Dropbox Lack of Security • Hacker News Board

Re: Dropbox Lack of Security

#31

Post by huhtenberg » Tue, Apr 19, 2011, 5:24 AM UTC

arashf wrote: post #15

tzs wrote: post #5

It is possible to design a Dropbox-like system with the following properties: 1. Files are stored encrypted. 2. The service provider does not have the ability to arbitrarily decrypt the files. By "arbitrarily decrypt" I mean decrypt at any time they wish. They will be able to decrypt if the owner's client is actively connected. 3. When someone uploads a file that is identical to an existing file, it initially is stor…

at the expense of conveniences like web access, document previewing, simple sharing, etc. - sure :-). if your answer to the web access concern is: derive the key from the password, who's to say we wouldn't store the key and later use it to decrypt your data? web access non-withstanding, you'd be making a leap of faith to believe that the client is 100% trustworthy and that encryption is actually happening. at some po…

> make a decision as to whether or not you trust the entity

If I don't trust the entity, how could I be installing any of its software on my machines? I have to trust what I am told if I am to use the software for its intended purpose.

If Dropbox claims what Miguel has quoted in his post, and then it happens that claims are (basically) not true, then it raises the question of integrity, i.e. what other assumptions that I have made were off? Say, that your .sys is not doubling as a key logger or your software is not scanning my disks at government's request, etc.

Re: Dropbox Lack of Security

#32

Post by patio11 » Tue, Apr 19, 2011, 5:28 AM UTC

This is the first time I've heard someone on HN actually ask for more security theatre. Sure, Dropbox could spend seven figures to get a ISOxxxx whatever consultancy to draw up a 125 page document describing their internal checks, do the obligatory all-hands yearly mandatory training where you have to get 10/10 questions right and question 1 is "A user has uploaded naked pictures of themselves to their account. True or false: it is permissible to download these and take them home with you.", etc etc.

And they'd be exactly where we are today:

1) Yes, we could look at your data any time we want to. This is an inevitable consequence of letting you look at your data any time you want to.

2) We promise not to abuse our power #1.

3) If you don't trust us on #2, you should not do business with us.

Except they'd be out seven figures.

Re: Dropbox Lack of Security

#33

Post by jackowayed » Tue, Apr 19, 2011, 5:28 AM UTC

bradgessler wrote: post #30

arashf wrote: post #8

hi there, arash from dropbox here. all data is (as we state in the referenced help article) encrypted before it's stored on the backend. all data on dropbox can be made shareable and is web viewable. as a consequence, we do need the ability to decrypt in the cloud. re. employee access to files - there are controls to prevent this. for example, even drew (founder/CEO), doesn't have physical access to our storage serve…

Technically speaking, whats the point of encrypting data on the backend if you can decrypt it? This strikes me as a waste of computations for no real gain.

Someone in an Amazon datacenter that gets ahold of a random backup tape/hard drive can't read it. I'm not sure if Dropbox is hosted on EC2, but if not, it means that Amazon couldn't read the data at all. (If it's hosted on EC2, Amazon could probably get ahold of the key if they really wanted to)

Re: Dropbox Lack of Security

#34

Post by msg » Tue, Apr 19, 2011, 5:29 AM UTC

bradgessler wrote: post #30

arashf wrote: post #8

hi there, arash from dropbox here. all data is (as we state in the referenced help article) encrypted before it's stored on the backend. all data on dropbox can be made shareable and is web viewable. as a consequence, we do need the ability to decrypt in the cloud. re. employee access to files - there are controls to prevent this. for example, even drew (founder/CEO), doesn't have physical access to our storage serve…

Technically speaking, whats the point of encrypting data on the backend if you can decrypt it? This strikes me as a waste of computations for no real gain.

If their storage API is compromised your data isn't... you need to compromise their decryption API and the storage API.

With luck the same sets of staff will not have access to both, et cetera.

Re: Dropbox Lack of Security

#35

Post by arashf » Tue, Apr 19, 2011, 5:34 AM UTC

huhtenberg wrote: post #31

arashf wrote: post #15

Earlier quoted context omitted.

at the expense of conveniences like web access, document previewing, simple sharing, etc. - sure :-). if your answer to the web access concern is: derive the key from the password, who's to say we wouldn't store the key and later use it to decrypt your data? web access non-withstanding, you'd be making a leap of faith to believe that the client is 100% trustworthy and that encryption is actually happening. at some po…

> make a decision as to whether or not you trust the entity If I don't trust the entity, how could I be installing any of its software on my machines? I have to trust what I am told if I am to use the software for its intended purpose. If Dropbox claims what Miguel has quoted in his post, and then it happens that claims are (basically) not true, then it raises the question of integrity, i.e. what other assumptions th…

it's unclear to me what statements we're making are 'not true'.

if you don't believe our statements, I'm not going to be able to convince you to trust us over the discourse in this thread :-)

Re: Dropbox Lack of Security

#36

Post by tlrobinson » Tue, Apr 19, 2011, 5:37 AM UTC

theFco wrote: post #28

tlrobinson wrote: post #17

Earlier quoted context omitted.

I'm guessing tarsnap doesn't satisfy the 3rd criteria, nor is tarsnap able to decrypt the user's files, even when the client is connected. Perhaps cperciva can comment.

3rd criteria can be considered a vulnerability, it may allow to know that certain user has a known file. It can be exploited to reveal information about the encrypted files.

Yes, I read that article too. That information leakage vulnerability can be eliminated by requiring the user always upload the file the first time they store it. Subsequent uploads of the same file for the same user could be skipped. De-duplication across users in storage is also possible without leaking information.

What is not possible (AFAIK) is the combination of the two requirements: 1) de-duplication across users, and 2) service provider is not able to decrypt your files. The latter requires the encryption/decryption be done on the client only (service provider doesn't have the keys at all). The former requires access to the unencrypted file, or for the clients to share keys.

Re: Dropbox Lack of Security

#37

Post by bradgessler » Tue, Apr 19, 2011, 5:39 AM UTC

arashf wrote: post #20

AndyNemmity wrote: post #9

Earlier quoted context omitted.

What about allowing government access to files? Do you require a warrant? Under what circumstances?

we take as firm as stance as possible on user privacy (google faces and fights these very issues) the government needs to comply with the provisions of the electronic communications privacy act by obtaining a warrant supported by probable cause (or in some cases a court order from a judge). these safeguards protect user privacy, even when the government is involved.

Assuming you store files as a combination of a hash digest function as a key and file data as a value; what controls do you have in place to handle situations where law enforcement discovers some sort of 'illegal' file data on one users account subsequently requests details on users with hash digests that match the data in that file?

Re: Dropbox Lack of Security

#38

Post by shin_lao » Tue, Apr 19, 2011, 5:42 AM UTC

patio11 wrote: post #32

This is the first time I've heard someone on HN actually ask for more security theatre. Sure, Dropbox could spend seven figures to get a ISOxxxx whatever consultancy to draw up a 125 page document describing their internal checks, do the obligatory all-hands yearly mandatory training where you have to get 10/10 questions right and question 1 is "A user has uploaded naked pictures of themselves to their account. True…

I might have misunderstood what you meant, but #1 is invalid.

If I can look at my data any time I want, I just need the key to it. Dropbox just gives me access to the encrypted stream.

Giving access to my data to someone else would therefore just be a question of sharing the key with that person, again, without Dropbox ever having access to this key.

Your killer argument is to me #3. If you don't trust a company, don't do business with it. It all comes down to this.

Re: Dropbox Lack of Security

#39

Post by huhtenberg » Tue, Apr 19, 2011, 5:42 AM UTC

arashf wrote: post #35

huhtenberg wrote: post #31

Earlier quoted context omitted.

> make a decision as to whether or not you trust the entity If I don't trust the entity, how could I be installing any of its software on my machines? I have to trust what I am told if I am to use the software for its intended purpose. If Dropbox claims what Miguel has quoted in his post, and then it happens that claims are (basically) not true, then it raises the question of integrity, i.e. what other assumptions th…

it's unclear to me what statements we're making are 'not true'. if you don't believe our statements, I'm not going to be able to convince you to trust us over the discourse in this thread :-)

If you publish security spec and adhere to it in a way that allows independent verification of its implementation, then - yes, you will convince that what was claimed is true.

Perhaps, the easier route for you would be to just drop the whole "encrypted" angle and simply state that you provide reasonable protection of files while in transit and in your possession. That would satisfy 99.9% of real users and it will not rub cryptographic pedants the wrong way. The issue at hand is not that you don't encrypt properly, but that you over-promised, and over-promised in a very sensitive area.

(correction) "over-promised" = "implied more than what was said", i.e. what Miguel referred to as "wishy-washy statement".

Re: Dropbox Lack of Security

#40

Post by bradgessler » Tue, Apr 19, 2011, 5:43 AM UTC

jackowayed wrote: post #33

bradgessler wrote: post #30

Earlier quoted context omitted.

Technically speaking, whats the point of encrypting data on the backend if you can decrypt it? This strikes me as a waste of computations for no real gain.

Someone in an Amazon datacenter that gets ahold of a random backup tape/hard drive can't read it. I'm not sure if Dropbox is hosted on EC2, but if not, it means that Amazon couldn't read the data at all. (If it's hosted on EC2, Amazon could probably get ahold of the key if they really wanted to)

Going off of that assumption, what if the decryption keys were also stored in an Amazon data center? It is then possible for Amazon read the contents of these files.

I'd like to hear from Dropbox how this works instead of speculation.