/etc/bind/rndc.key - permission denied

Operating system: Ubuntu
OS version: 20.04

In syslog I found this issue today:

Dec 10 15:16:44 xst01 named[1202250]: none:100: 'max-cache-size 90%' - setting to 3456MB (out of 3840MB)
Dec 10 15:16:44 xst01 named[1202250]: configuring command channel from '/etc/bind/rndc.key'
Dec 10 15:16:44 xst01 named[1202250]: open: /etc/bind/rndc.key: permission denied
Dec 10 15:16:44 xst01 named[1202250]: couldn't add command channel 127.0.0.1#953: permission denied
Dec 10 15:16:44 xst01 named[1202250]: configuring command channel from '/etc/bind/rndc.key'
Dec 10 15:16:44 xst01 named[1202250]: open: /etc/bind/rndc.key: permission denied
Dec 10 15:16:44 xst01 named[1202250]: couldn't add command channel ::1#953: permission denied

The Permission are looks like this:

root@xst01:/etc/bind# ls -als
total 64
 4 drwxr-sr-x   2 root bind  4096 Dec 10 15:16 .
12 drwxr-xr-x 121 root root 12288 Dec  9 14:02 ..
 4 -rw-r--r--   1 root root  1991 Aug 18  2020 bind.keys
 4 -rw-r--r--   1 root root   237 Apr 15  2020 db.0
 4 -rw-r--r--   1 root root   271 Apr 15  2020 db.127
 4 -rw-r--r--   1 root root   237 Apr 15  2020 db.255
 4 -rw-r--r--   1 root root   353 Apr 15  2020 db.empty
 4 -rw-r--r--   1 root root   270 Apr 15  2020 db.local
 4 -rw-r--r--   1 root bind   544 Dec 10 15:13 named.conf
 4 -rw-r--r--   1 root bind   498 Apr 15  2020 named.conf.default-zones
 4 -rw-r--r--   1 root bind  3966 Dec 10 15:16 named.conf.local
 4 -rw-r--r--   1 root bind  1115 Dec 10 15:08 named.conf.options
 4 -rw-r-----   1 bind bind   100 Oct  8  2020 rndc.key
 4 -rw-r--r--   1 root root  1317 Apr 15  2020 zones.rfc1918

What permissions are here expected for rndc.key?