I found this video today featuring Dr Yan Wong from the BBC. Whilst it is very short, the video does provide a nice simple introduction to some of the ideas behind public key cryptography, which secures most of e-commerce on the web. Definitely worth a watch if you don’t want to get into the messy details.

However, if you do want to get into the messy details of public key cryptography, I suggest perusing the Wikipedia article on the subject.