Earlier quoted context omitted.
Agreed. I AES-encrypt information that's actually private on my Dropbox. But Dropbox is providing a service grounded in simplicity. Sorry, that's the product angle. And exchanging this key without Dropbox intermediating would be much more complex than what Dropbox does now. Also, the web interface, sharing, public folders, perhaps iPhone and Android apps (you have the question of how to get the key TO the device), wo…
> Agreed. I AES-encrypt information that's actually private on my Dropbox. But Dropbox is providing a service grounded in simplicity. Sorry, that's the product angle. And exchanging this key without Dropbox intermediating would be much more complex than what Dropbox does now. A bit more complex, but not much more complex. See Firefox Sync's setup screen for a great execution of strong secret shared over weak password…
My desktop is down right now (power supply burned out, ouch) so I think I actually use the web interface more than Dropbox itself, since I only have one computer... And encryption in Javascript is a pain, since you open yourself to man-in-the-middle attacks and such.
I don't know about shared secrets for sharing and such, but I haven't heard of anything even applicable beyond a few academic papers. Beyond, you know, using a different key for every file and then you can email the key to share it. But that doesn't let you revoke access from one person (I've seen papers on how to do that though) and that's also a waste of entropy. I think this is actually a nice area for research (well, maybe it's being done and I'm not aware; again, not a security guy).
Personally, I don't trust closed-source systems with my encryption code, client-side or server-side or not. I'm ok with Firefox Sync, I'm sure someone would notice if it had side channel leaks, but if you want Dropbox to ask for the encryption key, how do you know what it does?
Anyway, I think we're just entering the era where we understand encryption in consumer products.