

• Christian Hundt, Maciej Liskiewicz, Ulrich Wölfel:
  Provably Secure Steganography and the Complexity of Sampling.
  In Algorithms and Computation, Volume 4288 of Lecture Notes in Computer Science, pp. 754-763. Springer, 2006.
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2005

• Maciej Liskiewicz, Ulrich Wölfel:
  On the Intractability of Inverting Geometric Distortions in Watermarking Schemes.
  In Proc. 7th Information Hiding Workshop (IH 2005), Volume 3727 of Lecture Notes in Computer Science, pp. 176-188. Springer, 2005.
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