diff -r bd25d9f9d9dc -r 34775227c84f hws/hw05.tex --- a/hws/hw05.tex Sat Sep 23 14:19:09 2017 +0100 +++ b/hws/hw05.tex Sat Sep 23 19:32:21 2017 +0100 @@ -79,6 +79,20 @@ achieve that the transponder $T$ authenticates itself to the car $C$? Does the car authenticate itself to the transponder? +\item What are the main disadvantages of the following + protocol that establishes a mutual key between two + parties $A$ and $B$ with the help of a mutually trusted + third party $S$: + +\begin{center} +\begin{tabular}{l@{\hspace{2mm}}l} +$A \to S :$ & $A, B$\\ +$S \to A :$ & $\{K_{AB}\}_{K_{AS}}$ and $\{\{K_{AB}\}_{K_{BS}} \}_{K_{AS}}$\\ +$A \to B :$ & $\{K_{AB}\}_{K_{BS}}$\\ +$A \to B :$ & $\{m\}_{K_{AB}}$\\ +\end{tabular} +\end{center} + \item \POSTSCRIPT \end{enumerate}