End to End Encryption

In most systems, a central server relays messages between users. A secure connection is usually established between a user and the central server, which can thus see all user messages.

A protocol providing end-to-end encryption encrypts communications from one user up to its intended recipient, preventing any server in the middle from observing messages in cleartext.

Effectively, these MITM servers sit in between users, are necessary for the

application to function, and are trusted third parties of the protocol. That is to

say,

we have to trust these parts of the system in order for the protocol to be

considered secure

Even if traffic is encrypted, some middleboxes are set up to end the TLS connection

(we say that they terminate TLS) and either forward the traffic in clear from that point on or start another TLS connection with the next hop.

TLS termination is sometimes done for “good” reasons: to better filter traffic, balance connections geographically or within a data center, and so on.

This adds to the attack surface as traffic is now visible in the clear in more places.

Sometimes, TLS termination is done for “bad” reasons:

to intercept, record, and spy on traffic.