ssh-keysign —
OpenSSH helper for host-based authentication
ssh-keysign is used by
  ssh(1) to access the local host
  keys and generate the digital signature required during host-based
  authentication.
ssh-keysign is disabled by default and can
    only be enabled in the global client configuration file
    /etc/ssh/ssh_config by setting
    EnableSSHKeysign to “yes”.
ssh-keysign is not intended to be invoked
    by the user, but from ssh(1). See
    ssh(1) and
    sshd(8) for more information
    about host-based authentication.
  - /etc/ssh/ssh_config
- Controls whether ssh-keysignis enabled.
- /etc/ssh/ssh_host_dsa_key
-  
- /etc/ssh/ssh_host_ecdsa_key
-  
- /etc/ssh/ssh_host_ed25519_key
-  
- /etc/ssh/ssh_host_rsa_key
- These files contain the private parts of the host keys used to generate
      the digital signature. They should be owned by root, readable only by
      root, and not accessible to others. Since they are readable only by root,
      ssh-keysignmust be set-uid root if host-based
      authentication is used.
- /etc/ssh/ssh_host_dsa_key-cert.pub
-  
- /etc/ssh/ssh_host_ecdsa_key-cert.pub
-  
- /etc/ssh/ssh_host_ed25519_key-cert.pub
-  
- /etc/ssh/ssh_host_rsa_key-cert.pub
- If these files exist, they are assumed to contain public certificate
      information corresponding with the private keys above.
ssh-keysign first appeared in OpenBSD
  3.2.