Generation of key streams in wireless communication systems

1. A method comprising:

using a count parameter and a bearer parameter as inputs in generation of a security key stream in a communication apparatus, a value of said count parameter being incremented as security key streams are generated and the value of said count parameter having a finite maximum value defining a wrap-around point that represents an upper limit for the count parameter,

detecting the value of said count parameter reaching a predetermined value, and

responsive to said detecting, changing a value of said bearer parameter into a new value, and resetting the value of said count parameter to a value below said maximum value;

wherein the value of said bearer parameter is changed to an unused bearer parameter value for a given bearer in response to the value of said count parameter reaching the wrap-around point.

2. The method of claim 1 , wherein said predetermined value is said maximum value of said count parameter.

3. The method of claim 1 , wherein said value of said count parameter is reset to a minimum value of said count parameter representing a lowest possible value that the count parameter may attain.

4. The method of claim 1 , wherein said value of said bearer parameter is changed to a previously used bearer parameter value, wherein the previously used bearer parameter value is not currently in use in said communication apparatus.

5. The method of claim 4 , wherein said previously used bearer parameter value has a partially used count value space.

6. The method of claim 5 , wherein said value of said count parameter is reset to a smallest unused count value in count value space of said previously used bearer parameter.

7. The method of claim 1 , further comprising performing said security key stream generation in user plane.

8. An apparatus, comprising:

at least one processor; and

at least one memory embodying computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform:

using a count parameter and a bearer parameter as inputs in generation of a security key stream, the apparatus being configured to increment a value of said count parameter as security key streams are generated and the value of said count parameter having a finite maximum value defining a wrap-around point that represents an upper limit for the count parameter, and

changing a value of said bearer parameter to an unused bearer parameter value for a given bearer in response to the value of said count parameter reaching the wrap-around point; and

resetting the value of said count parameter to a value below said finite maximum value.

9. The apparatus of claim 8 , wherein said predetermined value is said maximum value of said count parameter.

10. The apparatus of claim 8 , wherein the memory, computer program and processor are configured to cause the apparatus to reset said value of said count parameter to a minimum value of said count parameter representing a lowest possible value that the count parameter may attain.

11. The apparatus of claim 8 , wherein the memory, computer program and processor are configured to cause the apparatus to change said value of said bearer parameter to a previously used bearer parameter value, wherein the previously used bearer parameter value is not currently in use in said communication apparatus.

12. The apparatus of claim 11 , wherein said previously used bearer parameter value has a partially used count value space.

13. The apparatus of claim 12 , wherein the memory, computer program and processor are configured to cause the apparatus to reset said value of said count parameter to a smallest unused count value in count value space of said previously used bearer parameter.

14. The apparatus according to claim 8 , wherein said apparatus is configured for use in a Long Term Evolution system.

15. A non-transitory computer readable memory medium embodying a computer program executable in an apparatus, comprising computer executable program code which, when executed by at least one processor of an apparatus, causes the apparatus to perform:

using a count parameter and a bearer parameter as inputs in generation of a security key stream in a communication apparatus, a value of said count parameter being incremented as security key streams are generated and the value of said count parameter having a finite predetermined maximum value defining a wrap-around point that represents an upper limit for the count parameter,

detecting the value of said count parameter reaching the finite predetermined maximum value,

responsive to said detecting, changing a value of said bearer parameter to an unused bearer parameter value for a given bearer in response to the value of said count parameter reaching the wrap-around point; and

resetting the value of said count parameter to a value below said finite predetermined maximum value.

16. The non-transitory computer readable memory medium of claim 15 , wherein said predetermined value is said maximum value of said count parameter.

17. The non-transitory computer readable memory medium of claim 15 , wherein the computer executable program code which, when executed by at least one processor of an apparatus, causes the apparatus to perform: changing said value of said bearer parameter to an unused bearer parameter value.

18. The non-transitory computer readable memory medium of claim 15 , wherein the computer executable program code which, when executed by at least one processor of an apparatus, causes the apparatus to perform: changing said value of said bearer parameter to a previously used bearer parameter value, wherein the previously used bearer parameter value is not currently in use in said communication apparatus.