Jörn Engel  wrote:
>Depends on how much security you really care about.  If you really
>don't mind the pain involved, some metadata should explicitly *not* be
>encrypted, to avoid known plaintext attacks.

What?  No.  Modern cryptosystems are designed to be secure against
known plaintext attacks.  Making your system more convoluted merely to
avoid providing known plaintext is a lousy design approach: the extra
complexity usually adds more risk than it removes.