Privacy, Security and Your Dropbox
blog.dropbox.com
blog.dropbox.com
> My problem is that for as long as I have tried to figure out, Dropbox made some bold claims about how your files were encrypted and how nobody had access to them, with statements like:…
> - Dropbox employees aren't able to access user files, and when troubleshooting an account they only have access to file metadata (filenames, file sizes, etc., not the file contents)…
> But this announcement that they are able to decrypt the files on behalf of the government contradicts their prior public statements.
Dropbox are avoiding answering this. If they derived the encryption key from your password, as JWZ explained http://www.jwz.org/blog/2011/04/dropbox-doesnt-actually-encr... and as occurred to any halfway decent hacker, they wouldn't need to have the ability for their employees to decrypt your files — an ability which they are still claiming to not have.
And this is just insulting:
> We understand that many of you have been confused by this situation — and some folks even felt like we misled them
The problem isn't that we were confused or what we felt or that we were unintentionally "misled". The problem is that, apparently, you lied to us in order to defraud your customers.
In reality.
Knowing that they have millions of customers, and that they have invested years of work into their current infrastructure.
So, playing devil's advocate for the moment --- and taking the above facts into account --- what, precisely, would you do in their position?
Granted, they can still steal your password...
You are now Drew. You start this morning by visiting Hacker News. "Dear god," you exclaim, "I've been such a fool! We've been Doing It Rong all these years!"
Inspired by this new revelation, you spring out of your chair and out the door. You stride into "The Programmer Pit" and over to the new hire, backhanding him across the face. "Get the hell off of Portal 2! We have work to do! Jessica, go pick up four cases of Red Bull --- It worked at MIT, it'll work here."
Now that you have Acquired Their Attention, you say, "Okay, here's-a what we gonna do. Step 1: Jimmy, I want you to ..."
... Now. What, exactly, fellow HNers, is Step 1? Fill in the blank.
What, step-by-step, do you want Dropbox to do?
Maybe they don't need to do anything else. Dropbox is a fine service as it stands; security must be traded off against convenience, and the trade-off that Dropbox makes is acceptable to lots of people. They do have a responsibility to make sure that those people understand the trade-off, though, as well as a responsibility to admit that they've swept important details under the carpet in the past.
The only way Dropbox could access those files then would be to backdoor the Dropbox client. But if they were going to do that, it wouldn't even be safe to use TrueCrypt or GnuPG either.
ecryptfs isn't a suitable alternative to my suggested solution which would involve all Dropbox clients having the capability built in. Of course, people who are really paranoid can use their own layer of encryption on top as well/instead.
"Our goal is for no single employee acting alone is able to access your files. However, there is a procedure where multiple people working in concert can recover your files and provide them to law enforcement. Unfortunately, it is possible for a hacker / programmer to create a backdoor and there is nothing we can do about this."
Encryption is always a trade-off, since it introduces the possibility of total data loss if the key is mismanaged.
Personally, I'd let them off the hook if they admitted their previous deception and explained the limitations of their security model in terms that any user can understand.
That depends on the law. Is it legal in the US to store someone else's strongly encrypted data on one's server? Assuming it is, then they should encrypt by default and then if law enforcement forces them to give up data, give what they have.
No-one with any technical expertise would think that Dropbox was incapable of reading stored files. They'd have to know the encryption key in order to provide their web interface.
So as a technically proficient user, my interpretation of their statement is that they don't give normal employees access to their production encryption keys. However, if the government asks, then presumably they have a legal responsibility to comply.
My guess is that the Dropbox employees who made those statements were also technically proficient, and made the same assumptions I did.
I did. That is exactly what they made me think.
All of this should have been obvious to anyone that bothered to think about what was going on before they stored their precious secrets in Dropbox. Obviously they are holding the encryption keys. Hell, that much was obvious to me when I started using/testing Dropbox just over a year ago and saw my files served over a web page. I can't help but muster a "meh".
The value I saw in their use of encryption is this: when they or amazon or whoever dispose of their drives it will be harder to harvest data off of them. That's all I've come to expect from them and that's all any of their information has ever warranted.
I still derive great value from their service.
Now, I will admit the one that I personally didn't think through back then was the key file thing, but really that's just the same as having an ssh private key. I was aware that it wasn't constantly prompting me for a password so at some level I knew it was going on. Maybe I would prefer some sort of passphrase at login using a keyring for that file. Minor issue.
I do trust them that the run-of-the-mill support personnel are barred from accessing the keystore. Its entirely feasible that there is no mechanism for them to just go browse around your files.
However, it should be blatantly obvious to anyone that understands anything about encryption that someone somewhere at dropbox can access your files. This has always been the case and obvious.
I guess I'm mostly amused by people that are surprised by any of this. The smarter they pretend to think they are, the more amusing they "fell" for something this obvious. It's like the people that fall for mint.com's attempts to obscure the fact that they store your bank account usernames and passwords (oh, sorry, I forgot, they pay a third party to do that for them instead). People just don't think through the mechanisms of their shiny trinkets. You get to just point and laugh.
Now, if only there was an cross-platform (mobile + desktop) solution that would allow me to store files I encrypted on Dropbox. That would be pretty killer.
It's a consumer service, and consumers don't know or care how encryption works. They just need to be told the consequences of whatever technical decisions have been made on their behalf, so it's important for Dropbox to be honest in explaining them.
This is easy to claim, but we live in a world of tech. You need to step back and get some perspective. We have piles and piles of domain specific knowledge, the layman can barley set up a home router. Dropbox claims to have over 25 million customers. How many of those people do you expect to even have the knowledge to be able to figure this out?
You're putting the burden of realizing dropbox's claims don't hold water on the consumer, who probably doesn't understand a single thing about cryptography. Even if every one could figure it out, they still shouldn't have to.
>I guess I'm mostly amused by people that are surprised by any of this.
I wasn't surprised by any of this, what I am surprised by is people who see others trying to raise consumer awareness and are so quick to dismiss them just because they happen to be among the few who actually do understand the technical limitations of the cryptography implementation used.
I never assumed that it was impossible for them to get access to my files. I just assumed that only certain people had access to the keys, and they only gave them out to third parties when forced to by law.
Trusting companies to, for example, only give access to our data when forced to by law just doesn't cut it anymore, for a lot of people. Not when companies collectively have a very poor track record in this regard, and not when the law continues to be murky and dynamic (and abused).
It's the abused dog effect: even if you, personally, treat a previously abused dog really well and swear up and down that you will never hurt it, if you raise your hand around it, it'll cower.
Since technical solutions exist for this problem, Dropbox's reasoning gets a bit thinner.
> If they're going to supply access via the website, or allow you to share with others then they need to be able to decrypt the file.
Not necessarily. For example, a key derivation function could be used to transform a password into a key, and that password could be required for users that want that kind of thing. As far as website access goes, I'm about to commit a terrible security crime here and suggest that the key derivation function could also be run in the browser. This would prevent direct access to your data by anybody at Dropbox, at least until the next time you log in, at which point they could serve up some malicious code that would record your password and ship it off to them. There are workarounds for that, too, though.
They need to be able to decrypt the file right then to give you access via the website. They don't need to be able to decrypt the file the rest of the time. If the encryption key depends on your password, this is easy to implement. In modern browsers, this could actually be done in the browser, so that the keys for decrypting the file never reach their servers.
To allow you to share individual files with others, they could encrypt each file with a randomly-generated session key, which is encrypted with your user key. When you give access to the file to a recipient, you would be encrypting a copy of that session key with the recipient's public key.
In actual fact, it appears that anyone who knows the secure hash of the file's content is able to discover that Dropbox is storing it: http://paranoia.dubfire.net/2011/04/how-dropbox-sacrifices-u... — and there's at least well-founded speculation, if not proof, that this means that knowing the secure hash is sufficient to read the file: http://news.ycombinator.com/item?id=2440074
For their previous statements to be true — that their employees have no access to your files — they would have to be doing something like this.
And also that you losing your password is apocalyptically bad.
It's understandable that they chose a less-secure system design. It's not understandable that they chose to lie to their customers about it.
"For users who feel more comfortable managing their own encryption keys, we recommend using products like TrueCrypt to store encrypted volumes within their Dropboxes. Those users will unfortunately lose access to some functionality, but we leave this decision to the user."
It's the sign of a good company in my opinion that they don't treat their users as unable to understand such things.
The magic words: "Like most major online services, we have a small number of employees who must be able to access user data when legally required to do so. But that’s the exception, not the rule. We have strict policy and technical access controls that prohibit employee access except in these rare circumstances. In addition, we employ a number of physical and electronic security measures to protect user information from unauthorized access."
If it were impossible for them to get at the unencrypted data, the encrypted data would be all that that had to had over.
We manage the encryption keys on our users’ behalf.
To be completely clear to users, they should instead write:
We hold the decryption keys and can decrypt your data if compelled to do so. If you don't want us to be able to decrypt your data, encrypt it yourself with GPG or OpenSSL before sending your data to our site.
Edit: Spelling & clarity.
Dropbox is a consumer file storage company. Statements like that will confuse the majority of their target market and stall adoption of the service.
What Dropbox is doing in relation to security/encryption is about the best possible solution that balances features and function with data protection for files that might be leaked or stolen.
If you have suggestions for Dropbox, lay out concise technical suggestions. Writing new legalese for them is not solving any of the problems that people are getting so worked up about.