Data exchange system comprising a plurality of user terminals each containing a chip card reading device

摘要

A secret cipher (Ki) that is the same for all user terminals is formed of two sub-components (KTi, KT'i) whereof the one sub-component (KTi) is deposited in an erasable, programmable read-only memory (EEPROM). For the second sub-component (KT'i), an encoded data block (E(KT'i)) is transmitted from the outside to a decoder means (DEC) provided in the security module, the decoded output signal thereof being deposited as second sub-component (KT'i) in a first sub-area of a write-read memory (RAM) present in the security module of the user terminal. An overall cipher (Ki) is calculated from the two sub-components (KTi, KT'i) and the result is deposited in a second sub-area of the write-read memory (RAM).