Add placeholder function _ecies_gen_ephemeral_key to _internal.py

nkms/crypto/_internal.py

@@ -0,0 +1,16 @@
+from nkms.crypto import api as API
+from typing import Tuple, Union
+from npre import elliptic_curve
+
+
+def _ecies_gen_ephemeral_key(
+        recp_pubkey: Union[bytes, elliptic_curve.ec_element]
+) -> Tuple[bytes, bytes]:
+    """
+    Generates and encrypts an ephemeral key for the `recp_pubkey`.
+
+    :param recp_pubkey: Recipient's pubkey
+
+    :return: Tuple of encrypted symmetric key, and encrypted ephemeral privkey
+    """
+    pass