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by twright0 2027 days 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)
2 comments
pmiller2 2027 days 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.

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ghayes 2027 days 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).
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Dylan16807 2027 days ago
Convergent encryption, not homomorphic, is what you use to deduplicate encrypted files.
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rvnx 2027 days ago
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.

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TeMPOraL 2027 days 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?

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londons_explore 2027 days 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.

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