stunnel

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stunnel
Developer(s)Michał Trojnara
Stable release
5.49[1] / 3 September 2018; 6 months ago (2018-09-03)
Repositoryhttps://www.stunnel.org/downloads.html
Operating systemMulti-platform
TypeProxy, Encryption
LicenseGNU General Public License
Websitewww.stunnel.org

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

stunnel can be used to provide secure encrypted connections for clients or servers that do not speak TLS or SSL natively.[1] It runs on a variety of operating systems,[2] 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.[3]

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

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

Example scenario[edit]

For example, one could use stunnel to provide a secure SSL connection to an existing non-SSL-aware SMTP mail server. Assume the SMTP server expects TCP connections on port 25. One would configure stunnel to map the SSL port 465 to non-SSL port 25. A mail client connects via SSL to port 465. Network traffic from the client initially passes over SSL to the stunnel application, which transparently encrypts/decrypts traffic and forwards unsecured traffic to port 25 locally. The mail server sees a non-SSL mail client.

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 (so that an intruder could not make its own unsecured connection directly to port 25).

References[edit]

External links[edit]