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6 \begin{document} |
6 \begin{document} |
7 |
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8 \section*{Homework 5} |
8 \section*{Homework 5} |
9 |
9 |
10 \begin{enumerate} |
10 \begin{enumerate} |
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11 \item Consider the following simple mutual authentication protocol: |
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12 |
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13 \begin{center} |
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14 \begin{tabular}{ll} |
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15 $A \rightarrow B$: & $N_a$\\ |
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16 $B \rightarrow A$: & $\{N_a, N_b\}_{K_{ab}}$\\ |
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17 $A \rightarrow B$: & $N_b$\\ |
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18 \end{tabular} |
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19 \end{center} |
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20 |
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21 Explain how an attacker $B'$ can launch an impersonation attack by |
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22 intercepting all messages for $B$ and make $A$ decrypt her own challenges. |
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23 |
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24 |
11 \item Access control is about deciding whether a principal that |
25 \item Access control is about deciding whether a principal that |
12 issues a request should be trusted on this request. Explain |
26 issues a request should be trusted on this request. Explain |
13 how such decision problems can be solved by using logic. |
27 how such decision problems can be solved by using logic. |
14 |
28 |
15 \item The informal meaning of the formula $P\;\textit{controls}\;F$ is |
29 \item The informal meaning of the formula $P\;\textit{controls}\;F$ is |