p384: use generic prime order formulas (#601)

Uses the generic implementation of Renes-Costello-Batina 2015 added to
the `elliptic-curve` crate:

RustCrypto/traits#1022

Author: tarcieri

Cargo.lock

@@ -17,7 +17,7 @@ edition = "2021"
 rust-version = "1.57"
 
 [dependencies]
-elliptic-curve = { version = "0.12", default-features = false, features = ["hazmat", "sec1"] }
+elliptic-curve = { version = "0.12.1", default-features = false, features = ["hazmat", "sec1"] }
 
 # optional dependencies
 ecdsa-core = { version = "0.14", package = "ecdsa", optional = true, default-features = false, features = ["der"] }

p384/Cargo.toml

@@ -28,8 +28,8 @@ use self::field_impl::*;
 use crate::FieldBytes;
 use core::ops::{AddAssign, MulAssign, Neg, SubAssign};
 use elliptic_curve::{
-    bigint::{self, ArrayEncoding, Encoding, Integer, Limb, U384},
-    subtle::{Choice, ConstantTimeEq, ConstantTimeLess, CtOption},
+    bigint::{self, Encoding, Limb, U384},
+    subtle::{Choice, ConstantTimeEq, CtOption},
 };
 
 /// Constant representing the modulus
@@ -40,7 +40,7 @@ pub(crate) const MODULUS: U384 = U384::from_be_hex("ffffffffffffffffffffffffffff
 #[derive(Clone, Copy, Debug)]
 pub struct FieldElement(pub(super) U384);
 
-impl_field_element!(
+elliptic_curve::impl_field_element!(
     FieldElement,
     FieldBytes,
     U384,