Constructing perfect steganographic systems |
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Authors: | Boris Ryabko Daniil Ryabko |
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Affiliation: | a Siberian State University of Telecommunications and Information Sciences and Institute of Computational Technology of Siberian Branch of Russian Academy of Science, Kirov str. 86, Novosibirsk, 630102, Russia b INRIA Lille, 40, avenue Halley, Parc Scientifique de la Haute Borne, 59650, Villeneuve d?Ascq, France |
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Abstract: | We propose steganographic systems for the case when covertexts (containers) are generated by a finite-memory source with possibly unknown statistics. The probability distributions of covertexts with and without hidden information are the same; this means that the proposed stegosystems are perfectly secure, i.e. an observer cannot determine whether hidden information is being transmitted. The speed of transmission of hidden information can be made arbitrary close to the theoretical limit — the Shannon entropy of the source of covertexts. An interesting feature of the suggested stegosystems is that they do not require any (secret or public) key.At the same time, we outline some principled computational limitations on steganography. We show that there are such sources of covertexts, that any stegosystem that has linear (in the length of the covertext) speed of transmission of hidden text must have an exponential Kolmogorov complexity. This shows, in particular, that some assumptions on the sources of covertext are necessary. |
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Keywords: | Steganography Kolmogorov complexity Information theory Shannon entropy |
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