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| Ensuring data integrity by locked-load and conditional-store operations in a multiprocessor system |
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| Multiplexing communication card and scanning method for run-in testing |
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| Fixture for motor controller power substrate and motor controller incorporating |
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| Asynchronous digital time-division multiplexing system with distributed bus |
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| Method for executing overlays in an expanded memory data processing system |
| OF THE INVENTION FIG. 1 shows an Expanded Memory System (EMS). The system includes a one megabyte (... |
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Method for preventing unauthorized modification of data in a device with a nonvolatile memory
| Details |
Inventors: Pockrandt, Wolfgang; Schrenk, Hartmut;
Assignee: Siemens Aktiengesellschaft (Munich, DE)
Primary Examiner: Chan; Eddie P.
Assistant Examiner: Ellis; Kevin L.
Attorney, Agent or Firm: Lerner; Herbert L., Greenberg; Laurence A.
A method for preventing unauthorized data modification is carried out in a device, such as a chip card, having a nonvolatile memory, a central processing unit, and a program memory assigned to the central processing unit. A command is given to set a check bit in a check register being triggerable by the central processing unit, with a program for modifying data in a memory region of the nonvolatile memory. A check is made to determine if the command derives from a defined address region of the data modification program. The command is carried out by setting the check bit in the check register, if the command derives from the defined address region. A check is made for special permission for a data modification in a memory region of the nonvolatile memory. A check is made to determine if the check bit is set, if the special permission has been given. The data in the memory region is modified if a control bit is set. The check bit in the check register is reset and the permission to write is rescinded, after an allowed data modification, or if a data modification was not allowed, or if no check bit was set. |
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DETAILED DESCRIPTION It is accordingly an object of the invention to provide a method for preventing unauthorized data modification in a device with a nonvolatile memory, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, in which the flexibility of a software version is attained on one hand, and the functional reliability of a hardware version is virtually attained on the other hand.
With the foregoing and other objects in view there is provided, in accordance with the invention, in a method for preventing unauthorized data modification in a device, such as a chip card, having a nonvolatile memory, a central processing unit, and a program memory assigned to the central processing unit, the improvement which comprises giving a command to set a check bit in a check register being triggerable by the central processing unit, with a program for modifying data in a memory region of the nonvolatile memory; checking if the command derives from a defined address region of the data modification program; carrying out the command by setting the check bit in the check register, if the command derives from the defined address region; checking for special permission for a data modification in a memory region of the nonvolatile memory; checking if the check bit is set, if the special permission has been given; modifying the data in the memory region, if a control bit is set; and resetting the check bit in the check register and rescinding the permission to write, after an allowed data modification, and if a data modification was not allowed, and if no check bit was set.
In a method according to the invention, a check bit is set in a check register before performing a check for permission to make a data modification in a memory region of the nonvolatile memory, which can be done, for instance, by polling a secret number.
After permission has been checked and before the data modification itself, a check is then made as to whether or not the check bit has been set
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I/O Systems 
