By default K3b or brasero burning software will refuse burn encrypted dvd. One way to overcome this problem is by using libdvdcss library whish allows K3b or brasero to look at your encrypted DVD within DVD-device as a block device and thus disregarding its encryption. Before running K3b or brasero install libdvdcss library to allow it clone / burn encrypted DVD.

On Debian or Ubuntu libdvdcss installation to allow K3b burn encrypted DVD's:

apt-get install libdvdcss2

If you are using debian and libdvdcss2 is missing make sure that you have in your repository. Once done palce encrypted DVD into your DVD-Burner and start copy.