Abstract: In a mobile communication system, communication credits are stored in a secure module 30 of a mobile communication appliance 10. Credits are reloaded over-the-air (OTA) from a reload server 20. For requesting a reload, the secure module 30 generates an authenticated reload request message 50, which is transmitted to the reload server 20. In response to receiving the reload request message 50, the reload server 20 informs the secure module 30 of how many credits have been granted in the form of an authenticated reload grant message 60. Successive messages are made to differ by using different transaction numbers. A received authenticated message is only accepted if a transaction number in the message matches a local transaction number.

Abstract: The arithmetic unit in a data processing system with a microprocessor and an additional arithmetic unit carries out special arithmetic operations, preferably integrated in a single semiconductor chip, is controlled by the microprocessor via a number of registers. Several sets of such registers are provided. The registers of one set are selected via a selection circuit. As a result, a set of registers which is not required during execution of a calculation by the arithmetic unit can be filled with new data by the microprocessor and, after completion of the calculation in the arithmetic unit, switching over to a newly filled set of registers takes place so that the arithmetic unit can continue with a new set of operands without having to observe a waiting period.

Abstract: This provides a first device for implementing an RSA-type protected data exchange system for the signing of messages and the verification of the signed messages, and a second device for inhibiting the encryption anti decryption functions inherent of such systems so as to authorize only the signature and signature functions and public key authentication.