I'd say the point of security in communication is being able to verify that all participants are who they say they are. More so than hiding the content from third party. ;-)
That's a debatable definition, to say the least. I'm not saying authentication is not an important part of security, but saying it is the only important part is quite a stretch, don't you think?
I was only trying to make a point because d_theorist seemed to only think security is about hiding the message from third party. Secure communication could even mean not to get a electric shock from your phone while using it.