Stunnel is an open source command-line program that has been designed to encrypt remote and local TCP (Transmission Control Protocol) connection using SSL (Secure Sockets Layer) encryption between the client and the server.
Features at a glance
The software is mostly used to add SSL functionality to IMAP and POP2/3 daemons. In order to support any cryptographic algorithm, Stunnel makes use of both SSLeay and OpenSSL libraries.
Additionally, Stunnel uses the FIPS 140-2 validation, which is part of the OpenSSL FIPS Object Module. It is currently available in the default software repositories of many Linux-based operating systems. The program also comes with support for various other sockets, including IPv6, poll or systemd.
Getting started with Stunnel
To install Stunnel in your GNU/Linux operating system, you must first download the latest version from Softpedia (it is distributed as a universal sources archive), save it in a location of your choice, extract it and open a terminal windows.
Type the “./configure && make” command to configure and compile the program for your hardware architecture and OS (supported architectures include 32-bit and 64-bit). After a successful compilation, you can type the “make install” command as root or with sudo, without quotes.
When first used, the program will attempt to read its configuration file, which is located on /usr/local/etc/stunnel/stunnel.conf. You will be able to use a specific config file, as well as to read the config file from a file descriptor.
Under the hood and availability
Stunnel is written entirely in the C programming language and it’s distributed as a universal sources archive for optimizing the application on your GNU/Linux system. It has been successfully installed on both 32-bit and 64-bit machines.