gh-155426: correctly accept bytes-like keys in hmac.digest

picnixz · picnixz · commit 0c1bf69e13e9 · 2026-08-09T14:42:20.000+02:00
This only affects keys of length smaller than the HMAC blocksize
since larger keys are hashed first.
diff --git a/Lib/hmac.py b/Lib/hmac.py
@@ -267,6 +267,9 @@ def digest(key, msg, digest):
 
 
 def _compute_digest_fallback(key, msg, digest):
+    if not isinstance(key, (bytes, bytearray)):
+        raise TypeError(f"key: expected bytes or bytearray, "
+                        f"but got {type(key).__name__!r}")
     digest_cons = _get_digest_constructor(digest)
     if _is_shake_constructor(digest_cons):
         raise ValueError(f"unsupported hash algorithm {digest}")
diff --git a/Lib/test/test_hmac.py b/Lib/test/test_hmac.py
@@ -1519,6 +1519,12 @@ def test_with_fallback(self):
         finally:
             cache.pop('foo')
 
+    @hashlib_helper.requires_hashdigest("md5")
+    def test_hmac_digest_reject_memoryview_for_key(self):
+        hmac = import_fresh_module("hmac", blocked=["_hashlib", "_hmac"])
+        with self.assertRaises(TypeError):
+            hmac.digest(memoryview(b"small"), b"world", "md5")
+
     @hashlib_helper.requires_openssl_hashdigest("md5")
     @bigmemtest(size=_4G + 5, memuse=2, dry_run=False)
     def test_hmac_digest_overflow_error_openssl_only(self, size):
diff --git a/Misc/NEWS.d/next/Library/2026-08-09-14-06-27.gh-issue-155426.zZVPMd.rst b/Misc/NEWS.d/next/Library/2026-08-09-14-06-27.gh-issue-155426.zZVPMd.rst
@@ -0,0 +1,3 @@
+Make sure that the pure Python fallback of :func:`hmac.digest` reject
+keys that are neither :class:`bytes` or :class:`bytearray`. Patch by
+Bénédikt Tran.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Make sure that the pure Python fallback of :func:`hmac.digest` reject
	`2`	+keys that are neither :class:`bytes` or :class:`bytearray`. Patch by
	`3`	`+Bénédikt Tran.`