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

@@ -475,6 +475,15 @@ def _encode_der_oid(cls, oid: str) -> bytes:
         if len(parts) < 2:
             raise ValueError("OID must contain at least two components")
 
+        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}'")
+
         first, second = parts[0], parts[1]
         if first not in (0, 1, 2):
             raise ValueError("Invalid OID first component")

tests/unit/keys_public_test.py

@@ -260,10 +260,10 @@ def test_encode_der_oid_invalid_components_raise():
     with pytest.raises(ValueError, match="at least two"):
         PublicKey._encode_der_oid("1")
 
-    with pytest.raises(ValueError, match="first component"):
+    with pytest.raises(ValueError, match="Invalid OID structure for '3.1.1'"):
         PublicKey._encode_der_oid("3.1.1")
 
-    with pytest.raises(ValueError, match="second component"):
+    with pytest.raises(ValueError, match="Invalid OID structure for '1.40.1'"):
         PublicKey._encode_der_oid("1.40.1")
 
     with pytest.raises(ValueError, match="non-negative"):