4 ms·

Fascinating, but wasn’t... Dropbox supposed to have client-side encryption? If the backend is recompressing JPG images, that means it has full access to the fil

Fascinating, but wasn’t... Dropbox supposed to have client-side encryption? If the backend is recompressing JPG images, that means it has full access to the file’s plaintext. That’s a bit uncomfortable.

lsiebert 6y ago
Presumably shared images?
twright0 6y ago
Dropbox does not have client-side encryption; its servers have full access to the content of synced files. You can verify this yourself by uploading a common image filetype like jpeg and seeing that the website shows you compressed file thumbnails. (I'm a former Dropbox employee who worked on related things, though not specifically the linked paper)
- pmiller2 6y ago
  Yep, that makes sense. IIRC, they also have some sort of global deduplication system, don't they? That also implies they have access to your unencrypted files. Edit: That's what I get for commenting before reading the paper. They literally mention deduplication in there.
  - ghayes 6y ago
    Not necessarily. You could use homomorphic encryption and, for example, encode the file with a hash of the file as the key material for encryption. All such files will encode identically for each user, but it will be opaque to the server what the contents are unless the server already has the plain-text of the original file. This was used by other cloud storage companies (that are now defunct).
    - rvnx 6y ago
      https://techcrunch.com/2011/06/20/dropbox-security-bug-made-passwords-optional-for-four-hours/ https://techcrunch.com/2011/06/20/dropbox-security-bug-made-... This makes me believe there is no problem for Dropbox to read content in clear.
    - TeMPOraL 6y ago
      > Not necessarily. You could use homomorphic encryption I think that's still far from being possible in practice. IIRC, the best homomorphic encryption can do now is to run simple queries on very small datasets, on a supercomputer, with performance of a 386?
    - Dylan16807 6y ago
      Convergent encryption, not homomorphic, is what you use to deduplicate encrypted files.
- londons_explore 6y ago
  Mega does client side e2e encryption (or at least they claim to), yet their web interface still shows thumbnails... I'd guess they implement it by having the client upload an encrypted version of both the original image and a thumbnail, and then decrypting the thumbnails on the client at display time. Javascript has reasonably performant crypto primitives now, so it's very doable to download data from a server, decrypt it with a client side key, and display it. If mega can do this, it's a shame other services don't.
foobiekr 6y ago
Dropbox has "client-side" weasel encryption: they use TLS. It is obvious that they do not encrypt the files in any way that would prevent access to Dropbox itself, and probably not to any Dropbox employee.
harikb 6y ago
Dropbox never claimed end-to-end client side encryption. That said, neither do any of the popular cloud drive options - for example Google drive or One drive. End to end client side encryption is a tough problem from usability. Most people don’t like being told they can’t recover their “cloud backup” if they lose their laptop or phone or forget their password. I think even iCloud only does end-to-end for specific sensitive data. There are special providers like SpiderOak who do this, but it is non trivial to use safely.
- justinc8687 6y ago
  I've always found Cryptomator or encfs to be great solutions for this.
Tommy_Flowers 6y ago
The only safe assumptions about encryption of your data in the cloud is that 1) its not encrypted, or 2) it is encrypted but at some unknown time in the future there will be a security compromising bug, and the data will be in the wild. But you won't know its in the wild, because the service provider doesn't know about the bug, or it isn't in their interest to tell you.
toast0 6y ago
It seems you're right that Dropbox has the plaintext server side from elsewhere in the thread. It would also have been possible that they did the recompession client side though, and send enough metadata to calculate metrics. I had thought that's what they were doing, to save bandwidth/reduce upload times as well as save space on the servers.

lsiebert 6y ago

Presumably shared images?

twright0 6y ago

Dropbox does not have client-side encryption; its servers have full access to the content of synced files. You can verify this yourself by uploading a common image filetype like jpeg and seeing that the website shows you compressed file thumbnails. (I'm a former Dropbox employee who worked on related things, though not specifically the linked paper)

pmiller2 6y ago
Yep, that makes sense. IIRC, they also have some sort of global deduplication system, don't they? That also implies they have access to your unencrypted files. Edit: That's what I get for commenting before reading the paper. They literally mention deduplication in there.
- ghayes 6y ago
  Not necessarily. You could use homomorphic encryption and, for example, encode the file with a hash of the file as the key material for encryption. All such files will encode identically for each user, but it will be opaque to the server what the contents are unless the server already has the plain-text of the original file. This was used by other cloud storage companies (that are now defunct).
  - rvnx 6y ago
    https://techcrunch.com/2011/06/20/dropbox-security-bug-made-passwords-optional-for-four-hours/ https://techcrunch.com/2011/06/20/dropbox-security-bug-made-... This makes me believe there is no problem for Dropbox to read content in clear.
  - TeMPOraL 6y ago
    > Not necessarily. You could use homomorphic encryption I think that's still far from being possible in practice. IIRC, the best homomorphic encryption can do now is to run simple queries on very small datasets, on a supercomputer, with performance of a 386?
  - Dylan16807 6y ago
    Convergent encryption, not homomorphic, is what you use to deduplicate encrypted files.
londons_explore 6y ago
Mega does client side e2e encryption (or at least they claim to), yet their web interface still shows thumbnails... I'd guess they implement it by having the client upload an encrypted version of both the original image and a thumbnail, and then decrypting the thumbnails on the client at display time. Javascript has reasonably performant crypto primitives now, so it's very doable to download data from a server, decrypt it with a client side key, and display it. If mega can do this, it's a shame other services don't.

foobiekr 6y ago

Dropbox has "client-side" weasel encryption: they use TLS. It is obvious that they do not encrypt the files in any way that would prevent access to Dropbox itself, and probably not to any Dropbox employee.

harikb 6y ago

Dropbox never claimed end-to-end client side encryption. That said, neither do any of the popular cloud drive options - for example Google drive or One drive. End to end client side encryption is a tough problem from usability. Most people don’t like being told they can’t recover their “cloud backup” if they lose their laptop or phone or forget their password. I think even iCloud only does end-to-end for specific sensitive data. There are special providers like SpiderOak who do this, but it is non trivial to use safely.

justinc8687 6y ago
I've always found Cryptomator or encfs to be great solutions for this.

Tommy_Flowers 6y ago

The only safe assumptions about encryption of your data in the cloud is that 1) its not encrypted, or 2) it is encrypted but at some unknown time in the future there will be a security compromising bug, and the data will be in the wild. But you won't know its in the wild, because the service provider doesn't know about the bug, or it isn't in their interest to tell you.

toast0 6y ago

It seems you're right that Dropbox has the plaintext server side from elsewhere in the thread. It would also have been possible that they did the recompession client side though, and send enough metadata to calculate metrics. I had thought that's what they were doing, to save bandwidth/reduce upload times as well as save space on the servers.