fix spelling
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Andre Henriques 2023-11-07 22:06:05 +00:00
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@ -145,10 +145,22 @@
where $R$ is the list of random values generated for each pair where $R$ is the list of random values generated for each pair
\subsection*{4.3} \subsection*{4.3}
Our random value is $R = u-bit long digit$ which means that it has $2^u$ possible values.
And since we know that $q$ balls into $p$ holes a colision is bound to happend at the probability of $\frap{q^2}{2p}$ we can calculate:
$$\frac{q^2}{2(2^u)}\gt\frac{1}{2}\iff q\gt 2^{\frac{u}{2}}$$
\subsection*{4.4}
The size of TripleDES is 64 bit long which makes $u=64/2=32$ making the q
$q\gt 2^\frac{32}{2}\iff q \gt 65536$
\subsection*{4.5}
The size of AES is 128 bit long which makes $u=128/2=64$ making the q
$q\gt 2^\frac{64}{2}\iff q \gt 4294967296$
\subsection*{4.6}
Since in in both 4.4 and 4.5 the value of $q$ is not large enough the scheme is not CPA secure
\section*{5} \section*{5}
\subsection*{5.1} \subsection*{5.1}
The hash function is collision resistante for $n=1$, since if the block size is one the hash function is the encryption. Therefore: The hash function is collision resistanteeee for $n=1$, since if the block size is one the hash function is the encryption. Therefore:
if the message is only one block long: if the message is only one block long:
$$H=E$$ $$H=E$$
$$m\ne m'$$ $$m\ne m'$$