The stunnel program is designed to work as an SSL encryption wrapper between remote client and local (inetd-startable) or remote servers. It can be used to add SSL functionality to commonly used inetd daemons like POP2, POP3, and IMAP servers without any changes in the program’s code.
It will negotiate an SSL connection using the OpenSSL or SSLeay libraries. It calls the underlying crypto libraries, allowing stunnel to support whatever cryptographic algorithms were compiled into the crypto package.
The pfSense® package implements only a subset of the configuration options available in stunnel. For more advanced configurations, please consider configuring stunnel manually on the pfSense host, run it in a dedicated jail, or on a different system.
The package has two configuration screens (tabs):
For each tunnel, the following options are available:
Listening socket IP address and port.
Certificate to use for the listening socket.
Target IP address and port.
IP address to bind to when connecting to the target.
If no certificate is specified for a tunnel, the default certificate will be used. This is a self-signed certificate which is generated upon package (re)installation, and is not suited for production use.
Certificates are managed in the simplest possible way, by requiring the user to provide RSA key and certificates/chains in PEM format. The Certificates tab will list the configured certificates along with status information, indicating whether the certificate is valid, will expire soon, or is already expired. A sanity check is also performed to make sure the key and certificate matches.
Note that for private certificates and certain commercial ones (Extended Validation), a complete certificate chain may be required. This is to ensure that the client is able to verify the certificate validity. A chain should be built in the following way:
Root certificate of the certificate issuer/CA
Any intermediate certificates between the root and the server certificate
Refer to the stunnel documentation for more information on how to format a certificate chain.
You can find a list of known issues with the stunnel package on the pfSense bug tracker.