Bad SSH2 KexAlgorithms 'dha-sha1'

Issue

• The sshd service started failing after adding weak ssh key exchange algorithm (dha-sha1) in sshd configuration file.

  # cat /etc/ssh/sshd_config
  KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,dha-sha-1
  
  # journalctl -u sshd
  Jun 13 21:00:48 rh7 sshd[2297]: /etc/ssh/sshd_config line 144: Bad SSH2 KexAlgorithms 'dha-sha1'.
  Jun 13 21:00:48 rh7 systemd[1]: sshd.service: main process exited, code=exited, status=255/n/a
  Jun 13 21:00:48 rh7 systemd[1]: Failed to start OpenSSH server daemon.