Add mul, add, sub, neg, eq of Scalar

Multliplication took the place of multiplying with point. To multiply a
scalar with a point use multiply operator of the point instead.

src/scalar.rs

@@ -1,6 +1,6 @@
 use pyo3::prelude::*;
 use curve25519_dalek::scalar::Scalar as _Scalar;
-use crate::ristretto::{RistrettoPoint};
+use pyo3::basic::CompareOp;
 
 #[pyclass]
 pub struct Scalar(pub _Scalar);
@@ -12,8 +12,30 @@ impl Scalar {
         Scalar(_Scalar::from(x))
     }
 
-    pub fn __mul__(&self, p : &RistrettoPoint) -> RistrettoPoint {
-        RistrettoPoint(self.0 * p.0)
+    pub fn __mul__(&self, p : &Scalar) -> Scalar {
+        Scalar(self.0 * p.0)
+    }
+
+    pub fn __add__(&self, p : &Scalar) -> Scalar {
+        Scalar(self.0 + p.0)
+    }
+
+    pub fn __sub__(&self, p : &Scalar) -> Scalar {
+        Scalar(self.0 - p.0)
+    }
+
+    pub fn __neg__(&self) -> Scalar {
+        Scalar(-self.0)
+    }
+
+    // Overriding comparison operators, currently only supporting == and !=
+    fn __richcmp__(&self, other: PyRef<Scalar>, op: CompareOp) -> Py<PyAny> {
+        let py = other.py();
+        match op {
+            CompareOp::Eq => (self.0 == other.0).into_py(py),
+            CompareOp::Ne => (self.0 != other.0).into_py(py),
+            _ => py.NotImplemented(),
+        }
     }
 }
 

tests/test_ristretto.py

@@ -2,23 +2,14 @@
 from curve25519_dalek.scalar import Scalar
 from curve25519_dalek.constants import RISTRETTO_BASEPOINT_POINT
 
-def test_scalarmult_ristrettopoint_works_both_ways():
+def test_scalarmult():
     P = RISTRETTO_BASEPOINT_POINT
     s = Scalar.from_u64(999)
     P1 = P * s
-    P2 = s * P
-
-    assert P1.compress().as_bytes() == P2.compress().as_bytes()
-
-def test_impl_sum():
-    BASE = RISTRETTO_BASEPOINT_POINT
-    s1 = Scalar.from_u64(999)
-    P1 = BASE * s1
-
-    s2 = Scalar.from_u64(333);
-    P2 = BASE * s2;
-
-    vec = [P1, P2]
+    assert P1.compress().as_bytes() == bytes([
+        70, 101, 76, 35, 4, 33, 130, 159, 62, 231, 63, 205, 135, 227, 60, 26,
+        147, 227, 5, 110, 18, 24, 124, 104, 111, 26, 24, 111, 8, 181, 54, 33
+        ])
 
 def test_elligator_vs_ristretto_sage():
     data =  bytes([184, 249, 135, 49, 253, 123, 89, 113, 67, 160, 6, 239,

tests/test_scalar.py

@@ -0,0 +1,33 @@
+from curve25519_dalek.ristretto import RistrettoPoint, CompressedRistretto
+from curve25519_dalek.scalar import Scalar
+
+zero = Scalar.from_u64(0)
+zero2 = Scalar.from_u64(0)
+one = Scalar.from_u64(1)
+two = Scalar.from_u64(2)
+five = Scalar.from_u64(5)
+ten = Scalar.from_u64(10)
+
+def test_scalar_eq():
+    assert zero == zero2
+    assert zero2 == zero
+    assert zero != one
+    assert ten != one
+
+def test_sub():
+    assert one - one == zero
+    assert one - zero == one
+    assert ten - five == five
+
+def test_add():
+    assert one + one == two
+    assert two + two + one == five
+    assert zero + zero == zero
+    assert one + zero == one
+
+def test_scalar_mul():
+    assert one * one == one
+    assert one * zero == zero
+    assert zero * ten == zero
+    assert one * ten == ten
+    assert five * two == ten