The technical details get very complicated very quickly, but what it all amounts to is simple enough. The proposal expects Internet users to provide “informed consent” that they “trust” intermediate sites (e.g. Verizon, AT&T, etc.) to decode their encrypted data, process it in some manner for “presumably” innocent purposes, re-encrypt it, then pass the re-encrypted data along to its original destination.
In essence it’s a kind of sucker bait. Average users could easily believe they were “kinda sorta” doing traditional SSL but they really wouldn’t be, ’cause the ISP would have access to their unencrypted data in the clear. And as the proposal itself suggests, it would take significant knowledge for users to understand the ramifications of this — and most users won’t have that knowledge.
This editorial illustrates that Man In The Middle (MITM) attacks cannot happen without user consent. This blogger fears that ISPs will require consent for all SSL sessions making all users’ end to end encryption vulnerable to a “trusted” proxy. Here is a blurb in the draft.
From the IETF draft: Explicit Trusted Proxy in HTTP/2.0 draft-loreto-httpbis-trusted-proxy20-01
This document describes two alternative methods for an user-agent to automatically discover and for an user to provide consent for a Trusted Proxy to be securely involved when he or she is requesting an HTTP URI resource over HTTP2 with TLS. The consent is supposed to be per network access. The draft also describes the role of the Trusted Proxy in helping the user to fetch HTTP URIs resource when the user has provided consent to the Trusted Proxy to be involved.
The consent is supposed to be on a per network (or destination) basis which means there may be a reason the user agent will want to use a trusted proxy — perhaps they do not trust the destination network. The blogger implies ISPs will want blanket consent over all destinations which 1) they could implement now without this standard and 2) this would not make for a good PR move because it would not go unnoticed.