Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W12/00—Security arrangements; Authentication; Protecting privacy or anonymity
  • H04W12/04—Key management, e.g. using generic bootstrapping architecture [GBA]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0011—Control or signalling for completing the hand-off for data sessions of end-to-end connection
  • H04W36/0033—Control or signalling for completing the hand-off for data sessions of end-to-end connection with transfer of context information
  • H04W36/0038—Control or signalling for completing the hand-off for data sessions of end-to-end connection with transfer of context information of security context information
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W12/00—Security arrangements; Authentication; Protecting privacy or anonymity
  • H04W12/04—Key management, e.g. using generic bootstrapping architecture [GBA]
  • H04W12/041—Key generation or derivation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L2463/00—Additional details relating to network architectures or network communication protocols for network security covered by H04L63/00
  • H04L2463/061—Additional details relating to network architectures or network communication protocols for network security covered by H04L63/00 applying further key derivation, e.g. deriving traffic keys from a pair-wise master key
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0055—Transmission or use of information for re-establishing the radio link
  • H04W36/0066—Transmission or use of information for re-establishing the radio link of control information between different types of networks in order to establish a new radio link in the target network

Definitions

• the present invention relates to cellular communication systems, and more particularly to the handover of calls between cellular communication systems that support different security contexts.
• Cellular communication systems typically comprise a land-based network that provides wireless coverage to mobile terminals that can continue to receive service while moving around within the network's coverage area.
• the term “cellular” derives from the fact that the entire coverage area is divided up into so-called “cells”, each of which is typically served by a particular radio transceiver station (or equivalent) associated with the land-based network.
• Such transceiver stations are often generically referred to as “base stations”, even when particular communication standards setting bodies apply different terminology (e.g., "NodeB” in WCDMA, and “eNodeB” in LTE) for the purpose of very precisely pointing out the distinctive capabilities and architectures of their version of the base station.
• FIG. 1 illustrates a cellular communication system providing a system coverage area 101 by means of a plurality of cells 103.
• UE User Equipment
• UE The mobile communication equipment
• UE must operate in a way that is compatible with the system with which it is expected to communicate.
• UEs are often designed to be compatible with more than one system. In one respect, this enables a user to continue using the UE as it is carried from a geographical area covered by one type of communication system into another area, served by a different type of communication system.
• FIG. 2 depicts a portion of a cellular communication system in which a UE 201 is presently being served within a first cell 203 that is supported by equipment 205 that conforms to an older communications standard (e.g., one of the 2G - e.g., GERAN - or 3G - e.g., UTRAN - standards).
• an older communications standard e.g., one of the 2G - e.g., GERAN - or 3G - e.g., UTRAN - standards.
• the UE 201 is in the vicinity of a second (neighboring) cell 207 that is supported by equipment 209 that conforms to a newer communication standard (e.g., a 4G specification, such as E-UTRAN which is also known as "Long Term Evolution" or "LTE").
• a newer communication standard e.g., a 4G specification, such as E-UTRAN which is also known as "Long Term Evolution" or "LTE"
• the foregoing and other objects are achieved in, for example, methods and apparatuses for operating a first node to generate a security context for a client in a cellular communication system, wherein the first node comprises processing circuitry.
• Such operation includes the first node receiving at least one cryptographic key from a second node, and receiving identities of security algorithms supported by the client from a third node. The at least one cryptographic key and the identities are used to generate the security context for the client.
• the first and third nodes are packet switched nodes and the second node is a circuit switched node.
• the first node can be an MME
• the second node can be an MSC
• the third node can be an SGSN.
• the first node is a first SGSN
• the second node is an MSC
• the third node is a second SGSN.
• operation further comprises the first node receiving one or more authentication vectors from the second node.
• the authentication vectors received from the second node are then discarded.
• operation comprises using one or more of the at least one cryptographic key to protect traffic between a fourth node and the client.
• operation includes deriving a key for an Access Security Management Entity (K_ASME) from one or more of the at least one cryptographic key.
• K_ASME Access Security Management Entity
• operation includes receiving, from the third node, packet switched encryption keys for use in a packet switched connection, and discarding the packet switched encryption keys.
• operation includes receiving at least one authentication vector from the third node and storing the received at least one authentication vector.
• operation includes receiving additional information from the third node, and in some of these embodiments using the at least one cryptographic key and the identities to generate the security context for the client includes using the at least one
• Some embodiments cover operation in both the first and second nodes, such that the second node generates at least one new cryptographic key from at least one existing key associated with the client and a nonce generated by the second node, and communicates the at least one new cryptographic key to the first node.
• the first node then receives identities of security algorithms supported by the client from a third node and uses the at least one cryptographic key and the identities to generate the security context for the client.
• FIG. 1 illustrates a cellular communication system providing a system coverage area by means of a plurality of cells.
• FIG. 2 depicts a portion of a cellular communication system in which a UE is presently being served within a first cell that is supported by equipment that conforms to an older communications standard (e.g., one of the 2G or 3G standards) and that should be handed over to a second cell that is supported by equipment that conforms to a newer communications standard.
• an older communications standard e.g., one of the 2G or 3G standards
• FIG. 3 depicts aspects of signaling involved in the handover of a call from source UTRAN or GERA supporting equipment operating in the circuit switched domain to target UTRAN/GERAN supporting equipment operating in the PS domain.
• FIG. 4 depicts aspects of signaling involved in the handover of a call from source UTRAN or GERA supporting equipment operating in the CS domain to target E-UTRAN (i.e., 4G equipment) supporting equipment operating in the PS domain.
• E-UTRAN i.e., 4G equipment
• FIG. 5 is, in one respect, a flow chart of steps/processes performed by a target PS node in accordance with some but not necessarily all exemplary embodiments of a handover mechanism consistent with the invention.
• FIG. 6 is a signaling diagram of aspects of one embodiment of handover signaling and steps consistent with the invention.
• FIG. 7 is a signaling diagram of an alternative embodiment of handover signaling and steps consistent with the invention.
• FIG. 8 is a block diagram of a target node (e.g., SGSN/MME) that operates in the PS domain.
• a target node e.g., SGSN/MME
• circuitry configured to perform one or more described actions is used herein to refer to any such embodiment (i.e., one or more specialized circuits and/or one or more programmed processors).
• the invention can additionally be considered to be embodied entirely within any form of computer readable carrier, such as solid- state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.
• any such form of embodiments as described above may be referred to herein as "logic configured to” perform a described action, or alternatively as “logic that” performs a described action.
• 3GPP TSG SA WG3 (3rd Generation Partnership Project Technical Specification Group System Architecture Work Group 3)
• E-UTRAN Evolved-Universal Terrestrial Radio Access Network
• HSS Home Subscriber Server
• IMS IP Multimedia Subsystem
• IMSI International Mobile Subscriber Identity
• ISDN Integrated Services Digital Network
• LA Lication Area
• MSC Mobile Switching Centre
• MSISDN Mobile Subscriber ISDN
• NONCE Numberer Used Once
• PLMN Public Land Mobile Network
• PRNG Pulseudo Random Number Generator
• RNC Radio Network Controller
• SIM Subscriber Identity Module
• SRNC Serving RNC
• SRVCC Single Radio Voice Call Continuity
• ⁇ UTRAN Universal Terrestrial Radio Access Network
• the 4G network node to which a call is to be handed over should receive information indicating what the UE's 4G security parameters (e.g., keys, selected and supported ciphering algorithms, etc.) are. But consider what happens during a conventional handover from 2G/3G equipment to 4G equipment:
• Any 2G/3G call (which can operate in either circuit switched - CS - or packet switched -
• PS - mode PS - mode
• 4G equipment which operates exclusively in a PS mode
• SGSN PS equipment
• MSC CS equipment
• the UE attaches to the network in the packet switched domain it provides the SGSN with the so-called "UE Network capabilities", which includes the security algorithms that the terminal supports in E-UTRAN.
• UE Network capabilities includes the security algorithms that the terminal supports in E-UTRAN.
• Clause 6.14 of 3GPP TS 23.060 VI 0.6.0 (2011 -12) specifies that the "radio access classmark" contains the "UE Network capability.”
• the "UE Network capability” contains the E-UTRAN security algorithms supported by the UE.
• clause 6.14.1 of 3GPP TS 23.060 states that the UE (referred to in the specification as “MS”, “Mobile Station” for historical reasons) sends the radio access capability to the network.
• the interested reader can refer to 3GPP TS 23.060 for more information about this aspect.
• the UE does not provide the "UE Network capability" to the network (in this case, the MSC), but instead only provides its 2G/3G
• the Packet Switched Inter RAT handover from UTRAN (3G) to E-UTRAN (4G) is described in clause 5.5.2.2 of 3GPP TS 23.401 VIO.6.0 (2011-12).
• step 3 Forward relocation request
• the security parameters e.g., keys, selected and supported ciphering algorithms, etc.
• the MM context contains security related information, such as UE
• the UE Network capabilities includes the E-UTRAN security capabilities, which include for example the identities of the LTE encryption and integrity algorithms the UE supports (these algorithm identifiers are called EPS encryption algorithms and EPS integrity protection algorithms in the LTE security specification TS 33.401).
• the Packet Switched Inter RAT handover from GERAN to E-UTRAN is described in clause 5.5.2.4 of 3GPP TS 23.401.
• the principle of having the source node (SGSN for the PS domain) forward the UE Network capabilities to the target node is exactly the same as the specified handover procedure when the call originates in the CS domain.
• the source node is an MSC which, as mentioned above, does not have the UE's E-UTRAN security capabilities.
• FIG. 3 depicts aspects of signaling involved in the handover of a call from source UTRAN or GERAN supporting equipment operating in the CS domain to target UTRAN supporting equipment operating in the PS domain.
• the illustrated components that participate in this signaling are a UE 301, a source BSC/RNC 303, a target RNC 305, an MSC server 307, a source SGSN/MME 309, and a target SGSN 311.
• the UE 301 is engaged in a CS call, supported by the various source UTRAN or GEPvAN equipment.
• a decision being made to perform the CS (UTRAN or
• step 1 the source BSC/RNC 303 sends a "HO required" message to the MSC server 307.
• the MSC server 307 then generates (step 313) a NONCE M sc, and uses this to generate a cryptographic key in accordance with:
• IK' P S KDF(CKcs, HC CS , NONCE M sc), where the symbol "
• step 2 the MSC server 307 communicates a "CS to PS HO request" to the target SGSN 31 1 , and includes the generated cryptographic key (CK' PS
• step 3 the target SGSN 311 sends a "Context request" to the source SGSN/MME 309 for the purpose of requesting context information for the UE 301.
• the SGSN/MME 309 then sends a "Context response" (including the requested information) back to the target SGSN 311 (step 4).
• the target SGSN 31 1 receives a GPRS Kc * and a CKSN* PS from the MSC server 307 enhanced for SRVCC, then the target SGSN 31 1 computes (step 315) CK' PS and IK' PS from the GPRS Kc'.
• the target SGSN 311 associates the CK PS and IK PS with KSI' PS , which is set equal to CKSN'ps received from the source MSC server 307 enhanced for SRVCC.
• the target SGSN 311 then sends the CK PS , IK' PS to the target RNC 305 (step 5).
• the target RNC 305 sends an Allocate resources response (step 6).
• step 7 the target SGSN 311 sends a CS to PS HO Response message to the source MSC server 307.
• step 8 the MSC server 307 sends a CS to PS HO Response to the source BSC/RNC 303.
• This CS to PS HO Response includes, among other things, the NONCE M sc-
• step 9 the source BSC/RNC 303 sends a CS to PS HO command to the UE 301.
• This command includes, among other things, the NONCE M sc-
• the UE 301 uses the received NONCE MSC to derive CK' PS and IK' PS using key derivation formulas specified by the applicable standard (step 317).
• step 10 the UE 301 returns a CS to PS HO Confirmation to the target RNC 305.
• FIG. 4 depicts aspects of signaling involved in the handover of a call from source UTRAN or GERAN supporting equipment operating in the CS domain to target E-UTRAN (i.e., 4G equipment) supporting equipment operating in the PS domain.
• the illustrated components that participate in this signaling are a UE 401 , a source BSC/RNC 403, a target eNB 405, an MSC server 407, a source SGSN/MME 409, and a target MME 41 1.
• the UE 401 is engaged in a CS call, supported by the various source UTRAN or GERAN equipment.
• the source BSC/RNC 403 sends a "HO required" message to the MSC server 407.
• the MSC server 407 then generates (step 413) a NONCE M sc, and uses this to generate a cryptographic key in accordance with:
• IK' P S KDF(CKcs, HC CS , NONCE M sc), where the symbol "
• step 2' the MSC server 407 communicates a "CS to PS HO request" to the target
• MME 411 includes the generated cryptographic key (CK' PS
• step 3' the target MME 411 sends a "Context request" to the source SGSN/MME 409 for the purpose of requesting context information for the UE 401.
• the SGSN/MME 409 then sends a "Context response" (including the requested information) back to the target MME 411 (step 4') ⁇
• the target MME 411 creates a mapped EPS security context by setting the K' ASME of the mapped EPS security context equal to the concatenation CK' PS
• the target MME 41 1 further associates the K' A S ME with a KSISGSN- The value of the KSISGSN is the same as the value of the KSI'ps received in the CS to PS handover request.
• the target MME 41 1 derives K eNB by applying the KDF as defined in the applicable standard, using the mapped key K' ASME and 2 32 -l as the value of the uplink NAS COUNT parameter.
• the uplink and downlink NAS COUNT values for the mapped EPS security context are set to start value (i.e., 0) in the target MME 411.
• the target MME 41 1 then sends the K eNB and NAS parameters to the target eNB 405
• step 5 the target eNB 405 sends an Allocate resources response (step 6').
• step 7' the target MME 41 1 sends a CS to PS HO Response message to the source MSC server 407.
• step 8 ' the MSC server 407 sends a CS to PS HO Response to the source BSC/RNC 403.
• This CS to PS HO Response includes, among other things, the NONCE M sc-
• step 9' the source BSC/RNC 403 sends a CS to PS HO command to the UE 401.
• This command includes, among other things, the NONCE M sc- The UE 401 uses the received
• NONCE M SC to derive K' A S ME , associate it with KSISGSN received in the NAS Security Transparent Container IE and derive NAS keys and Ke B following the same key derivations as the MSC server 407 and target MME 411 performed in steps 2', 3' and 4' (step 417), all as specified by the applicable standard.
• step 10' the UE 401 returns a CS to PS HO Confirmation to the target eNB 405.
• the mapped EPS security context established as above becomes the current EPS security context at AS.
• FIG. 5 is a flow chart of steps/processes performed by a target PS node (e.g., a Target SGSN or Target MME) in accordance with some but not necessarily all exemplary embodiments of the invention.
• FIG. 5 can be considered to depict exemplary means 500 comprising the various illustrated circuitry (e.g., hard-wired and/or suitably programmed processor) configured to perform the described functions.
• the target PS node can, in the context of this processing, be considered a "first node" that generates a security context for a client in a cellular communication system.
• the first node receives at least one cryptographic key from a second node (step 501).
• the second node can be a source CS node such as an MSC.
• the first node solicits from a third node (e.g., a source SGSN), and in response receives, identities of security algorithms supported by the client (step 503).
• a third node e.g., a source SGSN
• the first node may also receive other information such as one or more authentication vectors and/or cryptographic key(s).
• the first node then uses the at least one cryptographic key received from the second node and the security algorithm identities to generate the security context for the client (step 505).
• authentication vectors received from the second node may be used as well.
• the first node has generated the security context for the client.
• the first node may perform any one or combination of additional functions, such as but not limited to:
• the target PS node is an SGSN
• saving e.g., if the target PS node is an MME
• additional information received from the second and/or third nodes e.g., authentication vectors received from the second and/or third nodes.
• Saving the authentication vectors can be useful, for example, if the target PS node is an MME and a later handover will be made to the exact same source SGSN from which they were received (in which case, the authentication vectors are returned to the SGSN at the time of that later handover).
• FIG. 6 is a signaling diagram of one embodiment consistent with the invention.
• this diagram focuses on aspects that support a target PS node being able to create a security context for a client as part of a handover of a call from source UTRAN or GERAN supporting equipment operating in the CS domain to target UTRAN supporting equipment operating in the PS domain.
• An aspect of the illustrated embodiment is that the target PS node collects security related information from the source PS node and also from the source CS node, and selected parts of the collected information are combined to generate a new set of security related information. This is described in greater detail in the following.
• the illustrated components that participate in the signaling of this exemplary embodiment are a UE 601 (client), a source BSC/RNC 603, a target RNC 605, an MSC server 607, a source SGSN/MME 609, and a target SGSN 61 1.
• the UE 601 is engaged in a CS call, supported by the various source UTRAN or GERAN equipment.
• the source BSC/RNC 603 sends a "HO required" message to the MSC server 607.
• the MSC server 607 then generates (step 613) a ONCE M sc, and uses this and existing keys shared with the UE 601 to generate a cryptographic key in accordance with:
• IK' P S KDF(CKcs, IK CS , NONCE M sc), where the symbol "
• step 2 the MSC server 607 communicates a "CS to PS HO request" to the target
• SGSN 611 includes the generated cryptographic key (CK' PS
• step 3 the target SGSN 611 sends a "Context request" to the source SGSN/MME 609 for the purpose of requesting context information for the UE 601.
• dashed lines used here and in other representations of signaling represent an optional step.
• SGSN/MME 609 then sends a "Context response" (including the requested information which includes the PS cryptographic keys and other security parameters such as the IDs of security algorithms supported by the UE 601) back to the target SGSN 611 (step 4").
• Context response including the requested information which includes the PS cryptographic keys and other security parameters such as the IDs of security algorithms supported by the UE 601
• step 615 the target SGSN 611 performs:
• the data in the AVs may be used to re- authenticate the UE 601
• step 615 the signaling is in accordance with steps 5, 6, 7, 8, 9, and 10 such as are shown in FIG. 3 and described in FIG. 3's supporting text above.
• FIG. 7 is a signaling diagram of an alternative embodiment consistent with the invention.
• this diagram focuses on aspects that support a target PS node being able to create a security context for a client as part of a handover of a call from source UTRAN or GERAN supporting equipment operating in the CS domain to target E-UTRAN (i.e., 4G) supporting equipment operating in the PS domain.
• the illustrated components that participate in this signaling are a UE 701 (client), a source BSC/RNC 703, a target eNB 705, an MSC server 707, a source SGSN/MME 709, and a target MME 711.
• the UE 701 is engaged in a CS call, supported by the various source UTRAN or
• the source BSC/RNC 703 sends a "HO required" message to the MSC server 707.
• the MSC server 707 then generates (step 713) a NONCEMSc, and uses this to generate new cryptographic keys from existing keys shared with the UE 701.
• This key derivation is in accordance with:
• IK' P S KDF(CKcs, HC CS , NONCE M sc), where the symbol "
• the MSC server 707 communicates a "CS to PS HO request" to the target MME 711 , and includes the newly generated cryptographic keys (CK' PS 11 IK' PS ) and AVs in this message. It will be observed that the MSC server 707 does not have LTE security parameters, so none are (or can be) transferred in this communication.
• the target MME 711 sends a "Context request" to the source SGSN/MME 709 for the purpose of requesting context information for the UE 701.
• the SGSN/MME 709 then sends a "Context response" (including the requested information) back to the target MME 711 (step 4"').
• This requested information includes PS keys and LTE security parameters (i.e., IDs of LTE security algorithms that are supported by the UE 701). In the context of a source SGSN 709, such information is available if the source SGSN 709 complies with Release 8 or newer of the LTE standard.
• step 715 the target MME 711 performs:
• MME 711 derives Ke NB by applying the KDF as defined in the applicable standard, using the mapped key K'ASME and 2 -1 as the value of the uplink NAS COUNT parameter.
• the uplink and downlink NAS COUNT values for the mapped EPS security context are set to start value (i.e., 0) in the target MME 71 1.
• AVs received from a source SGSN 709. There will not be any AVs received from a source MME 709.
• These stored AVs can later be used if there is to be a PS IRAT HO back to the very same source SGSN 709 as the one from which they were received (in which case they are transferred back to that SGSN at the time of that later handover).
• KSI KSI or the CKSN, each of which is a 3-bit long string.
• the MME 711 can use the KSI/CKSN to identify the security context in LTE.
• step 715 the signaling is in accordance with steps 5', 6', 7', 8', 9', and 10' such as are shown in FIG. 4 and described in FIG. 4's supporting text above.
• FIG. 8 is a block diagram of a target node 800 (e.g., SGSN/MME) that operates in the PS domain, wherein the target node 800 comprises a controller 801 that is circuitry configured to carry out, in addition to typical communications system node functionality, any one or any combination of the aspects described in connection with any one or combination of FIGS. 5 through 7 above.
• Such circuitry could, for example, be entirely hard-wired circuitry (e.g., one or more ASICs).
• programmable circuitry comprising a processor 803 coupled to one or more memory devices 805 (e.g., Random Access Memory, Magnetic Disc Drives, Optical Disk Drives, Read Only Memory, etc.).
• the memory device(s) 805 store program means 807 (e.g., a set of processor instructions) configured to cause the processor 803 to control other node circuitry/hardware components 809 so as to carry out any of the functions described above.
• the memory 805 may also store data 811 representing various constant and variable parameters as may be received, generated, and/or otherwise needed by the processor 803 when carrying out its functions such as those specified by the program means 807.
• the various aspects such as obtaining some information from a source CS node and other information from a source PS node and filtering and/or processing this information to derive a security context that is useful in the target PS node are applicable even when some other details have changed.
• embodiments can be foreseen in which, instead of having an MSC generate a NONCE that is communicated to the target PS node (e.g., target SGSN or MME), the target node (target MME) can generate a NONCE itself, and then derive cryptographic keys from this generated NONCE.
• the target PS node e.g., target SGSN or MME

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