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stunnel

stunnel is a proxy that adds TLS encryption to existing clients and servers without changing their code, written by Michał Trojnara. It is distributed under the GNU GPL version 2 or later with an OpenSSL exception, with commercial support and non-GPL licences available from the author.

Licensing at a Glance

  • Open source

  1. stunnel is distributed under the GNU GPL version 2 or later with an OpenSSL exception.[1]

  2. The project states that stunnel is not a community project: the authors retain the copyright in the source code and offer commercial support or non-GPL licences on request.[2]

  3. Commercial licences are offered for distributing a modified stunnel without sharing the source code of the modifications, or for distributing stunnel linked against GPL-incompatible code such as cryptographic engine drivers.[3]

  4. Commercial support fees are negotiated individually based on the number of stunnel users and the required service level; a basic plan of up to 10 hours of email support within 3 months can be bought online for $740 or €690.[4]

  5. The licence page states copyright 1998-2026 Michal Trojnara and allows redistribution and modification under the GNU General Public License version 2 or, at the user's option, any later version.[5]

Products

References

  1. stunnel: Home · stunnel.org · retrieved 2026-09-27
  2. stunnel: Home · stunnel.org · retrieved 2026-09-27
  3. stunnel: Support · stunnel.org · retrieved 2026-09-27
  4. stunnel: Support · stunnel.org · retrieved 2026-09-27
  5. stunnel: Free License · stunnel.org · retrieved 2026-09-27
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