Refactor and rename Scalar::from_bytes_wide

It now used a 512-bit large destination string to hash into.
New name: `from_blake2b`.

Resolves #137

CHANGELOG.md

@@ -13,7 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Add `from_var_bytes` to scalar [#133]
+- Add `from_var_bytes` to scalar [#133] and refactor and rename to `from_blake2b` [#137]
 
 ## [0.12.3] - 2023-11-01
 
@@ -228,6 +228,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Rename `S` to `TWO_ADACITY` and export it
 
 <!-- Issues -->
+[#137]: https://github.com/dusk-network/bls12_381/issues/137
 [#135]: https://github.com/dusk-network/bls12_381/issues/135
 [#133]: https://github.com/dusk-network/bls12_381/issues/133
 [#125]: https://github.com/dusk-network/bls12_381/issues/125

src/scalar/dusk.rs

@@ -262,34 +262,31 @@ impl Scalar {
         res
     }
 
-    /// Creates a `Scalar` from arbitrary bytes by hashing the input with BLAKE2b into a 256-bits
-    /// number, and then converting it into its `Scalar` representation.
-    pub fn from_var_bytes(input: &[u8]) -> Scalar {
+    /// Creates a `Scalar` from arbitrary bytes by hashing the input with
+    /// BLAKE2b into a 512-bits number, and then converting the number into its
+    /// `Scalar` representation by reducing it by the modulo.
+    ///
+    /// This implementation follows the first conversion of
+    /// https://hackmd.io/zV6qe1_oSU-kYU6Tt7pO7Q with concrete numbers:
+    /// ```text
+    /// p = 0x73eda753299d7d483339d80809a1d80553bda402fffe5bfeffffffff00000001
+    /// p = 52435875175126190479447740508185965837690552500527637822603658699938581184513
+    ///
+    /// s = 2^512
+    /// s = 13407807929942597099574024998205846127479365820592393377723561443721764030073546976801874298166903427690031858186486050853753882811946569946433649006084096
+    ///
+    /// r = 255699135089535202043525422716183576215815630510683217819334674386498370757523
+    ///
+    /// m = 3294906474794265442129797520630710739278575682199800681788903916070560242797
+    /// ```
+    pub fn from_blake2b(input: &[u8]) -> Scalar {
         let state = blake2b_simd::Params::new()
-            .hash_length(32)
+            .hash_length(64)
             .to_state()
             .update(input)
             .finalize();
 
-        let h = state.as_bytes();
-        let mut r = [0u64; 4];
-
-        // will be optmized by the compiler, depending on the available target
-        for i in 0..4 {
-            r[i] = u64::from_le_bytes([
-                h[i * 8],
-                h[i * 8 + 1],
-                h[i * 8 + 2],
-                h[i * 8 + 3],
-                h[i * 8 + 4],
-                h[i * 8 + 5],
-                h[i * 8 + 6],
-                h[i * 8 + 7],
-            ]);
-        }
-
-        // `from_raw` converts from arbitrary to congruent scalar
-        Self::from_raw(r)
+        Self::from_bytes_wide(state.as_bytes())
     }
 
     /// SHR impl