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Add solution for 5a

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Tobias Eidelpes 2022-06-21 19:14:04 +02:00
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exam/ex.tex
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@ -264,7 +264,19 @@
\item \textbf{(33 points)}
\begin{enumerate}
\item \TODO
\item Let there be an adversary $\mathcal{A}$ which breaks CGI. We can then
construct an adversary $\mathcal{B}$ which breaks CGI2.
Suppose $\mathcal{B}$ is given a CGI2 instance
$(\mathcal{G}_a,\mathcal{G}_b)$ where $a\neq b$ and $\mathcal{G}_a$ and
$\mathcal{G}_b$ are in the set of $2^{130}$ graphs isomorphic to
$\mathcal{G}$. The goal of $\mathcal{B}$ is to find an isomorphism $\phi$
with non-negligible advantage such that $\mathcal{G}_a =
\phi(\mathcal{G}_b)$. $\mathcal{B}$ will give
$(\mathcal{G}_a,\mathcal{G}_b)$ to $\mathcal{A}$ and $\mathcal{A}$ will
output an isomorphism $\phi$ which satisfies $\mathcal{G}_a =
\phi(\mathcal{G}_b)$. $\mathcal{B}$ can then take this isomorphism and
apply it to its own problem to obtain the solution.
\item \TODO