X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/16dcc.git/blobdiff_plain/e944a6e5c1d0ba117954365dfedad16f183cf681..b67a97afb3770294e649ce1a1ed53af685be00b9:/generating.tex?ds=inline diff --git a/generating.tex b/generating.tex index ace2f7a..b4839db 100644 --- a/generating.tex +++ b/generating.tex @@ -3,9 +3,7 @@ It has been shown~\cite[Theorem 4]{bcgr11:ip} that if its iteration graph $\Gamma(f)$ is strongly connected, then the output of $\chi_{\textit{14Secrypt}}$ follows a law that tends to the uniform distribution -if and only if its Markov matrix is a doubly stochastic matrix. - - +if and only if its Markov matrix is a doubly stochastic one. In~\cite[Section 4]{DBLP:conf/secrypt/CouchotHGWB14}, we have presented a general scheme which generates function with strongly connected iteration graph $\Gamma(f)$ and @@ -19,11 +17,11 @@ is removed, an edge $(x,x)$ is added. For instance, the iteration graph $\Gamma(f^*)$ (given in Figure~\ref{fig:iteration:f*}) is the $3$-cube in which the Hamiltonian cycle -$000,100,101,001,011,111,110,010,000$ +$000,100,101,001,011,111,$ $110,010,000$ has been removed. \end{xpl} -We first have proven the following result, which +We have first proven the following result, which states that the ${\mathsf{N}}$-cube without one Hamiltonian cycle has the awaited property with regard to the connectivity. @@ -31,10 +29,10 @@ has the awaited property with regard to the connectivity. \begin{thrm} The iteration graph $\Gamma(f)$ issued from the ${\mathsf{N}}$-cube where an Hamiltonian -cycle is removed is strongly connected. +cycle is removed, is strongly connected. \end{thrm} -Moreover, if all the transitions have the same probability ($\frac{1}{n}$), +Moreover, when all the transitions have the same probability ($\frac{1}{n}$), we have proven the following results: \begin{thrm} The Markov Matrix $M$ resulting from the ${\mathsf{N}}$-cube in @@ -45,34 +43,40 @@ cycle is removed, is doubly stochastic. Let us consider now a ${\mathsf{N}}$-cube where an Hamiltonian cycle is removed. Let $f$ be the corresponding function. -The question which remains to solve is -can we always find $b$ such that $\Gamma_{\{b\}}(f)$ is strongly connected. +The question which remains to be solved is: +\emph{can we always find $b$ such that $\Gamma_{\{b\}}(f)$ is strongly connected?} -The answer is indeed positive. We furtheremore have the following strongest -result. +The answer is indeed positive. Furthermore, we have the following results which are stronger +than previous ones. \begin{thrm} -There exist $b \in \Nats$ such that $\Gamma_{\{b\}}(f)$ is complete. +There exists $b \in \Nats$ such that $\Gamma_{\{b\}}(f)$ is complete. \end{thrm} \begin{proof} There is an arc $(x,y)$ in the graph $\Gamma_{\{b\}}(f)$ if and only if $M^b_{xy}$ is positive where $M$ is the Markov matrix of $\Gamma(f)$. It has been shown in~\cite[Lemma 3]{bcgr11:ip} that $M$ is regular. -There exists thus $b$ such there is an arc between any $x$ and $y$. +Thus, there exists $b$ such that there is an arc between any $x$ and $y$. \end{proof} This section ends with the idea of removing a Hamiltonian cycle in the $\mathsf{N}$-cube. In such a context, the Hamiltonian cycle is equivalent to a Gray code. -Many approaches have been proposed a way to build such codes, for instance -the Reflected Binary Code. In this one, one of the bits is switched -exactly $2^{\mathsf{N}-}$ for a $\mathsf{N}$-length cycle. - -%%%%%%%%%%%%%%%%%%%%% - -The function that is built -from the +Many approaches have been proposed as a way to build such codes, for instance +the Reflected Binary Code. In this one and +for a $\mathsf{N}$-length cycle, one of the bits is exactly switched +$2^{\mathsf{N}-1}$ times whereas the other bits are modified at most +$\left\lfloor \dfrac{2^{\mathsf{N-1}}}{\mathsf{N}-1} \right\rfloor$ times. +It is clear that the function that is built from such a code would +not provide a uniform output. The next section presents how to build balanced Hamiltonian cycles in the $\mathsf{N}$-cube with the objective to embed them into the pseudorandom number generator. + +%%% Local Variables: +%%% mode: latex +%%% TeX-master: "main" +%%% ispell-dictionary: "american" +%%% mode: flyspell +%%% End: