I just wanted to share my success of using BTSync and EncFS. I tried BoxCrypter for Mac, but I didn't like how my friend could still see the filenames (didn't want to pay for the service) so I used vanilla EnFS to do it. I used the help of this page: http://blog.scottlowe.org/2012/11/23/using-encfs-with-dropbox-and-boxcryptor/ However, i had to muck about with homebrew, xtools etc to get EncFS installed, just to find it was probably installed with BoxCrypter! Anyway, I like it