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Dropbox Lack of Security

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Re: Dropbox Lack of Security

#71

Post by [deleted] »

itistoday wrote: post #42
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…

Everything on your website that in any way addresses "Dropbox's security" should make absolutely clear the extent to which users can expect their data to be "secure". In Dropbox's case, users can expect the following: - Data is probably secure from sniffers That's it. It matters little whether "Drew has physical access to our storage servers anymore". Your code obviously has easy access to the keys used to encrypt an…

[deleted]

Re: Dropbox Lack of Security

#72

Post by shin_lao »

palish wrote: post #60
shin_lao wrote: post #56

Earlier quoted context omitted.

The authentication token can be generated and managed by the software. It would then be protected by the account password, if any (Windows and MacOS X offer this feature). Doable, and even better, you can make that a 30 € / month corporate option. ;)

If the key file is stored on Dropbox servers, then Dropbox has access to all of your files. This defeats the original purpose (security). If the key file is not stored on Dropbox servers, then you can't easily use Dropbox across several different computers. This defeats the other purpose (accessibility).

You can store a key escrow on the dropbox server protected by a password or a token. Just a matter of designing something secure and useable. Not easy, but possible.

Re: Dropbox Lack of Security

#73

Post by bdhe »

kennywinker wrote: post #50

forgive me if I'm naive, but can file hashes be spoofed in any way? I'm thinking upload a bunch of files that hash to random numbers, then download the de-duplicated original files. could someone more knowledgable in this area tell me if this is a credible threat?

You're looking for two files f1 and f2 that hash to the same thing? And hoping that f1 is randomly generated by you, but f2 is someone else's original file which can be downloaded because of dedup?

In general, solving for f1 and f2 (i.e., you get to control both) such that h(f1)=h(f2) is called finding collisions in hash functions and hash functions like SHA are considered collision-resistant. It is very difficult to find collisions. http://en.wikipedia.org/wiki/Collision_resistance

Of course, if f1=f2, then you've magically guessed the original file, so that is highly unlikely. What you're asking for is something stronger than collision resistance; you're asking for a second preimage, given a first. This is for all practical purposes (requires at least 2^120 or more computations) impossible for any well designed hash function.

Re: Dropbox Lack of Security

#74

Post by patrickaljord »

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…

Check http://camlistore.org/ it's by a few googlers including the guy that did memcached (Brad Fitz).

Re: Dropbox Lack of Security

#75

Post by joanou »

gst wrote: post #67
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…

This system already exists. * Wuala (using encryption but somewhat insecure deduplication) * SpiderOak (using more secure deduplication: https://spideroak.com/blog/20100827150530-why-spideroak-does... )

* AltDrive - client side deduplication.

Re: Dropbox Lack of Security

#76

Post by wahnfrieden »

oconnore wrote: post #64
shin_lao wrote: post #56

Earlier quoted context omitted.

The authentication token can be generated and managed by the software. It would then be protected by the account password, if any (Windows and MacOS X offer this feature). Doable, and even better, you can make that a 30 € / month corporate option. ;)

Isn't one of the major cool things about dropbox that if your computer hard drive gets smashed (and thus the key is destroyed), you can still access your files somewhere else?

That's why you should always keep backups of your key somewhere. Even on paper in a safe deposit box.

Re: Dropbox Lack of Security

#77

Post by piaskal »

shin_lao wrote: post #72
palish wrote: post #60

Earlier quoted context omitted.

If the key file is stored on Dropbox servers, then Dropbox has access to all of your files. This defeats the original purpose (security). If the key file is not stored on Dropbox servers, then you can't easily use Dropbox across several different computers. This defeats the other purpose (accessibility).

You can store a key escrow on the dropbox server protected by a password or a token. Just a matter of designing something secure and useable. Not easy, but possible.

When you forget your password you'll lose access to all of your data. Password recovery won't be possible if the key is password protected.

Re: Dropbox Lack of Security

#78

Post by Groxx »

shin_lao wrote: post #38
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…

Have fun decrypting AES in Javascript, and downloading the file through your browser. (edit: on your cell phone...)

Re: Dropbox Lack of Security

#79

Post by otterley »

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.

Yes, but under the Stored Communications Act (18 U.S.C. 2703), no warrant is needed to obtain communications stored longer than 180 days.

This is why encryption of data in the cloud, where the keys are not held by the provider, is essential.

Re: Dropbox Lack of Security

#80

Post by cpeterso »

bradgessler wrote: post #37
arashf wrote: post #20

Earlier quoted context omitted.

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?

Due to Dropbox's implementation of de-duplication of identical files, any user can (in theory) determine whether (but not who) some other user is storing the same file. If you upload a file that any other user has aleady uploaded, your file transfer will be nearly instantaneous.

See: "How Dropbox sacrifices user privacy for cost savings"

http://paranoia.dubfire.net/2011/04/how-dropbox-sacrifices-u...

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