From 7ab5f8759ff93e8152b88eda5e14fad7a925c43f Mon Sep 17 00:00:00 2001
From: Jeff Burdges <burdges@gnunet.org>
Date: Sat, 15 Sep 2018 15:41:28 +0200
Subject: Add sigma to blindness property

---
 taler-fc19/paper.tex | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

(limited to 'taler-fc19')

diff --git a/taler-fc19/paper.tex b/taler-fc19/paper.tex
index fde7bf4..8ea12ed 100644
--- a/taler-fc19/paper.tex
+++ b/taler-fc19/paper.tex
@@ -780,10 +780,20 @@ We require the following two security properties for $\textsc{BlindSign}$:
 \begin{itemize}
   \item \emph{blindness}: Let $M$ be the set of all possible messages and $\overline{M}$ be the
     set of all possible blinded messages. Then the distribution of
-    \[ \left\{ (m, \overline{m}) \,\middle| m\, \randsel M, \overline{m} \leftarrow \algo{Blind}_{BS}(\mathcal{S}(\V{sk}), m) \right\} \]
+    \[ \left\{ (m, \simga, \overline{m}, \overline{\simga}) \,\middle| 
+	   m\, \randsel M, 
+	   \overline{m} \leftarrow \algo{Blind}_{BS}(\mathcal{S}(\V{sk}), m),
+	   \overline{\simga} \leftarrow \algo{Sign}_{BS}(\V{sk}, \overline{m}),
+	   \sigma \leftarrow \algo{UnblindSig}_{BS}(r, m, \overline{\sigma})
+	   \right\} \]
     must be computationally
     indistinguishable from
-    \[ \left\{ (m, x) \,\middle|\, m \randsel M, x \randsel \overline{M} \right\}. \]
+    \[ \left\{ (m, \simga, x, \simga_x) \,\middle|\, 
+	   m \randsel M, 
+	   \sigma \eftarrow \algo{UnblindSig}_{BS}(r, m, \algo{Sign}_{BS}(\V{sk}, \algo{Blind}_{BS}(\mathcal{S}(\V{sk}), m)) )
+	   x \randsel \overline{M},
+	   \sigma_x \leftarrow \algo{UnblindSig}_{BS}(r, x, \algo{Sign}_{BS}(\V{sk}, \algo{Blind}_{BS}(\mathcal{S}(\V{sk}), x)) )
+	   \right\}. \]
   \item \emph{unforgeability}:  An adversary that requests $k$ signatures with $\algo{Sign}_{BS}$
     is unable to produce $k+1$ valid signatures with non-negligible probability.
 \end{itemize}
-- 
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