feat: add DER encoding methods and update key type alias in key_utils

Signed-off-by: MonaaEid <monaa_eid@hotmail.com>

Author: MonaaEid

src/hiero_sdk_python/crypto/public_key.py

@@ -452,12 +452,7 @@ def _encode_der_oid(cls, oid: str) -> bytes:
         """
         parts = [int(part) for part in oid.split(".")]
 
-        is_valid = (
-            len(parts) >= 2 and
-            parts[0] in (0, 1, 2) and
-            parts[1] >= 0 and
-            (parts[0] == 2 or parts[1] < 40)
-        )
+        is_valid = len(parts) >= 2 and parts[0] in (0, 1, 2) and parts[1] >= 0 and (parts[0] == 2 or parts[1] < 40)
         if not is_valid:
             raise ValueError(f"Invalid OID structure for '{oid}'")
 
@@ -495,8 +490,7 @@ def to_bytes_der_ecdsa_compressed(self) -> bytes:
 
         # id-ecPublicKey + secp256k1 OID algorithm identifier
         algorithm_id = self._encode_der_sequence(
-            self._encode_der_oid("1.2.840.10045.2.1")
-            + self._encode_der_oid("1.3.132.0.10")
+            self._encode_der_oid("1.2.840.10045.2.1") + self._encode_der_oid("1.3.132.0.10")
         )
         compressed_point = self.to_bytes_ecdsa(compressed=True)
         subject_public_key = self._encode_der_bit_string(compressed_point)
@@ -529,7 +523,7 @@ def to_string_der(self) -> str:
         Hex-encoded DER form of the public key.
         """
         return self.to_bytes_der().hex()
-    
+
     def to_string_der_ecdsa_compressed(self) -> str:
         """
         Returns DER SPKI hex for ECDSA secp256k1 using a compressed SEC1 point.

src/hiero_sdk_python/utils/key_utils.py

@@ -7,16 +7,14 @@
 
 from __future__ import annotations
 
-from typing import Union
-
 from hiero_sdk_python.crypto.key import Key as SdkKey
 from hiero_sdk_python.crypto.private_key import PrivateKey
 from hiero_sdk_python.crypto.public_key import PublicKey
 from hiero_sdk_python.hapi.services import basic_types_pb2
 
 
 # Type alias for keys that can be either PrivateKey or PublicKey
-Key = Union[PrivateKey, PublicKey, SdkKey]
+Key = PrivateKey | PublicKey | SdkKey
 
 
 def key_to_proto(key: Key | None) -> basic_types_pb2.Key | None:

tests/unit/keys_public_test.py

@@ -344,13 +344,9 @@ def test_encode_der_length_negative_raises():
 
 def test_encode_der_oid_known_values():
     # id-ecPublicKey
-    assert PublicKey._encode_der_oid("1.2.840.10045.2.1") == bytes.fromhex(
-        "06072a8648ce3d0201"
-    )
+    assert PublicKey._encode_der_oid("1.2.840.10045.2.1") == bytes.fromhex("06072a8648ce3d0201")
     # secp256k1
-    assert PublicKey._encode_der_oid("1.3.132.0.10") == bytes.fromhex(
-        "06052b8104000a"
-    )
+    assert PublicKey._encode_der_oid("1.3.132.0.10") == bytes.fromhex("06052b8104000a")
 
 
 def test_encode_der_oid_combined_root_multibyte():
@@ -390,11 +386,9 @@ def test_to_bytes_der_ecdsa_compressed_structure_and_roundtrip(ecdsa_keypair):
     compressed_point = public_key.to_bytes_ecdsa(compressed=True)
 
     # Fixed SPKI prefix for secp256k1 compressed-point encoding.
-    expected_prefix = bytes.fromhex(
-        "3036301006072a8648ce3d020106052b8104000a032200"
-    )
+    expected_prefix = bytes.fromhex("3036301006072a8648ce3d020106052b8104000a032200")
     assert der.startswith(expected_prefix)
-    assert der[len(expected_prefix):] == compressed_point
+    assert der[len(expected_prefix) :] == compressed_point
 
     # Ensure produced DER is parseable and preserves the same public key bytes.
     loaded = PublicKey.from_der(der)