k256::FieldElement: PrimeField + FromUniformBytes<64>

k256/src/arithmetic/field.rs

@@ -29,13 +29,16 @@ use core::{
 use elliptic_curve::{
     Generate,
     bigint::{Odd, U256, modular::Retrieve},
-    ff::{self, Field, PrimeField},
+    ff::{self, Field, FromUniformBytes, PrimeField},
     ops::Invert,
     rand_core::{TryCryptoRng, TryRng},
     subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption},
     zeroize::DefaultIsZeroes,
 };
 
+#[cfg(feature = "bits")]
+use {crate::ScalarBits, elliptic_curve::group::ff::PrimeFieldBits};
+
 #[cfg(test)]
 use num_bigint::{BigUint, ToBigUint};
 
@@ -324,6 +327,33 @@ impl PrimeField for FieldElement {
     }
 }
 
+impl FromUniformBytes<64> for FieldElement {
+    fn from_uniform_bytes(bytes: &[u8; 64]) -> Self {
+        let hi = U256::from_be_slice(&bytes[..32]);
+        let lo = U256::from_be_slice(&bytes[32..]);
+        let modulus = const { *Odd::from_be_hex(MODULUS_HEX).as_nz_ref() };
+        Self(FieldElementImpl::from_u256_unchecked(
+            U256::rem_wide_vartime((lo, hi), &modulus),
+        ))
+    }
+}
+
+#[cfg(feature = "bits")]
+impl PrimeFieldBits for FieldElement {
+    cpubits! {
+        32 => { type ReprBits = [u32; 8]; }
+        64 => { type ReprBits = [u64; 4]; }
+    }
+
+    fn to_le_bits(&self) -> ScalarBits {
+        self.into()
+    }
+
+    fn char_le_bits() -> ScalarBits {
+        U256::from_be_hex(MODULUS_HEX).to_words().into()
+    }
+}
+
 impl Retrieve for FieldElement {
     type Output = U256;
 
@@ -509,6 +539,13 @@ impl<'a> Product<&'a FieldElement> for FieldElement {
     }
 }
 
+#[cfg(feature = "bits")]
+impl From<&FieldElement> for ScalarBits {
+    fn from(scalar: &FieldElement) -> ScalarBits {
+        scalar.0.to_u256().to_words().into()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use elliptic_curve::Generate;