First, make sure that AES is supported by your kernel as well as the following programs:
Next, check if you have
aespipe installed (this package is part of the Debian distribution).
mkisofs -r /backup | /usr/local/bin/aespipe -e AES128 -T >backup.iso
will create a crypted DVD-Image. In this example a keylength of 128 bit is used, thus AES asks for a password of (at least) 20 characters. Make sure that your image is not violating the maximum DVD size!
To check the integrity of the crypted image you can do a loopback mount with
mount -t iso9660 backup.iso /mnt/cdrom -o loop=/dev/loop0,encryption=AES128
Now, we have to get the image onto a disk. This is quite easily done with
growisofs -Z /dev/dvdrecorder=backup.iso
If you are creating a crypted CD (check the size of your image!) then you could use
cdrecord -v dev=/dev/cdrecorder backup.iso
Finally, we should check the data on our new disk before deleting any files from the harddrive.
Typing (as root)
mount -t iso9660 /dev/dvdrom /mnt/dvdrom -o loop=/dev/loop0,encryption=AES128
should ask you for the password and afterwards the data should be accessible at the mountpoint.
Just to remind you, device names and mountpoints are subject to your local installation.