new

diff --git a/intro.tex b/intro.tex
index 18ea7ab2e50632db6ab394ac4d5440010f687877..871b5fbc2204710140336841d3235ac9ba18e0cf 100644 (file)
--- a/intro.tex
+++ b/intro.tex
@@ -85,8 +85,9 @@ the better the approach is said to be.
 Contrarely, we argue that some images should not be taken as a cover because of the nature of their signal.
 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.
+cover signal. 
 
+For some applications it might be interesting to be have a reversible procedure to compute the same edge detection pixel set for the cover and the stego image. For this, we propose to apply the edge detection algorithm not on all the bits of the image but only on all the bits without taking into consideration the LSB. 
  
 
 \JFC{Christophe : énoncer la problématique du besoin de crypto et de ``cryptographiquement sûr'',  les algo déjà cassés....

diff --git a/ourapproach.tex b/ourapproach.tex
index 0f2d7b598d7b08088b6035568d6fe3b027285d6b..3e012ea14be1f065c0c9afe484860357fbd85352 100644 (file)
--- a/ourapproach.tex
+++ b/ourapproach.tex
@@ -67,6 +67,8 @@ why we have  chosen Canny algorithm which is well  known, fast and implementable
 on many  kinds of architecture, such  as FPGA, smartphone,  desktop machines and
 GPU. And of course, we do not pretend that this is the best solution.
 
+In order to be able to compute the same set of edge pixels, we suggest to consider all the bits of the image (cover or stego) without the LSB. With an 8 bits image, only the 7 first bits are considered. In our flowcharts, this is represented by LSB(7 bits Edge Detection).
+
 
 % First of all, let us discuss about compexity of edge detetction methods.
 % Let then $M$ and $N$ be the dimension of the original image. 
@@ -126,21 +128,24 @@ it would thus be not possible to retrieve the original one in a
 polynomial time.   
 
 
-\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.   
+%%RAPH: paragraphe en double :-)
+
+%% \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. 
+
 
 
 
@@ -152,7 +157,7 @@ polynomial time.
 \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,
+First of all, the same edge detection is applied (on the 7 first bits) 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