参考
步骤：
外网电脑：
创建一个文件夹i
pip download cryptography

Collecting cryptography
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/26/d6/e8b087b9ae062d737c67c3bf76e30333bda9295ca17205062e8ed2c872de/cryptography-3.0-cp35-abi3-manylinux1_x86_64.whl
  Saved ./cryptography-3.0-cp35-abi3-manylinux1_x86_64.whl
Collecting cffi!=1.11.3,>=1.8 (from cryptography)
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/f1/c7/72abda280893609e1ddfff90f8064568bd8bcb2c1770a9d5bb5edb2d1fea/cffi-1.14.0-cp36-cp36m-manylinux1_x86_64.whl
  Saved ./cffi-1.14.0-cp36-cp36m-manylinux1_x86_64.whl
Collecting six>=1.4.1 (from cryptography)
  Using cached https://pypi.tuna.tsinghua.edu.cn/packages/ee/ff/48bde5c0f013094d729fe4b0316ba2a24774b3ff1c52d924a8a4cb04078a/six-1.15.0-py2.py3-none-any.whl
  Saved ./six-1.15.0-py2.py3-none-any.whl
Collecting pycparser (from cffi!=1.11.3,>=1.8->cryptography)
  Downloading https://pypi.tuna.tsinghua.edu.cn/packages/ae/e7/d9c3a176ca4b02024debf82342dab36efadfc5776f9c8db077e8f6e71821/pycparser-2.20-py2.py3-none-any.whl (112kB)
    100% |████████████████████████████████| 112kB 2.6MB/s 
  Saved ./pycparser-2.20-py2.py3-none-any.whl
Successfully downloaded cryptography cffi six pycparser
You are using pip version 9.0.3, however version 20.1.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

将这个文件夹传输到内网电脑，然后根据下载时显示的安装顺序倒序安装
pip install pycparser-2.20-py2.py3-none-any.whl
pip install cffi-1.14.0-cp36-cp36m-manylinux1_x86_64.whl
pip install six-1.15.0-py2.py3-none-any.whl
pip install cryptography-3.0-cp35-abi3-manylinux1_x86_64.whl
也可以
pip install cryptography-3.0-cp35-abi3-manylinux1_x86_64.whl cffi-1.14.0-cp36-cp36manylinux1_x86_64.whl six-1.15.0-py2.py3-none-any.whl pycparser-2.20-py2.py3-none-any.whl
ok！安装成功