fix test and remove coverage skip

Author: reaperhulk

src/rust/src/backend/kdf.rs

@@ -834,12 +834,10 @@ impl HkdfExpand {
     }
 }
 
-// NO-COVERAGE-START
 #[pyo3::pyclass(
     module = "cryptography.hazmat.primitives.kdf.x963kdf",
     name = "X963KDF"
 )]
-// NO-COVERAGE-END
 struct X963Kdf {
     algorithm: pyo3::Py<pyo3::PyAny>,
     length: usize,
@@ -863,15 +861,15 @@ impl X963Kdf {
         let digest_size = algorithm
             .bind(py)
             .getattr(pyo3::intern!(py, "digest_size"))?
-            .extract::<usize>()?;
+            .extract::<u64>()?;
 
-        let max_len = digest_size.checked_mul(u32::MAX as usize).ok_or_else(|| {
+        let max_len = digest_size.checked_mul(u32::MAX as u64).ok_or_else(|| {
             pyo3::exceptions::PyValueError::new_err(
                 "Digest size too large, would cause overflow in max length calculation",
             )
         })?;
 
-        if length > max_len {
+        if length as u64 > max_len {
             return Err(CryptographyError::from(
                 pyo3::exceptions::PyValueError::new_err(format!(
                     "Cannot derive keys larger than {max_len} bits."

tests/hazmat/primitives/test_x963kdf.py

@@ -4,7 +4,6 @@
 
 
 import binascii
-import sys
 
 import pytest
 
@@ -111,13 +110,8 @@ def test_unicode_typeerror(self, backend):
             xkdf.verify(b"foo", "bar")  # type: ignore[arg-type]
 
     def test_digest_size_overflow(self):
-        # Create a mock algorithm with a digest_size that would overflow
-        # when multiplied by u32::MAX (2^32 - 1)
-        # Using sys.maxsize // 2 works on both 32-bit and 64-bit:
-        # - 32-bit: ~2^30 * 2^32 = 2^62 > 2^32-1 (overflow)
-        # - 64-bit: ~2^62 * 2^32 = 2^94 > 2^64-1 (overflow)
         class MockHashAlgorithm(hashes.HashAlgorithm):
-            digest_size = sys.maxsize // 2
+            digest_size = 2**62
             name = "MockHashAlgorithm"
             block_size = 2**16