equal
deleted
inserted
replaced
77 what the purpose of this split is? Assume the key $K$ is shared |
77 what the purpose of this split is? Assume the key $K$ is shared |
78 only between the car and the transponder. Does the protocol |
78 only between the car and the transponder. Does the protocol |
79 achieve that the transponder $T$ authenticates itself to the car |
79 achieve that the transponder $T$ authenticates itself to the car |
80 $C$? Does the car authenticate itself to the transponder? |
80 $C$? Does the car authenticate itself to the transponder? |
81 |
81 |
|
82 \item What are the main disadvantages of the following |
|
83 protocol that establishes a mutual key between two |
|
84 parties $A$ and $B$ with the help of a mutually trusted |
|
85 third party $S$: |
|
86 |
|
87 \begin{center} |
|
88 \begin{tabular}{l@{\hspace{2mm}}l} |
|
89 $A \to S :$ & $A, B$\\ |
|
90 $S \to A :$ & $\{K_{AB}\}_{K_{AS}}$ and $\{\{K_{AB}\}_{K_{BS}} \}_{K_{AS}}$\\ |
|
91 $A \to B :$ & $\{K_{AB}\}_{K_{BS}}$\\ |
|
92 $A \to B :$ & $\{m\}_{K_{AB}}$\\ |
|
93 \end{tabular} |
|
94 \end{center} |
|
95 |
|
96 \item Explain briefly the purpose of the certification authority in |
|
97 the public-private key encryption scheme. |
|
98 |
|
99 \item Explain briefly what is meant by a certification authority |
|
100 becoming ``too big to fail'' when it has issued a large number |
|
101 of certificates. |
|
102 |
|
103 \item In which situations does it make sense to install |
|
104 invalid (self-signed) certificates? |
|
105 |
82 |
106 |
83 \item \POSTSCRIPT |
107 \item \POSTSCRIPT |
84 \end{enumerate} |
108 \end{enumerate} |
85 \end{document} |
109 \end{document} |
86 |
110 |