ecdsa: refactor field bytes encoding (#1388)

Companion PR to RustCrypto/traits#2457

Author: tarcieri

Cargo.lock

@@ -71,3 +71,6 @@ ml-dsa = { path = "./ml-dsa" }
 rfc6979 = { path = "./rfc6979" }
 slh-dsa = { path = "./slh-dsa" }
 xmss = { path = "./xmss" }
+
+crypto-bigint = { git = "https://github.com/RustCrypto/crypto-bigint" }
+elliptic-curve = { git = "https://github.com/RustCrypto/traits" }

Cargo.toml

@@ -1,6 +1,7 @@
 //! Low-level ECDSA primitives.
 //!
-//! # ⚠️ Warning: Hazmat!
+//! <div class="warning">
+//! <b>Security️ Warning: Hazardous Materials!</b>
 //!
 //! YOU PROBABLY DON'T WANT TO USE THESE!
 //!
@@ -9,20 +10,20 @@
 //! If you are an end user / non-expert in cryptography, do not use these!
 //! Failure to use them correctly can lead to catastrophic failures including
 //! FULL PRIVATE KEY RECOVERY!
+//! </div>
 
 use crate::{EcdsaCurve, Error, Result};
 use core::cmp;
 use elliptic_curve::{FieldBytes, array::typenum::Unsigned};
 
 #[cfg(feature = "algorithm")]
 use {
-    crate::{
-        RecoveryId, Signature, SignatureSize,
-        elliptic_curve::{FieldBytesEncoding, array::ArraySize},
-    },
+    crate::{RecoveryId, Signature, SignatureSize},
     elliptic_curve::{
         CurveArithmetic, NonZeroScalar, ProjectivePoint, Scalar,
+        array::ArraySize,
         ff::PrimeField,
+        field,
         group::{Curve as _, Group},
         ops::{Invert, MulByGeneratorVartime, Reduce},
         point::AffineCoordinates,
@@ -179,7 +180,7 @@ where
 
     let k = NonZeroScalar::<C>::from_repr(rfc6979::generate_k::<D, _>(
         &d.to_repr(),
-        &C::ORDER.encode_field_bytes(),
+        &field::uint_to_bytes::<C>(&C::ORDER),
         &z2.to_repr(),
         ad,
     ))

ecdsa/src/hazmat.rs

@@ -10,14 +10,16 @@ use {
     },
     digest::{Digest, FixedOutputReset, Update},
     elliptic_curve::{
-        AffinePoint, FieldBytesEncoding, FieldBytesSize, Group, PrimeField, ProjectivePoint,
+        AffinePoint, CurveArithmetic, FieldBytes, FieldBytesSize, Group, PrimeField,
+        ProjectivePoint, Scalar,
+        array::ArraySize,
         bigint::CheckedAdd,
+        field,
+        ops::Invert,
         ops::{LinearCombination, Reduce},
         point::DecompressPoint,
         sec1::{self, FromSec1Point, ToSec1Point},
-    },
-    elliptic_curve::{
-        CurveArithmetic, FieldBytes, Scalar, array::ArraySize, ops::Invert, subtle::CtOption,
+        subtle::CtOption,
     },
     signature::{
         DigestSigner, MultipartSigner, RandomizedDigestSigner, Signer,
@@ -363,11 +365,12 @@ where
         let z = Scalar::<C>::reduce(&bits2field::<C>(prehash)?);
 
         let r_bytes = if recovery_id.is_x_reduced() {
-            C::Uint::decode_field_bytes(&r.to_repr())
+            let uint = field::bytes_to_uint::<C>(&r.to_repr())
                 .checked_add(&C::ORDER)
                 .into_option()
-                .ok_or_else(Error::new)?
-                .encode_field_bytes()
+                .ok_or_else(Error::new)?;
+
+            field::uint_to_bytes::<C>(&uint)
         } else {
             r.to_repr()
         };