code: def cmd_signing_setup(self, args):
          '''setup signing key on board'''
          if len(args) == 0:
              print("usage: signing setup passphrase")
              return
          if not self.master.mavlink20():
              print("You must be using MAVLink2 for signing")
              return
          passphrase = args[0]
          key = self.passphrase_to_key(passphrase)
          secret_key = []
          for b in key:
              secret_key.append(ord(b))
  
          epoch_offset = 1420070400
          now = max(time.time(), epoch_offset)
          initial_timestamp = int((now - epoch_offset)*1e5)
          self.master.mav.setup_signing_send(self.target_system, self.target_component,
                                             secret_key, initial_timestamp)
          print("Sent secret_key")
          self.cmd_signing_key([passphrase]f cmd_signing_setup(self, args):
          '''setup signing key on board'''
          if len(args) == 0:
              print("usage: signing setup passphrase")
              return
          if not self.master.mavlink20():
              print("You must be using MAVLink2 for signing")
              return
          passphrase = args[0]
          key = self.passphrase_to_key(passphrase)
          secret_key = []
          for b in key:
              secret_key.append(ord(b))
  
          epoch_offset = 1420070400
          now = max(time.time(), epoch_offset)
          initial_timestamp = int((now - epoch_offset)*1e5)
          self.master.mav.setup_signing_send(self.target_system, self.target_component,
                                             secret_key, initial_timestamp)
          print("Sent secret_key")
          self.cmd_signing_key([passphrase])
docs: setup signing key on board