[Cryptography-dev] Problems with importing OpenSSL on Windows

[Łukasz Hanuszczak]

Hello,

Our team uses two continuous integration systems that build and package the
Windows distribution of our project. One of them is internal and runs on
Windows 7, the other one is AppVeyor (running Windows 2012, which is based
on Windows 8 best to my knowledge) that works with our open-source
repository on GitHub.

Both systems use the same script that initializes the virtual environment,
upgrades pip, installs dependencies. The only significant difference is
that the internal pipeline does not have internet access and uses vendored
wheels (though downloaded from PyPI upfront).

Both systems use exactly the same version of Python and pip, as witnessed
by the output of `pip debug --verbose`:

```
(...)
pip version: pip 21.0.1 from c:\buildenv\python_64\lib\site-packages\pip
(python 3.6)
sys.version: 3.6.8 (tags/v3.6.8:3c6b436a57, Dec 24 2018, 00:16:47) [MSC
v.1916 64 bit (AMD64)]
(...)
```

Unfortunately, after upgrading `cryptography` from 2.9.2 to 3.3.2, the
AppVeyor task started to fail with the following error (during runtime, the
package installation process itself works fine):

```
(...)
  File
"c:\buildenv\python_64\lib\site-packages\cryptography\hazmat\backends\openssl\__init__.py",
line 7, in <module>
    from cryptography.hazmat.backends.openssl.backend import backend
  File
"c:\buildenv\python_64\lib\site-packages\cryptography\hazmat\backends\openssl\backend.py",
line 117, in <module>
    from cryptography.hazmat.bindings.openssl import binding
  File
"c:\buildenv\python_64\lib\site-packages\cryptography\hazmat\bindings\openssl\binding.py",
line 14, in <module>
    from cryptography.hazmat.bindings._openssl import ffi, lib
ImportError: DLL load failed: The specified module could not be found.
```

I have verified that on both systems there is the `cryptography` OpenSSL
DLL available
(`c:\buildenv\python_64\lib\site-packages\cryptography\hazmat\bindings\_openssl.pyd`)
and that it has exactly the same size (3,107,328 bytes). I have also
checked and tried using a newer version of `cryptography` (3.4.7) on
AppVeyor but the problem does not go away.

Has there been any change in handling of the OpenSSL DLL between 2.9.2 and
3.3.2? Or is there any other reason that might hint the source of issues?
Is it possible that the DLL itself introduced some new system dependency
that has to be installed first?

Thank you,
Łukasz
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