\begin{tabular}{ l | r | r | r | r }
& \multicolumn{2}{c|}{Chiffrement} & \multicolumn{2}{|c}{Déchiffrement} \\
\cline{2-5}
& \multicolumn{1}{c}{\emph{Mono}} & \multicolumn{1}{|c|}{\emph{MS .NET}} & \multicolumn{1}{|c|}{\emph{Mono}} & \multicolumn{1}{c}{\emph{MS .NET}} \\
\cline{2-5}
\begin{tabular}{ l | r | r | r | r }
& \multicolumn{2}{c|}{Chiffrement} & \multicolumn{2}{|c}{Déchiffrement} \\
\cline{2-5}
& \multicolumn{1}{c}{\emph{Mono}} & \multicolumn{1}{|c|}{\emph{MS .NET}} & \multicolumn{1}{|c|}{\emph{Mono}} & \multicolumn{1}{c}{\emph{MS .NET}} \\
\cline{2-5}