File:Ring-signature.svg

\documentclass{standalone}

\usepackage[utf8]{inputenc}
%\usepackage[frenchb]{babel}
\usepackage[T1]{fontenc}
\usepackage{libertine}
\usepackage{tikz}
\usetikzlibrary{chains, positioning}

\begin{document}
\begin{tikzpicture}[xor/.style={draw, circle, inner sep=0pt, minimum size=.5em, append after command={(\tikzlastnode.east) edge (\tikzlastnode.west) (\tikzlastnode.south) edge (\tikzlastnode.north)}}]
  \node (v) at (90:1.5) {|};
  \node[above=0cm of v] {$v$};
  \node[xor] (o1) at (60:1.5) {};
  \node[] (E1) at (30:1.5) {$E_\sigma$};
  \node[xor] (o2) at (0:1.5) {};
  \node[] (E2) at (-30:1.5) {$E_\sigma$};
  \node[xor] (o3) at (160:1.5) {};
  \node[] (E3) at (120:1.5) {$E_\sigma$};
  \draw[->] (0,0) ++ (85:1.5) arc (85:65:1.5);
  \draw[->] (0,0) ++ (55:1.5) arc (55:40:1.5);
  \draw[->] (0,0) ++ (55:1.5) arc (55:40:1.5);
  \draw[->] (0,0) ++ (20:1.5) arc (20:5:1.5);
  \draw[->] (0,0) ++ (-5:1.5) arc (-5:-20:1.5);
  \draw[->] (0,0) ++ (-40:1.5) arc (-40:-195:1.5);
  \draw[->] (0,0) ++ (155:1.5) arc (155:130:1.5);
  \draw[->] (0,0) ++ (115:1.5) arc (115:95:1.5);
  \path (-110:1.4) -- node[sloped]{\ldots} (-130:1.4);

  \node[scale=.7] at (60:2.7) (e1) {$\textrm{Enc}_{pk_1}(x_1)$};
  \node[scale=.7] at (0:3) (e2) {$\textrm{Enc}_{pk_2}(x_2)$};
  \node[scale=.7] at (160:3.2) (e3) {$\textrm{Enc}_{pk_r}(x_r)$};
  \foreach \i in {1,2,3}
    \draw[->] (e\i) -- (o\i);
  \node[scale=.7] at (-120:2.7) (dec) {$\textrm{Dec}_{sk_s}(E_\sigma(v) \oplus v_s)$};
  \draw[dashed,->] (dec) -- (-120:1.5);
\end{tikzpicture}
\end{document}