I had a mad idea last week, which I shared with the NSS team. The fact is that some companies want to monitor everything going into and out of their network. And, my view is, as it’s their network, it’s their right legally, and it’s OK with me morally too as long as everyone using the network is aware of it.
However, the current SSL trust model makes this MITMing of all connections very difficult (which is a good thing, in many ways). Companies such as BlueCoat sell boxes which will MITM SSL connections and log the data, but browsers will complain that the auto-generated certs presented are not trusted. Companies are supposed to deploy their own root to all endpoints – but this is a massive administrative hassle, particularly for mobile devices. As we have found out anew recently, this creates an incentive for trusted CAs to sell trusted intermediate certificates to these big companies. However, such certificates could potentially be abused to silently MITM anyone.
So my mad idea was that Firefox should have one cert in the root store for which the private key was published. However, when an SSL connection occurred which chained up to that root, the browser would bring up an irremovable red infobar which said: “Your connection is not private – all data transferred is being monitored by X”, where X was the O field from the intermediate cert being used. (We would require the use of exactly one intermediate.) If the O field was empty, it would say “by Unknown Attackers”, or something equally scary.
This week I found Phillip Hallam-Baker of Comodo proposing something very similar on the “therightkey” mailing list:
What I find wrong with the MITM proxies is that they offer a
completely transparent mechanism. The user is not notified that they
are being logged. I think that is a broken approach because the whole
point of accountability controls is that people behave differently
when they know they are being watched.
I don’t mean just changing the color of the address bar either. I
would want to see something like the following:
0) The intercept capability is turned on in the browser, this would be
done using a separate tool and lock the browser to a specific
intercept cert root.
1) User attempts to connect to https://www.example.com
2) Browser throws up splash screen for 5secs stating ‘Your connection
has been intercepted’
3) Business as usual.
The splash screen would appear once per session with a new host and
It should show the interception cert being used as well.
Phil’s point 0 rather defeats the point – if you had to reconfigure the browser, then companies would just add their own root. But if it were built in by default, his point 0 is not necessary. He is right that you’d need a splash screen or confirmation step – we can’t sent initial data or cookies or anything until we know the user knows they are being MITMed, and gives permission to continue.
What do people think?