The use of the Transport Layer Security (TLS, formerly known as SSL) is becoming increasingly prevalent to secure network communication, particularly with the browser and search companies pushing web sites to move to HTTPS instead of HTTP. This post discusses the options for using TLS over Tcl sockets and specifically some important potential pitfalls to keep in mind with respect to certificate validation. The discussion is limited to client-side operation.

This post may be partially, or even completely, out of date. Both OpenSSL and the TLS extension have had major updates since it was written.

Building the Tcl TLS extension on Unix/Linux is straightforward because OpenSSL libraries are already present and installed. It's a different matter on Windows where you need to build OpenSSL yourself. This short article describes the process.