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fix(crypto): add safety check for odd lengths in vector_karatsuba #3557

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fix(crypto): add safety check for odd lengths in vector_karatsuba #3557

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199e56d
fix(crypto): add safety check and panic test for vector_karatsuba odd…
kimyee1 Aug 9, 2026
612596e
style: apply nightly rustfmt formatting
kimyee1 Aug 10, 2026
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16 changes: 16 additions & 0 deletions crates/crypto/src/dsa/falcon512_poseidon2/math/polynomial.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -476,6 +476,10 @@ fn vector_karatsuba<
right: &[F],
) -> Vec<F> {
let n = left.len();

// ??? ADD THIS SAFETY NET:
assert!(n.is_power_of_two(), "vector_karatsuba only supports power-of-two lengths");

if n <= 8 {
let mut product = vec![F::zero(); left.len() + right.len() - 1];
for (i, l) in left.iter().enumerate() {
Expand Down Expand Up @@ -667,4 +671,16 @@ mod tests {
Polynomial::reduce_negacyclic(&Polynomial::mul_modulo_p(&poly1, &poly2))
);
}

// ?? PASTE THE NEW TEST RIGHT HERE! ??

#[test]
#[should_panic(expected = "vector_karatsuba only supports power-of-two lengths")]
fn karatsuba_panics_on_non_power_of_two() {
// We are intentionally using length 9 (not a power of 2)
// This should trigger our safety guard and panic!
let p1 = Polynomial::new(vec![1, 2, 3, 4, 5, 6, 7, 8, 9]);
let p2 = Polynomial::new(vec![1, 2, 3, 4, 5, 6, 7, 8, 9]);
p1.karatsuba(&p2);
}
}
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