refactor: hoist shared RSA-OAEP padding to a constant; restore encrypt_aes_key_with_rsa docstring

hoists the byte-identical OAEP(MGF1(SHA256), SHA256, label=None) construction out
of encrypt_aes_key_with_rsa and decrypt_aes_key_with_rsa into a module-level
_OAEP_PADDING constant so a future scheme change lands in one place instead of
two in lockstep. also restores encrypt_aes_key_with_rsa's Args/Returns/Raises
docstring block, matching its four siblings, after Wave-1 over-stripped it to
bare prose.

Signed-off-by: disqualifier <dev@disqualifier.me>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "envelope_crypto"
-version = "0.1.8"
+version = "0.1.9"
 description = "Envelope encryption (RSA-OAEP wrapped AES-256-GCM) for dict records — config-free, storage-agnostic, installable."
 requires-python = ">=3.10"
 dependencies = [

src/envelope_crypto/envelope_crypto.py

@@ -36,6 +36,12 @@ from cryptography.hazmat.primitives.serialization import load_ssh_public_key
 
 _log = logging.getLogger(__name__)
 
+_OAEP_PADDING = padding.OAEP(
+    mgf=padding.MGF1(algorithm=hashes.SHA256()),
+    algorithm=hashes.SHA256(),
+    label=None,
+)
+
 
 def _password_mismatch_message(pw: Optional[bytes]) -> str:
     """clear ValueError text for a TypeError raised by a password/encryption mismatch"""
@@ -263,10 +269,22 @@ class EnvelopeCrypto:
     def encrypt_aes_key_with_rsa(
         self, aes_key: bytes, rsa_key: str, is_file: bool = True
     ) -> Tuple[str, str]:
-        """wrap an AES key with an RSA public key; returns (fingerprint, wrapped_b64)
+        """wrap an AES key with an RSA public key
 
-        raises ValueError if rsa_key is not an RSA key (this lib is RSA-envelope only;
-        e.g. an Ed25519/EC key loads and fingerprints fine but cannot wrap).
+        Args:
+            aes_key: the AES data key to wrap.
+            rsa_key: path to (or, if is_file=False, raw PEM/OpenSSH data of)
+                the RSA public key to wrap with.
+            is_file: True (default) treats rsa_key as a path.
+
+        Returns:
+            (fingerprint, wrapped_b64): the wrapping key's fingerprint and the
+            RSA-OAEP wrapped key, base64-encoded.
+
+        Raises:
+            ValueError: rsa_key is not an RSA key (this lib is RSA-envelope
+                only; e.g. an Ed25519/EC key loads and fingerprints fine but
+                cannot wrap), or is malformed.
         """
         if is_file:
             with open(rsa_key, "rb") as key_file:
@@ -277,14 +295,7 @@ class EnvelopeCrypto:
         public_key = _load_public_key(key_data)
         _require_rsa(public_key)
 
-        wrapped = public_key.encrypt(
-            aes_key,
-            padding.OAEP(
-                mgf=padding.MGF1(algorithm=hashes.SHA256()),
-                algorithm=hashes.SHA256(),
-                label=None,
-            ),
-        )
+        wrapped = public_key.encrypt(aes_key, _OAEP_PADDING)
         fingerprint = _fingerprint_of(public_key)
         wrapped_b64 = base64.b64encode(wrapped).decode()
         _log.info("wrapped data key for fingerprint %s", fingerprint[:8])
@@ -321,14 +332,7 @@ class EnvelopeCrypto:
         _require_rsa(private_key)
 
         wrapped = base64.b64decode(encrypted_key_base64)
-        aes_key = private_key.decrypt(
-            wrapped,
-            padding.OAEP(
-                mgf=padding.MGF1(algorithm=hashes.SHA256()),
-                algorithm=hashes.SHA256(),
-                label=None,
-            ),
-        )
+        aes_key = private_key.decrypt(wrapped, _OAEP_PADDING)
         _log.info("unwrapped data key with RSA private key")
         return aes_key