The file /etc/ssh/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/Reference:
From the man pages:
the host key files are normally not readable by anyone but root. The default is /etc/ssh/ssh_host_key for protocol version 1, and /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for protocol version 2.