diff --git a/thesis/Abschlussarbeit.tex b/thesis/Abschlussarbeit.tex index 47eb640..c7c7296 100644 --- a/thesis/Abschlussarbeit.tex +++ b/thesis/Abschlussarbeit.tex @@ -352,7 +352,6 @@ The adversary has to call the \ioracle oracle with a commitment $\groupelement{R Assuming that $r_2 + 2^c c$ is invertable in $\field{L}$ (not equal to $0$) we can use both equations to calculate the discrete logarithm of $\groupelement{A}$. To ensure that $r_2 + 2^c c$ is invertable the reduction has to abort if $-r_2$ equals $2^c c$ with $c$ being randomly choosen in the \ioracle oracle. \begin{figure} - % TODO: set caption \hrule \begin{multicols}{2} \large @@ -398,11 +397,9 @@ Game $G_0$ is defined in Figure \ref{fig:igamewithabort} by ignoring all boxes. % TODO: hard bezüglich ggen % TODO: min entropy von {0,1}^{2b} mod L? - \[ \advantage{\igame}{\adversary{A}} \leq \advantage{\sdlog}{\adversary{B}} - \frac{\oraclequeries}{L} \] + \[ \advantage{\igame}{\adversary{A}} \leq \advantage{\sdlog}{\adversary{B}} - \frac{\oraclequeries}{2^{\log_2(\lceil \frac{2^{2b} - 1}{L} \rceil 2^{-2b})}} \] \end{theorem} -TODO: vielleicht doch eher $\oraclequeries$ durch min entropy von $\{0,1\}^{2b} \pmod L$? - \begin{proof} \item \paragraph{\underline{$G_0$:}} Let $G_0 \assign \igame$ be \igame. By definition, @@ -413,9 +410,9 @@ TODO: vielleicht doch eher $\oraclequeries$ durch min entropy von $\{0,1\}^{2b} \[ \Pr[G_0^{\adversary{A}} \Rightarrow 1] = \Pr[G_1^{\adversary{A}} \Rightarrow 1] \] % TODO: wählen von - \item \paragraph{\underline{$G_2:$}} Game $G_2$ aborts if the flag bad is set. For each individual \ioracle query the bad flag is set with probability at most $\frac{1}{L}$, since $c$ is chosen from $\field{L}$ uniformly at random. By the Union bound over all $\oraclequeries$ queries we obtain $\Pr[bad] = \frac{\oraclequeries}{L}$. Since $G_1$ and $G_2$ are identical-until-bad games, we have + \item \paragraph{\underline{$G_2:$}} Game $G_2$ aborts if the flag bad is set. For each individual \ioracle query the bad flag is set with probability at most $\frac{1}{2^{\log_2(\lceil \frac{2^{2b} - 1}{L} \rceil 2^{-2b})}}$, since $c$ is chosen from $\{0,1\}^{2b}$ uniformly at random and then reduced modulo $L$. By the Union bound over all $\oraclequeries$ queries we obtain $\Pr[bad] = \frac{\oraclequeries}{2^{\log_2(\lceil \frac{2^{2b} - 1}{L} \rceil 2^{-2b})}}$. Since $G_1$ and $G_2$ are identical-until-bad games, we have - \[ |\Pr[G_1^{\adversary{A}} \Rightarrow 1] - \Pr[G_2^{\adversary{A}} \Rightarrow 1]| \leq \Pr[bad] \leq \frac{\oraclequeries}{L} \] + \[ |\Pr[G_1^{\adversary{A}} \Rightarrow 1] - \Pr[G_2^{\adversary{A}} \Rightarrow 1]| \leq \Pr[bad] \leq \frac{\oraclequeries}{2^{\log_2(\lceil \frac{2^{2b} - 1}{L} \rceil 2^{-2b})}} \] \item Finally, Game $G_2$ is well prepared to show that there exists an adversary $\adversary{B}$ satisfying