Method and apparatus for generating a key stream

• US 20030174836A1
• Filed: 01/23/2003
• Published: 09/18/2003
• Est. Priority Date: 01/23/2002
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Certicom Corporation (Blackberry Limited)
• Inventors: Vadekar, Ashok
• Granted Patent: US 7,769,169 B2
• Time in Patent Office: Days
• US Class Current: 380/37
• CPC Class Codes: H04L 9/0662 with particular pseudorandom sequence generator

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.

Claims

1. A method of generating a key stream from a precomputed state information table comprising:

a) initialising a counter and an accumulator with non-zero values;

b) combining state information identified by the counter with the accumulator;

c) swapping state information identified by the counter with state information identified by the accumulator;

d) combining the two pieces of state information from step (c);

e) outputting the state information identified by the combination from step (d) as a byte of the key stream;

f) combining a predetermined odd number with the counter; and

g) repeating steps b to f to produce each byte of the key stream.

2. A method according to claim 1, wherein computations are performed modulo a number n.

3. A method according to claim 2, wherein said predetermined odd number is relatively prime to n.

4. A method according to claim 2, wherein the combinations in steps b, d, and f are additions modulo n.

5. A method according to claim 2 wherein said number n is 256.

6. A method according to claim 3 wherein said number n is 256.

7. A method according to claim 4 wherein said number n is 256.

8. A computer readable medium containing instructions for a computer to generate a key stream from a precomputed state information table by the steps of:

a) initialising a counter and an accumulator with non-zero values;

b) combining state information identified by the counter with the accumulator;

c) swapping state information identified by the counter with state information identified by the accumulator;

d) combining the two pieces of state information from step (c);

e) outputting the state information identified by the combination from step (d) as a byte of the key stream;

f) combining a predetermined odd number with the counter; and

g) repeating steps b to f to produce each byte of the key stream.

9. A computer readable medium according to claim 8 wherein computations are performed modulo a number n.

10. A computer readable medium according to claim 9 wherein said predetermined odd number is relatively prime to n.

11. A computer readable medium according to, claim 10 wherein the combinations in steps b, d and f are additions modulo n.

12. A computer readable medium according to claim 9 wherein said number n is 256.

13. A computer readable medium according to claim 10 wherein said number n is 256.

14. A computer readable medium according to claim 11 wherein said number n is 256.

15. In a stream cipher, a method of generating a key stream from state information derived from a secret key, the improvement comprising:

a) initialising registers to non-zero values; and

b) incrementing a counter with a predetermined odd number greater than 1.