Sorry, maybe I wasn't clear... With encrypted-trusted if you try an MITM, unless you have a valid SSL key, the browser will show a big error screen and not send any cookies. With encrypted-untrusted the browser wouldn't do that, so the cookies would still be sent. You don't even need to route the connection, you could just present an "Error connection to server" page and most users would just think the wifi isn't working.
My question is given that what is the purpose of encrypted-untrusted? It's no more secure than HTTP for anything that uses session cookies or the like. Sure the connection is encrypted, but then all you are doing is stopping people seeing that you are accessing My Little Pony shows on YouTube. If it's a public hotspot at the coffee shop, they can probably see you watching it (IRL) anyway. Given the connection is untrusted, it wouldn't be hard for the NSA to do a MITM attack at the ISP level.
Thanks, that makes sense. As long as people understand that although it's encrypted it's still not really safe. That could be the hard part though, as I expect a lot of people assume anything encrypted is safe (related, see malicious SHA1 - https://news.ycombinator.com/item?id=8136526).
My question is given that what is the purpose of encrypted-untrusted? It's no more secure than HTTP for anything that uses session cookies or the like. Sure the connection is encrypted, but then all you are doing is stopping people seeing that you are accessing My Little Pony shows on YouTube. If it's a public hotspot at the coffee shop, they can probably see you watching it (IRL) anyway. Given the connection is untrusted, it wouldn't be hard for the NSA to do a MITM attack at the ISP level.