使用paramiko报错：CryptographyDeprecationWarning: Support for unsafe construction of public numbers from encoded data will be removed in a future version. Please use EllipticCurvePublicKey.from_encoded_poi
1. paramiko does not support cryptography-2.6.1
pip3 uninstall cryptography==2.6.1
2. paramiko supports cryptography-2.4.2
pip install cryptography==2.4.2