Struct MontParams 

pub struct MontParams {
    pub n: BigInt,
    pub n_limbs: usize,
    pub n_inv_neg: u64,
    pub r_mod_n: BigInt,
    pub r2_mod_n: BigInt,
}

Parameters for Montgomery modular arithmetic.

Fields

n: BigInt

The modulus n.

n_limbs: usize

Number of limbs.

n_inv_neg: u64

-n^{-1} mod 2^64.

r_mod_n: BigInt

R = 2^{64*n_limbs} (not stored, implicit). R mod n.

r2_mod_n: BigInt

R^2 mod n.

Implementations

impl MontParams

pub fn new(n: &BigInt) -> Self

Create Montgomery parameters for modulus n.

pub fn to_mont(&self, a: &BigInt) -> BigInt

Convert a into Montgomery form: a * R mod n.

pub fn from_mont(&self, a: &BigInt) -> BigInt

Convert from Montgomery form: a * R^{-1} mod n.

pub fn mont_mul(&self, a: &BigInt, b: &BigInt) -> BigInt

Montgomery multiplication: (a * b * R^{-1}) mod n. Uses the CIOS (Coarsely Integrated Operand Scanning) method.

pub fn mod_exp(&self, base: &BigInt, exp: &BigInt) -> BigInt

Modular exponentiation via a Montgomery ladder. Computes base^exp mod n.

Not constant-time yet. The ladder is square-always in structure, but it branches on the secret exponent bit (exp.bit(i)) rather than using a constant-time conditional swap, and mont_mul’s conditional final subtract is not black_box-shielded (Walter 2002). Per the module header, do not use on secret exponents until T1-E lands the CT rework. [CESTI]