Noob asks: Encrypted Root filesystem with CGD?

hello,

I'm a total crypto and *BSD newbie and this question may sound stupid.
However, maybe some of you find the time to answer.

Is it possible to encrypt the root filesystem with the Cryptographic Disk
Driver under NetBSD?
All I could find is that it is possible to encrypt the SWAP.
http://www.netbsd.org/guide/en/chap-cgd.html
As far as I understood, CGD is similar to the Linux loopback device, main
difference seems to be that it uses a native disk or partition as a backing
store.

Thx for your help.

best wishes, Richard