Apparatus and method for applying ciphering in a universal mobile telecommunications system

1. A method for applying ciphering in a user equipment device (UE) configurable for operation in a mobile telecommunications system comprising a network of a plurality of cells, the method comprising:

receiving a wireless communication over a radio bearer (RB);

selecting, from a plurality of ciphering configurations stored in the UE and based on the RB, a subset of the plurality of ciphering configurations that may be used on the wireless communication;

determining, based on the RB and the wireless communication, which type of ciphering configuration to use on the wireless communication;

using one ciphering configuration from the selected subset and of the determined type on the RB; and

where the UE is configurable to periodically audit stored ciphering configurations by which to determine whether stored ciphering configurations are applicable based on sequence numbers of messages sent and received and to delete stored ciphering configurations deemed no longer applicable based on the audit and sequence numbers of messages sent and received over the RB in question.

2. The method according to claim 1 wherein the types of ciphering configuration comprise at least one of the group comprising: new ciphering configuration, old ciphering configuration and ciphering configuration.

3. The method according to claim 1 , wherein a maximum limit is applied to the number of ciphering configuration of a given type that are stored.

4. The method according to claim 1 further comprising determining whether parameters of a ciphering configuration are required, and removing parameters that are determined to be no longer required.

5. The method according to claim 1 wherein the UE is capable of communicating via a plurality of radio bearers, the method further comprising storing parameters relating to a plurality of ciphering configurations for a given type of ciphering configuration for each radio bearer.

6. The method according to claim 1 further comprising storing parameters in a layer of a protocol stack which layer applies the ciphering.

7. A mobile telecommunications device configured for use in a mobile telecommunications system, the device comprising:

a receiver enabled to receive wireless communications over a plurality of radio bearers (RBs); and

a microprocessor, memory, and software operable to select, from a plurality of stored ciphering configurations, one stored ciphering configuration for use on an RB, and operable to periodically audit stored ciphering configurations by determining whether stored ciphering configurations are applicable based on sequence numbers of messages sent and received and to delete any ciphering configuration deemed no longer applicable based on the audit sequence numbers of messages sent and received over the RB in question.

8. The device according to claim 7 , stored ciphering configurations including at least one of the group comprising: new ciphering configuration, old ciphering configuration and ciphering configuration.

9. The device according to claim 7 , wherein a maximum limit is applied to the number configurations of a given type that are stored.

10. The device according to claim 7 further arranged to determine whether parameters of a ciphering configuration are required, and to delete parameters that are determined to be no longer required.

11. The device according to claim 7 further arranged to apply the appropriate ciphering configuration according to parameters stored with each ciphering configuration.

12. The device according to claim 7 wherein the device is further arranged to store parameters associated with the ciphering configurations in a layer of a protocol stack which applies ciphering.

13. The device according to claim 12 wherein the device is operable in a Universal Mobile Telecommunications System and the parameters are stored in at last one of the Radio Link Control Layer and the Medium Access Control (MAC) layer of the protocol stack of the device.

14. A mobile telecommunications network comprising a network of a plurality of cells from a plurality of Node B transceivers and at least one radio network controller (RNC), comprising:

a microprocessor, memory, and software operable to select, from a plurality of stored ciphering configurations, the stored ciphering configurations including a plurality of types of ciphering configurations, one cipher configuration to use on one radio bearer (RB), and operable to periodically audit stored ciphering configurations by determining whether stored ciphering configurations are applicable based on the audit and sequence numbers of messages sent and received over the RB in question and to delete any ciphering configuration deemed no longer applicable.

15. The network according to claim 14 , the types of ciphering configuration being at least one of the group comprising: new ciphering configuration, old ciphering configuration and ciphering configuration.

16. The network according to claim 14 , wherein a maximum limit is applied to the number of ciphering configurations of a given type that are stored.

17. The network according to claim 14 further arranged to determine whether parameters of a ciphering configuration are required, and to delete parameters that are determined to be no longer required.

18. The network according to claim 14 further arranged to apply the appropriate ciphering configuration according to parameters stored with each ciphering configuration.

19. The network according to claim 14 wherein the device is further arranged to store parameters associated with the ciphering configurations in a layer of a protocol stack which applies ciphering.

20. The network according to claim 19 wherein the network is operable in a Universal Mobile Telecommunications System and the parameters are stored in at-least one of the Radio Link Control Layer and the Medium Access Control (MAC) layer of the protocol stack.

21. The network according to claim 14 wherein the microprocessor, memory, and software reside on the RNC.