Add P256.scalarMul

Crypto/PubKey/ECC/P256.hs

@@ -34,6 +34,7 @@ module Crypto.PubKey.ECC.P256
     , scalarIsZero
     , scalarAdd
     , scalarSub
+    , scalarMul
     , scalarInv
     , scalarCmp
     , scalarFromBinary
@@ -237,6 +238,14 @@ scalarSub a b =
     withNewScalarFreeze $ \d -> withScalar a $ \pa -> withScalar b $ \pb ->
         ccryptonite_p256e_modsub ccryptonite_SECP256r1_n pa pb d
 
+-- | Perform multiplication between two scalars
+--
+-- > a * b
+scalarMul :: Scalar -> Scalar -> Scalar
+scalarMul a b =
+    withNewScalarFreeze $ \d -> withScalar a $ \pa -> withScalar b $ \pb ->
+         ccryptonite_p256_modmul ccryptonite_SECP256r1_n pa 0 pb d
+
 -- | Give the inverse of the scalar
 --
 -- > 1 / a

tests/KAT_PubKey/P256.hs

@@ -92,6 +92,10 @@ tests = testGroup "P256"
             let v = unP256 r `mod` curveN
                 v' = P256.scalarSub (unP256Scalar r) P256.scalarZero
              in v `propertyEq` p256ScalarToInteger v'
+        , testProperty "mul" $ \r1 r2 ->
+            let r = (unP256 r1 * unP256 r2) `mod` curveN
+                r' = P256.scalarMul (unP256Scalar r1) (unP256Scalar r2)
+             in r `propertyEq` p256ScalarToInteger r'
         , testProperty "inv" $ \r' ->
             let inv  = inverseCoprimes (unP256 r') curveN
                 inv' = P256.scalarInv (unP256Scalar r')