### changeset 1227:5636b02c6bef

Implementation of subtraction command.
author Janus Dam Nielsen Tue, 06 Oct 2009 10:05:24 +0200 94086392cb3c a62e12c9947a viff/orlandi.py viff/test/test_orlandi_runtime.py 2 files changed, 128 insertions(+), 0 deletions(-) [+]
line wrap: on
line diff
```--- a/viff/orlandi.py	Tue Oct 06 10:05:24 2009 +0200
+++ b/viff/orlandi.py	Tue Oct 06 10:05:24 2009 +0200
@@ -350,6 +350,39 @@
return result

+    def sub(self, share_a, share_b):
+        """Subtraction of shares.
+
+        Communication cost: none.
+
+        Each party ``P_i`` computes:
+        ``[z]_i = [x]_i - [y]_i
+                = (x_i - y_i mod p, rho_x,i - rho_y,i mod p, C_x * C_y)``.
+
+        """
+        def is_share(s, field):
+            if not isinstance(s, Share):
+                if not isinstance(s, FieldElement):
+                    s = field(s)
+                (v, rhov, Cv) = self._additive_constant(field(0), s)
+                return OrlandiShare(self, field, v, rhov, Cv)
+            return s
+
+        # Either share_a or share_b must have an attribute called "field".
+        field = getattr(share_a, "field", getattr(share_b, "field", None))
+
+        share_a = is_share(share_a, field)
+        share_b = is_share(share_b, field)
+
+        # Subtract xi and yi, rhoxi and rhoyi, and compute the commitment
+        def compute_subs((x, y)):
+            zi, (rhozi1, rhozi2), Cz = self._minus(x, y)
+            return OrlandiShare(self, field, zi, (rhozi1, rhozi2), Cz)
+
+        result = gather_shares([share_a, share_b])
+        return result
+

@@ -380,6 +413,23 @@
Cz = Cx * Cy
return (zi, (rhozi1, rhozi2), Cz)

+    def _minus(self, x, y):
+        """Subtraction of share-tuples *x* and *y*.
+
+        Each party ``P_i`` computes:
+        ``[x]_i = (x_i, rho_x,i, C_x)``
+        ``[y]_i = (y_i, rho_y,i, C_y)``
+        ``[z]_i = [x]_i - [y]_i
+                = (x_i - y_i mod p, rho_x,i - rho_y,i mod p, C_x / C_y)``.
+        """
+        xi, (rhoxi1, rhoxi2), Cx = x
+        yi, (rhoyi1, rhoyi2), Cy = y
+        zi = xi - yi
+        rhozi1 = rhoxi1 - rhoyi1
+        rhozi2 = rhoxi2 - rhoyi2
+        Cz = Cx / Cy
+        return (zi, (rhozi1, rhozi2), Cz)
+
def error_handler(self, ex):
print "Error: ", ex
return ex```
```--- a/viff/test/test_orlandi_runtime.py	Tue Oct 06 10:05:24 2009 +0200
+++ b/viff/test/test_orlandi_runtime.py	Tue Oct 06 10:05:24 2009 +0200
@@ -161,3 +161,81 @@
d = runtime.open(z2)
return d
+
+    @protocol
+    def test_sub(self, runtime):
+        """Test subtration of two numbers."""
+
+        self.Zp = GF(6277101735386680763835789423176059013767194773182842284081)
+
+        x1 = 42
+        y1 = 7
+
+        def check(v):
+            self.assertEquals(v, x1 - y1)
+
+        if 1 == runtime.id:
+            x2 = runtime.secret_share([1], self.Zp, x1)
+        else:
+            x2 = runtime.secret_share([1], self.Zp)
+
+        if 3 == runtime.id:
+            y2 = runtime.secret_share([3], self.Zp, y1)
+        else:
+            y2 = runtime.secret_share([3], self.Zp)
+
+        z2 = runtime.sub(x2, y2)
+        d = runtime.open(z2)
+        return d
+
+    @protocol
+    def test_sub_minus(self, runtime):
+        """Test subtration of two numbers."""
+
+        self.Zp = GF(6277101735386680763835789423176059013767194773182842284081)
+
+        x1 = 42
+        y1 = 7
+
+        def check(v):
+            self.assertEquals(v, x1 - y1)
+
+        if 1 == runtime.id:
+            x2 = runtime.secret_share([1], self.Zp, x1)
+        else:
+            x2 = runtime.secret_share([1], self.Zp)
+
+        if 3 == runtime.id:
+            y2 = runtime.secret_share([3], self.Zp, y1)
+        else:
+            y2 = runtime.secret_share([3], self.Zp)
+
+        z2 = x2 - y2
+        d = runtime.open(z2)
+        return d
+
+    @protocol
+    def test_sub_constant(self, runtime):
+        """Test subtration of two numbers."""
+
+        self.Zp = GF(6277101735386680763835789423176059013767194773182842284081)
+
+        x1 = 42
+        y1 = 7
+
+        def check(v):
+            self.assertEquals(v, x1 - y1)
+
+        if 1 == runtime.id:
+            x2 = runtime.secret_share([1], self.Zp, x1)
+        else:
+            x2 = runtime.secret_share([1], self.Zp)
+
+        z2 = x2 - y1
+        d = runtime.open(z2)