dd_string(self.Q_C.public_numbers().encode_point())
/python3.7.2/lib/python3.7/site-packages/paramiko/kex_ecdh_nist.py:96: CryptographyDeprecationWarning: Support for unsafe construction of public numbers from encoded data will be removed in a future version. Please use EllipticCurvePublicKey.from_encoded_point
self.curve, Q_S_bytes
/python3.7.2/lib/python3.7/site-packages/paramiko/kex_ecdh_nist.py:111: CryptographyDeprecationWarning: encode_point has been deprecated on EllipticCurvePublicNumbers and will be removed in a future version. Please use EllipticCurvePublicKey.public_bytes to obtain both compressed and uncompressed point encoding.
hm.add_string(self.Q_C.public_numbers().encode_point())
解决方法来自：https://yq.aliyun.com/articles/690717 ，感谢：sy9876
原因
paramiko 2.4.2 依赖 cryptography，而最新的cryptography==2.5里有一些弃用的API。
解决
删掉cryptography 2.5，安装2.4.2，就不会报错了。
pip uninstall cryptography==2.5
pip install cryptography==2.4.2