What encrypts the information in a data transmission?

There are many different methods of encryption of data being transmitted and they are as varied, if not more so, then the methods of transmission themselves. It could be as simple as a SSL connection to another service or even HTTPS for browsing websites.

It could become more advanced such as a 128bit or 256bit AES VPN tunnel between one network to another, or to a proxy server. It could be custom crypto methods on radio packet transfer or even encryption on microwave or line-of-site laser communication.

I would need to know the method before I could give you any useful info.