Abstract: A terminal (10) in a data exchange system with exchangeable portable user data carriers (4) has for their connection at least one connecting unit (3) and has further at least one data input unit (5). Exchangeable control modules (8, 9) are connected through one or more other, preferably similar, connecting units (6, 7). The modules are equipped with microprocessors and contain mechanically and cryptographically protected memory areas which receive secret data and keys for the secure carrying out of identity and authenticity tests, as well as application specific operational programs. These construction methods offer high security against unauthorized data access as well as against fraudulent manipulation of the device. They also greatly simplify the application independent design and construction of the terminal.

Abstract: With portable data carrying devices, which are intended for the required connection (for example by means of contacts 9) to an external read/write unit in a data exchange system and which contain besides a control unit (2) an additional data memory (5) (both implemented as integrated circuits), a high level of security should be achieved against access to the stored data and manipulations without authorization. For this purpose entry to the additional data memory (5) from the control unit (2) is protected. Various possibilities are specified such as access coding, cryptographic circuit means and methods or secret microcodes. The data carrying device (1) can be implemented with two or more separate integrated circuit components interconnected by a multiple conductor strip (3) (multi-chip), or with all functional units integrated on a common carrier (single chip).