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Check if the signature is correct size #23

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Merged
GiacomoPope merged 1 commit into from
Oct 3, 2025
Merged

Check if the signature is correct size #23

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10 changes: 10 additions & 0 deletions src/dilithium_py/ml_dsa/ml_dsa.py
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Original file line number Diff line number Diff line change
Expand Up @@ -152,6 +152,14 @@ def _sk_size(self) -> int:
t0_len = 416 * self.k
return 2 * 32 + 64 + s1_len + s2_len + t0_len

def _sig_size(self) -> int:
if self.gamma_1 == 131072:
s_bytes = 18
else:
assert self.gamma_1 == 524288
s_bytes = 20
return self.c_tilde_bytes + self.l * 32 * s_bytes + self.omega + self.k

def _unpack_sk(
self, sk: bytes
) -> tuple[bytes, bytes, bytes, Vector, Vector, Vector]:
Expand Down Expand Up @@ -220,6 +228,8 @@ def _unpack_h(self, h_bytes: bytes) -> Vector:
return self.M.vector(vector_coeffs)

def _unpack_sig(self, sig: bytes) -> tuple[bytes, Vector, Vector]:
if len(sig) != self._sig_size():
raise ValueError("Incorrect signature size")
c_tilde = sig[: self.c_tilde_bytes]
z_bytes = sig[self.c_tilde_bytes : -(self.k + self.omega)]
h_bytes = sig[-(self.k + self.omega) :]
Expand Down
13 changes: 13 additions & 0 deletions tests/test_ml_dsa.py
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,10 @@ def generic_test_ml_dsa(self, ML_DSA, count=5):
sig = ML_DSA.sign(sk, msg, ctx=ctx)
check_verify = ML_DSA.verify(pk, msg, sig, ctx=ctx)

check_short_verify = ML_DSA.verify(pk, msg, sig[:-1], ctx=ctx)
check_long_verify = ML_DSA.verify(pk, msg, sig + b"\x00", ctx=ctx)
check_empty_verify = ML_DSA.verify(pk, msg, b"", ctx=ctx)

# Sign with external_mu instead
external_mu = ML_DSA.prehash_external_mu(pk, msg, ctx=ctx)
sig_external_mu = ML_DSA.sign_external_mu(sk, external_mu)
Expand All @@ -40,6 +44,15 @@ def generic_test_ml_dsa(self, ML_DSA, count=5):
# Check that signature works
self.assertTrue(check_verify)

# Check that too short signature is rejected
self.assertFalse(check_short_verify)

# Check that too short signature is rejected
self.assertFalse(check_long_verify)

# Check that empty signature is rejected
self.assertFalse(check_empty_verify)

# Check that external_mu also works
self.assertTrue(check_external_mu)

Expand Down