methods enabling the use of an office printer connected to a microcomputer in order to print legitimate postal marks . it uses a cartridge of special fonts in which there are stored the franking marks according to the standards laid down for the printer . a known security component is provided , on the one hand to protect access to the memory contained in the cartridge and , on the other hand , to perform the computation , for each printing of a franking mark , of a security mark that contains encrypted information elements that are readable by the postal authority , enabling the franking mark to be authenticated . it provides for the elimination of specific franking machines and limits the handling operations to the handling of a small - sized cartridge .