Data-processing system which protects the secrecy of confidential data

Abstract

A data processing system is provided which protects the secrecy of confidential data at the stages where it is formulated and transmitted to a card (first auxiliary member) having a code key thereon. The data processing system includes a data-processing machine having a device or terminal for transmitting data, including confidential data, and a plurality of first members auxiliary to the machine which are each intended to receive the confidential data from the transmitting device via the same transmission line and to process this confidential data. The transmitting device includes a plurality of second auxiliary members which correspond to respective ones of the first auxiliary members. Each pair of corresponding first and second auxiliary members include respective generators for generating first and second code keys and the system includes a means for causing one of the first code keys to correspond with one of the second code keys. One of the pair of corresponding first and second members includes modulating means to mix the confidential data with the code key corresponding to the said members of that pair to form a combined signal, while the corresponding members of the other pair include a demodulating means which reacts to the code key which has been made to correspond and to the said combined signal to reconstitute the said confidential data.