The Secure Socket Layer is a protocol for encrypting communication on a network socket. It turned out not to be very secure after all, and has been deprecated in favour of TLS. It is a way of doing secure communications without application programmers having to actually understand a lot about how cryptosystems work, which is good because implementing a truly secure crypto-engine is (by all reports) really hard indeed.

Secure communication is also the purpose of SSH, but that has its own encryption and authentication mechanisms, quite separate from those of SSL.

The main Tcl package used to provide SSL support is TLS.

APN TWAPI (as of V4.0b40) has the tls_socket command as a drop-in replacement for socket on Windows that supports SSL/TLS. Layered on CryptoAPI, it integrates with the certificate store on Windows.

Other (older) implementations:

 What: SSLtcl
 Description: SSLtcl is a free, loadable module for Tcl that
        extends the socket command with SSL (secure socket layer)
        functions.  It is a thin layer over Eric Young's free
        SSLeay.  Be sure to carefully research the import and
        export restrictions of your country before fetching and
        building this package.  It requires Tcl 8 and either
        SSLeay-0.6.6 or SSleay-0.8.1.
 Updated: 10/1999
 Contact: mailto:[email protected] (Peter Antman)

 What: tclSSL
 Description: Tcl dynamic load package that provides an interface to
        Eric Young's mailto:[email protected] implementation of
        SSL and supporting libraries with Tcl to provide SSL
        protection to sockets. SSL capability is added to the socket
        with a -ssl option.
 Updated: 10/1999
 Contact: mailto:[email protected] (Tony Bringardner)

 What: TinyCA
 Description: Simple Perl/Tk gui to manage a small certification
        authority.  Based on OpenSSL and Perl modules from
        the OpenCA project. 
        Currently at version 0.4.4 .
 Updated: 05/2002
 Contact: See web site