The stunnel is an open-source multi-platform computer program, used to provide universal TLS/SSL tunneling service. The stunnel can be 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 a separate library, such as OpenSSL or SSLeay, to implement the underlying TLS or SSL protocol. If linked against libwrap, it can be configured to act as a proxy-firewall service as well.