local old_on_rightclick = minetest.registered_nodes["default:chest"].on_rightclick
minetest.override_item("default:chest_shared", {
    on_rightclick = function(pos, node, clicker, itemstack, pointed_thing)
        local name = clicker:get_player_name()
        if minetest.is_protected(pos,name) then
            minetest.chat_send_all(name,"You cannot use this shared chest, because you are not part of the protection.")
            return itemstack
        end
        old_on_rightclick(pos, node, clicker, itemstack, pointed_thing)
    end
})