4 ms·
I still don't understand how files are "cryptographically safe" on Mega The problem is, somehow they know if two people upload the same file even though this s
by lubos 14y ago
I still don't understand how files are "cryptographically safe" on Mega
The problem is, somehow they know if two people upload the same file even though this should be impossible if they do bullet proof client-side encryption.
This does make Mega anything but "cryptographically safe"
- StavrosK 14y agoIt does work, if you read up on how the encryption works, you'll see it's sound. I don't know how secure mega is, but deduplicating encrypted data is possible.
- jonpeda 14y agobut then 'duplication" only happens if the source file is shared post-encryption, which is far less common than sharing pre-encryption, sync post-encryption sharing requires sharing the key as well.
- StavrosK 14y agoYou should read about convergent encryption. You can deduplicate plaintext files without knowing what they are.
- JeremyBanks 14y agoThey don't use convergent encryption, they randomly generated keys when files are uploaded. The only deduplication that exists is when you copy a file that's been shared with you by another user, because in this particular case you also copy the key. "Secure" isn't boolean. Although convergent encryption will prevent people from accessing your secret data, it does have different security properties: Mega would be able to determine whether you have a particular file, which they cannot with the current system.
- pkulak 14y agoBitcasa does it as well.
- przemoc 14y agoIt's explained clearly at https://mega.co.nz/#blog_3 https://mega.co.nz/#blog_3 "Fact #1: Once this feature is activated [deduplication], chunk MACs will indeed be stored on the server side, but they will of course be encrypted (and we will not use ECB!). Fact #2: MEGA indeed uses deduplication, but it does so based on the entire file post-encryption rather than on blocks pre-encryption. If the same file is uploaded twice, encrypted with the same random 128-bit key, only one copy is stored on the server. Or, if (and this is much more likely!) a file is copied between folders or user accounts through the file manager or the API, all copies point to the same physical file." So no, they don't know that two different users upload the same file, unless the key used for encryption is the same, which is almost impossible in practice.
- urza 14y agoDropbox works the same way, doesnt it?
- icebraining 14y agoNo, Dropbox actually holds all the keys; they can access the data if they want to. MEGA actually doesn't have the key, except for files of which they already have an unencrypted copy (since the key is derived from it).
- rscale 14y agoDropbox has access to all your files at all times, and will honor government requests to view your data. They used to claim that your data was inaccessible without your password, but this was always a lie.
- doublec 14y agoMega only de-dup the encrypted result of the file. This means only files from the same user are de-duped. Given that this is likely to be rare, in practice de-dup doesn't happen.