nsd users - Jul 2021 - Location of temporary zone files

Hi!

The man page mentions xfrdfile option, but I also see directories/files 
in /tmp:
darilion at tld-all-vnn1:~$ ls -l /tmp/

drwx------ 2 nsd  nsd  4096 Jul  8 11:03 nsd-xfr-683
drwx------ 2 nsd  nsd  4096 Jul  8 12:16 nsd-xfr-684
drwx------ 2 nsd  nsd  4096 Jul  8 12:02 nsd-xfr-685
drwx------ 2 nsd  nsd  4096 Jul  8 12:16 nsd-xfr-686
drwx------ 2 nsd  nsd  4096 Jul  8 12:07 nsd-xfr-687
drwx------ 2 nsd  nsd  4096 Jul  8 12:01 nsd-xfr-688
drwx------ 2 nsd  nsd  4096 Jul  8 12:03 nsd-xfr-689
drwx------ 2 nsd  nsd  4096 Jul  8 12:01 nsd-xfr-690


Does NSD also store zone data in /tmp? I need to store zone files 
encrypted on the disk and wonder if I need to encrypt /tmp too.

Thanks
Klaus