% Resizing and relocating MSC diagrams
\newcommand{\msccenter}[1]{\centering{\scalebox{1.0}{#1}}}

\setmscvalues{normal}	
\normalsize           %the MSC command 'setmscvalues normal' is broken.
\setlength{\instwidth}{1.8cm}
\setlength{\instdist}{4cm}
\setlength{\markdist}{0.4cm}
\setlength{\actionwidth}{\instwidth}
\setlength{\labeldist}{0.2cm}
\setlength{\conditionoverlap}{0.8cm}
%
  \msccenter{
    \begin{msc}{Needham-Schroeder Public Key}

      \declinst{I}{$\pkR,\pkIinv$}{$I$}
      \declinst{R}{$\pkI,\pkRinv$}{$R$}
      
      \action{$\z{nonce~} \nI$}{I}
      \nextlevel[2.7]
      \mscmark[tl]{1}{I}
      \mess{$\{ I , \nI \}_{\pkR}$}{I}{R}

      \nextlevel[0.5]

      \action{$\z{nonce~} \nR$}{R}
      \nextlevel[2.7]

      \mess{$\{ R , \nI , \nR \}_{\pkI}$}{R}{I}
      \mscmark[tr]{2}{R}
      
      \nextlevel[1.25]

      \mscmark[tl]{3}{I}
      \mess{$\{ \nR \}_{\pkR}$}{I}{R}

      \nextlevel[1.5]

      \mscmark[tl]{i1}{I}
      \condition{$\secret(\nI)$}{I}
      \mscmark[tr]{r1}{R}
      \condition{$\secret(\nI)$}{R}

      \nextlevel[1.0]
    \end{msc}
    }