X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/canny.git/blobdiff_plain/e477428ed31d945b364bd9064476c1f0a34f86ef..222b1caaf60e918817a332b5ce7774cf792fef59:/intro.tex?ds=sidebyside diff --git a/intro.tex b/intro.tex index e385cc9..d1ee499 100644 --- a/intro.tex +++ b/intro.tex @@ -5,27 +5,27 @@ It belongs to the well-known large category of spatial least significant bits (LSBs) replacement schemes. Let us recall that, in this LSBR category, a subset of all the LSBs of the cover image is modified with a secret bit stream depending on: a secret key, the cover, and the message to embed. -In this well studied steganographic approach, +In this well-studied steganographic approach, if we consider that a LSB is the last bit of each pixel value, pixels with an even value (resp. an odd value) are never decreased (resp. increased), thus such schemes may break the structural symmetry of the host images. And these structural alterations can be detected by -well designed statistical investigations, leading to known steganalysis methods~\cite{DBLP:journals/tsp/DumitrescuWW03,DBLP:conf/mmsec/FridrichGD01,Dumitrescu:2005:LSB:1073170.1073176}. +well-designed statistical investigations, leading to known steganalysis methods~\cite{DBLP:journals/tsp/DumitrescuWW03,DBLP:conf/mmsec/FridrichGD01,Dumitrescu:2005:LSB:1073170.1073176}. Let us recall too that this drawback can be corrected considering the LSB matching (LSBM) subcategory, in which the $+1$ or $-1$ is randomly added to the cover pixel LSB value only if this one does not correspond to the secret bit. %TODO : modifier ceci -Since it is possible to make that probabilities of increasing or decreasing the pixel value, for instance by considering well encrypted hidden messages, usual statistical approaches +By considering well-encrypted hidden messages, probabilities of increasing or of decreasing value of pixels are equal. Then usual statistical approaches cannot be applied here to discover stego-contents in LSBM. The most accurate detectors for this matching are universal steganalysers such as~\cite{LHS08,DBLP:conf/ih/Ker05,FK12}, which classify images according to extracted features from neighboring elements of residual noise. -Finally, LSB matching revisited (LSBMR) has been recently introduced in~\cite{Mielikainen06}. +Finally, LSB matching revisited (LSBMR) has recently been introduced in~\cite{Mielikainen06}. It works as follows: for a given pair of pixels, the LSB of the first pixel carries a first bit of the secret message, while the parity relationship (odd/even combination) of the two pixel values carries @@ -45,7 +45,7 @@ LSBM approach. % based on our experiments Instead of (efficiently) modifying LSBs, there is also a need to select pixels whose value modification minimizes a distortion function. -This distortion may be computed thanks to feature vectors that are embedded for instance in steganalysers +This distortion may be computed thanks to feature vectors that are embedded for instance in the steganalysers referenced above. Highly Undetectable steGO (HUGO) method~\cite{DBLP:conf/ih/PevnyFB10} is one of the most efficient instance of such a scheme. It takes into account so-called SPAM features @@ -53,8 +53,8 @@ It takes into account so-called SPAM features to avoid overfitting a particular steganalyser. Thus a distortion measure for each pixel is individually determined as the sum of the differences between the features of the SPAM computed from the cover and from the stego images. -Thanks to this features set, HUGO allows to embed $7\times$ longer messages with the same level of -indetectability than LSB matching. +Thanks to this features set, HUGO allows to embed messages that are $7\times$ longer than the former ones with the same level of +indetectability as LSB matching. However, this improvement is time consuming, mainly due to the distortion function computation. @@ -72,18 +72,18 @@ Edge based steganographic schemes have already been studied, the most interesting approaches being detailed in~\cite{Luo:2010:EAI:1824719.1824720} and in~\cite{DBLP:journals/eswa/ChenCL10}. -In the former, the authors presents the Edge Adaptive -Image Steganography based on lsb matching revisited further denoted as to +In the former, the authors present the Edge Adaptive +Image Steganography based on LSB matching revisited further denoted as EAISLSBMR. This approach selects sharper edge regions with respect to a given embedding rate: the larger the number of bits to be embedded, the coarser the edge regions are. -Then the data hiding algorithm is achieved by applying LSBMR on pixels of these regions. +Then the data hiding algorithm is achieved by applying LSBMR on some of the pixels of these regions. The authors show that their proposed method is more efficient than all the LSB, LSBM, and LSBMR approaches thanks to extensive experiments. However, it has been shown that the distinguishing error with LSB embedding is lower than the one with some binary embedding~\cite{DBLP:journals/tifs/FillerJF11}. -We thus propose to take benefit of these optimized embedding, provided they are not too time consuming. +We thus propose to take advantage of these optimized embeddings, provided they are not too time consuming. In the latter, an hybrid edge detector is presented followed by an ad hoc embedding. The Edge detection is computed by combining fuzzy logic~\cite{Tyan1993} @@ -96,7 +96,7 @@ schemes~\cite{Luo:2010:EAI:1824719.1824720,DBLP:journals/eswa/ChenCL10,DBLP:conf produce stego contents by only considering the payload, not the type of image signal: the higher the payload is, the better the approach is said to be. -Contrarily, we argue that some images should not be taken as a cover because of the nature of their signal. +Contrarily, we argue that some images should not be taken as a cover because of the nature of their signals. Consider for instance a uniformly black image: a very tiny modification of its pixels can be easily detectable. The approach we propose is thus to provide a self adaptive algorithm with a high payload, which depends on the cover signal. % Message extraction is achieved by computing the same @@ -105,7 +105,7 @@ The approach we propose is thus to provide a self adaptive algorithm with a high % but to exclude the LSBs which are modified. Finally, even if the steganalysis discipline - has done great leaps forward these last years, it is currently impossible to prove rigorously + has known great innovations these last years, it is currently impossible to prove rigorously that a given hidden message cannot be recovered by an attacker. This is why we add to our scheme a reasonable message encryption stage, to be certain that, @@ -113,18 +113,20 @@ even in the worst case scenario, the attacker will not be able to obtain the original message content. Doing so makes our steganographic protocol, to a certain extend, an asymmetric one. -To sum up, in this research work, well studied and experimented +To sum up, in this research work, well-studied and experimented techniques of signal processing (adaptive edges detection), -coding theory (syndrome-treillis codes), and cryptography +coding theory (syndrome-trellis codes), and cryptography (Blum-Goldwasser encryption protocol) are combined to compute an efficient steganographic scheme, whose principal characteristic is to take into consideration the cover image and to be compatible with small computation resources. The remainder of this document is organized as follows. -Section~\ref{sec:ourapproach} presents the details of the proposed steganographic scheme and applies it on a running example. -Section~\ref{sec:experiments} shows experiments on image quality, steganalytic evaluation, complexity of our approach, -and compares it to the state of the art steganographic schemes. +Section~\ref{sec:ourapproach} presents the details of the proposed steganographic scheme and applies it on a running example. Among its technical description, +its adaptive aspect is emphasized. +Section~\ref{sub:complexity} presents the overall complexity of our approach +and compare it to the HUGO's one. +Section~\ref{sec:experiments} shows experiments on image quality, steganalysis evaluation, and compare them to the state of the art steganographic schemes. Finally, concluding notes and future work are given in Section~\ref{sec:concl}.