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Stunnel

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Stunnel
Developer(s)Michał Trojnara
Stable release
4.34[1] / September 19, 2010
Operating systemMulti-platform
TypeProxy, Encryption
LicenseGNU General Public License
Websitewww.stunnel.org

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[2]. It runs on a variety of operating systems [3], 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.

Stunnel uses Public-key cryptography with X.509 digital certificates to secure the SSL connection. Clients can optionally be authenticated via a certificate too[4].

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

Stunnel is maintained by Michał Trojnara. Released under the terms of the GNU General Public License with OpenSSL exception.

Example scenario

The application can present an external secure SSL port that is mapped to an internal unsecured TCP 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 from the unsecured mail application; however, both machines would typically be behind a firewall on a secure internal network.

References

  1. ^ Stunnel ChangeLog
  2. ^ O'Donovan, Barry Secure Communication with Stunnel, Linux Gazette, Issue 107, October 2004
  3. ^ Stunnel Ports
  4. ^ stunnel(8) manual


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