Stunnel

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Stunnel
Developed by	Michal Trojnara & Brian Hatch
Latest release	4.24 / May 4, 2008
OS	Multi-platform
Genre	Proxy, Encryption
License	GNU General Public License
Website	stunnel.mirt.net

Stunnel is a free multi-platform computer program, used to provide universal TLS/SSL tunnelling service.

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. It relies on a separate library such as OpenSSL or SSLeay to implement the underlying TLS or SSL protocol.

Stunnel uses Public-key cryptography with X.509 digital certificates to secure the SSL connection. Clients can optionally be authenticated via a certificate too.

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

Stunnel is maintained by Michal Trojnara and Brian Hatch. Released under the terms of the GNU General Public License.

[edit] Example Scenario

The application can present an external secure SSL port that is mapped to an internal unsecured TCP or UDP port of an existing application.

For example, to provide a secure SSL connection to an existing SMTP mail server, Stunnel might map the SSL port 465 to port 25 of the mail server. Network traffic from clients connecting to the mail server on port 465 would initially pass over SSL to the Stunnel application, which would then transparently forward unsecured traffic to port 25 of the mail server. The Stunnel process could be running on the same or a different server to the unsecured mail application, however both machines would typically be behind a firewall on a secure internal network.