Abstract:
Aspects of the present invention provide a mechanism to utilize IMS media security mechanisms in a CS network and, thereby, provide end-to-end media security in the case where the media traffic travels across both a CS network and a PS network.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of Ser. No. 13/127,832, filed on May 5, 2011 (published as US 20110213958), which is a 35 U.S.C. §371 National Phase Entry Application from PCT/IB2008/002973, filed Nov. 5, 2008, and designating the United States. The above identified applications and publications are incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to IP multimedia subsystem (IMS) data security mechanisms. 
       BACKGROUND 
       [0003]    Migration from circuit switched (CS) based networks to packet switched (PS) based networks (e.g., IMS based networks) will be done in steps, and the two networks may co-exist for a long time. A number of solutions have been standardized over the last years for enabling migration towards an IMS based infrastructure, such as, for example Voice Call Continuity (VCC). Most of these solutions allow a CS bearer to be used to carry speech traffic for a user, while providing the service control in IMS. The solutions may also allow the user to transfer traffic between CS bearers and PS bearers. With respect to media security, it is desired to provide a means for providing end-to-end media security in the case where the media traffic travels across both a CS network and a PS network. 
       SUMMARY 
       [0004]    Aspects of the present invention provide a mechanism to utilize IMS media security mechanisms in a CS network and, thereby, provide end-to-end media security in the case where the media traffic travels across both a CS network and a PS network. 
         [0005]    In one aspect, the invention provides a method performed by a gateway. In some embodiments, this method includes the following steps: establishing a circuit switched connection with a communication device; receiving from the communication device via the circuit switched connection a frame including a payload comprising an encrypted encoded data intended for a remote communication device and one or more encryption parameters (e.g., a counter value, an integrity tag, a key identifier) that is required by the remote communicate device to decrypt the encrypted encoded data; creating a protocol data unit that includes the encoded data and the encryption parameter; and transmitting via a packet switched network the protocol data unit so that it will be received by the remote communication device. 
         [0006]    In some embodiments, the protocol data unit (PDU) (e.g., an SRTP PDU) includes a header portion and a payload portion, and the encoded data is placed in the payload portion and the encryption parameter is placed in the header portion. In some embodiments, the encoded data immediately follows or immediately precedes the encryption parameter in the frame. In some embodiments, the payload consist of the encrypted encoded data and the one or more encryption parameters. 
         [0007]    In another aspect, the present invention provides an improved communication device (e.g., a mobile terminal). In some embodiments, the communication device includes: a key retrieving module configured to obtain or create an encryption key; a circuit switched connection establishment module for initiating a circuit switched connection; a payload creating module configured to produce a payload for a frame, wherein the payload includes encrypted encoded data and one or more encryption parameters; and a transmitter operable to transmit the frame to a gateway using the circuit switched connection. In some embodiments, the payload creating comprises an adaptive multi-rate (AMR) codec for producing the encoded data; and a security module configured to encrypt the encoded data and generate the frame payload. The key retrieving module may be operable to receive a message transmitted from the key management server, wherein the message includes the requested key. The key retrieving module may be further operable to transmit a message to a key management server, wherein the message includes a request for a key. In some embodiments, the key retrieving module is configured to transmit the message to the key management server using a short message service (SMS) or an Unstructured Supplementary Service Data (USSD) protocol. 
         [0008]    In another aspect, the present invention provides a method performed by an application server. In some embodiments, the method includes the following steps: receiving at the application server a session initiation message transmitted from a mobile terminal, the session initiation message comprising a voucher (e.g., an encrypted key and/or other encryption information); storing the voucher included in the session initiation message; receiving at the application server a session initiation message transmitted from a gateway; determining whether the session initiation message transmitted from the gateway correlates with the session initiation message transmitted from the mobile terminal; retrieving the voucher in response to determining that the session initiation message transmitted from the gateway correlates with the session initiation message transmitted from the mobile terminal; and transmitting an session initiation message to another server after retrieving the voucher, wherein the session initiation message transmitted to the another server includes the voucher. 
         [0009]    In some embodiments, the session initiation message transmitted from the mobile terminal is received via a packet switched network and includes information indicating that the mobile terminal shall use a circuit switched connection when communicating with the another terminal. In some embodiments, the step of determining whether the session initiation message transmitted from the gateway correlates with the session initiation message transmitted from the mobile terminal comprises determining whether information included in the session initiation message transmitted from the gateway matches information that was included in the session initiation message transmitted from the mobile terminal. 
         [0010]    In another aspect, the present invention provides an application server for facilitating communications between a mobile terminal and another terminal. In some embodiments, the application server includes: a receiver operable to receive a session initiation message transmitted from the mobile terminal, the session initiation message comprising a voucher; a data storage unit for storing the voucher included in the session initiation message; a message correlating module configured to determine whether a session initiation message transmitted from a gateway correlates with the session initiation message transmitted from the mobile terminal; a voucher retrieving modules configured to retrieve the voucher in response to a determination that the session initiation message transmitted from the gateway correlates with the session initiation message transmitted from the mobile terminal; and a transmitter operable to transmit a session initiation message to another server after retrieving the voucher, wherein the session initiation message transmitted to the another server includes the voucher. In some embodiments, the receiver is operable to receive the session initiation message via a packet switched network, and the session initiation message includes information indicating that the mobile terminal shall use a circuit switched connection when communicating with the other terminal. Also, in some embodiments, the message correlating module is configured to determine whether the session initiation message transmitted from the gateway correlates with the session initiation message transmitted from the mobile terminal by determining whether information included in the session initiation message transmitted from the gateway matches information included in the session initiation message transmitted from the mobile terminal. 
         [0011]    In other embodiments, the application server includes: a receiver operable to receive from a gateway an initiation message indicating that the mobile terminal has requested establishment of a secure session with the other terminal; a key management module configured to retrieve a voucher from a key management system in response to the receiver receiving the initiation message from the gateway; and a transmitter operable to transmit the retrieved voucher to another application server in response to the key management module retrieving the voucher. 
         [0012]    In yet other embodiments, the application server includes: a receiver operable to receive a key request message transmitted from the mobile terminal; a key management module configured to transmit a key to the mobile terminal in response to receipt of the key request message; a data storage unit for storing the key; an initiation message transmitting module configured to (a) determine whether the stored key is associated with information that matches information included in an initiation message transmitted from a gateway and (b) in response to determining that that the stored key is associated with information that matches information included in the initiation message transmitted from the gateway, transmit to another server an initiation message. In some embodiments, the key management module is further configured, such that, in response to receipt of the key request message and prior to transmitting the key to the mobile terminal, the key management module obtains the key from a key management system. 
         [0013]    The above and other aspects and embodiments are described below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements. 
           [0015]      FIG. 1  illustrates a system according to an embodiment of the invention. 
           [0016]      FIG. 2  further illustrate the system shown in  FIG. 1 . 
           [0017]      FIGS. 3-8  are data flow diagrams illustrating different embodiments of the invention. 
           [0018]      FIGS. 9-11  are flow charts illustrating various processes according to different embodiments of the invention. 
           [0019]      FIG. 12  is a functional block diagram of a gateway according to an embodiment of the invention. 
           [0020]      FIGS. 13 and 14  are functional block diagrams of a UE according to an embodiment of the invention. 
           [0021]      FIG. 15  is a functional block diagram of an application server according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring now to  FIG. 1 ,  FIG. 1  illustrates a system  100  according to some embodiments of the invention. As shown, system  100  includes a communication device  102  (a.k.a., user equipment (UE)  102 ) that is operable to communicate with components of a network  101 . As shown in  FIG. 1 , UE  102 , which may be a mobile terminal, is operable to communicate with a “gateway”  104  using a circuit switched (CS) network and is operable to communicate with an “application server”  106  using a packet switched network (PS). As further shown, gateway  104  and application server  106  can communicate with each other using a PS network. Additionally, gateway  104  and application server  106  may be able to send messages to and receive messages from a remote network  110  using a PS network. Accordingly, gateway  104  functions to enable UE  102  to communicate with devices connected to remote network  110  by using both a CS connection and a PS connection. 
         [0023]    Referring now to  FIG. 2 ,  FIG. 2  further illustrates system  100 . As illustrated in  FIG. 2 , gateway  104  may includes one or more servers. For example, as shown, gateway  104  may include a switching center server  212  (e.g., a Mobile Switching Center) and a gateway server  214  (e.g., a media gateway (MGW)). As also illustrated, application server  106  may include one or more severs (e.g., one or more Session Initiation Protocol (SIP) servers). For example, as shown, application server  106  may include a proxy Call Session Control Function (P-CSCF) server  222 , a serving CSCF (S-CSCF)  224 , and a Service Centralization and Continuity Application Server (SCC AS) server. As further shown, system  100  may also include a Short Message Service Center (SMSC)  202  and a key management system  204 , both of which may be components of network  101 . 
         [0024]    Referring now to  FIG. 3 ,  FIG. 3  is a data flow diagram illustrating a process, according to an embodiment of the invention, for enabling UE  102  (e.g., a mobile terminal such as a mobile phone) to originate a call (e.g., a voice call) with a device connected to network  110  and to communicate with the device utilizing both a CS network (e.g., a wireless CS radio access network) and a PS network in a secure manner. In this embodiment, the UE  102  has the capability of communicating with application server  106  using nothing but a PS network and has the capability of establishing a CS call with gateway  104 . 
         [0025]    As illustrated in  FIG. 3 , the process may begin with UE  102  transmitting to application server  106  a message  302  (e.g., an SIP invite message or other session initiation message) via a PS network. Message  302  may include the following information: (1) information identifying the called party, (2) encryption key management information (e.g., an encryption key and/or other information necessary to secure the communications), which may be referred to herein as a “voucher”, (3) information indicating that UE  102  will use a CS bearer to connect with network  101 ; and (4) information identifying UE  102  and/or the user of UE  102 . In some embodiments, prior to UE  102  transmitting message  302 , UE obtains encryption key management information from KMS  204  and/or creates the encryption key management information. 
         [0026]    In response to message  302 , server  106  may transmit a response message  304  to UE  102 . Because message  302  indicates that UE will use a CS bearer to connect with network  101 , application server  106  waits to receive a particular message  308  from gateway  104  before transmitting a message  310  to remote network  110 . Additionally, in response to receiving message  302 , server  106  stores the voucher and associates the voucher with the information identifying the called party and the information identifying UE  102  and/or the user of UE  102 . 
         [0027]    In response to receiving message  304  from server  106 , UE  102  transmits a call setup request  306  to gateway  104 . In response, gateway  104  transmits message  308  to application server  106 , which message indicates to server  106  that UE  102  has established (or is about to establish) a connection with gateway  104  using a CS bearer. Message  304  may include the following information: (1) information identifying UE  102  and/or the user of UE  102  and (2) information identifying the called party. 
         [0028]    In response to receiving message  308 , server  106  correlates the message  302  with message  308 . For example, server  106  uses the information included in message  308  (i.e., the information identifying UE  102  and/or the user of UE  102  and the information identifying the called party) to retrieve the voucher it had previously received from UE  102 . After retrieving the voucher, server  106  transmits to remote network  110  message  310  (e.g., an initiation message, such as, for example, a SIP invite message), which includes the retrieved voucher. After server  106  transmits message  310  additional messages may be transmitted to complete the set-up of the session and bearers, as is well known in the art. 
         [0029]    After the session and bearers are set-up, UE  102  may begin transmitting fames of encrypted data (e.g., frames of encrypted voice data) to gateway  104  using the CS bearer  312 . Preferably, the frames include not only the encrypted data but also encryption parameters needed by the called party to decrypt the encrypted data. For example, the encryption parameters may include a sequence number (a.k.a., counter value), an integrity tag, and a key identifier (e.g., an SRTP master key identifier (MKI)). An exemplary payload  1306  of the frame is illustrated in  FIG. 13 . 
         [0030]    Gateway  104  is configured to receive the frames and for each frame, extract the encrypted data and encryption parameters from the frame, create a secure real-time transport protocol (SRTP) protocol data unit (“SRTP packet”) that includes the encrypted data and encryption parameters, and transmit the SRTP packet to remote network  110  so that the data is ultimately received by the called party. In this manner, end-to-end media security is established between UE  102  and remote network  110  even though UE  102  connects to network  101  using a CS bearer. 
         [0031]    Referring now to  FIG. 4  is a data flow diagram illustrating a process, according to an embodiment of the invention, for enabling UE  102  to terminate a call (e.g., a voice call) from a device connected to network  110  and to communicate with the device utilizing both a CS network and a PS network in a secure manner. In this embodiment, the UE  102  has the capability of communicating with application server  106  using nothing but a PS network and has the capability of establishing a CS call with gateway  104 . 
         [0032]    As illustrated in  FIG. 4 , the process may begin with server  106  receiving from remote network  110  a message  402  (e.g., an initiation message) via a PS network. Message  402  may include the following information: (1) information identifying the called party (i.e., UE  102 ), (2) a voucher; and (3) information identifying the calling device or the user of the calling device. In response to receiving message  402 , server  106  transmit to UE  102  a message  404  (e.g., an initiation message), which contains the voucher. 
         [0033]    In response to message  404 , UE  102  transmits a call setup request  406  to gateway  104 . In response, gateway  104  transmits to application server  106  a message  408  (e.g., an initiation message), which message may include the following information: (1) information identifying UE  102  and/or the user of UE  102  and (2) information identifying the calling party. 
         [0034]    In response to receiving message  408 , server  106  determines that message  408  is correlated with message  402 . In response to this determination, server  106  transmits to network  110  a response message  410 , which is a response to message  402 . After server  106  transmits response message  410 , additional messages may be transmitted to complete the set-up of the session and bearers, as is well known in the art. 
         [0035]    After the session and bearers are set-up, UE  102  may begin transmitting fames of encrypted data (e.g., frames of encrypted voice data) to gateway  104  using the CS bearer  412 . Preferably, the frames include not only the encrypted data but also the encryption parameters needed by the called party to decrypt the encrypted data. Gateway  104 , as described above, receives the frames and, for each frame, extracts the encrypted data and encryption parameters from the frame, creates an SRTP packet that includes the encrypted data and encryption parameters, and transmit the SRTP packet to remote network  110  so that the data is ultimately received by the calling party. In this manner, end-to-end media security is established between UE  102  and remote network  110  even though UE  102  connects to network  101  using a CS bearer. 
         [0036]    Referring now to  FIG. 5 ,  FIG. 5  is a data flow diagram illustrating a process, according to an embodiment of the invention, for enabling UE  102  to originate a call (e.g., a voice call) with a device connected to network  110  and to communicate with the device utilizing both a CS network and a PS network in a secure manner. In this embodiment, the UE  102  does not have the capability of communicating with application server  106  using a PS network, but has the capability of establishing a CS call with gateway  104 . 
         [0037]    As illustrated in  FIG. 5 , the process may begin with UE  102  transmitting to KMS  204  a key request message  502 . Message  502  may be a short message service (SMS) message, an Unstructured Supplementary Service Data (USSD) message, or other like message. KMS  204 , in response to message  502 , transmits to UE  102  a message  504  that includes an encryption key. In response to message  504 , UE  102  transmits to gateway  104  a call setup request  506 . In response, gateway  104  transmits to application server  106  a message  508  (e.g., an initiation message), which message may include the following information: (1) information identifying UE  102  and/or the user of UE  102  and (2) information identifying the called party. Message  508  may also include information indicating that a secure session should be established. 
         [0038]    After receiving message  508 , server  106  determines whether the message includes information indicating that a secure session should be established. If server  106  determines that a secure session should be established, server  106  transmits to KMS  204  a request message  510  (e.g., a request for a voucher), which includes information identifying UE  102  and/or the user of UE  102 . In response to message  510 , KMS  204  transmits to server  106  a voucher  512  containing the key (e.g., an encrypted version of the key) that KMS  204  transmitted to UE  102  in message  504 . In response to receiving message  512 , server  106  transmits to network  110  a message  514  (e.g., an initiation message) that includes the voucher received from KMS  204 . 
         [0039]    After server  106  transmits message  514 , additional messages may be transmitted to complete the set-up of the session and bearers, as is well known in the art. After the session and bearers are set-up, UE  102  may begin transmitting fames of encrypted data (e.g., frames of voice data encrypted using the key received from KMS  204 ) to gateway  104  using the CS bearer  516 . Preferably, the frames include not only the encrypted data but also the encryption parameters needed by the called party to decrypt the encrypted data. Gateway  104 , as described above, receives the frames and, for each frame, extracts the encrypted data and encryption parameters from the frame, creates an SRTP packet that includes the encrypted data and encryption parameters, and transmits the SRTP packet to remote network  110  so that the data is ultimately received by the called party. In this manner, end-to-end media security is established between UE  102  and remote network  110  even though UE  102  connects to gateway  104  using CS bearer  512 . 
         [0040]    Referring now to  FIG. 6  is a data flow diagram illustrating a process, according to an embodiment of the invention, for enabling UE  102  to terminate a call (e.g., a voice call) from a device connected to network  110  and to communicate with the device utilizing both a CS network and a PS network in a secure manner. In this embodiment, the UE  102  does not have the capability of communicating with application server  106  using a PS network, but has the capability of establishing a CS call with gateway  104 . 
         [0041]    As illustrated in  FIG. 6 , the process may begin with server  106  receiving from remote network  110  a message  602  (e.g., an initiation message) via a PS network. Message  602  may include the following information: (1) information identifying the called party (i.e., UE  102 ), (2) a voucher; and (3) information identifying the calling device or the user of the calling device. In response to receiving message  602 , server  106  (a) transmits to gateway  604  a message  604  (e.g., an initiation message), which may include information indicating that a secure session should be established and (b) transmits to KMS  204  a message  608  containing the voucher and information identifying UE  102  and/or the user of UE  102  and information identifying the calling party. 
         [0042]    In response to message  604 , gateway  104  transmits to UE  102  a call setup request  606 . In response, UE  102  may transmit to KMS  204  (via SMS or USSD) a message  610  requesting the keys for the session. KMS  204 , in response to message  610  or in response to message  608 , transmits to UE  102  (via SMS or USSD) the requested keys and possibly also the voucher in message  612 . 
         [0043]    After transmitting to UE  102 , the call set-up message  606 , gateway  104  transmits to server  106  a response  614  to message  604 . In response to receiving message  614 , server  106  transmits to network  110  a response to message  602 . 
         [0044]    After server  106  transmits response message  614 , additional messages may be transmitted to complete the set-up of the session and bearers, as is well known in the art. After the session and bearers are set-up, UE  102  may begin transmitting fames of encrypted data (e.g., frames of voice data encrypted using a key included in the voucher received from KMS  204 ) to gateway  104  using the CS bearer  618 . Preferably, the frames include not only the encrypted data but also the encryption parameters needed by the called party to decrypt the encrypted data. Gateway  104 , as described above, receives the frames and, for each frame, extracts the encrypted data and encryption parameters from the frame, creates an SRTP packet that includes the encrypted data and encryption parameters, and transmits the SRTP packet to remote network  110  so that the data is ultimately received by the calling party. In this manner, end-to-end media security is established between UE  102  and remote network  110  even though UE  102  connects to gateway  104  using CS bearer  618 . 
         [0045]    Referring now to  FIG. 7 ,  FIG. 7  is a data flow diagram illustrating a process, according to an embodiment of the invention, for enabling UE  102  to originate a call (e.g., a voice call) with a device connected to network  110  and to communicate with the device utilizing both a CS network and a PS network in a secure manner. In this embodiment, the UE  102  has the capability of communicating with application server and has the capability of establishing a CS call with gateway  104 . 
         [0046]    As illustrated in  FIG. 7 , the process may begin with UE  102  transmitting to application server  106  a key request message  702 . Message  702  may include (1) information identifying UE  102  and/or the user of UE  102  and (2) information identifying the called party. In response to message  702 , server  106  transmits to KMS  204  a key request message  704 . In response to message  704 , KMS  204  transmits to server  106  a message  706  containing a key and a voucher. 
         [0047]    After receiving message  706 , server  106  (a) stores the voucher and associates the stored voucher with information identifying UE  102  and/or the user of UE  102  and (2) information identifying the called party and (b) transmits to UE  102  a message  708  in response to message  702 . Message  708  includes the key received from KMS  204 . After receiving message  708  from server  106 , UE  102  transmits a call setup request  710  to gateway  104 . In response, gateway  104  transmits message  712  (e.g., an initiation message) to application server  106 , which message indicates to server  106  that UE  102  has established (or is about to establish) a connection with gateway  104  using a CS bearer. Message  712  may include the following information: (1) information identifying UE  102  and/or the user of UE  102  and (2) information identifying the called party. 
         [0048]    In response to receiving message  712 , server  106  correlates the key request message  702  with message  712 . For example, server  106  uses the information included in message  712  (i.e., the information identifying UE  102  and/or the user of UE  102  and the information identifying the called party) to retrieve the voucher it had previously received from KMS  204 . After retrieving the voucher, server  106  transmits to remote network  110  a message  714  (e.g., an initiation message), which includes the retrieved voucher. 
         [0049]    After server  106  transmits message  714  additional messages may be transmitted to complete the set-up of the session and bearers, as is well known in the art. After the session and bearers are set-up, UE  102  may begin transmitting fames of encrypted data (e.g., frames of voice data encrypted using the key received from server  106 ) to gateway  104  using the CS bearer  716 . Preferably, the frames include not only the encrypted data but also the encryption parameters needed by the called party to decrypt the encrypted data. Gateway  104 , as described above, receives the frames and, for each frame, extracts the encrypted data and encryption parameters from the frame, creates an SRTP packet that includes the encrypted data and encryption parameters, and transmits the SRTP packet to remote network  110  so that the data is ultimately received by the calling party. In this manner, end-to-end media security is established between UE  102  and remote network  110  even though UE  102  connects to gateway  104  using CS bearer  716 . 
         [0050]    Referring now to  FIG. 8 ,  FIG. 8  is a data flow diagram illustrating a process, according to an embodiment of the invention, for enabling UE  102  to terminate a call (e.g., a voice call) from a device connected to network  110  and to communicate with the device utilizing both a CS network and a PS network in a secure manner. In this embodiment, the UE  102  has the capability of communicating with application server and has the capability of establishing a CS call with gateway  104 . 
         [0051]    As illustrated in  FIG. 8 , the process may begin with server  106  receiving from network  110  a message  802  (e.g., an initiation message). Message  802  may include (1) information identifying UE  102  and/or the user of UE  102 , (2) information identifying the calling party, and (3) a voucher that contains an encrypted key. In response to message  802 , server  106  transmits to KMS  204  a key request message  804 , which includes the voucher. In response to message  804 , KMS  204  transmits to server  106  a message  806  containing the key included in the voucher. 
         [0052]    After receiving message  806 , server  106  transmits to UE  102  a message  808 . Message  808  includes the key received from KMS  204  and indicates to UE  102  that a party is calling UE  102 . After receiving message  808  from server  106 , UE  102  transmits a call setup request  810  to gateway  104 . In response, gateway  104  transmits message  812  (e.g., an initiation message) to application server  106 , which message indicates to server  106  that UE  102  has established (or is about to establish) a connection with gateway  104  using a CS bearer. Message  812  may include the information that enables server  106  to correlate message  812  with message  802 . 
         [0053]    In response to receiving message  812 , server  106  correlates message  802  with message  812  and transmits to remote network  110  a response message  814 . After server  106  transmits response message  814 , additional messages may be transmitted to complete the set-up of the session and bearers, as is well known in the art. After the session and bearers are set-up, UE  102  may begin transmitting fames of encrypted data (e.g., frames of voice data encrypted using the key received from server  106 ) to gateway  104  using the CS bearer  816 . Preferably, the frames include not only the encrypted data but also the encryption parameters needed by the called party to decrypt the encrypted data. Gateway  104 , as described above, receives the frames and, for each frame, extracts the encrypted data and encryption parameters from the frame, creates an SRTP packet that includes the encrypted data and encryption parameters, and transmits the SRTP packet to remote network  110  so that the data is ultimately received by the calling party. In this manner, end-to-end media security is established between UE  102  and remote network  110  even though UE  102  connects to gateway  104  using CS bearer  816 . 
         [0054]    Referring now to  FIG. 9 ,  FIG. 9  is a flow chart illustrating a process performed by gateway  104 , according to some embodiments. The process may begin in step  902 , where gateway  104  establishes a CS connection with UE  102  (e.g., gateway  104  terminates a CS call initiated by UE  102  or originates a CS call to UE  102 ). In step  904 , gateway  104  receives from UE  102  via the CS connection a frame that includes encrypted encoded data intended for a remote device and one or more encryption parameters that are needed by the remote device to decrypt the encoded data. In step  906 , gateway  104  creates a protocol data unit (e.g., an SRTP protocol data unit) that includes the encrypted encoded data and the encryption parameter(s). For example, the encrypted encoded data may be placed in a payload portion of the SRTP packet and the encryption parameter(s) may be placed in a header portion of the packet. In step  908 , gateway  104  transmits the packet so that it will be received by the remote device. In this manner, gateway  104  functions to map secure media from CS domain to the SRTP domain, thereby enabling end-to-end security even though UE  102  access network  101  using the CS technology and not PS technology. 
         [0055]    Referring now to  FIG. 10 ,  FIG. 10  is a flow chart illustrating another process performed by gateway  104 , according to some embodiments. The process may begin in step  1002 , where gateway  104  establishes a CS connection with UE  102 . In step  1004 , gateway  104  receives from a remote device an SRTP packet containing encrypted data and one or more encryption parameter(s) (e.g., a sequence number). The encrypted data is stored in a payload portion of the packet and the encryption parameter is stored in a header of the packet. In step  1006 , gateway  104  transmits to UE  102  via the CS connection a frame containing the encrypted data and encryption parameters, where the encrypted data and encryption parameter are included in the same payload portion of the packet. In some embodiments, the payload portion of the frame consists of (or consists essentially of) the encrypted data and encryption parameters. 
         [0056]    Referring now to  FIG. 11 ,  FIG. 11  is a flow chart illustrating a process performed by UE  102 , according to some embodiments. The process may begin in step  1102 , where UE  102  transmits a key request. For example, in step  1102 , UE  102  may send to KMS  204  an SMS/USSD message that includes a request for a key or UE  102  may send to server  106 , via a CS network, a message that includes a request for a key. In step  1104 , UE  102  receives a key in response to the key request. For example, in step  1104 , UE  102  may receive the key from the KMS via an SMS/USSD message or may receive the key, via a CS network, from server  106 . In step  1106 , UE  102 , establishes a CS connection with gateway  104  (e.g., UE  102  transmit a CS call set up message to MSC server  212 ). In step  1108 , UE  102  obtains or generates media (e.g., voice data) to be transmitted securely to a remote device via the CS connection. In step  1110 , UE  102  encodes the media and then encrypts the encoded media using a key received in step  1104 . In step  1112 , UE  102  creates a secure data frame that includes the encrypted encoded data and one or more encryption parameters (e.g., a counter value and an integrity protection tag). In step  1114 , UE  102  transmits the secure data frame to gateway  104  using the CS connection. In step  1116 , UE  102  receives a frame transmitted from gateway  104  using the CS connection, which frame has a payload portion that includes encrypted encoded data and one or more encryption parameters. In step  1118 , UE  102  uses a key received in step  1104  and the encryption parameters included in the frame to decrypt the encrypted data included in the frame, decodes the encoded data to produce decoded data, and then outputs the decoded data (e.g., in the case the data includes an audio signal, the data may be provided to a speaker included in the UE to produce a sound wave corresponding to the audio signal and in the case the data includes a video signal, the data may be provided to a driver that drives a display of the UE so that the video can be reproduced on the UE&#39;s display). 
         [0057]    Referring now to  FIG. 12 ,  FIG. 12  is a functional block diagram of gateway  104  according to some embodiments of the invention. As shown, gateway  104  may comprise a data processing system  1202  (e.g., one or more microprocessors), a data storage system  1206  (e.g., one or more non-volatile storage devices) and computer software  1208  stored on the storage system  1206 . Configuration parameters  1210  may also be stored in storage system  1206 . Gateway  102  also may comprise transmit/receive (Tx/Rx) circuitry  1204  for transmitting frames to and receiving frames from UE  102  and transmit/receive (Tx/Rx) circuitry  1205  for transmitting packets to and receiving packets from network  110 . 
         [0058]    Software  1208  is configured such that when processor  1202  executes software  1208 , gateway  104  performs steps described herein. For example, software  1208  may include: ( 1 ) a connection establishing module for establishing a circuit switched connection with a communication device (e.g., UE  102 ); a receiving module for receiving from the communication device via the circuit switched connection a frame including encrypted encoded data intended for a remote communication device and an encryption parameter that is required by the remote communicate device to decrypt the encrypted encoded data; a protocol data unit creating module for creating a protocol data unit that includes the encoded data and the encryption parameter; and a transmitting module for transmitting, via a packet switched network, the protocol data unit so that it will be received by the remote communication device. 
         [0059]    Referring now to  FIG. 13 ,  FIG. 13  is a functional block diagram of UE  102  according to some embodiments. In the embodiment illustrated, UE  102  includes a data generator  1301 , a codec  1302 , a security module  1304  and a transmit/receive circuit  1308  for transmitting and receiving data. Data generator  1301  may include a microphone for converting sound waves (e.g., speech) to an electrical signal, an amplifier for amplifying the signal, and an analog to digital converter for converting the continuous electrical signal to a digital signal. The data generated by generator  1301  is input into codec  1302  (e.g., a speech codec such as the adaptive multi-rate (AMR) codec) that produces encoded data  1303 . Encoded data  1303  is an input to a security module  1304 . Security module  1304  is configured to encrypt the encoded data using an encryption key and is configured to form a fame payload  1306  that contains one or more encryption parameters and the encrypted encoded data. In the embodiment illustrated, the frame payload  1306  of the frame includes only the encrypted data and the encryption parameters. Payload  1306  is then obtained by transmitter  1308 , which is configured to include payload  1306  in a frame and transmit the frame using a CS connection. 
         [0060]    While security module  1304  is shown as being separate and distinct from codec  1302 , this is not a requirement. It is contemplated that codec  1302  can be configured to perform not only normal encoding operations, but also the functions of security module  1304 . 
         [0061]    Codec  1302  and/or security module  1304  may be implemented in software and/or hardware. Accordingly, UE  102  may include (i) a data storage system  1406  for storing encryption keys, encryption parameters  1410 , and software  1408  for implementing codec  1302  and/or module  1304  and (ii) a processor  1402  for executing the software (see  FIG. 14 ). UE  102  may also have an antenna  1420 . 
         [0062]    Referring now to  FIG. 15 ,  FIG. 15  is a functional block diagram of application server  226  according to some embodiments of the invention. As shown, server  226  may comprise a data processing system  1502  (e.g., one or more microprocessors), a data storage system  1506  (e.g., one or more non-volatile storage devices) and computer software  1508  stored on the storage system  1506 . Configuration parameters  1510  may also be stored in storage system  1506 . Server also may comprise transmit/receive (Tx/Rx) circuitry  1504  for communicating with other servers and clients. 
         [0063]    Software  1508  is configured such that when processor  1502  executes software  1508 , server  226  performs steps described herein. For example, software  1508  may include: (1) an initiation message receiving module for receiving an initiation message (e.g., a SIP invite message or other initiation message) transmitted from UE, (2) a voucher storing module for storing a voucher included in the initiation message; (3) a voucher retrieving module for retrieving the voucher in response to receiving from gateway  104  an initiation message that correlates with an earlier initiation message received from UE  102 ; (4) an initiation creating and transmitting module for creating and transmitting an initiation message to network  110  in response to receiving from gateway  104  the initiation message that correlates with the earlier initiation message received from UE  102 ; (5) an initiation message receiving module for receiving an initiation message transmitted from network  110  which initiation message identifies UE  102  as a called party; (6) an initiation transmitting module for transmitting an initiation message to UE  102  in response to receiving the initiation message from network  110 ; (7) an initiation response creating and transmitting module for creating and transmitting an initiation response message to network  110  in response to receiving from gateway  104  an initiation message that correlates with the earlier initiation message received from network  110 ; (8) a voucher requesting module for transmitting a voucher request to KMS  204  in response to receiving an initiation message from gateway  104 ; and (9) an initiation message transmitting module for transmitting to network  110  an initiation message containing a voucher received from KMS  204 . 
         [0064]    While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. 
         [0065]    Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, and the order of the steps may be re-arranged.