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ml-dsa: Add support for external mu #1023

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118 changes: 114 additions & 4 deletions ml-dsa/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -373,12 +373,18 @@ impl<P: MlDsaParams> SigningKey<P> {
// the concatenated M'.
// XXX(RLB) Should the API represent this as an input?
let mu = message_representative(&self.tr, Mp);
self.raw_sign_mu(&mu, rnd)
}

fn raw_sign_mu(&self, mu: &B64, rnd: &B32) -> Signature<P>
where
P: MlDsaParams,
{
// Compute the private random seed
let rhopp: B64 = H::default()
.absorb(&self.K)
.absorb(rnd)
.absorb(&mu)
.absorb(mu)
.squeeze_new();

// Rejection sampling loop
Expand All @@ -389,7 +395,7 @@ impl<P: MlDsaParams> SigningKey<P> {

let w1_tilde = P::encode_w1(&w1);
let c_tilde = H::default()
.absorb(&mu)
.absorb(mu)
.absorb(&w1_tilde)
.squeeze_new::<P::Lambda>();
let c = sample_in_ball(&c_tilde, P::TAU);
Expand Down Expand Up @@ -448,6 +454,24 @@ impl<P: MlDsaParams> SigningKey<P> {
Ok(self.sign_internal(Mp, &rnd))
}

/// This method reflects the randomized ML-DSA.Sign algorithm with a pre-computed μ.
///
/// # Errors
///
/// This method can return an opaque error if it fails to get enough randomness.
// Algorithm 2 ML-DSA.Sign (optional pre-computed μ variant)
#[cfg(feature = "rand_core")]
pub fn sign_mu_randomized<R: TryCryptoRng + ?Sized>(
&self,
mu: &B64,
rng: &mut R,
) -> Result<Signature<P>, Error> {
let mut rnd = B32::default();
rng.try_fill_bytes(&mut rnd).map_err(|_| Error::new())?;

Ok(self.raw_sign_mu(mu, &rnd))
}

/// This method reflects the optional deterministic variant of the ML-DSA.Sign algorithm.
///
/// # Errors
Expand All @@ -458,6 +482,14 @@ impl<P: MlDsaParams> SigningKey<P> {
self.raw_sign_deterministic(&[M], ctx)
}

/// This method reflects the optional deterministic variant of the ML-DSA.Sign algorithm with a
/// pre-computed μ.
// Algorithm 2 ML-DSA.Sign (optional deterministic and pre-computed μ variant)
pub fn sign_mu_deterministic(&self, mu: &B64) -> Signature<P> {
let rnd = B32::default();
self.raw_sign_mu(mu, &rnd)
}

fn raw_sign_deterministic(&self, M: &[&[u8]], ctx: &[u8]) -> Result<Signature<P>, Error> {
if ctx.len() > 255 {
return Err(Error::new());
Expand Down Expand Up @@ -616,7 +648,13 @@ impl<P: MlDsaParams> VerifyingKey<P> {
{
// Compute the message representative
let mu = message_representative(&self.tr, Mp);
self.raw_verify_mu(&mu, sigma)
}

fn raw_verify_mu(&self, mu: &B64, sigma: &Signature<P>) -> bool
where
P: MlDsaParams,
{
// Reconstruct w
let c = sample_in_ball(&sigma.c_tilde, P::TAU);

Expand All @@ -630,19 +668,25 @@ impl<P: MlDsaParams> VerifyingKey<P> {

let w1p_tilde = P::encode_w1(&w1p);
let cp_tilde = H::default()
.absorb(&mu)
.absorb(mu)
.absorb(&w1p_tilde)
.squeeze_new::<P::Lambda>();

sigma.c_tilde == cp_tilde
}

/// This algorithm reflect the ML-DSA.Verify algorithm from FIPS 204.
/// This algorithm reflects the ML-DSA.Verify algorithm from FIPS 204.
// Algorithm 3 ML-DSA.Verify
pub fn verify_with_context(&self, M: &[u8], ctx: &[u8], sigma: &Signature<P>) -> bool {
self.raw_verify_with_context(&[M], ctx, sigma)
}

/// This algorithm reflects the ML-DSA.Verify algorithm with a pre-computed μ from FIPS 204.
// Algorithm 3 ML-DSA.Verify (optional pre-computed μ variant)
pub fn verify_mu(&self, mu: &B64, sigma: &Signature<P>) -> bool {
self.raw_verify_mu(mu, sigma)
}

fn raw_verify_with_context(&self, M: &[&[u8]], ctx: &[u8], sigma: &Signature<P>) -> bool {
if ctx.len() > 255 {
return false;
Expand Down Expand Up @@ -1006,4 +1050,70 @@ mod test {
many_round_trip_test::<MlDsa65>();
many_round_trip_test::<MlDsa87>();
}

#[test]
fn sign_mu_verify_mu_round_trip() {
fn sign_mu_verify_mu<P>()
where
P: MlDsaParams,
{
let kp = P::key_gen_internal(&Array::default());
let sk = kp.signing_key;
let vk = kp.verifying_key;

let M = b"Hello world";
let rnd = Array([0u8; 32]);
let mu = message_representative(&sk.tr, &[&[M]]);
let sig = sk.raw_sign_mu(&mu, &rnd);

assert!(vk.raw_verify_mu(&mu, &sig));
}
sign_mu_verify_mu::<MlDsa44>();
sign_mu_verify_mu::<MlDsa65>();
sign_mu_verify_mu::<MlDsa87>();
}

#[test]
fn sign_mu_verify_internal_round_trip() {
fn sign_mu_verify_internal<P>()
where
P: MlDsaParams,
{
let kp = P::key_gen_internal(&Array::default());
let sk = kp.signing_key;
let vk = kp.verifying_key;

let M = b"Hello world";
let rnd = Array([0u8; 32]);
let mu = message_representative(&sk.tr, &[&[M]]);
let sig = sk.raw_sign_mu(&mu, &rnd);

assert!(vk.verify_internal(&[M], &sig));
}
sign_mu_verify_internal::<MlDsa44>();
sign_mu_verify_internal::<MlDsa65>();
sign_mu_verify_internal::<MlDsa87>();
}

#[test]
fn sign_internal_verify_mu_round_trip() {
fn sign_internal_verify_mu<P>()
where
P: MlDsaParams,
{
let kp = P::key_gen_internal(&Array::default());
let sk = kp.signing_key;
let vk = kp.verifying_key;

let M = b"Hello world";
let rnd = Array([0u8; 32]);
let mu = message_representative(&sk.tr, &[&[M]]);
let sig = sk.sign_internal(&[M], &rnd);

assert!(vk.raw_verify_mu(&mu, &sig));
}
sign_internal_verify_mu::<MlDsa44>();
sign_internal_verify_mu::<MlDsa65>();
sign_internal_verify_mu::<MlDsa87>();
}
}