Useful Links:

OpenSSL API Documentation: https://www.openssl.org/docs

Github: https://github.com/openssl/openssl

OpenSSL Wiki: https://wiki.openssl.org/index.php/Main_Page

Original Simple Server: https://wiki.openssl.org/index.php/Simple_TLS_Server

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Generate self signed cert and key 'pem' files (good for 10 years):

openssl req -newkey rsa:4096 -x509 -sha256 -days 3650 -nodes -out cert.pem -keyout key.pem

You can just hit carriage returns to accept the default values, except for "Common Name"; you
should enter 'localhost', or an actual hostname.

The same keys can be used for both communicating instances; same or different machines.