The file /etc/ssh_host_key should be:

A.
world-readable
B.
readable to group sys
C.
readable to root only
D.
readable by all SSH users
Explanation:
Note: If you really mean the private ssh server key, it should bre readable only be root.
The public key have to readable by all SSH users.
C) readable to root only is correct.
ls -lt /etc/ssh/ssh_host_key
-rw——- 1 root root 978 Nov 7 2014 /etc/ssh/ssh_host_key
ls -lt /etc/ssh/ssh_host_key.pub
-rw-r–r– 1 root root 643 Nov 7 2014 /etc/ssh/ssh_host_key.pub
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