In a method and arrangement for variable generation of cryptographic securities of communications in a host device, for cryptographic security of a communication for a first purpose a first signature is used and for cryptographic security of a communication for a second purpose a second signature is used, the signatures being differentiated from each other by the type of their generation. A cryptologic module has a number of logic circuits and a changeover switch and is arranged externally of the postal security device and is connected at its output with an information input of the postal security device that has a logic circuit that applies a digital signal algorithm to the output signal supplied by the output in order to generate a signature.