Anordning och förfarande för försäkring av datautbyte mellan en teledataterminal och en hjälpanordning

摘要

The securing of data exchange between a teletext terminal (TVX) and a host (SE) is done with the aid of an additional box (BA) connected to the computer-peripheral port (PPI) of the terminal (TVX). In a pre- session mode, the box acts on the switching element (AIG) of the terminal (TVX) whilst monitoring all other action on this switching element; the box and the host communicate in accordance with a predetermined sequence of operations comprising the definition of a session key which is transmitted or ciphered in accordance with a basic key. Any anomaly during this communication causes the aborting of the pre-session mode.