|We've been trying to solve this problem for longer than Dropbox has existed: how can you maintain plaintext locally and ciphertext remotely, easily, with efficient changes-only (a la rsync) sync ?|
We created a lot of half-working Truecrypt/Filevault/encfs schemes and fiddled with a lot of --partial --progress --whatever switches to rsync, but eventually we just told people to use duplicity and call it a day.
Then Mr. Raymii came along and dropped this in our lap:
The tl;dr there is:
"This article describes my truly secure, encrypted file synchronization service. It used EncFS and dvcs-autosync which lets me share only the encrypted data and mount that locally to get the plaintext."
... and we couldn't be happier. Finally we (and anyone using rsync.net, or any ssh host with git on it) have an elegant way to sidestep the issues of trust and authority over remote data on systems you don't control.
 ... and it's still a very good solution.
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