first protocol part in math scratchpad

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Markus Teich 2016-06-16 00:08:49 +02:00
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@ -15,7 +15,7 @@ Alice and Bob know $v$ and $g$ with $|g| = n$, but only Alice knows $x$, so that
\item Bob checks that $rg = a + cv$. \item Bob checks that $rg = a + cv$.
\end{enumerate} \end{enumerate}
\subsection{Proof of equality of two EC DL} \subsubsection{Proof of equality of two EC DL}
Alice and Bob know $v$, $w$, $g_1$ and $g_2$, but only Alice knows $x$, so that Alice and Bob know $v$, $w$, $g_1$ and $g_2$, but only Alice knows $x$, so that
$v = xg_1$ and $w = xg_2$. $v = xg_1$ and $w = xg_2$.
@ -27,7 +27,7 @@ $v = xg_1$ and $w = xg_2$.
\item Bob checks that $rg_1 = a + cv$ and $rg_2 = b + cw$. \item Bob checks that $rg_1 = a + cv$ and $rg_2 = b + cw$.
\end{enumerate} \end{enumerate}
\subsection{Proof that an encrypted value is one out of two values} \subsubsection{Proof that an encrypted value is one out of two values}
Alice proves that an El Gamal encrypted value $(\alpha, \beta) = (m + ry, rg)$ Alice proves that an El Gamal encrypted value $(\alpha, \beta) = (m + ry, rg)$
either decrypts to $0$ or to the fixed value $g$ without revealing which is the either decrypts to $0$ or to the fixed value $g$ without revealing which is the
@ -55,6 +55,64 @@ Then regardless of the value of $m$:
\item Alice sends $(\alpha, \beta), a_1, b_1, a_2, b_2, c, d_1, d_2, r_1, r_2$ to Bob. \item Alice sends $(\alpha, \beta), a_1, b_1, a_2, b_2, c, d_1, d_2, r_1, r_2$ to Bob.
\item Bob checks that $c=d_1+d_2$ mod n, $a_1=r_1g+d_1\beta$, $b_1=r_1y+d_1(\alpha-g)$, $a_2=r_2g+d_2\beta$ and $b_2=r_2y+d_2\alpha$. \item Bob checks that $c=d_1+d_2$ mod n, $a_1=r_1g+d_1\beta$, $b_1=r_1y+d_1(\alpha-g)$, $a_2=r_2g+d_2\beta$ and $b_2=r_2y+d_2\alpha$.
\end{enumerate} \end{enumerate}
\subsection{Protocol}
\subsubsection{Generate public key}
\begin{enumerate}
\item Choose $x_a$ and $m_{ij}, r_{aj}$ for each $i$ and $j$ at random.
\item Publish $y_a=g^{x_a}$ along with a zero-knowledge proof of knowledge of $y_a$'s EC DL.
\item Compute $y=\sum_{i=1}^ny_i$.
\end{enumerate}
\subsubsection{Round 1: Encrypt bid}
\begin{enumerate}
\item Set $b_{aj}=\begin{cases}g & \mathrm{if}\quad j=b_a\\0 & \mathrm{else}\end{cases}$ and publish $\alpha_{aj}=b_{aj}+r_{aj}y$ and $\beta_{aj}=r_{aj}g$ for each j.
\end{enumerate}
\subsubsection{Round 2: Compute outcome}
\begin{enumerate}
\item
\end{enumerate}
\subsubsection{Round 3: Decrypt outcome}
\begin{enumerate}
\item
\end{enumerate}
\subsubsection{Epilogue: Outcome determination}
\begin{enumerate}
\item
\end{enumerate}
\section{first price auction with tie breaking and private outcome} \section{first price auction with tie breaking and private outcome}
\begin{align} \begin{align}