The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 14, 1997
Filed:
Dec. 08, 1994
Wolfgang Pockrandt, Reichertshausen, DE;
Hartmut Schrenk, Haar, DE;
Siemens Aktiengesellschaft, Munich, DE;
Abstract
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 The check bit in the check register is reset and the permission to write is rescinded, after an allowed data modification, or if a data modification was not allowed, or if no check bit was set.