Method and apparatus for generating a key stream
First Claim
1. 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.
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Accused Products
Abstract
A method of generating a key stream for a precomputed state information table. The method comprises initialising a counter and an accumulator with non-zero values; combining state information identified by the counter with the accumulator; swapping state information identified by the counter with state information identified by the accumulator; combining the two pieces of state information; outputting the state information identified by the combination as a byte of the key stream; adding a predetermined number odd number to the counter; and repeating the above steps to produce each byte of the key stream.
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Citations
23 Claims
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1. 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:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A computer readable storage medium residing on a computer containing instructions for said computer to generate a key stream from a precomputed state information table, the state information table including state information, said instructions comprising instructions for:
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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. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A key stream generator for generating a key stream, the key stream generator comprising a counter, an accumulator and a precomputed state information table including state information, said key stream generator being configured for generating said key stream from said precomputed state information table by executing computer executable instructions for:
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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 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. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23)
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Specification