Stunnel is an
open-source
Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ...
multi-platform
application
Application may refer to:
Mathematics and computing
* Application software, computer software designed to help the user to perform specific tasks
** Application layer, an abstraction layer that specifies protocols and interface methods used in a c ...
used to provide a universal
TLS/SSL
Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. The protocol is widely used in applications such as email, instant messaging, and voice over IP, but its use in securi ...
tunneling 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. Stunnel relies on the
OpenSSL
OpenSSL is a software library for applications that provide secure communications over computer networks against eavesdropping or need to identify the party at the other end. It is widely used by Internet servers, including the majority of HTT ...
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.
"stunnel(8) manual"
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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
OpenSSL is a software library for applications that provide secure communications over computer networks against eavesdropping or need to identify the party at the other end. It is widely used by Internet servers, including the majority of HTT ...
exception.
Example scenario
For example, one could use stunnel to provide a secure SSL SSL may refer to:
Entertainment
* RoboCup Small Size League, robotics football competition
* ''Sesame Street Live'', a touring version of the children's television show
* StarCraft II StarLeague, a Korean league in the video game
Natural language ...
connection to an existing non-SSL-aware SMTP mail server. Assuming 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 and 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).
See also
* Tunneling protocol
References
External links
*
{{Portal bar, Free and open-source software
Cryptographic software
Free security software
Unix network-related software
Transport Layer Security implementation
Tunneling protocols
Network protocols