diff --git a/libp2p/crypto/key_exchange.py b/libp2p/crypto/key_exchange.py new file mode 100644 index 0000000..a204de3 --- /dev/null +++ b/libp2p/crypto/key_exchange.py @@ -0,0 +1,27 @@ +from typing import Callable, Tuple + +import Crypto.PublicKey.ECC as ECC + +from libp2p.crypto.ecc import create_new_key_pair +from libp2p.crypto.keys import PublicKey + +SharedKeyGenerator = Callable[[bytes], bytes] + + +def create_ephemeral_key_pair(curve_type: str) -> Tuple[PublicKey, SharedKeyGenerator]: + """ + Facilitates ECDH key exchange. + """ + if curve_type != "P-256": + raise NotImplementedError() + + key_pair = create_new_key_pair(curve_type) + + def _key_exchange(serialized_remote_public_key: bytes) -> bytes: + remote_public_key = ECC.import_key(serialized_remote_public_key) + curve_point = remote_public_key.pointQ + secret_point = curve_point * key_pair.private_key.impl.d + byte_size = secret_point.size_in_bytes() + return secret_point.x.to_bytes(byte_size, byteorder="big") + + return key_pair.public_key, _key_exchange