Merge branch 'negative-multiplication'

AntonKueltz · Jul 14, 2021 · bc203c5 · bc203c5
2 parents f2c8337 + 184beb6
commit bc203c5
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Showing 2 changed files with 16 additions and 2 deletions.
diff --git a/fastecdsa/point.py b/fastecdsa/point.py
@@ -140,7 +140,7 @@ def __mul__(self, scalar: int):
         x, y = curvemath.mul(
             str(self.x),
             str(self.y),
-            str(scalar),
+            str(abs(scalar)),
             str(self.curve.p),
             str(self.curve.a),
             str(self.curve.b),
@@ -152,7 +152,7 @@ def __mul__(self, scalar: int):
         y = int(y)
         if x == 0 and y == 0:
             return self.IDENTITY_ELEMENT
-        return Point(x, y, self.curve)
+        return Point(x, y, self.curve) if scalar > 0 else -Point(x, y, self.curve)
 
     def __rmul__(self, scalar: int):
         """Multiply a :class:`Point` on an elliptic curve by an integer.

diff --git a/fastecdsa/tests/test_prime_field_curve_math.py b/fastecdsa/tests/test_prime_field_curve_math.py
@@ -226,3 +226,17 @@ def test_point_at_infinity_arithmetic(self):
 
             self.assertEqual(P + Q, Point.IDENTITY_ELEMENT)
             self.assertEqual((P + Q) + P, P)
+
+    def test_mul_by_negative(self):
+        for curve in CURVES:
+            P = -1 * curve.G
+            self.assertEqual(P.x, (-curve.G).x)
+            self.assertEqual(P.y, (-curve.G).y)
+
+            a = randint(0, curve.q)
+            P = -a * curve.G
+            Q = a * -curve.G
+
+            self.assertEqual(P.x, Q.x)
+            self.assertEqual(P.y, Q.y)
+