Hi RĂ¼diger,
To be honest, my previous post was quite incomplete: At the moment, this feature is only available on Boxcryptor for Windows.
However, there is an easy workaround for OSX: Enable filename encryption via the settings menu, create an encrypted folder, disable filename encryption again.
=> As filename encryption is inherited, all files and folders dropped into that folder will obtain filename encryption.
Cheers,
Florian