[3.14] gh-161383: Fix inverted FIPS property query in _hashlib

In FIPS mode, usedforsecurity worked the wrong way round:
usedforsecurity=False MD5 was refused, usedforsecurity=True MD5 was
allowed, and hashlib.md5() fell back to the built-in _md5 without any
error.

disable_fips_property() returns 1 for usedforsecurity=False, but
py_digest_by_name() uses 'fips' as "1 = strict FIPS lookup". main
inverts the value with "!"; the 3.14 backport of gh-149816 (GH-160006)
lost it. Invert it after the -1 error check.

Tests:
- Add a FIPS-only test: MD5 must work with usedforsecurity=False and be
  refused with usedforsecurity=True.
- Copy check_file_digest() from main (gh-136547). The 3.14 version
  checks hashlib.new(name), which works through the built-in MD5, and
  then also calls _hashlib.openssl_md5, which FIPS refuses. With only
  the C fix, test_case_md5_* fail in FIPS mode. The main version skips
  each blocked constructor.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: prashant1221

Lib/test/test_hashlib.py

@@ -277,6 +277,18 @@ def test_usedforsecurity_false(self):
             self._hashlib.new("md5", usedforsecurity=False)
             self._hashlib.openssl_md5(usedforsecurity=False)
 
+    @unittest.skipUnless(get_fips_mode(), "requires FIPS mode")
+    def test_md5_usedforsecurity_in_fips_mode(self):
+        # In FIPS mode, OpenSSL must allow MD5 only with usedforsecurity=False.
+        if self._hashlib is None:
+            self.skipTest("OpenSSL hashlib is not available")
+        self._hashlib.new("md5", usedforsecurity=False)
+        self._hashlib.openssl_md5(usedforsecurity=False)
+        with self.assertRaises(ValueError):
+            self._hashlib.new("md5", usedforsecurity=True)
+        with self.assertRaises(ValueError):
+            self._hashlib.openssl_md5(usedforsecurity=True)
+
     @unittest.skipIf(get_fips_mode(), "skip in FIPS mode")
     def test_clinic_signature(self):
         for constructor in self.hash_constructors:
@@ -512,13 +524,17 @@ def check(self, name, data, hexdigest, shake=False, **kwargs):
 
     def check_file_digest(self, name, data, hexdigest):
         hexdigest = hexdigest.lower()
-        try:
-            hashlib.new(name)
-        except ValueError:
-            # skip, algorithm is blocked by security policy.
-            return
-        digests = [name]
-        digests.extend(self.constructors_to_test[name])
+        digests = []
+        for digest in [name, *self.constructors_to_test[name]]:
+            try:
+                if callable(digest):
+                    digest(b"")
+                else:
+                    hashlib.new(digest)
+            except ValueError:
+                # skip, algorithm is blocked by security policy.
+                continue
+            digests.append(digest)
 
         with tempfile.TemporaryFile() as f:
             f.write(data)

Misc/NEWS.d/next/Library/2026-10-30-09-00-00.gh-issue-161383.fIpS3a.rst

@@ -0,0 +1,5 @@
+Fix :mod:`hashlib` in OpenSSL FIPS mode: the :mod:`!_hashlib` digest lookup
+introduced by the fix for :gh:`149816` used the FIPS property query the wrong
+way round, so ``usedforsecurity=False`` digests such as MD5 failed to load and
+``usedforsecurity=True`` ones were no longer refused. Python then silently
+fell back to the built-in implementation of the algorithm.

Modules/_hashopenssl.c

@@ -421,6 +421,9 @@ py_digest_by_name(PyObject *module, const char *name, enum Py_hash_type py_ht)
     if (fips == -1) {
         goto finally;
     }
+    // 'fips' must be 1 for usedforsecurity=True: the opposite of what
+    // disable_fips_property() returns.
+    fips = !fips;
 
     if (entry != NULL) {
         PY_EVP_MD **cached = fips ? &entry->evp : &entry->evp_nosecurity;