content: Your first edit is wrong on several counts. 1 - On the internet there is always a Man In The Middle. This is the nature of the network. 2 - Parties who can share a secret by off-channel means are not effected by MITM. They are still vulnerable to frequency and network analysis though. 3 - Security protocols employing Perfect Forward Secrecy are less vulnerable to MITM even if they don't share secrets off-channel.