Importance

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Abstract

Microprocessor-based cards use application programs contained in a non-volatile user memory (MU), under the control of an operating system in a read-only memory (MSYS). To provide flexibility and security of access to the various memory zones without using a specific rigidly fixed circuitry, it is proposed that the memory access instructions of the application programs (PG1, PG2, PG3) should be interpreted and not performed directly. The interpreter is in the read-only memory (MSYS) or in the user memory and it carries out an access instruction as follows: it explores a reserved zone (ZR) of the user memory to find out if the requested access (access for reading, writing or performance) is cleared for the requested address. It performs the instruction only if the clearance is present. The reserved zone (ZR) which contains these clearances is updated during the writing, in the user memory, of a new application program. The updating can be done only by the operating system.

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First Claim