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Michela Ceria edited section_Some_cryptographic_applications_This__.tex
about 6 years ago
Commit id: d42c098b5275da11b39157bdef93af546ce1fff2
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We now describe another cryptographic algorithm that provides public-key encryption:
\begin{itemize}
\item Bob chooses a prime $p$ and a primitive element $g$ of
$Z_p$. $\mathbb{Z}_p$.
\item Bob chooses secretly a positive integer $x$ smaller than $p-1$.
\item Bob computes the exponentiation: $h=g^{x}$ in
$Z_p$. $\mathbb{Z}_p$.
\item Bob sends $p$, $g$ and $h$ to Alice (the enemies may intercept them);
\item Alice has received $p$,$g$ and $h$; she has a message $m$ to send to Bob; she chooses secretely a positive integer $y$ smaller than $p-1$;
\item Alice computes two
preliinary exponentiatos preliminary exponentiations in
$Z_p$\,: $\mathbb{Z}_p$\,: $c_{1}c\,=\,g^{y}$ and $s\,=\,h^{y}$ (obviously $h=g^{xy}$).
\item Alice finally encrypts her message $m$ by computing $c_{2} \,=\, m s$ and sends it to Bob together with $c_2$ (the enemies may intercept them);
\item Bob computes $s$ by an
exponentiaitoin exponentiation in $z_p$, since $s \,=\, {c_1}^{x}$;
\item Finally, Bob computes the message $m$ by another
exponentiaitoin exponentiation in
$Z_p$, $\mathbb{Z}_p$, i.e. $m \, =\, c_{2}\cdot s^{{-1}}$
\end{itemize}