\nonstopmode

\documentclass [tikz]{standalone}

\usetikzlibrary{positioning,arrows}
\usetikzlibrary{backgrounds}
\usetikzlibrary{calc}

\def\backgroundcolour { yellow!30 }

\newcommand{\lhbackground}{
  \begin{scope}[on background layer]
    \draw[line width=1pt,black,fill=\backgroundcolour] ($ (current bounding box.south west) + (-5mm,-8mm) $) rectangle ($ (current bounding box.north east) + (+5mm,+8mm) $);
  \end{scope}
}

\def\p{
    \begin{scope}[file/.style={rectangle,rounded corners,draw,fill=red!40,minimum width=11em,minimum height=3em,align=center},
                        cafile/.style={rectangle,rounded corners,draw,fill=green!40,minimum width=11em,minimum height=3em,align=center},
                        command/.style={font={\ttfamily\bfseries}},
                        program/.style={file,fill=blue!40},
                        flow1/.style={->,shorten <=-0.5mm,shorten >=+1.0mm},
                        flow2/.style={->,shorten <=+1.0mm,shorten >=+0.0mm},
                        flow3/.style={->,shorten <=+1.0mm,shorten >=+1.0mm,very thick,dashed,black!60},
                        node distance=5mm]
        \node[command                        ] (c1) { {\char36} openssl genrsa };
        \node[file,    below=of c1           ] (f1) { Password-protected \\ private RSA key };
        \ifplaintext
            \node[command, below=of f1       ] (c2) { {\char36} openssl rsa };
            \node[file,    below=of c2       ] (f2) { Unprotected \\ private RSA key };
            \def\tmp{f2}
        \else
            \def\tmp{f1}
        \fi
        \node[command, below=of \tmp,xshift=0em] (c3) { {\char36} openssl req };
        \node[file,    below=of c3,  xshift=0em] (f3) { Certificate Signing \\ request };
        \node[command, below=of f3,  xshift=0em] (c4) { {\char36} openssl x509 };
        \node[file,    below=of c4             ] (f4) { Website \\ certificate };
        \path (f4) +(0mm,-15mm) node[program,anchor=north] (server) { Web server };


        \path (f1.north) +(-1mm,-1mm) node[above left,font={\scriptsize}] { Encrypted };
        \path (f3.north) +(-1mm,-1mm) node[above left,font={\scriptsize}] { Not encrypted };
        \path (f4.north) +(-1mm,-1mm) node[above left,font={\scriptsize}] { Not encrypted };



        \draw[flow1] (c1) -- (f1);
        \ifplaintext
            \path (f2.north) +(-1mm,-1mm) node[above left,font={\scriptsize}] { Not encrypted };
            \draw[flow2] (f1) -- (c2);
            \draw[flow1] (c2) -- (f2);
            \draw[flow2] (f2) -- (c3);
            \draw[flow3,<-] (server.west) -- +(-7mm,0) |- (f2.west);
            \path ($ (f1.west)!.5!(f2.west) $) node[rotate=90,yshift=+10mm] { \strut Choose one };
        \else
            \path ($ (f1.west)!.5!(f3.west) $) node[rotate=90,yshift=+10mm,\backgroundcolour] { \strut }; % Phantom with same effect as "Choose one"
            \draw[flow2] (f1) -- (c3);
        \fi
        \draw[flow1] (c3) -- (f3);
        \draw[flow2] (f3) -- (c4);
        \draw[flow1] (c4) -- (f4);

        \draw[flow3] (f4) -- (server);
        \draw[flow3,<-] (server.west) -- +(-7mm,0) |- (f1.west);

        \ifca
            \node                       [cafile,  right=of f1] (f5)      { Password-protected \\ private RSA key };
            \node                       [command, above=of f5] (c5)      { {\char36} openssl genrsa };
            \node                       [cafile,  right=of f4] (f6)      { Certification Authority \\ certificate };
            \path (c3) -| (f5) node     [command,midway      ] (c6)      { { \char36} openssl req };
            \path (f6) +(0mm,-15mm) node[program,anchor=north] (browser) { Browser };

            \path (f5.north) +(+1mm,-1mm) node[above right,font={\scriptsize}] { Encrypted };
            \path (f6.north) +(+1mm,-1mm) node[above right,font={\scriptsize}] { Not encrypted };

            \draw[flow3] (f6) -- (browser);
            \draw[flow1] (c5) -- (f5);
            \draw[flow2] (f5) -- (c6);
            \draw[flow1] (c6) -- (f6);
            \draw[flow2] (f6.north west) -- ($ (c4.east)+(0mm,-0.5mm) $);
            \draw[flow2] (f5.south) +(-13mm,0mm) .. controls +(down:20mm) and +(20:15mm) .. ($ (c4.east) +(up:1mm) $);
        \else
            \draw[flow2] (\tmp.south east) .. controls +(+8mm,-8mm) and +(right:20mm) .. (c4.east);        
        \fi

        \lhbackground
    \end{scope}
}

\newif\ifca
\newif\ifplaintext

%---------------- body
  

\begin {document}
    \begin{tikzpicture}
  \catrue \plaintextfalse \p    \end{tikzpicture}
\end {document}