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Method and apparatus for securing executable programs against copying

  • US 5,675,645 A
  • Filed: 04/18/1995
  • Issued: 10/07/1997
  • Est. Priority Date: 04/18/1995
  • Status: Expired
First Claim
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1. An apparatus for executing a secure program in a computer system, wherein the ability to make workable copies of the secure program from the computer system is inhibited, the apparatus comprising:

  • a program memory in which the secure program data is stored in an encrypted form;

    a security chip coupled to the program memory, the security chip comprising;

    means for decrypting portions of the secure program into a clear portion and a remainder portion;

    means for providing the clear portion to memory locations accessible by a processor; and

    remainder memory for storing the remainder portion of the secure program, the remainder memory not directly accessible by the processor;

    means for requesting subsets of the remainder portion for use by the processor; and

    means, within the security chip, for checking that the requested subset is within a valid predetermined set of requested subsets dependent on a stored state for the processor.

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