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It's possible: http://crypto.stackexchange.com/questions/729/is-convergent-encryption-really-secure http://crypto.stackexchange.com/questions/729/is-convergent-
by B-Con 14y ago
It's possible: http://crypto.stackexchange.com/questions/729/is-convergent-encryption-really-secure http://crypto.stackexchange.com/questions/729/is-convergent-... .
The trick lies in ensuring the key used for encryption is linked to the file, not the user. You then have to store a separate key for each encrypted file (and that encryption key is probably going to need to be wrapped by your actual user key for storage).
- loeg 14y agoTrue.
- loeg 14y agoBut, how does the second user to upload the same file know the file's encryption key (since presumably the server only knows ENCRYPT(FILE_KEY with USER1_KEY))? It seems like either the server must know the file's encryption key, or the key must be derivable from the contents... which is no good.