Stunnel

5.72 SSL encryption wrapper for Windows

Fernando Ortega

Security tool used to create SSL-encrypted tunnels to protect data transmission across unsecured networks.

A useful and easy utility tool that can add secure layers with SSL to inetd daemons and servers including HTTP, NNTP and SMTP.

Stunnel is a free and open source SSL encryption wrapper app and Windows server developed by Michal Trojnara for Windows. It's advanced, straightforward and easy to setup.

The download has been tested by an editor here on a PC and a list of features has been compiled; see below. We've also created some screenshots of Stunnel to illustrate the user interface and show the overall usage and features of this SSL encryption wrapping program.

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Adds a layer of SSL encryption between clients and local servers

The stunnel program is designed to work as an SSL encryption wrapper between remote client and local (inetd-startable) or remote server. It can be used to add SSL functionality to commonly used inetd daemons like POP2, POP3, and IMAP servers without any changes in the programs' code. Stunnel uses the OpenSSL library for cryptography, so it supports whatever cryptographic algorithms are compiled into the library.

Stunnel can benefit from FIPS 140-2 validation of the OpenSSL FIPS Object Module, as long as the building process meets its Security Policy. A scanned FIPS 140-2 Validation Certificate document is available for download on the NIST web page. The Windows binary installer is compiled with FIPS 140-2 support. The FIPS mode of operation is no longer enabled by default since stunnel 5.00.

Stunnel is a free software authored by Michal Trojnara. Although distributed under GNU GPL version 2 or later with OpenSSL exception, stunnel is not a community project.

Features of Stunnel

  • Advanced support: Supports multiple protocols and ciphers.
  • Authentication: Supports username and password authentication.
  • Client/server support: Both server and client mode operations.
  • Data protection: Supports data compression and encryption.
  • Easy to use: GUI-based configuration and management.
  • Flexible configuration: Options to configure multiple services.
  • High performance: Low latency and high throughput.
  • Multi-threaded: Simultaneous connections support.
  • Networking: Supports IPv4, IPv6 and SSL/TLS tunneling.
  • SSL/TLS encryption: Secures traffic between two machines.
  • Scalable: Supports load balancing and failover scenarios.
  • Security: Supports certificate revocation lists and session caching.

Compatibility and License

Stunnel has been released under the open source GPL license on Windows from servers. The license provides the options to freely download, install, run and share this program without any restrictions. The source code for Stunnel should be freely available and modifications are certainly permitted as well as the option to inspect the software.

What version of Windows can Stunnel run on?

Stunnel can be used on a computer running Windows 11 or Windows 10. Previous versions of the OS shouldn't be a problem with Windows 8 and Windows 7 having been tested. It's only available as a 64-bit download.

Filed under:
  1. Stunnel Download
  2. Free Servers
  3. Open source and GPL software
  4. SSL Encryption Wrapping Software
Stunnel has been picked by our editors as good software.
Stunnel has been tested for viruses and malware.
We have tested Stunnel 5.72 against malware with several different programs. We certify that this program is clean of viruses, malware and trojans.