Its at two levels. Its trivial to make a system where the content of the messages can only be read by the recipient. PGP and GPG email is an example of this e

Its at two levels. Its trivial to make a system where the content of the messages can only be read by the recipient. PGP and GPG email is an example of this end-to-end encryption. The weakness in these schemes is two-fold: the update mechanism for the software (e.g. if its web-based, do you trust the server that serves the page?) and authentication: how do you know that the credentials you have for the recipient are accurate? Its less trivial to make a system where who-is-corresponding-with-whom is obscured. Onion Routing (e.g. TOR) is in this direction, but there are laborious ways to peel the onion. All in all, a hard problem.