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Method and apparatus for generating a key stream

  • US 8,396,212 B2
  • Filed: 06/23/2010
  • Issued: 03/12/2013
  • Est. Priority Date: 01/23/2002
  • Status: Expired due to Term
First Claim
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1. A method of generating a key stream, the method being performed by a correspondent in a communication system, the correspondent including a counter i, an accumulator j, and a state information table S having state information stored in n entries therein, the method comprising:

  • a) said correspondent using the counter i, the accumulator j, and the state information table S to;

    i) randomly distribute entries of the state information table S by swapping pairs of entries; and

    ,ii) generate a pair of non-zero values a and b by, for each swapping pair, adding an entry to a and adding the other entry to b;

    b) said correspondent initializing the counter i with a and said correspondent initializing the accumulator j with b;

    c) said correspondent obtaining a constant odd value, c, greater than 1;

    d) said correspondent combining with a current value for the accumulator j, state information identified by entry i in the state information table S to obtain a next value for the accumulator j;

    e) said correspondent swapping in said state information table S said state information identified by entry i in the state information table S with state information identified by entry j in the state information table S using said next value for the accumulator j;

    f) said correspondent combining the entry i state information with the entry j state information swapped in step d) to generate a combined value t;

    g) said correspondent outputting state information identified by entry t in the state information table S as a byte of the key stream; and

    h) said correspondent combining said odd value c with the current value for the counter i to generate a next value for said counter i;

    wherein said correspondent repeats steps d) to h) to produce each byte of the key stream.

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