fixed a bug that could have crashed when initing polring with specifi…

…c coefficients
PyryL · Dec 18, 2023 · d363224 · d363224
1 parent 9546c7f
commit d363224
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Showing 2 changed files with 6 additions and 1 deletion.
diff --git a/kyber/entities/polring.py b/kyber/entities/polring.py
@@ -34,7 +34,7 @@ def _apply_polynomial_modulo_limit(self) -> None:
         while coef_count >= n+1:
             self._coefs[-n-1] -= self._coefs[-1]
             self._coefs[-1] = 0
-            while self._coefs[-1] == 0:
+            while coef_count > 0 and self._coefs[-1] == 0:
                 self._coefs.pop()
                 coef_count -= 1
 

diff --git a/tests/test_polring.py b/tests/test_polring.py
@@ -22,6 +22,11 @@ def test_init_with_numpy_array(self):
         self.assertEqual(type(pol.coefs), list)
         self.assertEqual(type(pol.coefs[0]), int)
 
+    def test_init_with_remainder_zero(self):
+        # when taken modulo x^n+1, this polynomial should result 0
+        pol = PolynomialRing([1] + [0]*255 + [1])
+        self.assertEqual(pol.coefs, [])
+
     def test_init_with_random_inputs(self):
         # test with 1000 samples that randomily initialized polring matches expected
         seed(42)