Stunnel

Stunnel is an open-source multi-platform application used to provide a universal TLS/SSL tunneling service.

Stunnel is used to provide secure encrypted connections for clients or servers that do not speak TLS or SSL natively. It runs on a variety of operating systems, including most Unix-like operating systems and Windows. Stunnel relies on the OpenSSL library to implement the underlying TLS or SSL protocol.

Stunnel uses public-key cryptography with X.509 digital certificates to secure the SSL connection, and clients can optionally be authenticated via a certificate.

If linked against libwrap, it can be configured to act as a proxy–firewall service as well.

Stunnel is maintained by Polish programmer Michał Trojnara and released under the terms of the GNU General Public License (GPL) with OpenSSL exception.