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Change VerifyingKey::A_hat and SigningKey::A_hat field from stack-all… #1257

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Change VerifyingKey::A_hat and SigningKey::A_hat field from stack-all… #1257

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18 changes: 10 additions & 8 deletions ml-dsa/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,8 @@ use hybrid_array::{
use module_lattice::Truncate;
use sha3::Shake256;
use signature::{DigestSigner, DigestVerifier, MultipartSigner, MultipartVerifier, Signer};
extern crate alloc;
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@tarcieri tarcieri Mar 17, 2026

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We deliberately avoid having a hard dependency on liballoc and the heap.

This needs to at least be an optional alloc feature, although ideally the solution would not need such a dependency

use alloc::boxed::Box;

#[cfg(feature = "rand_core")]
use {
Expand Down Expand Up @@ -278,7 +280,7 @@ pub struct SigningKey<P: MlDsaParams> {
s1_hat: NttVector<P::L>,
s2_hat: NttVector<P::K>,
t0_hat: NttVector<P::K>,
A_hat: NttMatrix<P::K, P::L>,
A_hat: Box<NttMatrix<P::K, P::L>>,
}

impl<P: MlDsaParams> fmt::Debug for SigningKey<P> {
Expand Down Expand Up @@ -312,7 +314,7 @@ impl<P: MlDsaParams> SigningKey<P> {
t0: Vector<P::K>,
A_hat: Option<NttMatrix<P::K, P::L>>,
) -> Self {
let A_hat = A_hat.unwrap_or_else(|| expand_a(&rho));
let A_hat = Box::new(A_hat.unwrap_or_else(|| expand_a(&rho)));
let s1_hat = s1.ntt();
let s2_hat = s2.ntt();
let t0_hat = t0.ntt();
Expand Down Expand Up @@ -369,7 +371,7 @@ impl<P: MlDsaParams> SigningKey<P> {
// Rejection sampling loop
for kappa in (0..u16::MAX).step_by(P::L::USIZE) {
let y = expand_mask::<P::L, P::Gamma1>(&rhopp, kappa);
let w = (&self.A_hat * &y.ntt()).ntt_inverse();
let w = (&*self.A_hat * &y.ntt()).ntt_inverse();
let w1 = w.high_bits::<P::TwoGamma2>();

let w1_tilde = P::encode_w1(&w1);
Expand Down Expand Up @@ -601,13 +603,13 @@ impl<P: MlDsaParams> signature::Keypair for SigningKey<P> {
/// provide the precomputed public key associated with the private key
/// itself.
fn verifying_key(&self) -> Self::VerifyingKey {
let As1 = &self.A_hat * &self.s1_hat;
let As1 = &*self.A_hat * &self.s1_hat;
let t = &As1.ntt_inverse() + &self.s2;

/* Discard t0 */
let (t1, _) = t.power2round();

VerifyingKey::new(self.rho.clone(), t1, Some(self.A_hat.clone()), None)
VerifyingKey::new(self.rho.clone(), t1, Some((*self.A_hat).clone()), None)
}
}

Expand Down Expand Up @@ -667,7 +669,7 @@ pub struct VerifyingKey<P: ParameterSet> {
t1: Vector<P::K>,

// Derived values
A_hat: NttMatrix<P::K, P::L>,
A_hat: Box<NttMatrix<P::K, P::L>>,
t1_2d_hat: NttVector<P::K>,
tr: B64,
}
Expand All @@ -679,7 +681,7 @@ impl<P: MlDsaParams> VerifyingKey<P> {
A_hat: Option<NttMatrix<P::K, P::L>>,
enc: Option<EncodedVerifyingKey<P>>,
) -> Self {
let A_hat = A_hat.unwrap_or_else(|| expand_a(&rho));
let A_hat = Box::new(A_hat.unwrap_or_else(|| expand_a(&rho)));
let enc = enc.unwrap_or_else(|| Self::encode_internal(&rho, &t1));

let t1_2d_hat = (Elem::new(1 << 13) * &t1).ntt();
Expand Down Expand Up @@ -730,7 +732,7 @@ impl<P: MlDsaParams> VerifyingKey<P> {

let z_hat = sigma.z.ntt();
let c_hat = c.ntt();
let Az_hat = &self.A_hat * &z_hat;
let Az_hat = &*self.A_hat * &z_hat;
let ct1_2d_hat = &c_hat * &self.t1_2d_hat;

let wp_approx = (&Az_hat - &ct1_2d_hat).ntt_inverse();
Expand Down
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