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28 \title{On the interest and realization of chaos-based information hiding schemes: a review}
29 \author{Christophe Guyeux, Jean-Fran\c cois Couchot, and Jacques M. Bahi\\ \{christophe.guyeux,jean-francois.couchot,jacques.bahi\}@univ-fcomte.fr\\Institut Femto-st, Universit\'e de Franche-Comt\'e, France}
37 Information hiding schemes are studied
38 Spread-spectrum data-hiding techniques have been widely studied in recent years
39 under the scope of security. These techniques encompass several schemes, such as
40 Improved Spread Spectrum~(ISS), Circular Watermarking~(CW), and Natural
41 Watermarking~(NW). Some of these schemes have revealed various
42 security issues. On the contrary, it has
43 been proven in~\cite{Cayre2008} that the Natural Watermarking technique is
44 stego-secure. This stego-security is one of the security classes defined
45 in~\cite{Cayre2008}, where probabilistic models are used to
46 categorize the security of data hiding algorithms in the Watermark Only
47 Attack~(WOA) framework.
49 We have explained in our previous research works~\cite{guyeux13:bc}
50 that any algorithm can be rewritten as an iterative
51 process, leading to the possibility to study its
52 topological behavior. As a concrete example,
53 we have shown that the security level of some information hiding algorithms
54 (of the spread-spectrum kind) can be studied into a
55 novel framework based on unpredictability, as it is understood in the mathematical
56 theory of chaos~\cite{guyeux13:bc}.
57 The key idea motivating our research works is that: \emph{if artificial intelligence (AI)
58 tools seem to have difficulties to deal with chaos, then steganalyzers (software based
59 on AI that try to separate original from stego-contents) may
60 be proven defective against chaotic information hiding schemes}. Our work
61 has thus constituted in showing theoretically that such chaotic schemes can be constructed.
62 We are not looking to struggle with best available information hiding techniques and
63 we do not focus on effective and operational aspects, as
64 our questioning are more locating in a conceptual domain. Among other things, we do
65 not specify how to chose embedding coefficients, but the way to insert the hidden
66 message in a selection of these ``least significant coefficient'' in an unpredictable
67 manner. To say this another
68 way, our intention is not to realize an hidden channel that does not appear as sleazy
69 to a steganalyzer, but to construct an information hiding scheme whose behavior cannot
70 be predicted: supposing that the adversary has anything (algorithm, possible embedding
71 coefficient, etc.) but the secret key, we want to determine if he can predict which coefficients
72 will be finally used, and in which order. To do so, a new class of security has been
73 introduced in~\cite{bg10b:ip}, namely the topological security. This new class can be used to study
74 some categories of attacks that are difficult to investigate in the existing
75 security approach. It also enriches the variety of qualitative and quantitative
76 tools that evaluate how strong the security is, thus reinforcing the confidence
77 that can be added in a given scheme.
79 In addition of being stego-secure, we have proven in~\cite{gfb10:ip} that
80 Natural Watermarking (NW) technique is topologically secure. Moreover, this technique
81 possesses additional properties of unpredictability, namely, strong transitivity,
82 topological mixing, and a constant of sensitivity equal to $\frac{N}{2}$~\cite{Guyeux2012}.
83 However NW are not expansive, which is in our opinion problematic in the Constant-Message
84 Attack (CMA) and Known Message Attack (KMA) setups, when we
85 consider that the attacker has all but the embedding key~\cite{Guyeux2012}.
86 Since these initial investigations, our research works in that information hiding field have
87 thus consisted in searching more secure schemes than NW, regarding the
88 concerns presented in the first paragraph of this introduction. The objective
89 of this review paper is to list the results obtained by following such an approach.
91 This article is organized as follows. Notations and terminologies are firstly recalled in
92 the next section. Then the formerly published $\mathcal{CIW}_1$ chaotic iteration based one-bit watermarking
93 process is recalled in detail in Section~\ref{sec:ciw1}. Its steganographic version $\mathcal{CIS}_2$
94 is then explained in Section~\ref{sec:secrypt11}, while Section~\ref{di3sec} presents the
95 $\mathcal{DI}_3$ process, whose aims is to merge the two previous approaches.
96 This review article of chaotic iterations based information hiding algorithms
97 ends by a conclusion section containing intended future works.
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