Apex domains cannot have CNAME records.
Question and response
Question
dig keymachine.de. NS
Answer
keymachine.de. 5 NS ns2.megabit.at.
keymachine.de. 5 NS ns.megabit.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0