Abstract: A transaction system comprises terminal stations which can communicate with a host exchange. In order to improve the communication, concentrators are arranged between the host exchange and the terminal stations. Given functions can be accommodated within the concentrators so that they need not be provided in the terminal station. The concentrators as well as the terminal stations are provided with a security box in order to realize encryption/decryption of the data transport; for the terminal station this box is preferably realized in the form of a smart card which acts as an operator identification element. A customer can identify himself by means of a user identification element, for example a magstripe card or a further smart card. The encryption mechanism is preferably DES.