Struct Fp 

#[repr(transparent)]
pub struct Fp(pub [u64; 4]);

The P-256 coordinate field, GF(p) with p = 2^256 - 2^224 + 2^192 + 2^96 - 1.

Values are held in Montgomery form (a * R mod m). Arithmetic is branch-free and carries no data-dependent memory access.

Tuple Fields

0: [u64; 4]

Implementations

impl Fp

pub const MODULUS: [u64; 4] = crate::nist::p256_field::P

The modulus, as little-endian 64-bit limbs.

pub fn to_mont(limbs: [u64; 4]) -> Self

Convert a plain integer into Montgomery form, in constant time.

pub const fn to_mont_const(limbs: [u64; 4]) -> Self

Self::to_mont for a curve constant, evaluated at compile time. Not for secrets: it skips the barrier to_mont has.

pub fn from_mont(&self) -> [u64; 4]

Convert out of Montgomery form, in constant time.

pub fn square_n(&self, n: usize) -> Self

Repeated squaring, self^(2^n).

pub fn pow(&self, exponent: &[u64; 4]) -> Self

Exponentiation with a fixed four-bit window, branch-free in the exponent as well as the base.

The exponent is always a public constant here (m - 2 for inversion, (p + 1) / 4 for square roots), but nothing below relies on that: every window costs four squarings and one multiplication whatever its bits, and its power is chosen from the table by reading all sixteen entries with conditional moves, never by indexing or branching on the exponent. An earlier square-and-multiply branched on each exponent bit, and Valgrind’s secret-dependence harness reported that branch in the nonce inversion – whether the compiler had folded the secret into the condition or the tool was imprecise, the cure is to have no such branch at all.

One multiplication per four bits, where square-and-multiply made one per set bit: nearly one per bit for an m - 2 that is mostly ones.

Trait Implementations

impl Clone for Fp

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Fp

impl Debug for Fp

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Fp

impl PartialEq for Fp

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Fp