STABYLO for STeganography with cAnny, Bbs, binarY embedding at LOw cost.
What follows successively details all the inner steps and flow inside
the embedding stage (Fig.\ref{fig:sch:emb})
-and inside the extraction one(Fig.~\ref{fig:sch:ext}).
+and inside the extraction one (Fig.~\ref{fig:sch:ext}).
\begin{figure*}[t]
\subfloat[Data Embedding.]{
\begin{minipage}{0.49\textwidth}
\begin{center}
-% \includegraphics[width=5cm]{emb.pdf}
- \includegraphics[width=5cm]{emb.ps}
+ \includegraphics[width=5cm]{emb.pdf}
+ %\includegraphics[width=5cm]{emb.ps}
\end{center}
\end{minipage}
\label{fig:sch:emb}
\subfloat[Data Extraction.]{
\begin{minipage}{0.49\textwidth}
\begin{center}
-% \includegraphics[width=5cm]{rec.pdf}
- \includegraphics[width=5cm]{rec.ps}
+ \includegraphics[width=5cm]{rec.pdf}
+ %\includegraphics[width=5cm]{rec.ps}
\end{center}
\end{minipage}
\label{fig:sch:ext}
\subsection{Data Embedding}
-
+This section describes the main three steps of the STABYLO data embedding
+scheme.
\subsubsection{Edge Based Image Steganography}
-Image Quality: Edge Image Steganography
-\JFC{Raphael, les fuzzy edge detection sont souvent utilisés.
- il faudrait comparer les approches en terme de nombre de bits retournés,
- en terme de complexité. } \cite{KF11}
+Edge Based Image Steganography schemes
+already studied~\cite{Luo:2010:EAI:1824719.1824720,DBLP:journals/eswa/ChenCL10,DBLP:conf/ih/PevnyFB10} differ
+how they select edge pixels, and
+how they modify these ones.
-Presentation des algos de detection de contour
-Caractéristiques
+First of all, let us discuss about compexity of edge detetction methods.
+Let then $M$ and $N$ be the dimension of the original image.
+According to~\cite{Hu:2007:HPE:1282866.1282944},
+even if the fuzzy logic based edge detection methods~\cite{Tyan1993}
+have promising results, its complexity is in $C_3 \times O(M \times N)$
+whereas the complexity on the Canny method~\cite{Canny:1986:CAE:11274.11275}
+is in $C_1 \times O(M \times N)$ where $C_1 < C_3$.
+\JFC{Verifier ceci...}
+In experiments detailled in this article, the canny method has been retained
+but the whole approach can be updated to consider
+the fuzzy logic edge detector.
-Comparaison théoriques, références
+Next, following~\cite{Luo:2010:EAI:1824719.1824720}, our scheme automatically
+modifies canny parameters to get a sufficiently large set of edge bits: this
+one is practically enlarged untill its size is at least twice as many larger
+than the size of embedded message.
-Algo de stegano basé juste sur cela : (pas de bbs, pas de stc, même message).
-Quels paramètres sont optimaux ? Combinaison ?
+\subsubsection{Security Considerations}
+Among methods of message encryption/decryption
+(see~\cite{DBLP:journals/ejisec/FontaineG07} for a survey)
+we implement the Blum-Goldwasser cryptosystem~\cite{Blum:1985:EPP:19478.19501}
+which is based on the Blum Blum Shub~\cite{DBLP:conf/crypto/ShubBB82} Pseudo Random Number Generator (PRNG)
+for security reasons.
+It has been indeed proven~\cite{DBLP:conf/crypto/ShubBB82} that this PRNG
+has the cryptographically security property, \textit{i.e.},
+for any sequence $L$ of output bits $x_i$, $x_{i+1}$, \ldots, $x_{i+L-1}$,
+there is no algorithm, whose time complexity is polynomial in $L$, and
+which allows to find $x_{i-1}$ and $x_{i+L}$ with a probability greater
+than $1/2$.
+Thus, even if the encrypted message would be extracted,
+it would thus be not possible to retrieve the original one in a
+polynomial time.
-\subsubsection{Security Considerations}
-Security aspect:
-BBS-based cryptographic version of the message
\subsubsection{Minimizing Distortion with Syndrome-Treillis Codes}
-
\input{stc}
-\subsection{Data Extraction}
\ No newline at end of file
+\subsection{Data Extraction}
+Message extraction summarized in Fig.~\ref{fig:sch:ext} follows data embedding
+since there exists a reverse function for all its steps.
+First of all, the same edge detection is applied to get set,
+which is sufficiently large with respect to the message size given as a key.
+Then the STC reverse algorithm is applied to retrieve the encrypted message.
+Finally, the Blum-Goldwasser decryption function is executed and the original
+message is extracted.
