Patent Description:
As multiple access technologies are improved and augmented, new telecommunication standards emerge. An example of an emerging telecommunication standard is the fourth generation Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology, and/or for new generations telecommunication standards with improved capabilities.

Security configuration is an initial step in setting up a logical bearer or channel (e.g., a communication link between a mobile communication device and a network entity or access node) in LTE networks. Key derivation and establishment is a part of this security configuration. Most of the keys generated are ciphering and integrity keys for Non-Access Stratum (NAS) Security Mode Configuration (NAS SMC) and Access Stratum (AS) Security mode Configuration (AS SMC). As new generations of communications technology are deployed, vulnerabilities to attack may be exposed in the security configuration processes. Accordingly, there exists a need for improvements in security processes. Preferably, improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

<CIT> discloses a method and apparatus for attaching a wireless device to a foreign wireless domain of a 3GPP communication system using an alternative authentication mechanism, wherein wireless device performs the method, which includes: sending a first attach request message to an infrastructure device in the foreign wireless domain; receiving an attach reject message from the infrastructure device upon an unsuccessful attempt to obtain authentication credentials for the wireless device from a home wireless domain of the wireless device using a standard 3GPP authentication mechanism; responsive to the attach reject message sending a second attach request message to the infrastructure device, wherein the second attach request message indicates an alternative authentication mechanism to the standard 3GPP authentication mechanism; and receiving an attach accept message from the infrastructure device when the wireless device is successfully authenticated using the alternative authentication mechanism.

The invention relates to apparatuses and methods for securing wireless communication between a user equipment and a serving network as set out in the independent claims.

Other examples or aspects as listed in the following merely are for illustrative purposes.

According to certain aspects disclosed herein, a method of securing wireless communication between a user equipment (UE) and a serving network includes transmitting by the UE a connection request or tracking area request to a network function in a serving network after a security association has been established between the UE and the serving network where the request includes a nonce and a signature request, receiving by the UE a response to the connection request or tracking area request from the network function where the response includes a signature of the network function, and authenticating by the UE the serving network based on the signature of the network function and a public key certificate corresponding to the network function where the public key certificate is signed using a private key of the serving network provided by a network operator associated with the serving network.

According to certain aspects disclosed herein, an apparatus has a wireless transceiver, and a processor coupled to the transceiver. The processor may be configured to transmit a connection request or tracking area request to a network function in a serving network after a security association has been established between the UE and the serving network where the request includes a nonce and a signature request, receive a response to the connection request or tracking area request from the network function where the response includes a signature of the network function, and authenticate the serving network based on the signature of the network function and a public key certificate corresponding to the network function, where the public key certificate is signed using a private key of the serving network provided by a network operator associated with the serving network.

According to certain aspects disclosed herein, a method of proving membership of a serving network includes receiving a first message from a UE after the UE has established a secured connection with a home network, where the message is directed to a network function of the serving network and may include a nonce and a signature request, generating a signature using an operator-signed certificate maintained by the network function of the serving network, and transmitting a second message to the UE, where the signature is attached to the second message.

According to certain aspects disclosed herein, an apparatus includes means for receiving a first message from a UE after the UE has established a secured connection with a home network, where the message is directed to a network function of the serving network and includes a nonce and a signature request, means for generating a signature using an operator-signed certificate maintained by the network function of the serving network, and means for transmitting a second message to the UE, where the signature is attached to the second message. The signature attached to the second message may be generated to prove to the UE that the apparatus is a member of a serving network. The operator-signed certificate may be a public key certificate signed by an operator of the serving network.

The invention is shown in <FIG>, <FIG> and <FIG>.

The other figures serve for illustrative purposes.

The invention is described in the paragraphs relating to <FIG>.

These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements").

By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a computer or "processing system" that includes one or more processors.

Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. Computer-readable media may include transitory and non-transitory storage media that may be read and/or manipulated by one or more processors. By way of example, and not limitation, such computer-readable media can comprise random access memory (RAM), read only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), compact disc read only memory (CD-ROM), or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), and floppy disk where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

Certain aspects disclosed herein relate to systems and methods by which radio link setup and/or bearer establishment processes may be secured. Certain aspects of the disclosure address security issues that may arise in newer generations of radio access technologies (RATs), including in fifth generation (<NUM>) and later networks, as well as in fourth generation (<NUM>) and earlier networks. The configuration and operation of a <NUM> LTE network architecture is described herein by way example, and for the purpose of simplifying descriptions of certain aspects that may apply to multiple RATs.

<FIG> is a diagram illustrating an LTE network architecture <NUM>. The LTE network architecture <NUM> may be referred to as an Evolved Packet System (EPS). The EPS may include one or more user equipment (UE) <NUM>, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) <NUM>, an Evolved Packet Core (EPC) <NUM>, a Home Subscriber Server (HSS) <NUM>, and an Operator's Internet Protocol (IP) Services <NUM>. The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. As shown, the EPS provides packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNodeB) <NUM> and other eNodeBs <NUM>. The eNodeB <NUM> provides user and control planes protocol terminations toward the UE <NUM>. The eNodeB <NUM> may be connected to the other eNodeBs <NUM> via a backhaul (e.g., an X2 interface). The eNodeB <NUM> may also be referred to as a base station, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an eNB, or some other suitable terminology. The eNodeB <NUM> provides an access point to the EPC <NUM> for a UE <NUM>. Examples of UEs <NUM> include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a virtual reality device, a tablet computing device, a media player, an appliance, a gaming device, a wearable computing device such as a smartwatch or optical head-mounted display, or any other similarly functioning device. The UE <NUM> may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

The eNodeB <NUM> is connected by an "S1" interface to the EPC <NUM>. The EPC <NUM> includes an MME <NUM>, other MMEs <NUM>, a Serving Gateway <NUM>, and a Packet Data Network (PDN) Gateway <NUM>. The MME <NUM> is the control node that processes the signaling between the UE <NUM> and the EPC <NUM>. All user IP packets are transferred through the Serving Gateway <NUM>, which itself is connected to the PDN Gateway <NUM>. The PDN Gateway <NUM> is connected to the Operator's IP Services <NUM>. The Operator's IP Services <NUM> may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS).

<FIG> is a diagram illustrating an example of an access network <NUM> in an LTE network architecture. In this example, the access network <NUM> is divided into a number of cellular regions (cells) <NUM>. One or more lower-power class eNodeBs <NUM> may have cellular regions <NUM> that overlap with one or more of the cells <NUM>. The lower-power class eNodeB <NUM> may be a femto cell (e.g., home eNodeB (HeNB)), pico cell, micro cell, or remote radio head (RRH). The macro eNodeBs <NUM> are each assigned to a respective cell <NUM> and are configured to provide an access point to the EPC <NUM> for all the UEs <NUM> in the cells <NUM>. There is no centralized controller in this example of an access network <NUM>, but a centralized controller may be used in alternative configurations. The eNodeBs <NUM> are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway <NUM>.

The modulation and multiple access scheme employed by the access network <NUM> may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplexing (FDD) and time division duplexing (TDD). As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project <NUM> (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA; Global System for Mobile Communications (GSM) employing TDMA; and Evolved UTRA (E-UTRA), IEEE <NUM> (Wi-Fi), IEEE <NUM> (WiMAX), IEEE <NUM>, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

The eNodeBs <NUM> may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNodeBs <NUM> to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data steams may be transmitted to a single UE <NUM> to increase the data rate or to multiple UEs <NUM> to increase the overall system capacity. This is achieved by spatially precoding each data stream (i.e., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE(s) <NUM> with different spatial signatures, which enables each of the UE(s) <NUM> to recover the one or more data streams destined for that UE <NUM>. On the UL, each UE <NUM> transmits a spatially precoded data stream, which enables the eNodeB <NUM> to identify the source of each spatially precoded data stream.

Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming may be used to focus the transmission energy in one or more directions. This may be achieved by spatially precoding the data for transmission through multiple antennas. To achieve good coverage at the edges of the cell, a single stream beamforming transmission may be used in combination with transmit diversity.

In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread-spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides "orthogonality" that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR).

<FIG> is a diagram <NUM> illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNodeB is shown with three layers: Layer <NUM>, Layer <NUM>, and Layer <NUM>. Layer <NUM> (L1 layer) is the lowest layer and implements various physical layer signal processing functions. The L1 layer will be referred to herein as the physical layer <NUM>. Layer <NUM> (L2 layer) <NUM> is above the physical layer <NUM> and is responsible for the link between the UE and eNodeB over the physical layer <NUM>.

In the user plane, the L2 layer <NUM> includes a media access control sublayer (Media Access Sublayer) <NUM>, a radio link control (RLC) sublayer <NUM>, and a packet data convergence protocol (PDCP) sublayer <NUM>, which are terminated at the eNodeB on the network side. Although not shown, the UE may have several upper layers above the L2 layer <NUM> including a network layer (e.g., IP layer) that is terminated at the PDN gateway <NUM> on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer <NUM> provides multiplexing between different radio bearers and logical channels. The PDCP sublayer <NUM> also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNodeBs. The RLC sublayer <NUM> provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ). The Media Access Sublayer <NUM> provides multiplexing between logical and transport channels. The Media Access Sublayer <NUM> is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The Media Access Sublayer <NUM> is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNodeB is substantially the same for the physical layer <NUM> and the L2 layer <NUM> with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer <NUM> in Layer <NUM> (L3 layer). The RRC sublayer <NUM> is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNodeB and the UE.

<FIG> is a block diagram of an eNodeB <NUM> in communication with a UE <NUM> in an access network. In the DL, upper layer packets from the core network are provided to a controller/processor <NUM>. The controller/processor <NUM> implements the functionality of the L2 layer. In the DL, the controller/processor <NUM> provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE <NUM> based on various priority metrics. The controller/processor <NUM> is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE <NUM>.

The transmit (TX) processor <NUM> implements various signal processing functions for the L1 layer (i.e., physical layer). The signal processing functions include coding and interleaving to facilitate forward error correction (FEC) at the UE <NUM> and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. Each spatial stream is then provided to a different antenna <NUM> via a separate transmitter 418TX. Each transmitter 418TX modulates an RF carrier with a respective spatial stream for transmission.

At the UE <NUM>, each receiver 454RX receives a signal through its respective antenna <NUM>. Each receiver 454RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor <NUM>. The RX processor <NUM> implements various signal processing functions of the L1 layer. The RX processor <NUM> performs spatial processing on the information to recover any spatial streams destined for the UE <NUM>. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the eNodeB <NUM>. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNodeB <NUM> on the physical channel. The data and control signals are then provided to the controller/processor <NUM>.

The controller/processor <NUM> implements the L2 layer. The controller/processor can be associated with a memory <NUM> that stores program codes and data. In the UL, the controller/processor <NUM> provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink <NUM>, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink <NUM> for L3 processing. The controller/processor <NUM> is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

In the UL, a data source <NUM> is used to provide upper layer packets to the controller/processor <NUM>. The data source <NUM> represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNodeB <NUM>, the controller/processor <NUM> implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNodeB <NUM>. The controller/processor <NUM> is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNodeB <NUM>.

Channel estimates derived by a channel estimator <NUM> from a reference signal or feedback transmitted by the eNodeB <NUM> may be used by the TX processor <NUM> to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor <NUM> are provided to different antenna <NUM> via separate transmitters 454TX. Each transmitter 454TX modulates an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNodeB <NUM> in a manner similar to that described in connection with the receiver function at the UE <NUM>. Each receiver 418RX receives a signal through its respective antenna <NUM>. Each receiver 418RX recovers information modulated onto an RF carrier and provides the information to a RX processor <NUM>. The RX processor <NUM> may implement the L1 layer.

The controller/processor <NUM> implements the L2 layer. In the UL, the control/processor <NUM> provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE <NUM>. Upper layer packets from the controller/processor <NUM> may be provided to the core network.

Radio link setup in an LTE network may involve establishment of one or more radio bearers between an access node that provides access to a network and a communication device. Radio link setup typically includes a security activation exchange. A session bearer, which may be a logical bearer or logical channel, may then be established over the radio link and one or more services and/or communications may be established over the session bearer. The session bearer, services and/or communications may be secured by one or more security keys.

As part of the session bearer setup, an authentication request, and/or one or more key exchanges may take place. In networks operating according to an LTE-compatible protocol, keys may be derived by the communication device based on algorithms provided by one or more network entities.

<FIG> illustrates a typical E-UTRAN key hierarchy <NUM> that may be implemented within a typical LTE network. In the communication device, a Universal Subscriber Identity Module (USIM) and an Authentication Center (AuC) in a network entity at the network side use a master key (K) <NUM> to generate a cipher key (CK) <NUM> and integrity key (IK) <NUM>. The cipher key (CK) <NUM> and integrity key (IK) <NUM> may then be used by the communication device and a Home Subscriber Server (HSS) in the network entity to generate an Access Security Management Entity key (KASME) <NUM>. The security activation of a communication device operating in an LTE network may be accomplished through an Authentication and Key Agreement procedure (AKA), Non-Access Stratum (NAS) Security Mode Configuration (NAS SMC) and Access Stratum (AS) Security mode Configuration (AS SMC). AKA is used to derive the KASME <NUM>, which is then used as a base key for the calculation of NAS keys <NUM> and <NUM> and AS keys <NUM>, <NUM>, <NUM>, and <NUM>. The communication device and an MME at the network side may then use the KASME <NUM> to generate one or more of these security keys.

LTE packet-switched networks may be structured in multiple hierarchical protocol layers, where the lower protocol layers provide services to the upper layers and each layer is responsible for different tasks. For example, <FIG> illustrates an example of a protocol stack <NUM> that may be implemented in a communication device operating in a LTE packet-switched network. In this example, an LTE protocol stack <NUM> includes a Physical (PHY) Layer <NUM>, a Media Access Control Layer <NUM>, a Radio Link Control (RLC) Layer <NUM>, a Packet Data Convergence Protocol (PDCP) Layer <NUM>, a RRC Layer <NUM>, a NAS Layer <NUM>, and an Application (APP) Layer <NUM>. The layers below the NAS Layer <NUM> are often referred to as the Access Stratum (AS) Layer <NUM>.

The RLC Layer <NUM> may include one or more channels <NUM>. The RRC Layer <NUM> may implement various monitoring modes for the UE, including connected state and idle state. The NAS Layer <NUM> may maintain the communication device's mobility management context, packet data context and/or its IP addresses. Note that other layers may be present in the protocol stack <NUM> (e.g., above, below, and/or in between the illustrated layers), but have been omitted for the purpose of illustration. Radio/session bearers <NUM> may be established, for example at the RRC Layer <NUM> and/or NAS Layer <NUM>. Consequently, the NAS Layer <NUM> may be used by the communication device and an MME to generate the security keys KNAS enc <NUM> and KNAS-int <NUM>. Similarly, the RRC Layer <NUM> may be used by the communication device and an eNodeB to generate the security keys KUP-enc <NUM>, KRRC-enc <NUM>, and KRRC-int <NUM>. While the security keys KUP-enc <NUM>, KRRC-enc <NUM>, and KRRC-int <NUM> may be generated at the RRC Layer <NUM>, these keys may be used by the PDCP Layer <NUM> to secure signalling and/or user/data communications. For instance, the key KUP-enc <NUM> may be used by the PDCP Layer <NUM> to secure for user/data plane (UP) communications, while the keys KRRC-enc <NUM>, and KRRC-int <NUM> may be used to secure signalling (i.e., control) communications at the PDCP Layer <NUM>.

In one example, prior to establishing these security keys (keys KNAS-enc <NUM>, KNAS-int <NUM>, KUP-enc <NUM>, KRRC-enc <NUM>, and/or KRRC-int <NUM>), communications to/from a communication device may be transmitted (unprotected or unencrypted) over an unsecured common control channel (CCCH). After these security keys are established, these same user data and/or control/signaling communications may be transmitted over a Dedicated Control Channel (DCCH).

During the connection setup/session bearer setup procedures in an LTE-compatible network, AKA and NAS SMC procedures are optional if there is an existing native NAS security context already present from the previous setup sessions. The existing NAS context may be reused at the time of Service Requests, Attach Requests and TAU Requests. TAU requests may be sent periodically by a UE or when the UE enters a tracking area that was not associated with the UE, where the tracking area (or routing area) may be an area in which a UE is able to move without first updating the network.

Security keys used for ciphering and integrity algorithms, both at the AS (User plane and RRC) and NAS may be derived using an individual algorithm identity provided as one of the inputs. At the NAS level (e.g., NAS Layer <NUM>), this is provided to the communication device by the access node (eNodeB) in NAS Security Mode Command during the NAS SMC procedure. At the AS level, the algorithms to be used are provided by the Radio Resource Control (RRC) Security Mode Command. Key generation may be done with a key derivation function (KDF), such as the HMAC-SHA-<NUM> function. In generating the NAS security keys KNAS-enc <NUM> and integrity key KNAS-int <NUM> and RRC security keys KUP-enc <NUM>, KRRC-enc <NUM>, and integrity key KRRC-int <NUM>, the key derivation function KDF takes several types of inputs, including an input algorithm identity provided by the network during a security activation exchange. For instance, the input algorithm identity may identify either Advanced Encryption Standard (AES) or "SNOW-<NUM>.

It should be noted that, in some implementations, all security keys (e.g., NAS ciphering and integrity keys and RRC ciphering and integrity keys) are generated using the same key derivation function (KDF), e.g., HMAC-SHA-<NUM>, that uses a root/base key (e.g., KASME), one or more fixed inputs, and one of the plurality of possible input algorithm identities (i.e., security key = KDF(root/base key, fixed input(s), algorithm identity)).

<FIG> is a flow diagram <NUM> that illustrates an example of authentication in an LTE wireless network. A UE <NUM> may connect to the network through a serving network <NUM> in order to obtain services from a home network <NUM> provided by a network operator. During bearer setup, the UE <NUM> may establish a secured connection with an HSS <NUM> of the home network <NUM>. The UE <NUM> may trust the HSS <NUM>, while the eNodeB <NUM> of the serving network <NUM> may be untrusted. The UE <NUM> may transmit a NAS Attach Request <NUM> with identifying information such as an International Mobile Subscriber Identity (IMSI). The MME <NUM> receives the NAS Attach request <NUM> and forwards the request <NUM> in an Authentication Information Request message <NUM> to the HSS <NUM>. The Authentication Information Request message <NUM> may include the IMSI of the UE <NUM> and a serving network identifier (SN_id). The HSS <NUM> may respond with an Authentication Information Response message <NUM> that includes an authentication value (AUTN), an expected result value (XRES) a random number and a KASME. The AUTN is generated by an AuC and, together with the RAND, authenticates the HSS <NUM> to the UE <NUM>. The messages <NUM>, <NUM> between the MME <NUM> and the HSS <NUM> are communicated on a link <NUM> and protected an authentication, authorization, and accounting protocol (Diameter).

The MME <NUM> transmits a NAS Authentication Request <NUM> to the UE <NUM>, which responds with a NAS Authentication Response message <NUM>. The NAS Authentication Request <NUM> includes the AUTN, RAND and a Key Set Identifier (KSIASME). The MME <NUM> may transmit a Non-Access Stratum (NAS) Security Mode Configuration (NAS SMC) message <NUM> to the UE <NUM>. The UE <NUM> then transmits an "NAS Security Mode Complete" message <NUM> to the MME <NUM>, which signals the eNodeB <NUM> an "S1AP Initial Context Setup" message <NUM>. The eNodeB <NUM> may then transmit an RRC Non-Access Stratum (NAS) Security Mode Configuration (RRC SMC) message <NUM> to the UE <NUM>, which responds with an RRC Security Mode Complete message <NUM> when ready.

In certain network implementations, the serving network <NUM> is trusted for some period of time after authentication has been accomplished. In one example, the serving network <NUM> may be trusted after authentication until another authentication process (AKA) is performed with the HSS <NUM>. The duration of time that established trust survives may be determined by a network operator. The network operator may configure the period of trust to endure for a number of hours, days, or weeks.

Due to development of <NUM>, <NUM>, and other networking technologies, certain network functions may be pushed towards the network edge. In some instances, the relocation of one or more network functions can degrade or invalidate trust on a cellular core network.

In one example, a femtocell or home eNodeB (HeNB) may be deployed to provide localized wireless service from through a broadband connection. A femtocell may be characterized as a small, low-power cellular base station, typically designed for use in a home or small business environment. A femtocell may be any small cell, typically with limited range and/or a limited number of active attached UEs that connects to a network operator's network through a wide area network or connection. The femtocell may be operable in one or more networks, including WCDMA, GSM, CDMA2000, TD-SCDMA, WiMAX and LTE networks. The deployment of newer technologies and/or the use of femtocells may result in the handling of network functions in less protected and/or isolated locations that are more susceptible to attack. For these and other reasons, the level of security provided by a small cell or relay node may be significantly degraded with respect to the security provided by a macro cell. Increased deployment of small cells, and relays to support for multiple hops within a network can be expected.

In another example, network functions in certain newer technologies may be located in shared systems, and/or provided in a cloud environment. In such systems and environments, networking and computing functions may be virtualized, and often managed by a third party provider. While network operators may be capable of securing access paths to the cloud, security of the cloud interior cannot be guaranteed. In some instances, tradeoffs are made between internal security of the virtual (cloud) environment and virtualized system performance. In some instances, network operators need not own the network equipment used to connect UEs, and/or the different components of network equipment in a network may be owned by different operators. Reduced isolation between operators may result, and some network operators may have easier access to other network operator's credentials. For example, credentials of a first network operator may be more easily misappropriated by a second network operator when both network operators share a common eNodeB or MME.

Networks may be implied to be insecure when certain security assumptions are invalidated. In <NUM> AKA, for example, the HSS is a trusted network entity, and the HSS may be a root of trust. Mutual authentication between a UE and a serving network may depend on the security between the HSS and the serving network. The HSS authenticates the serving network on behalf of UE and provides the authentication credentials for the UE to the serving network through a secure channel.

<FIG> is a simplified block diagram <NUM> illustrating a network environment in which a UE <NUM> connects with a serving network <NUM> in order to obtain services from a home network <NUM>. In the example depicted, the UE <NUM> may establish a wireless connection <NUM> with an MME <NUM> through an eNodeB <NUM> provided in an E-UTRAN operated as part of a serving network <NUM>. The MME <NUM> is connected through a link <NUM> to an HSS <NUM> of the home network <NUM>.

The eNodeB <NUM> and/or MME <NUM> of the serving network may be compromised due to shared usage of network hardware, relocation of network functions to the network edge and/or the placement of the eNodeB <NUM> and/or MME <NUM> in a public or otherwise unsecured physical location.

<FIG> is a simplified block diagram <NUM> illustrating certain vulnerabilities of the serving network <NUM>. An attacker <NUM> may exploit certain protocol and/or software vulnerabilities in order to acquire session credentials. The attacker <NUM> may include functions that can use the session credentials to impersonate (through a communications link <NUM>) a valid operator's serving network <NUM> and to capture information from a UE <NUM> that attempts to establish a connection with the operator network <NUM> compromised by the attacker <NUM>.

In one example, an attack may be characterized as a heart-bleed attack when the attacker <NUM> exploits an implementation flaw in an otherwise sound security protocol. The attacker <NUM> may take advantage of colocation of network equipment or network functions to acquire credentials such as authentication vectors (AVs) <NUM> transmitted to an MME <NUM> and/or encryption keys (KeNB) <NUM> used, maintained or generated by the eNodeB <NUM>. The credentials may be acquired from the eNodeB <NUM>, the MME <NUM> and/or from portions of interconnects <NUM>, <NUM> available to collocated hardware that provide shared network equipment or functions.

Session credentials are retrieved from the HSS <NUM> infrequently, and may remain valid for a period of time that may be measurable in hours, or days. An attacker <NUM> having intercepted the credentials can impersonate a serving network <NUM> until the next authentication procedure is performed with the HSS <NUM>.

In one example, the attacker <NUM> may intercept the credentials after an AKA procedure. The attacker <NUM> may be a rogue public land mobile network (PLMN) that can impersonate a serving network <NUM> provided by a valid network operator. Vulnerabilities in the eNodeB <NUM>, the MME <NUM> and/or the interconnects <NUM>, <NUM> may be monitored by the attacker in order to capture an IMSI associated with the UE <NUM>, information including keys <NUM> and other credentials such as authentication vectors <NUM> related to the establishment of a connection by or on behalf of the UE <NUM>. In some instances, an MME in the attacker <NUM> may impersonate an MME <NUM> in the valid serving network <NUM> and establish a communications link <NUM> with the UE <NUM> using intercepted IMSI, authentication vectors <NUM> and keys <NUM>. Network entities of the attacker <NUM> may then have access to the information on the UE <NUM> and may monitor communications originating from the UE <NUM>.

According to certain aspects disclosed herein, the security of a network may be enhanced by authenticating the serving network <NUM> while network connections are being established. The UE <NUM> may be adapted or configured to authenticate a serving network <NUM> as completely as possible, and when necessary. That is to say, the UE <NUM> may be configured to avoid unnecessary authentication procedures when connections with the serving network are active and the serving network can be trusted based on prior authentication.

In order to authenticate the serving network and to avoid attacks based on acquisition of session secrets such as authentication vectors for the UE <NUM>, a list of trusted networks may be maintained at the UE <NUM>, where the list identifies public or shared keys, certificates and/or other credentials corresponding to the trusted networks. In one example, the UE <NUM> may be provisioned with a trusted PLMN list and corresponding public key certificates. The eNodeB <NUM> and MME <NUM> may be provisioned with public key certificates signed by their respective operators, which may be the same operator, and which may include the operator of the serving network <NUM>. The private key corresponding to the public key used by the network functions, including the eNodeB <NUM> and MME <NUM>, is maintained in a secure storage or secure execution environment, such as a TrE, and an attacker cannot typically acquire the private key held in the TrE.

<FIG>, <FIG> and <FIG> are message flow diagrams <NUM>, <NUM>, <NUM> that illustrate examples of on-demand processes for authenticating the serving network <NUM> using a public-key based approach. An operator-signed public key is used to authenticate the serving network <NUM>. The serving network <NUM> may be provisioned with a certificate signed by a trusted third party (TTP) such as Verisign or the Internet Assigned Numbers Authority (IANA). In some instances, the serving network <NUM> may employ a self-signed certificate that is provided by the home network <NUM> to the UE <NUM> in a list of trusted certification authorities (CAs). The list of trusted CAs may include operators and their corresponding public keys. The list of trusted CAs and public key or certificates may be distributed to roaming partners through a secure channel.

Network functions, including the MME <NUM> and the eNodeB <NUM> may prove their membership of the serving network <NUM> using an operator-signed certificate. An attacker that does not possess the private-key corresponding to the public key issued for network functions cannot authenticate itself to UE <NUM>.

According to certain aspects disclosed herein, signaling and/or messages initiated by the UE <NUM> may be leveraged to enable on-demand authentication of the serving network <NUM>. Baseline overhead and be avoided and idle state overhead may be eliminated through "piggybacking" authentication of the serving network <NUM> on such signaling.

RRC messages may be used to authenticate the eNodeB <NUM>. Examples of such RRC messages include RRC connection request, and RRC connection reestablishment. The UE <NUM> may request that the connection messages exchanged with the eNodeB <NUM> be signed. In some instances, the UE <NUM> may request the public key of the eNodeB <NUM>.

TAU or service request messages may be used to authenticate the MME <NUM>. In one example, the UE <NUM> may request that TAU or service request accept messages exchanged with the MME <NUM> be signed. In some instances, the UE <NUM> may request the public key of the MME <NUM>.

<FIG> is a message flow diagram <NUM> that illustrates a first example of the use of RRC messages <NUM> for on-demand authentication of the serving network <NUM> through the eNodeB <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using the RRC messages <NUM>. An RRC connection request (or connection establishment request) <NUM> may be employed as part of the authentication. In one example, an RRC connection request <NUM> may be transmitted to the eNodeB <NUM> during transitions from idle mode. When a UE <NUM> goes into idle mode, the eNodeB <NUM> may drop the security context for UE <NUM> for power-saving reasons. According to certain aspects, the UE <NUM> may transmit an RRC connection request <NUM> that includes additional fields. The additional fields may include a Nonce, and a request for the signature of the eNodeB <NUM>. In some instances, the additional fields may also include a request for the public key of the eNodeB <NUM>. The Nonce may be an arbitrary, random or pseudo-random number used to ensure that previous communications cannot be reused in replay attacks. The eNodeB <NUM> may transmit an RRC connection setup response <NUM> that is signed using its private key and, upon verification of the authenticity of the eNodeB <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>.

<FIG> is a message flow diagram <NUM> that illustrates a second example of the use of RRC messages <NUM> for on-demand authentication of the serving network <NUM> through the eNodeB <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using the RRC messages <NUM>. An RRC connection reestablishment request <NUM> may be employed, for example, during connection failure recovery. According to certain aspects, the UE <NUM> may transmit an RRC connection reestablishment request <NUM> that includes additional fields. The additional fields may include a Nonce, and a request for the signature of the eNodeB <NUM>. In some instances, the additional fields may also include a request for the public key of the eNodeB <NUM>. The eNodeB <NUM> may transmit a connection reestablishment response <NUM> that is signed using its private key and, upon verification of the authenticity of the eNodeB <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>. The process illustrated by the example of the message flow diagram <NUM> of <FIG> may prevent an attack that causes a disconnect in order to intercept credentials during failure recovery procedures.

The UE <NUM> may authenticate the serving network <NUM> using RRC messages as needed when there is data to be transmitted, data to be received, or before or after a handover to another network function. RRC connection, establishment and/or reestablishment requests are initiated by the UE <NUM> and such requests require a response from the eNodeB <NUM>. In some instances, the UE <NUM> may determine that it is unnecessary to continually authenticate the serving network <NUM>. For example, authentication need not be performed when the UE <NUM> is in an idle state and no handover is indicated. Overhead associated with the baseline protocol can be minimized when signatures are provided on-demand. The eNodeB <NUM> typically provides the network function certificate only upon request.

<FIG> is a message flow diagram <NUM> that illustrates a first example of TAU messages <NUM> used for on-demand authentication of the serving network through the MME <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using TAU messages. A TAU request <NUM> may be employed, for example, during periodic registration or after a handover. According to certain aspects, the UE <NUM> may transmit the TAU request <NUM> with additional fields that may include a Nonce, and a request for the signature of the MME <NUM>. In some instances, the additional fields may also include a request for the public key of the MME <NUM>. The MME <NUM> may transmit a response <NUM> that is signed using its private key and, upon verification of the authenticity of the MME <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>.

<FIG>, <FIG> and <FIG> are message flow diagrams <NUM>, <NUM>, <NUM> that illustrate examples of on-demand processes for authenticating the serving network <NUM> using a shared-key based approach to thwart attacks in which an attacker may compromise and exploit system or protocol vulnerabilities in order to acquire session secrets, such as NAS keys and AS keys. Network functions such as the eNodeB <NUM> and MME <NUM> may be provisioned with a trusted execution environment, which may be used to maintain Key-Derivation-Keys for the network functions. An attacker typically cannot acquire the keys stored in the trusted execution environment. In one example, the Key-Derivation-Key stored in the trusted execution environment for the MME <NUM> is the KASME key and the Key-Derivation-Key stored in the trusted execution environment for the eNodeB <NUM> is the KeNB key. The Key-Derivation-Keys are not directly used for encryption and integrity protection, and are typically used to generate keys that can be used for encryption and integrity protection. Network functions may prove their membership to the serving network <NUM> using their respective Key-Derivation-Keys. Attackers that do not have an access to Key-Derivation-Key stored in the trusted execution environment cannot prove impersonated membership to the serving network <NUM>.

Certain on-demand processes for authenticating the serving network <NUM> using shared-keys may leverage messages initiated by the UE <NUM>. The authentication process may be implemented as an on-demand process in order to limit baseline protocol overhead and to potentially eliminate idle state overhead.

RRC messages may be used to authenticate the eNodeB <NUM>. Examples of such RRC messages include RRC connection request, and RRC connection reestablishment. The UE <NUM> may request that the connection messages exchanged with the eNodeB <NUM> be signed. In some instances, the eNodeB <NUM> may not be in possession of the KeNB when an RRC connection setup message is transmitted. Hence, the signature or a message authentication code (MAC) is sent to the UE <NUM> after the Security Mode Control procedure. A MAC code may include information produced using a hash function or the like, where the MAC code may authenticate and/or assure the integrity of a message.

TAU messages may be used to authenticate the MME <NUM>. In one example, the UE <NUM> may request that TAU accept messages exchanged with the MME <NUM> be signed.

<FIG> is a message flow diagram <NUM> that illustrates a third example in which RRC messages are used for on-demand authentication of the serving network <NUM> through the eNodeB <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using the RRC messages <NUM>. An RRC connection request <NUM> may be employed, for example, during transitions from idle mode. According to certain aspects, the UE <NUM> may transmit an RRC connection request <NUM> that includes additional fields. The additional fields may include a Nonce and a signature request. The eNodeB <NUM> signs its response <NUM> using KeNB and, upon verification of the authenticity of the eNodeB <NUM>, the UE <NUM> may acknowledge completion of the procedure by signaling RRC connection setup complete <NUM>.

<FIG> is a message flow diagram <NUM> that illustrates a fourth example of RRC messages <NUM> used for on-demand authentication of the serving network <NUM> through the eNodeB <NUM>. The UE <NUM> may initiate an AKA procedure <NUM> and, upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using the RRC messages <NUM>. An RRC connection reestablishment request <NUM> may be employed, for example, during connection failure recovery. According to certain aspects, the UE <NUM> may transmit an RRC connect reestablishment request <NUM> that includes additional fields. The additional fields may include a Nonce and a signature request. The eNodeB <NUM> may transmit a response <NUM> that is signed using KeNB and, upon verification of the authenticity of the eNodeB <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>.

The UE <NUM> may authenticate the serving network <NUM> using RRC messages as needed when there is data to be transmitted, receives, or before or after a handover to another network function. RRC connection establishment, RRC connection, and/or RRC reestablishment requests are initiated by the UE <NUM> and such requests require a response from the eNodeB <NUM>. In some instances, the UE <NUM> may determine that it is unnecessary to continually authenticate the serving network <NUM>. For example, authentication need not be performed when the UE <NUM> is in an idle state and no handover is indicated. Overhead associated with the baseline protocol can be minimized when signatures are provided on-demand. The eNodeB <NUM> typically provides the network function certificate only upon request.

<FIG> is a message flow diagram <NUM> that illustrates a second example of TAU messages <NUM> used for on-demand authentication of the serving network through the MME <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using the TAU messages <NUM>. A TAU request <NUM> may be employed, for example, during periodic registration or after a handover. According to certain aspects, the UE <NUM> may transmit the TAU request <NUM> with additional fields that may include a Nonce and a signature request. The MME <NUM> may transmit a response <NUM> that is signed using the KASME key and, upon verification of the authenticity of the MME <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>.

<FIG> is a simplified block diagram <NUM> illustrating certain vulnerabilities of the serving network <NUM> that may arise when an attacker <NUM> has physical access to network equipment that provide certain network functions (e.g., the eNodeB <NUM> and/or the MME <NUM>) of a serving network <NUM>. Under this form of attack, the attacker <NUM> may gain access to permanent credentials including permanent keys <NUM>, <NUM> as well as session credentials. For example, the attacker <NUM> may have access to a permanent key <NUM>, and/or <NUM>, such as the private key of network equipment and/or a network function such as the eNodeB <NUM> or the MME <NUM>. The private key may be used to sign messages. Under this form of attack, the attacker <NUM> can impersonate the serving network <NUM> persistently, with respect to communications <NUM> with the UE <NUM> and with respect to communications <NUM> with the HSS <NUM>.

An attacker <NUM> that has physical access to network equipment may be able to acquire all credentials issued for network functions by compromising network equipment associated with those network functions. The network functions may maintain, provide or be associated with credentials such as authentication vectors for a UE <NUM> and/or a private key bound to the certificate signed by the network operator.

With reference to <FIG>, security of a network may be enhanced when the network operator provisions network functions (e.g., the eNodeB <NUM> and/or the MME <NUM>) with a public key certificate and employs the services of a certificate observatory (CertOb) <NUM>. The CertOb <NUM> may be operated by a trusted third party that cannot be compromised. The CertOb <NUM> may be used to prove the integrity of operator issued network function certificates. The CertOb <NUM> may be identified and/or accessed using an identifier of the certificate observatory that includes an IP address and/or a universal resource locator (URL). The serving network may be authenticated using a public-key based authentication process, with verification of the certificate status of the network function (e.g., the eNodeB <NUM> or the MME <NUM>).

A Certificate Server Function (CSF) <NUM> manages network function certificates and provides the network function certificates to a UE <NUM> on request. The CSF <NUM> reports certificate status changes to the CertOb <NUM>. The status changes may include issuance events, revocation events, etc. The CertOb <NUM> stores certificate integrity information of operators and provides the information to the HSS <NUM> and to the UE <NUM>. The certificate integrity information may be provided as a hash of all current certificates for a serving network <NUM>. In one example, the hash may be provided as a Merkel hash tree, which provides an efficient and secure verification of the certificate associated with multiple domains corresponding to operator networks.

A UE <NUM> may validate a certificate initially by comparing a first copy of the certificate integrity information provided by the serving network with a second copy of the certificate integrity information received at the UE <NUM> from the CertOb <NUM>. If the first and second copies of the certificate integrity information do not match, the UE <NUM> may request the CSF <NUM> to provide one or more certificates for the serving network <NUM> in order to authenticate a network function with which the UE <NUM> is actively communicating.

<FIG>, <FIG> and <FIG> are message flow diagrams <NUM>, <NUM>, <NUM> that illustrate examples of on-demand processes for authenticating the serving network <NUM> using an approach based on an operator-signed public key that is used to authenticate the serving network <NUM>. The serving network <NUM> may be provisioned with a certificate signed by a trusted third party (TTP) such as Verisign or Internet Assigned Numbers Authority (IANA). In some instances, the serving network <NUM> may employ a self-signed certificate that is provided to the UE <NUM> in a list of trusted certification authorities (CAs) by the home network. The trusted CA list may include operators and their corresponding public keys. The CA list and public key or certificates may be distributed to roaming partners through a secure channel.

<FIG> is a message flow diagram <NUM> that illustrates a fifth example of RRC messages <NUM> used for on-demand authentication of the serving network <NUM> through the eNodeB <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. The UE <NUM> may receive certificate integrity information of the serving network <NUM> from the HSS <NUM> during or after the AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using the RRC messages <NUM>. An RRC connection request <NUM> may be employed, for example, during transitions from idle mode. When a UE <NUM> goes into idle mode, the eNodeB <NUM> may drop the security context for UE <NUM> for power-saving reasons. According to certain aspects, the UE <NUM> may transmit an RRC connection request <NUM> that includes additional fields. The additional fields may include a Nonce, and a request for the signature of the eNodeB <NUM>. In some instances, the additional fields may also include a request for the public key of the eNodeB <NUM>. The Nonce may be an arbitrary, random or pseudo-random number used to ensure that previous communications cannot be reused in replay attacks. The eNodeB <NUM> may transmit a response <NUM> that is signed using its private key and, upon verification of the authenticity of the eNodeB <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>.

The UE <NUM> may retrieve <NUM> the current certificate integrity information of the serving network <NUM> from the CertOb <NUM>. The UE <NUM> may then verify that the current certificate integrity information is that same as the current certificate integrity information provided by the HSS <NUM>. If the current certificate integrity information of the serving network is different from the current certificate integrity information provided by the HSS <NUM> during the initial attach, the UE <NUM> verifies the network function certificate of the eNodeB <NUM> by querying <NUM> the CSF <NUM>, for example.

<FIG> is a message flow diagram <NUM> that illustrates a sixth example of RRC messages <NUM> used for on-demand authentication of the serving network <NUM> through the eNodeB <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. The UE <NUM> may receive certificate integrity information of the serving network <NUM> from the HSS <NUM> during or after the AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using the RRC messages <NUM>. An RRC connection reestablishment request <NUM> may be employed, for example, during connection failure recovery. According to certain aspects, the UE <NUM> may transmit an RRC connect reestablishment request <NUM> that includes additional fields. The additional fields may include a Nonce, and a request for the signature of the eNodeB <NUM>. In some instances, the additional fields may also include a request for the public key of the eNodeB <NUM>. The eNodeB <NUM> may transmit a response <NUM> that is signed using its private key and, upon verification of the authenticity of the eNodeB <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>.

The UE <NUM> may authenticate the serving network <NUM> using RRC messages as needed when there is data to be transmitted, receives, or before or after a handover to another network function. RRC connection/reestablishment requests are initiated by the UE <NUM> and such requests require a response from the eNodeB <NUM>. In some instances, the UE <NUM> may determine that it is unnecessary to continually authenticate the serving network <NUM>. For example, authentication need not be performed when the UE <NUM> is in an idle state and no handover is indicated. Overhead associated with the baseline protocol can be minimized when signatures are provided on-demand. The eNodeB <NUM> typically provides the network function certificate only upon request.

<FIG> is a message flow diagram <NUM> that illustrates a third example of TAU messages <NUM> used for on-demand authentication of the serving network through the MME <NUM>. The UE <NUM> may initiate an AKA procedure <NUM>. The UE <NUM> may receive certificate integrity information of the serving network <NUM> from the HSS <NUM> during or after the AKA procedure <NUM>. Upon successful completion of the AKA procedure <NUM>, the UE <NUM> may authenticate the serving network <NUM> using TAU messages. A TAU request <NUM> may be employed, for example, during periodic registration or after a handover. According to certain aspects, the UE <NUM> may transmit the TAU request <NUM> with additional fields that may include a Nonce, and a request for the signature of the MME <NUM>. In some instances, the additional fields may also include a request for the public key of the MME <NUM>. The MME <NUM> may transmit a response <NUM> that is signed using its private key and, upon verification of the authenticity of the MME <NUM>, the UE <NUM> may signal RRC connection setup complete <NUM>.

The UE <NUM> may retrieve <NUM> the current certificate integrity information of the serving network <NUM> from the CertOb <NUM>. The UE <NUM> may then verify that the current certificate integrity information is that same as the current certificate integrity information provided by the HSS <NUM>. If the current certificate integrity information of the serving network is different from the current certificate integrity information provided by the HSS <NUM> during the initial attach, the UE <NUM> verifies the network function certificate of the MME <NUM> by querying <NUM> the CSF <NUM>, for example.

<FIG> is a conceptual diagram <NUM> illustrating a simplified example of a hardware implementation for an apparatus employing a processing circuit <NUM> that may be configured to perform one or more functions disclosed herein. In accordance with various aspects of the disclosure, an element, or any portion of an element, or any combination of elements as disclosed herein may be implemented using the processing circuit <NUM>. The processing circuit <NUM> may include one or more processors <NUM> that are controlled by some combination of hardware and software modules. Examples of processors <NUM> include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, sequencers, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. The one or more processors <NUM> may include specialized processors that perform specific functions, and that may be configured, augmented or controlled by one of the software modules <NUM>. The one or more processors <NUM> may be configured through a combination of software modules <NUM> loaded during initialization, and further configured by loading or unloading one or more software modules <NUM> during operation.

In the illustrated example, the processing circuit <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing circuit <NUM> and the overall design constraints. The bus <NUM> links together various circuits including the one or more processors <NUM>, and storage <NUM>. Storage <NUM> may include memory devices and mass storage devices, and may be referred to herein as computer-readable media and/or processor-readable media. The bus <NUM> may also link various other circuits such as timing sources, timers, peripherals, voltage regulators, and power management circuits. A bus interface <NUM> may provide an interface between the bus <NUM> and one or more transceivers <NUM>. A transceiver <NUM> may be provided for each networking technology supported by the processing circuit. In some instances, multiple networking technologies may share some or all of the circuitry or processing modules found in a transceiver <NUM>. Each transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. Depending upon the nature of the apparatus, a user interface <NUM> (e.g., keypad, display, speaker, microphone, joystick) may also be provided, and may be communicatively coupled to the bus <NUM> directly or through the bus interface <NUM>.

One or more processors <NUM> in the processing circuit <NUM> may execute software. The software may reside in computer-readable form in the storage <NUM> or in an external computer readable medium. The external computer-readable medium and/or storage <NUM> may include a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a CD or a DVD), a smart card, a flash memory device (e.g., a "flash drive," a card, a stick, or a key drive), RAM, ROM, PROM, EPROM, EEPROM, a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium and/or storage <NUM> may also include, by way of example, a carrier wave, a transmission line, and any other suitable medium for transmitting software and/or instructions that may be accessed and read by a computer. Computer-readable medium and/or the storage <NUM> may reside in the processing circuit <NUM>, in the processor <NUM>, external to the processing circuit <NUM>, or be distributed across multiple entities including the processing circuit <NUM>. The computer-readable medium and/or storage <NUM> may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.

The storage <NUM> may maintain software maintained and/or organized in loadable code segments, modules, applications, programs, etc., which may be referred to herein as software modules <NUM>. Each of the software modules <NUM> may include instructions and data that, when installed or loaded on the processing circuit <NUM> and executed by the one or more processors <NUM>, contribute to a run-time image <NUM> that controls the operation of the one or more processors <NUM>. When executed, certain instructions may cause the processing circuit <NUM> to perform functions in accordance with certain methods, algorithms and processes described herein.

Some of the software modules <NUM> may be loaded during initialization of the processing circuit <NUM>, and these software modules <NUM> may configure the processing circuit <NUM> to enable performance of the various functions disclosed herein. For example, some software modules <NUM> may configure internal devices and/or logic circuits <NUM> of the processor <NUM>, and may manage access to external devices such as the transceiver <NUM>, the bus interface <NUM>, the user interface <NUM>, timers, mathematical coprocessors, and so on. The software modules <NUM> may include a control program and/or an operating system that interacts with interrupt handlers and device drivers, and that controls access to various resources provided by the processing circuit <NUM>. The resources may include memory, processing time, access to the transceiver <NUM>, the user interface <NUM>, and so on.

The following flowcharts illustrate methods and processes performed or operative on network elements adapted or configured in accordance with certain aspects disclosed herein. The methods and processes may be implemented in any suitable network technology, including <NUM>, <NUM>, and <NUM> technologies, to name but a few. Accordingly, the claims are not restricted to a single network technology. In this regard, a reference to a "UE" may be understood to refer also to a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. A reference to an "eNodeB" may be understood to refer to a base station, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set, an extended service set, or some other suitable terminology. A reference to an MME may refer also to an entity that serves as an authenticator in the serving network and/or a primary service delivery node such as a Mobile Switching Center, for example. A reference to the HSS may refer also to a database that contains user-related and subscriber-related information, provides support functions in mobility management, call and session setup, and/or user authentication and access authorization, including, for example, a Home Location Register (HLR), Authentication Centre (AuC) and/or an authentication, authorization, and accounting (AAA) server.

<FIG> is a flow chart <NUM> of a method of securing wireless communication between a UE and a serving network.

At block <NUM>, the UE may transmit a connection request or tracking area request to a network function in a serving network after a security association has been established between the UE and the serving network. The request includes a nonce and a signature request. The request sent to the serving network is sent while the UE is transitioning from an idle mode or after such transition from idle mode. In some instances, the request sent to the serving network is an RRC message. The RRC message may be an RRC connection request, an RRC connection reestablishment request, and/or an RRC reconfiguration complete message. In some instances, the request sent to the serving network is a TAU request.

At block <NUM>, the UE receives a response to the connection request or tracking area request from the network function. The response includes a signature of the network function.

At block <NUM>, the UE authenticates the serving network based on the signature of the network function and a public key certificate corresponding to the network function. The public key certificate may be signed using a private key of the serving network provided by a network operator associated with the serving network. The UE may maintain a list of trusted networks that identifies public keys or public key certificates corresponding to the trusted networks. The UE may authenticate the serving network by using the list of trusted networks to verify the public key of the network function and the signature generated by the network function. The serving network may be authenticated using a trusted third party to verify the public key certificate corresponding to the network function.

In some examples, a certificate integrity information request may be transmitted to the network, and first certificate integrity information received in a response from the network may be verified using second certificate integrity information received from a home subscriber server. The certificate integrity information request may include an identifier of a certificate observatory (such as the CertOb <NUM> of <FIG>) corresponding to the second certificate integrity information. The CertOb <NUM> may be configured to maintain integrity of a set of certificates for a network. The identifier of the CertOb <NUM> may be an IP address or URL. The first certificate integrity information may be verified by authenticating a response to the certificate integrity information request using a public key of the CertOb <NUM>. In some instances, the first certificate integrity information may be verified by comparing the first certificate integrity information with the second certificate integrity information, sending a certificate status request to a CSF <NUM> when a difference is determined between the first certificate integrity information and the second certificate integrity information, and verifying status of a network function certificate based on a response from the CSF <NUM>. The certificate status request may include first identifying information that identifies the network function, second identifying information that identifies the network function certificate, and a version number of the network function certificate. A response from the CSF <NUM> may include a certificate status response including status of the network function certificate, a public key of the network, and a signature of the certificate status response created by the CSF <NUM> using a private key of the network. Verification of the certificate status response may be performed using the public key of the network.

<FIG> is a diagram illustrating a simplified example of a hardware implementation for an apparatus <NUM> employing a processing circuit <NUM>. The processing circuit typically has a processor <NUM> that may include one or more of a microprocessor, microcontroller, digital signal processor, a sequencer and a state machine. The processing circuit <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing circuit <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware modules, represented by the processor <NUM>, the modules or circuits <NUM>, <NUM> and <NUM>, a wireless transceiver <NUM> adapted to communicate through an antenna <NUM> and the computer-readable storage medium <NUM>. The bus <NUM> may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable storage medium <NUM>. The software, when executed by the processor <NUM>, causes the processing circuit <NUM> to perform the various functions described supra for any particular apparatus. The computer-readable storage medium <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software, including data decoded from symbols transmitted over the antenna <NUM>, which may be configured as data lanes and clock lanes. The processing circuit <NUM> further includes at least one of the modules <NUM>, <NUM> and <NUM>. The modules <NUM>, <NUM> and <NUM> may be software modules running in the processor <NUM>, resident/stored in the computer-readable storage medium <NUM>, one or more hardware modules coupled to the processor <NUM>, or some combination thereof. The modules <NUM>, <NUM> and/or <NUM> may include microcontroller instructions, state machine configuration parameters, or some combination thereof.

In one configuration, the apparatus <NUM> for wireless communication includes a module and/or circuit <NUM> that is configured to authenticate and/or secure a connection with a home network, a module and/or circuit <NUM> that is configured to authenticate a serving network, and a module and/or circuit <NUM> that is configured to transmit and receive messages to the serving network.

In one example, the wireless transceiver <NUM> may be configured to transmit messages to a wireless base station in the serving network, and to receive messages from the wireless base station. The module and/or circuit <NUM> may include means for establishing a secured connection between the apparatus and a home network. The authenticated connection may be established responsive to a first authentication message transmitted through the wireless transceiver to the HSS. After the secured connection is established and before a second authentication request is transmitted to the HSS of the home network the modules and/or circuits <NUM>, <NUM> may include means for transmitting a request to a network function in the serving network, the request having a nonce and a signature request attached thereto, and receive a response to the request from the network function, where the response includes a signature of the network function. The module and/or circuit <NUM> may include means for authenticating the serving network based on the signature of the network function and a public key certificate corresponding to the network function and signed by a network operator. The public key certificate corresponding to the network function may be included in a list of trusted networks and their respective public key certificates maintained by the apparatus.

The modules and/or circuits <NUM>, <NUM> may include means for transmitting a certificate integrity information request to the network, and module and/or circuit <NUM> may include means for verifying first certificate integrity information received from the network using second certificate integrity information received from the HSS. The certificate integrity information request includes an identifier of a CertOb <NUM> corresponding to the second certificate integrity information. The CertOb <NUM> may be configured to maintain integrity of a set of certificates for a network.

The module and/or circuit <NUM> may be configured to compare the first certificate integrity information with the second certificate integrity information, cause the modules and/or circuits <NUM>, <NUM> to send a certificate status request to a CSF <NUM> when a difference is determined between the first certificate integrity information and the second certificate integrity information, and verify status of a network function certificate based on a response from the CSF <NUM>. The certificate status request may include an identifier of the network function, an identifier of the network function certificate, and a version number of the network function certificate.

<FIG> is a flow chart <NUM> of a method of proving membership of a serving network. The method may be performed by a network node (or network function) of a serving network.

At block <NUM>, the network node may receive a first message from UE after the UE has established a secured connection with a home network. The message may be directed to a network function of the serving network. The message may include a nonce and a signature request.

At block <NUM>, the network node may generate a signature using an operator-signed certificate maintained by the network function of the serving network. The operator-signed certificate may be a public key certificate signed by an operator of the serving network. A private key corresponding to the operator-signed certificate may be maintained in a secure storage or secure execution environment and/or in a trusted environment.

At block <NUM>, the network node may transmit a second message to the UE. The signature may be attached to the second message.

In some examples, the signature includes a MAC created using a session key shared between the UE and the network function. A symmetric cipher may be used for signing the second message response.

In some instances, the network node may be a MME and the session key may be a KASME. The MME may receive the KASME from an HSS in a message encrypted using a public key of the MME, decrypt the KASME using a private key stored in a trusted environment, and store the decrypted KASME in the trusted environment. The authentication request may be received in a TAU request.

In some instances, the network node may be an eNodeB and the session key may be a KeNB. The eNodeB may receive the KeNB from an MME in a message encrypted using a public key of the eNodeB, decrypt the KeNB using a private key stored in a trusted environment, and store the decrypted KeNB in the trusted environment. The first message may be a radio resource control (RRC) message and the second message may be a response to the RRC message. For example, the RRC message may be an RRC connection establishment request, an RRC connection reestablishment request or an RRC reconfiguration complete message.

In some examples, the signature includes a digital signature created using a private key of the network node. An asymmetric cipher may be used for signing the authentication response. The private key of the network node may be stored in a trusted environment and the signature is created within the trusted environment.

<FIG> is a diagram illustrating a simplified example of a hardware implementation for an apparatus <NUM> employing a processing circuit <NUM>. The processing circuit typically has a processor <NUM> that may include one or more of a microprocessor, microcontroller, digital signal processor, a sequencer and a state machine. The processing circuit <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing circuit <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware modules, represented by the processor <NUM>, the modules or circuits <NUM>, <NUM> and <NUM>, a wireless transceiver <NUM> configurable to communicate through an antenna <NUM> and the computer-readable storage medium <NUM>. The bus <NUM> may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

In one configuration, the apparatus <NUM> for wireless communication includes a module and/or circuit <NUM> that is configured to generate authentication signatures, a module and/or circuit <NUM> that is configured to transmit messages to a UE, and a module and/or circuit <NUM> that is configured to receive messages from a UE.

In one example, the module and/or circuit <NUM> may provide a means for receiving a first message from a UE after the UE has established a secured connection with a home network. The message may be directed to a network function of the serving network and includes a nonce and a signature request, the module and/or circuit <NUM> may provide a means for generating a signature using an operator-signed certificate maintained by the network function of the serving network, and the module and/or circuit <NUM> may provide a means for transmitting a second message to the UE, where the signature may be attached to the second message. The signature attached to the second message may be generated to prove to the UE that the apparatus <NUM> is a member of a serving network. The operator-signed certificate may be a public key certificate signed by an operator of the serving network.

In some examples, the network node is an eNodeB, the first message is an RRC message and the second message is a response to the RRC message.

In some examples, the network node is an MME, and the authentication request is received in a TAU request.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

Claim 1:
A method of securing wireless communication between a user equipment, UE, (<NUM>, <NUM>) and a serving network (<NUM>, <NUM>) performed by the UE, comprising:
transmitting (<NUM>) a Radio Resource Control, RRC, message (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) to a base station (<NUM>) or a Tracking Area Update, TAU, request (<NUM>, <NUM>, <NUM>) to an entity (<NUM>) that serves as an authenticator in the serving network (<NUM>, <NUM>) after the serving network has been authenticated by the UE or by a database that contains user-related and subscriber-related information on behalf of the UE, wherein the RRC message (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) or the TAU request (<NUM>, <NUM>, <NUM>) includes a nonce and a signature request;
receiving (<NUM>) a RRC response (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) to the RRC message (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) from the base station (<NUM>) or a TAU response (<NUM>, <NUM>, <NUM>) to the TAU request (<NUM>, <NUM>, <NUM>) from the entity (<NUM>) that serves as an authenticator, wherein the RRC response (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) or the TAU response (<NUM>, <NUM>, <NUM>) includes a signature of the base station (<NUM>) or the entity (<NUM>) that serves as an authenticator; and
authenticating (<NUM>) the serving network (<NUM>, <NUM>) based on the signature of and on a public key certificate corresponding to the base station (<NUM>) or the entity (<NUM>) that serves as an authenticator, wherein the RRC message comprises an RRC connection request, an RRC connection reestablishment request, or an RRC reconfiguration complete message.