KR20130009849A - Apparatus and method for transitioning enhanced security context from a utran-based serving network to a geran-based serving network - Google Patents

Abstract

A method is disclosed for transitioning an enhanced security context from a UTRAN based serving network to a GERAN based serving network. In this method, the remote station uses the enhanced security context root key and the first information element to generate first and second session keys in accordance with the enhanced security context. The remote station receives the first message from the UTRAN based serving network. The first message includes signaling second information element to the remote station to generate third and fourth session keys for use with the GERAN based serving network. The remote station generates third and fourth session keys using the second information element and the first and second session keys in response to the first message. The remote station protects wireless communications on the GERAN based serving network based on the third and fourth session keys.

Description

APPARATUS AND METHOD FOR TRANSITIONING ENHANCED SECURITY CONTEXT FROM A UTRAN-BASED SERVING NETWORK TO A GERAN-BASED SERVING NETWORK}

The present invention generally relates to an enhanced security context for user equipment operating in Universal Mobile Telecommunications Service (UMTS) and / or GSM Edge Radio Access Network (GERAN).

Cross reference of related applications

This application claims the priority of US Provisional Application No. 61 / 325,001, filed April 16, 2010, which is incorporated herein by reference.

background

In UMTS 3rd generation (3G) radio access network or GERAN networks using 3G AKA (Authentication and Key Agreement) authentication, successful AKA authentication is a pair of shared keys, an encryption key to secure communications between the user equipment (UE) and the network. resulting in a (cipher key; CK) and an integrity key (IK). Shared keys may be used directly to secure traffic between the UE and the network, such as in the case of the UMTS Terrestrial Radio Access Network (UTRAN), or keys, for example K _C , in the case of the GERAN (GSM Edge Radio Access Network). Or may be used to statically derive K _C128 .

The compromised key may lead to serious security issues until the keys are changed in the next AKA authentication. Typically, AKA authentication is often not performed due to the significant overhead required. Also, if both keys CK and IK are compromised, the GERAN keys are also compromised.

In UMTS / HSPA (High Speed Packet Access) deployments, some or all of the functions of the Radio Network Controller (RNC) and Node B may collaborate together into one node at the edge of the network. The RNC needs keys for functionality such as user plane ciphering and signaling plane ciphering and integrity protection. However, RNS functionality may be deployed at a home Node B in an exposed location, such as a UMTS femtocell. Thus, RNS functionality deployed at possibly insecure locations that provide access (including physical access) may allow keys, CK and IK to be compromised.

Session keys (modified versions of CK and IK) may be used to further lower security risks associated with exposed RNC functionality. Techniques for providing such session keys are disclosed in US 2007/0230707 A1.

Unfortunately, the use of such session keys requires upgrade variants for serving networks. However, network operators are easy to upgrade their serving networks in a phased manner.

Thus, there is a need for a technique for transitioning enhanced security context support from a UTRAN based serving network to a GERAN based serving network.

One aspect of the present invention may belong to a method of transitioning a first security context from a first type serving network to a second type serving network. In this method, the remote station uses the root key associated with the first security context and uses the first information element to generate first and second session keys in accordance with the first security context. The remote station receives the first message from the first type serving network. The first message includes second information element signaling to the remote station to generate third and fourth session keys for use with the second type serving network. The remote station generates third and fourth session keys using the second information element and the first and second session keys in response to the first message. The remote station protects wireless communications on the second type serving network based on the third and fourth session keys.

In more detailed aspects of the invention, the first information element may comprise a count value. The first security context may be an enhanced security context with security characteristics that are not supported by the second security context. The first type serving network may be a UTRAN based serving network, and the second type serving network may be a GERAN gibb or serving network. Alternatively, the first type serving network may be a GERAN based serving network and the second type serving network may be a UTRAN based serving network. The remote station may also include mobile user equipment.

Another aspect of the invention may belong to a remote station, which uses the root key associated with the first security context and uses the first information element to retrieve the first and second session keys in accordance with the first security context. Means for generating; Means for receiving a first message from a first type based serving network, the first message including third information element signaling to a remote station for use with the second type serving network; Means for receiving the first message; Means for generating third and fourth session keys using the second information element and the first and second session keys in response to the first message; And means for protecting wireless communications on the second type serving network based on the third and fourth session keys.

Another aspect of the invention may belong to a remote station comprising a processor, the processor using a root key associated with the first security context and using a first information element, in accordance with the first security context, in accordance with the first security context. Generate two session keys; Receiving a first message from a first type serving network, the first message generating second and fourth session keys for use with a second type serving network, including signaling a second information element to a remote station; Receive the first message; Generate third and fourth session keys using the second information element and the first and second session keys in response to the first message; Configure wireless communications on the second type serving network based on the third and fourth session keys.

Another aspect of the invention pertains to a computer program product comprising a computer readable storage medium, wherein the computer readable storage medium causes the computer to use a first information element using a root key associated with the first security context. Code for generating first and second session keys in accordance with a first security context; Code for causing a computer to receive a first message from a first type serving network, the first message including a second information element signaling to a remote station for use with the second type serving network; Code for receiving a first message, generating four session keys; Code for causing a computer to generate third and fourth session keys using the second information element and the first and second session keys in response to the first message; Code for protecting wireless communications on a second type serving network based on the third and fourth session keys.

1 is a block diagram of an example of a wireless communication system.
2 is a block diagram of an example of a wireless communication system in accordance with a UMTS / UTRAN architecture.
3 is a block diagram of an example of a wireless communication system in accordance with the GERAN architecture.
4 is a flow diagram of a method of transitioning enhanced security context support from a UTRAN based serving network to a GERAN based serving network.
5 is a flowchart of a method of establishing an enhanced security context between a remote station and a serving network based on an attach request message.
6 is a flowchart of a method of establishing at least one session key from an enhanced security context between a remote station and a serving network based on a service request message.
7 is a flowchart of a method of establishing at least one session key from an enhanced security context between a remote station and a serving network based on a routing area updater request message.
8 is a block diagram of a computer including a processor and a memory.
9 is a flow diagram of a method of transitioning enhanced security context support from a UTRAN based serving network to a GERAN based serving network.

The word "exemplary" is used herein to mean "functioning as an example, case, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

2-4, one aspect of the present invention may belong to a method 400 for transitioning an enhanced security context from a UTRAN based serving network 230 to a GERAN based serving network 230 ′. In this method, the remote station 210 uses the enhanced security context root key and the first information element to generate first and second session keys in accordance with the enhanced security context (step 410). The remote station receives the first message from the UTRAN based serving network (step 420). The first message includes signaling second information element to the remote station to generate third and fourth session keys for use with the GERAN based serving network. The remote station, in response to the first message, generates third and fourth session keys using the second information element and the first and second session keys (step 430). The remote station protects wireless communications on the GERAN based serving network based on the third and fourth session keys (step 440).

The first information element may comprise a count. In addition, the remote station may include a mobile user equipment (UE), such as a wireless device.

In addition, with reference to FIG. 8, another aspect of the present invention may belong to a remote station 210, which may be configured to include a first security element in accordance with an enhanced security context using an enhanced security context root key and a first information element. And means for generating second session keys (processor, 810); Means for receiving a first message from a UTRAN based serving network, the first message comprising signaling second information element to a remote station to generate third and fourth session keys for use with the GERAN based serving network. Means for receiving the first message; Means for generating third and fourth session keys in response to the first message, using the second information element and the first and second session keys; And means for protecting wireless communications on the GERAN based serving network based on the third and fourth session keys.

Another aspect of the invention may belong to a remote station 210, which generates first and second session keys in accordance with an enhanced security context using an enhanced security context root key and a first information element. and; Receiving a first message from a UTRAN based serving network, the first message comprising signaling second information element to a remote station to generate third and fourth session keys for use with a GERAN based serving network; Receive a first message; In response to the first message, generate third and fourth session keys using the second information element and the first and second session keys; A processor 810 may be configured to protect wireless communications on a GERAN based serving network based on the third and fourth session keys.

Another aspect of the present invention may belong to a computer program product comprising a computer readable storage medium 820, which computer readable storage medium uses the enhanced security context root key and the first information element. Code to generate first and second session keys in accordance with an enhanced security context; Code for causing a computer to receive a first message from a UTRAN based serving network, the first message being second information to a remote station to generate third and fourth session keys for use with the GERAN based serving network. Code for receiving the first message, comprising element signaling; Code for causing a computer to, in response to the first message, generate third and fourth session keys using the second information element and the first and second session keys; And code for causing a computer to protect wireless communications on the GERAN based serving network based on the third and fourth session keys.

The serving core network 230 is connected to a Radio Access Network (RAN) 220 which provides wireless communications to the remote station 210. In the UMTS / UTRAN architecture, the serving RAN includes a Node B and a Radio Network Controller (RNC). In the GERAN architecture, the serving RAN includes a Base Transceiver Station (BTS) and a Base Station Controller (BSC). The serving core network is a Mobile Switching Center / Visitor Location Register (MSC / VLR) for providing circuit-switched (CS) services, and Serving GPRS (SGSN) for providing packet-switched (PS) services. Support Node). Home networks include HLR (Home Location Register) and AuC (Authentication Center).

UE 210 and serving core network 230 may be enhanced with new security features to create an enhanced UMTS security context (ESC) using COUNT (counter value). When AKA authentication is performed, a 256 bit root key (K _ASMEU ) for ESC may be derived from CK and IK. The root key may be set the same as CK || IK, or may be derived using more complex derivations resulting in additional useful security features (eg, CK and IK need to be maintained). none). COUNT may be a 16-bit counter value maintained between the UE and the serving core network. (Note: Legacy UTRAN security contexts include the 3-bit Key Set Identifier (KSI), the 128-bit encryption key (CK), and the IK (128-bit integrity key). Consisting of).

The GERAN PS service differs from the UMTS / UTRAN PS service in that the security used to protect the traffic exits the idle mode. This means that if it is desired to have live UMTS keys for each active session, then hardening is needed.

UTRAN to GERAN handover may be done in a manner independent of the method used to determine session keys. The UE and SGSN share an enhanced security context that includes the following parameters: K _{ASMEU, which is the} key set identifier and also the KSI (also referred to as CKSN) currently used in UMTS / GERAN, and the 256-bit root key for the security context. . From the root key K _ASMEU and possibly from parameters exchanged between the UE and SGSN, the set of session keys CK _S and IK _S can be calculated. In handover, the source SGSN passes the session keys CK _S and IK _S and root key K _ASMEU to the target SGSN.

The target SGSN supporting ESC calculates the new session keys CK _S and IK _S from the root key K _ASMEU and the old session keys CK _S and IK _S and possibly some additional information. The target SGSN indicates to the UE that new session keys have been calculated and possibly used by the SGSN that is not already known to the UE in the parameters transmitted (eg, NAS container set for PS HO) as part of handover signaling. Included additional information, the UE performs the same calculation to obtain new session keys CK _S and I K _S. Thus, if the UE returns to UMTS / UTRAN, old session keys will not be used.

Referring to FIG. 5, in a method 500 related to UMTS attach procedures, the UE 210 may signal that it supports ESC with a UMTS attach request message (step 510). This support signal may be the presence of a new information element (IE) in the message. IE may contain a COUNT value. Serving network SN 230 that does not support ESC will ignore the new IE. Authentication data (RAND, XRES, CK, IK, AUTN) is obtained from HLR / AuC 240 (step 515). The SN may indicate the ESC support to the UE as an AKA challenge (authentication request) (step 520). The UE performs an authentication procedure (step 525) and returns a response RES to the SN (step 530). Upon successful authentication (step 530), the UE and SN _derive root key K _ASMEU and session keys CK _S and IK _S (step 535). The SN forwards the session keys to the RAN 220 in a Security Mode Command (SMC) message (step 540). The RAN session key using the IK _S generates a message authentication code (MAC), and, IK _S is forwarded to the UE to the SMC message (step 545). The UE checks the MAC using the session key IK _S derived by the UE (step 535) (step 550), returns the completion indication to the RAN (step 555), and the RAN forwards it to the SN (step 560). ). The UE can then protect the communications using the session keys (step 565).

Referring to FIG. 6, in the method 600 associated with the procedure 600 for idle to active mode, the UE forwards the service request message including the COUNT value to the SN 230 (step 610). The UE and SN _derive new session keys CK _S and IK _S from root key K _ASMEU (step 620). The SN forwards the session keys to the RAN 220 in an SMC message (step 630). The RAN generates a MAC, and the MAC is forwarded to the UE in an SMC message (step 640). The UE checks the MAC (step 650), returns the completion indication to the RAN (step 660), and the RAN forwards it to the SN (step 670). The UE can then protect the communications using the session keys (step 680).

Referring to FIG. 7, in a method 700 associated with a mobility management procedure 700 (eg, routing area update (RAU) or location area update (LAU)), the UE 210 includes a RAU (or a COUNT value) that includes a COUNT value. LAU) forward the request message to the SN 230 (step 710). Optionally, the UE and SN may _derive new session keys CK _S and IK _S from root key K _ASMEU (step 720). The SN may forward the session keys to the RAN 220 in an SMC message (step 730). The RAN may generate a MAC, which may be forwarded to the UE in an SMC message (step 740). The UE may check the MAC (step 750), return the completion indication to the RAN (step 760), and the RAN forwards it to the SN (step 770). The SN then sends a RAU accept message to the UE (step 780). Thereafter, the UE can protect the communications using the session keys.

New access stratum (AS) keys may be generated for each transition from idle to active. Similarly, keys may be generated at other events. The COUNT value may be sent in an idle mobility message and in initial layer 3 messages, eg, attach, RAU, LAU, for an idle, mobility, or service request. The SN may check that the transferred COUNT value has not been previously used and has updated the stored COUNT value in the process. If the COUNT value is new (e.g., the received COUNT value> stored COUNT value), the UE and the SN use the KDF (Key Derivation Function), e.g. HMAC-SHA256, from the root key K _ASMEU and the transmitted CONT value. Proceed with the calculation of the keys CK _S and IK _S. The KDF may include additional information, such as the RAN node identity, for the new key calculation. If the check fails (unless the COUNT value is new), the SN rejects the message. For GERAN use, K _C and K _C128 from CK _S and IK _S If this is calculated, it may be done in the same manner as when calculated from CK and IK.

Session keys (CK _S and IK _S ) no longer need to store keys for securely transmitting traffic between the UE and the network (UE moves to idle mode) or subsequent events (eg, AKA authentication or mobility events). The UE and the serving network may have a life time to maintain and use session keys until a new context is created.

With reference to FIG. 9, one aspect of the present invention is to transition an enhanced security context from UTRAN based serving network 230 (first type serving network) to GERAN based serving network 230 '(second type serving network). May belong to a method 900 for shuning. In this method, the remote station 210 uses the enhanced security context root key (eg, K _ASMEU ) and the first information element IE1 (eg, the COUNT value) to make the first and second session keys in accordance with the enhanced security context. Generate CK _SA and IK _SA (step 910). In handover, UTRAN based serving network 230 may pass session keys CK _SA and IK _SA and root key K _ASMEU to GERAN based serving network 230 '(step 920). The response of the GERAN based serving network including the second information element IE2 tells the UTRAN based serving network that it may hand over the remote station to the GERAN based serving network (step 930). The remote station receives the first message from the UTRAN based serving network (step 940). The first message includes a second information element IE2 signaling to the remote station to generate third and fourth session keys CK _SB and IK _SB for use with a GERAN based serving network. The remote station generates third and fourth session keys using the second information element and the first and second session keys in response to the first message (step 950). For GERAN use, if K _C and K _C128 are calculated from CK _SB and IK _SB , it may be done in the same way as if calculated from CK and IK (step 960). The remote station protects wireless communication on the GERAN based serving network based on the third and fourth session keys (step 970). In another aspect of the present invention, the first type serving network may be a GERAN based serving network and the second type serving network may be a UTRAN based serving network.

Referring again to FIG. 8, the remote station 210 may include a computer 800 that includes a storage medium 820, such as a memory, a display 830, and an input device 840, such as a keyboard. The apparatus may include a wireless connection 850.

Referring to FIG. 1, a wireless remote station (RS) 102 (or UE) may communicate with one or more base stations (BS, 104) of the wireless communication system 100. The wireless communication system 100 may further include one or more base station controllers (BSC) 106 and the core network 108. The core network may be connected to the Public Switched Telephone Network (PSTN) 112 and the Internet 110 via suitable backhauls. Typical wireless mobile stations may include handheld phones, or laptop computers. The wireless communication system 100 includes a number of multiple access technologies, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), spatial division multiple access (SDMA), polarization division multiplexing. Access (PDMA), or any of the other modulation techniques known in the art, may be used.

Wireless device 102 may include various components that perform functions based on signals received at and transmitted by the wireless device. For example, the wireless headset may include a transducer adapted to provide an audio output based on a signal received via the receiver. The wireless watch may include a user interface configured to provide an indication based on a signal received via the receiver. The wireless sensing device may include a sensor configured to provide data transmitted to another device.

The wireless device may communicate over one or more wireless communication links that are based on any suitable wireless communication technology or otherwise support any suitable wireless communication technology. For example, in some aspects a wireless device may be associated with a network. In some aspects, the network may include a body area network or a personal area network (eg, ultra-wideband network). In some aspects, the network may include a local area network or a broadband network. A wireless device may support or otherwise use one or more of standards, protocols, or various wireless communication technologies, such as, for example, CDMA, TDMA, OFDM, OFDMA, WiMAX, and Wi-Fi. Similarly, a wireless device may support one or more of various corresponding modulation or multiplexing schemes or otherwise use them. The wireless device may thus include suitable components (eg, a wireless interface) for communicating and establishing over one or more wireless communication links using the above or other wireless communication technologies. For example, a device may include associated transmitter and receiver components (eg, transmitter and receiver) that may include various components (eg, signal generators and signal processors) that facilitate communication over a wireless medium. It may include a wireless transceiver having a).

The teachings herein may be integrated (eg, performed by or implemented by an apparatus within the various apparatuses) (eg, devices). For example, one or more aspects taught herein include a phone (eg, a cellular phone), a personal digital assistant (“PDA”), an entertainment device (eg, a music or video device), a headset (eg, , Headphones, earphones, etc., microphones, medical equipment (e.g. biometric sensors, heart rate monitors, pedometers, EKG devices, etc.), user I / O devices (e.g. clocks, remote controls, light switches) , Keyboards, mice, etc.), tire pressure monitors, computers, point-of-sale devices, entertainment devices, hearing aids, set-top boxes, or any other suitable device.

These devices may have different power and data requirements. In some aspects, the teachings herein may be adapted for use in low power applications (eg, through the use of low duty cycle modes and an impulse based signaling scheme) and (eg, high bandwidth pulses). May support various data rates, including relatively high data rates.

In some aspects, the wireless device may include an access device (eg, a Wi-Fi access point) for the communication system. Such an access device may provide a connection to another network (eg, a wide area network such as the Internet or a cellular network) via, for example, a wired or wireless communication link. Thus, the access device may allow another device (eg, a Wi-Fi station) to access another network or some other functions. In addition, one or both of the devices may be portable or in some cases relatively non-portable.

Those skilled in the art will appreciate that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may include voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, It may be represented by optical systems or optical particles, or any combination thereof.

In addition, those skilled in the art will appreciate that various exemplary logical blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in conjunction with the embodiments disclosed herein are general purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), fields designed to perform the functions described herein. It may be implemented or performed in a programmable gate array (FPGA) or other programmable logic device, separate gate or transistor logic, separate hardware components, or any combination thereof. A general purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The methods, sequences, and / or algorithms described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module to be executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. One example storage medium is coupled to a processor such that the processor can read information from and write information to the storage medium. Alternatively, the storage medium may be integral with the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal (eg, an access terminal). In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more illustrative embodiments, the functions described above may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored or transmitted as one or more instructions or code on a computer readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. The storage medium may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer readable media may comprise desired program code in the form of RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or instructions or data structures. It can include any other medium that can be used to carry or store and can be accessed by a computer. Also, any connection is properly termed a computer readable medium. For example, if the software is transmitted from a website, server or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio and microwave, the definition of the medium Examples include coaxial cables, fiber optic cables, twisted pairs, DSL, or wireless technologies such as infrared, radio, and microwave. Discs and discs, as used herein, include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVD), Floppy disks and blu-ray discs, where the disks normally reproduce the data magnetically, while the discs optically reproduce the data using a laser. Let's do it. Combinations of the above should also be included within the scope of computer readable media.

While the foregoing disclosure represents exemplary embodiments of the invention, it should be noted that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims. The functions, steps and / or actions of the claims of the invention in accordance with embodiments of the invention described herein need not be performed in any particular order. Furthermore, elements of the invention may be described or claimed in the singular, but a plurality is contemplated unless limitation to the singular is explicitly stated.

Claims (23)

A method of transitioning a first security context from a first type serving network to a second type serving network, the method comprising:
Using a root key associated with the first security context and using a first information element, a remote station generating first and second session keys in accordance with the first security context;
The remote station receiving a first message from the first type serving network, the first message generating the third and fourth session keys for use with the second type serving network. Receiving the first message, the second information element signaling to a message;
The remote station generating the third and fourth session keys using the second information element and the first and second session keys in response to the first message; And
The remote station protecting wireless communications on the second type serving network based on the third and fourth session keys. The method of claim 1,
And the first information element comprises a count value. The method of claim 1,
Wherein the first security context is an enhanced security context having security characteristics that are not supported by a second security context. The method of claim 1,
And the first type serving network is a UMTS Terrestrial Radio Access Network (UTRAN) based serving network, and the second type serving network is a GSM Edge Radio Access Network (GERAN) based serving network. The method of claim 1,
Wherein the first type serving network is a GERAN based serving network, and the second type serving network is a UTRAN based serving network. The method of claim 1,
The remote station comprises a mobile user equipment. As a remote station,
Means for using the root key associated with a first security context and using a first information element to generate first and second session keys in accordance with the first security context;
Means for receiving a first message from the first type serving network, the first message being a second to the remote station to generate third and fourth session keys for use with a second type serving network. Means for receiving the first message, comprising information element signaling;
Means for generating the third and fourth session keys using the second information element and the first and second session keys in response to the first message; And
Means for protecting wireless communications on the second type serving network based on the third and fourth session keys. The method of claim 7, wherein
And the first information element comprises a count value. The method of claim 7, wherein
Wherein the first security context is an enhanced security context having a security characteristic that is not supported by the second security context. The method of claim 7, wherein
The first type serving network is a UMTS Terrestrial Radio Access Network (UTRAN) based serving network, and the second type serving network is a GSM Edge Radio Access Network (GERAN) based serving network. The method of claim 1,
The first type serving network is a GERAN based serving network, and the second type serving network is a UTRAN based serving network. The method of claim 1,
The remote station comprises mobile user equipment. A remote station comprising a processor, comprising:
The processor comprising:
Using the root key associated with the first security context and using a first information element to generate first and second session keys in accordance with the first security context;
Receiving a first message from a first type serving network, the first message providing second information element signaling to the remote station to generate third and fourth session keys for use with a second type serving network; Receive the first message;
Generate the third and fourth session keys using the second information element and the first and second session keys in response to the first message;
And protect wireless communications on the second type serving network based on the third and fourth session keys. The method of claim 13,
And the first information element comprises a count value. The method of claim 13,
Wherein the first security context is an enhanced security context having a security characteristic that is not supported by the second security context. The method of claim 13,
The first type serving network is a UMTS Terrestrial Radio Access Network (UTRAN) based serving network, and the second type serving network is a GSM Edge Radio Access Network (GERAN) based serving network. The method of claim 13,
The first type serving network is a GERAN based serving network, and the second type serving network is a UTRAN based serving network. The method of claim 13,
The remote station comprises mobile user equipment. A computer program product comprising a computer readable storage medium, comprising:
The computer readable storage medium comprising:
Code for causing a computer to use a root key associated with a first security context and use a first information element to generate first and second session keys in accordance with the first security context;
Code for causing a computer to receive a first message from a first type serving network, the first message being directed to the remote station to generate third and fourth session keys for use with a second type serving network. Code for receiving the first message, the second information element signaling of;
Code for causing a computer to generate the third and fourth session keys using the second information element and the first and second session keys in response to the first message; And
Computer code product comprising code for causing a computer to secure wireless communications on the second type serving network based on the third and fourth session keys. The method of claim 19,
And the first information element comprises a count value. The method of claim 19,
And the first security context is an enhanced security context having a security characteristic that is not supported by the second security context. The method of claim 19,
The first type serving network is a UMTS Terrestrial Radio Access Network (UTRAN) based serving network, and the second type serving network is a GSM Edge Radio Access Network (GERAN) based serving network, a computer program comprising a computer readable storage medium. product. The method of claim 19,
And the first type serving network is a GERAN based serving network and the second type serving network is a UTRAN based serving network.

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