Method and Arrangements for Ciphering Management in a Telecommuncation System

FIELD OF THE INVENTION

The present invention relates to ciphering of configuration messages in cellular mobile communication systems .

BACKGROUND

In the current UMTS architecture, a number of base stations called Node-Bs are connected to a Radio Network Controller (RNC), and a number of RNC : s are connected to a Serving GPRS Support Node (SGSN) . In this type of architecture, configuration messages such as RRC (Radio Resource Control) messages are terminated in the RNC, in which ciphering algorithms and ciphering keys are located. Thus, ciphering of e.g. configuration messages between User Equipment (UE) and the network takes place in the RNC.

However, in order to reduce the number of nodes and achieve a less complex network, a network architecture where a number of base stations are connected directly to a single network node could be preferred. In such network architecture, most of the RNC functionality of the conventional architecture has been transferred to the base stations, and the RNC nodes are omitted. In an architecture of the type described, the network node is handling, e.g., distribution of paging messages to the base stations, IP Header Compression and encryption of user data streams, termination of user plane packets for paging reasons and switching of U-plane for support of UE mobility. The base station handles functions for Radio Resource Management

such as Radio Bearer Control, Radio Admission Control, Connection Mobility Control, and Resource Allocation.

Thus, ciphering algorithms and ciphering keys are located in the central node. The reason for this is that a base station is not considered to be a secure node, since it is often located in places where it is within reach of the public.

According to this type of architecture, configuration signalling is terminated in the base station. Such configuration signalling can for example be messages ordering a handover, requesting a measurement report from the UE or any type of message for configuration of the UE. Most of the configuration messages do not contain any critical information and can be transmitted without requirements of ciphering or integrity protection. However, some specific configuration messages would be desirable to protect, for example messages containing information on UE identity or the like. A direct implication of the use of the distributed architecture described above is however that configuration messages terminated in the base station is not ciphered, since the ciphering means are located in a node that hierarchically is located "above" the base station.

SUMMARY

The problem experienced with previously known technique is thus that configuration messages terminated in the base station are sent unencrypted, since ciphering algorithms and keys and are not available in the base station. It is therefore an object of the present invention to provide a method for ciphering that solves this problem.

The present invention thus relates to ciphering of configuration messages in a system architecture where the ciphering means is located in a network node different from the node where the configuration message is terminated. More specifically, the invention relates to a method in a base station for ciphering of configuration messages in a cellular telecommunications system. The system comprises a network node in which means for ciphering are located, at least one base station connected to said network node and at least one User Equipment, hereinafter referred to as UE. Configuration messages are terminated in the base station. The method comprises the steps of receiving a ciphering mask from the network node and utilizing the ciphering mask for ciphering of a configuration message for downlink communication or deciphering of a ciphered configuration message received by the base station in uplink communication .

Hereby, according to one aspect of the invention, it is possible to apply ciphering to critical configuration messages in the base station without having a ciphering algorithm or ciphering key in the base station.

The term ciphering mask is herein intended to cover a cryptographically generated bit-string.

The invention furthermore relates to a base station capable of generating configuration messages and communicating such configuration messages with a UE in uplink and downlink communication. Said base station is arranged to receive a ciphering mask from a network node accommodating ciphering means . The base station furthermore comprises means for utilizing the ciphering mask for ciphering of a configuration message for downlink communication or

deciphering of a ciphered configuration message received in uplink communication.

The invention furthermore relates to a radio network node accommodating ciphering means . Said radio network node is capable of generating ciphering masks, and to transmit at least one ciphering mask to a base station as described above .

According to an embodiment of the invention, an x- or operation is applied on the ciphering mask and the configuration message in the base station in order to cipher or decipher the configuration message. The network node can transmit a ciphering mask to the base station upon request from the said base station, or the base station can request a number of ciphering masks and store the masks to be used when needed, which means that no delay would be associated with the ciphering. A request from the base station preferably comprises signaling of certain parameters, such as a configuration message sequence number and the length of the configuration message.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description of preferred embodiments as illustrated in the drawings.

Fig. Ia illustrates the current UMTS architecture

Fig. Ib illustrates the architecture that has been adopted for LTE.

Fig. 2 shows a flow chart schematically illustrating an embodiment of the invention.

DESCRIPTION

The present invention can be exemplified in the following non-limiting description of an embodiment of the invention.

The work of the study item UTRAN long term evolution (LTE) is currently ongoing in the 3rd Generation Partnership Project (3GPP) . As part of the study item a new architecture (compared to the current UMTS architecture) has been decided. Fig. 1 shows a comparison between the current UMTS architecture (Fig. Ia) and the architecture that has been adopted for LTE (Fig. Ib) . In the current UMTS architecture shown in Fig. Ia, interconnected Radio Network Controllers 2 (RNCs) are each connected to a number of base stations 4 such as Node-Bs . The RNCs are connected to a Serving GPRS Support Node 3 (SGSN) , which in turn is connected to a Gateway GPRS Support Node 1 (GGSN) . Ciphering means such as ciphering algorithms and security keys are located in the RNC 2, where configuration signaling such as RRC messages are terminated, whereby the RRC messages are ciphered and deciphered in the RNC 2.

An architecture to which the present invention is relevant is shown in Fig. Ib. A network node, here represented by an access gateway node (AGW) 6, is connected directly to a number of base stations 4 called Node-Bs, each of which are provided with most of the functionality that the RNC 2 has in the current UMTS architecture illustrated in Fig. Ia. However, since the Node-Bs 4 are not considered to be secure nodes, the ciphering means need to be located in the AGW 6, while the RRC messages are terminated in the Node- B 4.

The method according to the invention can be carried out in the following steps, as illustrated in Fig. 2:

When a critical RRC message needs to be transmitted from the Node-B 4 to the UE 5, the Node-B 4 signals a request for a ciphering mask for the critical message from the AGW 6 in step 10. There are several ways to do this. One example is that the Node-B 4 signals certain parameters to the AGW 6 such as RRC message sequence number, length of the RRC message and potentially other information. In step 12, the AGW 6 responds to the request by generating a ciphering mask with the received parameters as input and in step 14 the AGW 6 signals the ciphering mask back to the Node-B 4.

In step 16, the ciphering mask is available in the Node-B 4 and the RRC message is ciphered in the Node B by applying a bitwise x-or operation, which is a well known mathematic operation, on the ciphering mask and the RRC message.

In step 18, the message is transmitted to the UE 5 where the message is deciphered in accordance with known techniques .

The Node-B 4 can alternatively request ciphering masks in advance. This is done by requesting ciphering masks for a range of message sequence numbers and potentially stating a maximum length of the messages. The AGW 6 then responds with the requested number of ciphering masks with the length according to the indicated maximum length of the messages. In this case the Node-B has ciphering masks available when a critical RRC message needs to be transmitted. Thus, no delay would be associated with the ciphering in contrast to the case where the message is sent to the AGW for ciphering.

In the uplink direction, the same procedure as illustrated in Fig 2 is applied at reception of RRC messages

in the Node-B. The Node-B requests ciphering masks from the

AGW, (either when needed or in advance) for the expected RRC message sequence number (s) and performs deciphering when the message is received.

If only few of the RRC messages actually need to be ciphered, it could potentially happen that requested ciphering masks are left unused since the Node-B can not know in advance which RRC messages that needs to be ciphered or deciphered. That could however be avoided by using either separate RRC sequence numbering for ciphered and unciphered RRC messages or only applying RRC sequence numbers on the ciphered RRC messages.

Even though the invention has been described in relation to UTRAN Long Term Evolution, it could be applied to any type of network in which means for ciphering is located in a network node different from the node where configuration messages are terminated. The invention is thus not to be limited to the disclosed embodiments, but is intended to cover various modifications within the scope of the appended claims .