Patent ID: 7769169

Claim:
A method of generating a key stream from a precomputed state information table including state information, said method being performed by a correspondent in a communication system and comprising: a) initializing a counter and an accumulator with non-zero values by; i. initializing said counter; ii. combining with a value of the accumulator state information identified by a value of the counter and key information identified by the value of the counter to obtain another value of the accumulator; iii. combining state information identified by the value of the counter with a first of said non-zero values; iv. combining state information identified by said another value of the accumulator with a second of said non-zero values; v. swapping the state information identified by the value of the counter with the state information identified by the another value of the accumulator; vi. incrementing the counter to generate another value for the counter; and vii. repeating steps ii to vi to produce said non-zero values; b) obtaining a constant odd value, c greater than 1, derived from a publicly available session identifier; c) combining with a current value for the accumulator state information identified by a current value for the counter to obtain a next value for the accumulator; d) swapping said state information identified by the current value for the counter with state information identified by said next value for the accumulator; e) combining with said state information identified by said next value for the accumulator said state information identified by the current value for the counter to generate a combined value; f) outputting the state information identified by the combined value as a byte of the key stream; g) combining said odd value c with the current value for the counter to generate a next value for said counter; and h) repeating steps c) to g) to produce each byte of the key stream.