Question: I am running Qt 5.7.1 (MSVC 2015, 32 bit) with Qt Creator 4.2.0. I have a problem with `QSslSocket`. I am getting the following errors:

```
qt.network.ssl: QSslSocket: cannot call unresolved function SSLv23_client_method
qt.network.ssl: QSslSocket: cannot call unresolved function SSL_CTX_new
qt.network.ssl: QSslSocket: cannot call unresolved function SSL_library_init
qt.network.ssl: QSslSocket: cannot call unresolved function ERR_get_error
qt.network.ssl: QSslSocket: cannot call unresolved function ERR_get_error

```

I have gone to the following location [openssl github](https://github.com/openssl/openssl) and downloaded the zip file. I have moved the "libeay32.dll" and "ssleay32.dll" files to my release directory, and I am still getting these errors. Is there anyone who has gotten the `QSslSocket` working that can give me steps to get the socket working or has any suggestions?

Answer: 
I ended up here via Googling around. In my case, I was getting this error *on random machines* because they were missing the correct versions of `libeay32.dll` and `ssleay32.dll`. It's "random" because some computers have these loaded in `PATH` from other software and some do not.

I fixed this for Qt Creator by adding the DLLs to the `bin` folder of my Qt install, and I fixed this on distributions by including the aforementioned DLLs in my distribution.

The DLLs should be the same or similar to the version of OpenSSL that Qt was compiled with in the first place. If you didn't compile it yourself, starting in Qt 5.4 you can query this with [`QSslSocket::sslLibraryBuildVersionString()`](http://doc.qt.io/qt-5/qsslsocket.html#sslLibraryBuildVersionString). (Credit: <https://stackoverflow.com/a/42297296/1666676>)

Don't forget that your 64-bit apps should have a 64-bit version of the DLLs, and 32-bit apps should have 32-bit DLLs so you don't have the same problem as [this guy](https://stackoverflow.com/a/39497754/1666676).

---

Additional notes:

* Starting in Qt 5.2 you *must* use version 1.0.0 or newer. 0.9.8 doesn't work any more. (Source: <http://doc.qt.io/qt-5/ssl.html>)
* For my standard MSVC2017x64 distribution of Qt 5.10.1 `sslLibraryBuildVersionString()` returned "OpenSSL 1.0.2o". I use 1.0.2p for my distributions.
* The OpenSSL DLLs changed names to `libcrypto-1_1*.dll` and `libssl-1_1*.dll` starting in OpenSSL 1.1.0. Standard Qt distributions don't yet use those as of Sept. 2018.
* OpenSSL GitHub downloads are here: <https://github.com/openssl/openssl/tags>

Hope this helps the next person. Sorry for resurrecting an old post.
By combining existing answers here and some research I managed to make it work with MSVC2017 x64 compiler:

1. Download 1.0 version (Win64 OpenSSL **v1.0.2r** Light) from here:
<https://slproweb.com/products/Win32OpenSSL.html>
2. When installing, choose to copy DLLs to OpenSSL bin directory.
3. And then copy **libeay32.dll** and **ssleay32.dll** from OpenSSL bin folder to: `{Your_Qt_Folder}/{Qt_version}/msvc2017_64/bin`