The openssl program is a command line tool for using the various cryptography functions of OpenSSL's crypto library from the shell.
Usage
Zip archive contains 64-bit binaries of the openssl tool. Cygwin and required DLLs.
One liner for creation of a self-signed SSL certificate:
openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout selfsigned.key -out selfsigned.crt
Man pages: