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Encrypton system for digital cellular communications

  • US 5,148,485 A
  • Filed: 05/31/1991
  • Issued: 09/15/1992
  • Est. Priority Date: 07/20/1990
  • Status: Expired due to Term
First Claim
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1. A method of generating a pseudo-random bit sequence for use in enciphering digital data in which said bit sequence is a function of a plurality of selected key bits, said method comprising:

  • generating a plurality of multi-bit values each of which is a function of at least some of said selected key bits;

    storing each of said plurality of multi-bit values in a discrete location in a memory;

    storing each of a plurality of multi-bit values in a look-up table;

    generating a sequence of values in a register having a present value at a particular moment by changing the present value contained in said register in response to each cycle of operation;

    cyclically calculating a sequence of multi-bit values in accordance with a first preselected algorithm each of which values is a function of at least one of the multi-bit values stored in either said look-up table or in said memory and at least part of the value contained in said register;

    cyclically resetting the present value contained in said register with a value obtained as a result of each calculation;

    cyclically calculating a multi-bit keyword which is a function of a value obtained as a result of each multi-bit value calculation; and

    sequentially combining at least some of said multi-bit keywords into said pseudo-random bit sequence.

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