NTP client / server with authentication

SERVER CONFIG

ntp authentication-key 1 md5 0802657D2A36 7
ntp master 5

CLIENT CONFIG

ntp authentication-key 1 md5 1531223F2705 7
ntp authenticate
ntp trusted-key 1
ntp server 10.0.12.1 key 1

Notes: the client authenticates the time source, server must have the key.