I also wanted to use OpenSSL on Windows 10. An easy way to do it without running into the risk of installing unknown software from 3rd party websites and risking viruses, is by using the openssl.exe that comes inside your Git for Windows installation. In my case, I found the OpenSSL executable in the following location of the Git for Windows installation.

C:\Program Files\Git\usr\bin\openssl.exe

If you also want instructions on how to use OpenSSL to generate and use certificates, here is a write-up on my blog. The step by step instructions first explain how to use Microsoft Windows Default Tool and also OpenSSL and explains the difference between them.

Yes. You can do one of two things:

1. Build it yourself

   You'll need a build environment (either Visual Studio or msys2 based), and a few other pre-requisites. Download the source from here:

   https://www.openssl.org/source/

   And (assuming you downloaded the 1.1.0 version), read the INSTALL notes here:

   https://github.com/openssl/openssl/blob/OpenSSL_1_1_0-stable/INSTALL

   There are also some Windows specific notes here:

   https://github.com/openssl/openssl/blob/OpenSSL_1_1_0-stable/NOTES.WIN

2. Download a pre-compiled version

   The OpenSSL project doesn't distribute pre-compiled binaries, but they do maintain a list of third-party provided binaries. The list is here:

   https://wiki.openssl.org/index.php/Binaries