centralize our bytes check (#4622)

this will make life a bit easier when we support bytearrays

1 files changed, 6 insertions, 12 deletions

diff --git a/src/cryptography/hazmat/primitives/kdf/hkdf.py b/src/cryptography/hazmat/primitives/kdf/hkdf.py
index 917b4e9c..27dc9c93 100644
--- a/src/cryptography/hazmat/primitives/kdf/hkdf.py
+++ b/src/cryptography/hazmat/primitives/kdf/hkdf.py
@@ -26,11 +26,10 @@ class HKDF(object):
 
         self._algorithm = algorithm
 
-        if not (salt is None or isinstance(salt, bytes)):
-            raise TypeError("salt must be bytes.")
-
         if salt is None:
             salt = b"\x00" * self._algorithm.digest_size
+        else:
+            utils._check_bytes("salt", salt)
 
         self._salt = salt
 
@@ -44,9 +43,7 @@ class HKDF(object):
         return h.finalize()
 
     def derive(self, key_material):
-        if not isinstance(key_material, bytes):
-            raise TypeError("key_material must be bytes.")
-
+        utils._check_bytes("key_material", key_material)
         return self._hkdf_expand.derive(self._extract(key_material))
 
     def verify(self, key_material, expected_key):
@@ -77,11 +74,10 @@ class HKDFExpand(object):
 
         self._length = length
 
-        if not (info is None or isinstance(info, bytes)):
-            raise TypeError("info must be bytes.")
-
         if info is None:
             info = b""
+        else:
+            utils._check_bytes("info", info)
 
         self._info = info
 
@@ -102,9 +98,7 @@ class HKDFExpand(object):
         return b"".join(output)[:self._length]
 
     def derive(self, key_material):
-        if not isinstance(key_material, bytes):
-            raise TypeError("key_material must be bytes.")
-
+        utils._check_bytes("key_material", key_material)
         if self._used:
             raise AlreadyFinalized