bignp256 0.14.0-rc.10

Pure Rust implementation of the Bign P-256 (a.k.a. bign-curve256v1) elliptic curve as defined in STB 34.101.45-2013, with general purpose curve arithmetic
Documentation 
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//! bign-curve256v1 scalar field elements.

#![allow(clippy::arithmetic_side_effects)]

use crate::{BignP256, ORDER_HEX, U256};
use elliptic_curve::{
    Curve as _,
    bigint::cpubits,
    ff::PrimeField,
    scalar::{FromUintUnchecked, IsHigh},
    subtle::{Choice, ConstantTimeEq, ConstantTimeGreater, CtOption},
};

// TODO(tarcieri): remove this when we can use `const _` to silence warnings
cpubits! {
    32 => {
        #[path = "scalar/bignp256_scalar_32.rs"]
        #[allow(
            dead_code,
            clippy::cast_possible_truncation,
            clippy::cast_possible_wrap,
            clippy::cast_sign_loss,
            clippy::identity_op,
            clippy::needless_lifetimes,
            clippy::too_many_arguments,
            clippy::unnecessary_cast
        )]
        mod scalar_impl;
    }
    64 => {
        #[path = "scalar/bignp256_scalar_64.rs"]
        #[allow(
            dead_code,
            clippy::cast_possible_truncation,
            clippy::cast_possible_wrap,
            clippy::cast_sign_loss,
            clippy::identity_op,
            clippy::needless_lifetimes,
            clippy::too_many_arguments,
            clippy::unnecessary_cast
        )]
        mod scalar_impl;
    }
}

use self::scalar_impl::*;

#[cfg(doc)]
use core::ops::{Add, Mul, Neg, Sub};

primefield::monty_field_params! {
    name: ScalarParams,
    modulus: ORDER_HEX,
    uint: U256,
    byte_order: primefield::ByteOrder::LittleEndian,
    multiplicative_generator: 3,
    doc: "Montgomery parameters for the bign-curve256v1 scalar modulus"
}

primefield::monty_field_element! {
    name: Scalar,
    params: ScalarParams,
    uint: U256,
    doc: "Element in the bign-curve256v1 scalar field modulo n"
}

primefield::fiat_monty_field_arithmetic! {
    name: Scalar,
    params: ScalarParams,
    uint: U256,
    non_mont: fiat_bignp256_scalar_non_montgomery_domain_field_element,
    mont: fiat_bignp256_scalar_montgomery_domain_field_element,
    from_mont: fiat_bignp256_scalar_from_montgomery,
    to_mont: fiat_bignp256_scalar_to_montgomery,
    add: fiat_bignp256_scalar_add,
    sub: fiat_bignp256_scalar_sub,
    mul: fiat_bignp256_scalar_mul,
    neg: fiat_bignp256_scalar_opp,
    square: fiat_bignp256_scalar_square,
    divstep_precomp: fiat_bignp256_scalar_divstep_precomp,
    divstep: fiat_bignp256_scalar_divstep,
    msat: fiat_bignp256_scalar_msat,
    selectnz: fiat_bignp256_scalar_selectznz
}

primefield::monty_field_reduce! {
    name: Scalar,
    params: ScalarParams,
    uint: U256,
}

elliptic_curve::scalar_impls!(BignP256, Scalar);

impl AsRef<Scalar> for Scalar {
    fn as_ref(&self) -> &Scalar {
        self
    }
}

impl FromUintUnchecked for Scalar {
    type Uint = U256;

    fn from_uint_unchecked(uint: Self::Uint) -> Self {
        Self::from_uint_unchecked(uint)
    }
}

impl IsHigh for Scalar {
    fn is_high(&self) -> Choice {
        const MODULUS_SHR1: U256 = BignP256::ORDER.as_ref().shr_vartime(1);
        self.to_canonical().ct_gt(&MODULUS_SHR1)
    }
}

#[cfg(test)]
mod tests {
    use super::{Scalar, U256};
    use super::{
        ScalarParams, fiat_bignp256_scalar_montgomery_domain_field_element,
        fiat_bignp256_scalar_msat, fiat_bignp256_scalar_non_montgomery_domain_field_element,
        fiat_bignp256_scalar_to_montgomery,
    };

    primefield::test_primefield!(Scalar, U256);
    primefield::test_fiat_monty_field_arithmetic!(
        name: Scalar,
        params: ScalarParams,
        uint: U256,
        non_mont: fiat_bignp256_scalar_non_montgomery_domain_field_element,
        mont: fiat_bignp256_scalar_montgomery_domain_field_element,
        to_mont: fiat_bignp256_scalar_to_montgomery,
        msat: fiat_bignp256_scalar_msat
    );
}