Patent Publication Number: US-2011064219-A1

Title: Iptv security in a communication network

Description:
TECHNICAL FIELD 
     The invention relates to the field of IPTV Security in a Communication Network, and in particular to the field of setting up a secure IPTV session. 
     BACKGROUND 
     TV services broadcast over an IP network are referred to as IPTV. IPTV is typically broadcast using a broadband access network, in which channels are transmitted over a broadband network from a super head-end down to an end-user&#39;s set top box (STB). An example of an IPTV service is Broadcast TV, in which the most common IPTV channels, as well as additional channels with low penetration, are transmitted over a broadband network from a super head-end down to an end-user&#39;s set top box (STB). In order to minimize the bandwidth required for these transmissions it is desirable to use multicast techniques through the network. 
     Similarly, in mobile networks it is desirable to use broadcast/multicast delivery of Mobile TV (MTV). Multimedia Broadcast Multicast Service (MBMS) and Digital Video Broadcasting—Handheld (DVB-H) are examples of MTV broadcast technologies. A mobile telephone (such as User Equipment, UE) having an MTV client can be thought of as an equivalent to a STB in MTV implementations that receive content from a super head-end. 
     In a typical arrangement the content is delivered by a Media Delivery Function (MDF) which is a content delivery server controlled by an IP Multimedia Subsystem (IMS) Application Server (AS) for mobile TV (using a Multimedia Broadcast Multicast Service, MBMS, bearer or a Packet Switched Service, PSS, bearer) or an IMS AS for IPTV (using unicast or multicast delivery). 
     The following description refers to a UE for simplicity, although it will be appreciated that it equally applies where IPTV is received at another type of IPTV receiver such as a STB. Referring to  FIG. 1  herein, and before communication between the MDF and the UE  1  can start, the UE  1  and the content delivery control function (a Network Application Function, NAF  2 , which may be a MTV AS or IPTV AS) must participate in a Generic Bootstrapping Authentication (GBA) procedure (shown in steps S 1  to S 8 ) to establish GBA keys (Ks_naf from which MUK and MRK are derived. Ks_naf is described below) for authentication and service protection. 
     The result of a successful GBA procedure is the establishment of a bootstrapping transaction identifier (BTID), generated by a Bootstrapping Server Function (BSF)  3 , and a shared key, Ks_Naf that is locally generated by a USIM/SIM  4  in the UE  1  during bootstrapping (S 5 ). BTID is pulled by the UE  1  from the BSF  3  by using HTTP, shown in step S 4  of  FIG. 1 . The Ks_Naf and B_TID are stored as a part of the UE context in a secured area in the UE (S 4 ). Ks_Naf is available for later use to derive application specific keys (MUK, MRK) and to encrypt Long Term keys (MSK) when delivered to the UE  1 . 
     The BSF  3  retrieves a content key (Ck) and an integrity key (Ik), which are sent as part of an Authentication Vector from a Home Subscriber Server (HSS)  5  during the GBA procedure. Ks_naf is calculated by the BSF  3  by concatenating Ck and Ik (and a similar operation is performed by the USIM/ISIM  4  in the UE  1 ) and is stored at the BSF  3  for future reference by the UE  1 . 
     In order to retrieve data delivered using HTTP from an MTV AS/IPTV AS/BM-SC (NAF), the UE must first be authenticated by the MTV AS. Examples of such data include an Electronic Programme Guide (EPG) or an Electronic Service Guide (ESG). To authenticate the UE, the UE signals the BTID and Ks_naf in an HTTP request (HTTP digest authentication as defined in RFC 2617) sent from the UE  1  to the MTV AS. 
     When a UE  1  is involved in an HTTP signalling procedure where GBA is used for authentication purposes, the UE  1  interacts with a functional entity called the Authentication Proxy (AP), not shown in  FIG. 1 . The AP knows the BTID that represents the UE  1  during this process and the Ks_naf that corresponds to the BTID. 
     Referring to  FIG. 2 , the procedure by which a node such as NAF retrieves long term keys is illustrated. MTV signalling procedures require the delivery of long-term keys to protect the IPTV content that is to be sent to the UE  1 . During these signalling procedures, the UE  1  interacts with the MTV AS, which is not aware of the BTID used in earlier signalling procedures. However, the MTV AS requires Ks_naf to use it for encryption of the long-term content keys as part of the content access procedures. However, the MTV-AS does not have access to the Ks_naf, which is stored at the BSF  2 , and so this is currently not possible. 
     SUMMARY 
     The inventors have realised that there is a problem in authenticating a User Equipment or other IPTV receiving device before starting a session. A method is proposed for providing a Mobile TV Application Server with a BTID associated with the UE and allowing the MTV AS to act as a Network Application Function in the GBA architecture. 
     According to a first aspect of the invention, there is provided a method of setting up a secure IPTV session. An Application Server (AS) receives an invite message from an IPTV receiving node such as a mobile telephone or a Set Top Box (STB) to set up an IPTV session. The invite message includes a Bootstrapping Transaction Identifier (BTID) associated with the receiving node. The AS sends an authentication request to a Service Access Protection Server, the authentication request including the BTID. The AS then receives from the Service Access Protection Server an authentication response, which includes a long term key associated with the IPTV receiving node, the long term key having been previously provided to the IPTV receiving node. A request is sent to an IPTV content provider node, the request identifying the IPTV receiving node. The AS then encrypts a media encryption key that is used to encrypt the media sent by the IPTV content provider, using the received long term key. An invite response is then sent to the IPTV receiving node, the response including the encrypted media encryption key. The invention provides the AS with a long term key which can be used to encrypt the media encryption key. 
     As an option, the invite message is a Session Initiation Protocol (SIP) Invite message, and the BTID is included in a Proxy-Authorization header. The Service Access Protection Server is optionally a Bootstrapping Server Function (BSF). The invention is particular suitable for use in the filed of Mobile IPTV, and so as another option, the IPTV session is a Mobile IPTV session, and the AS is a Mobile IPTV AS. 
     Optionally, the IPTV session is either a linear IPTV broadcast, a linear IPTV unicast, or a Video on Demand unicast. 
     Optionally, if the IPTV session is a unicast than the media encryption key is a content key, and if the IPTV session is a broadcast then the media encryption key is a group key. 
     In an optional embodiment, the media encryption key is sent from the AS to the IPTV content provider node, and in an alternative embodiment the media encryption key is received at the AS from the IPTV content provider node. The media encryption key may be sent from the AS to the IPTV content provider node for subsequent use by the IPTV content provider node in encrypting media send to the IPTV receiving node. Alternatively, where the media encryption key is generated by the IPTV content provider node, it provides it to the AS to allow the AS to encrypt it using the long term key and send it to the IPTV receiving node. Where the media encryption key is a content key, the AS optionally sends it encrypted to the IPTV content provider node. 
     According to a second aspect of the invention, there is provided an AS. The AS comprises a first receiver for receiving an invite message from an IPTV receiving node to set up an IPTV session. The invite message includes a BTID associated with the IPTV receiving node. A first transmitter is provided for sending an authentication request to a Service Access Protection Server, the authentication request including the BTID. A second receiver is provided for receiving from the Service Access Protection Server an authentication response, the authentication response including a long term key associated with the IPTV receiving node. Note that the long term key has already been provided to the IPTV receiving node. A second transmitter is used for sending a request to an IPTV content provider node, the request identifying the IPTV receiving node. A processor is provided for encrypting a media encryption key using the received long term key. The media encryption key is the key used by the IPTV content provider node for encrypting IPTV content sent to the IPTV receiver node. A third transmitter is provided for sending an invite response message to the IPTV receiving node, the invite response message including the encrypted media encryption key. This allows the IPTV receiving node to access the media encryption key for decrypting media subsequently sent to it from the IPTV content provider node. 
     The AS optionally further comprises a third receiver for receiving a message from the IPTV content provider node that includes the media encryption key, in a scenario where the IPTV content provider node generates the media encryption key. Alternatively, the second transmitter is arranged to send the media encryption key in the request to the IPTV content provider node for subsequent use by the IPTV content provider node in encrypting media sent to the IPTV receiving node. 
     As an option, the invite message is a SIP Invite message, and the BTID is included in a Proxy-Authorization header. The AS is optionally a Mobile IPTV AS and the IPTV session is a Mobile IPTV session. The IPTV session is optionally either a linear IPTV broadcast, a linear IPTV unicast, or a Video on Demand unicast. 
     According to a third aspect of the invention, there is provided an IPTV receiving node that comprises a memory for storing a BTID and a long term key associated with the IPTV receiving node. A transmitter is provided for sending to an AS an invite message for initiating an IPTV session, the invite message including the BTID. A first receiver is provided for receiving from the AS a response message, the response message including a media encryption key encrypted using the long term key. This can be decrypted using a first processor and the stored long term key. A second receiver is provided for receiving IPTV media content sent from an IPTV content provider node, the IPTV media content having been encrypted using the media encryption key. A second processor is then used for decrypting the IPTV media content using the decrypted media encryption key. This allows a viewer to view the IPTV media. 
     As an option, the IPTV receiving node is User Equipment. As a further option, the invite message is a SIP Invite message, and the BTID is included in a Proxy-Authorization header. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates schematically in a block diagram a Generic Bootstrapping Authentication architecture and signalling; 
         FIG. 2  is a signalling diagram showing the signalling required for a NAF to obtain a long term key; 
         FIG. 3  is a signalling diagram showing the signalling required to set up a broadcast IPTV channel with an MTV client according to an embodiment of the invention; 
         FIG. 4  is a signalling diagram showing the signalling required to set up a Video on Demand unicast session according to an embodiment of the invention; 
         FIG. 5  is a signalling diagram showing the signalling required to set up a linear TV unicast session according to an embodiment of the invention; 
         FIG. 6  illustrates schematically in a block diagram an Application Server according to an embodiment of the invention; and 
         FIG. 7  illustrates schematically in a block diagram in IPTV receiving node according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     When a terminal such as a UE (or any other receiving node for receiving IPTV) wishes to access an IPTV channel (which may be broadcast, unicast, multicast, Video on Demand or any other type of deliver that requires media content protection), it sends a SIP Invite message. In an IMS network, the SIP Invite message is sent to a Proxy-Call Session Control Function (P-CSCF). The SIP Invite message is routed to an Application Server (AS) such as a Mobile TV Application Server (MTV AS). According to the invention, the UE includes BTID in a Proxy-Authorization-Header in the SIP Invite message. The BTID allows the MTV AS to retrieve the Ks_naf from the BSF, and the MTV AS can then use the Ks_naf to encrypt long-term content keys when they are delivered to the UE. 
     Referring now to  FIG. 3 , there is shown signalling to set up a linear TV broadcast with an MTV client  6  according to a first specific embodiment of the invention. The broadcast in this example is in the context of an MTV environment, and so the MTV client  6  is part of a User Equipment  1 . It will be appreciated that the following signalling may be modified to set up a linear TV broadcast with a different IPTV receiving node, such as a STB. The following numbering corresponds to the numbering in  FIG. 2 . 
     S 9 . The MTV client  6  sends a SIP Invite message to a P-CSCF  7 . The SIP Invite message includes an indication that a Linear broadcast IPTV delivery is required. The BTID, which has previously been provided to the UE in a GBA bootstrapping procedure, is included in SIP message Proxy-Authorization Header.
 
S 10 . The SIP Invite is forwarded from the P-CSCF  7  to a Serving-Call Session Control Function (S-CSCF)  8  in the IMS network.
 
S 11 . The S-CSCF  8  forwards the SIP invite to the MTV AS  9 .
 
S 12 - 13 . The MTV AS  9  uses the received BTID to authenticate the MTV client  6  with the BSF  3 , and to retrieve Ks_naf and Ks_naf specific attributes from the BSF  3 . Such attributes include Ks_naf life time validity period, a timestamp and so on.
 
S 14 - 15 . The MTV AS  9 , provides a MSK (MBMS Session Key) and a MTK (MBMS Traffic Key) for encryption in a BM-SC  10 , or MTK MSK encrypted together with MTK or (MSK) and MBMS Traffic Keys (MTK). The BM-SC  10  is responsible for providing the linear broadcast TV to the MTV client  6  and distribution of updated traffic keys to clients accessing the MBMS session.
 
S 16 . The MTV AS  9  encrypts the session keys using the retrieved Ks_naf.
 
S 16   a . A SIP  200  OK message is sent from the MTV AS  9  to the S-CSCF  8 , the  200  OK message including the session keys MSK encrypted using the retrieved Ks_naf.
 
S 17 . The SIP  200  OK message is sent from the S-CSCF  8  to the P-CSCF  7 .
 
S 18 - 19 . IMS Policy and Charging Control (PCC) functionality is used, although the PCRF  11  does not perform any policy enforcement or resource reservation or assignment of a bearer (defined by QoS requirements) for the broadcast or multicast IPTV delivery.
 
S 20 . The SIP  200  OK message is sent from the P-CSCF  7  to the MTV client  6 , providing the MTV client with the session keys MSK.
 
S 21 . Encrypted media content is delivered from the BM-SC  10  to the MTV client  6 . The MTV client  6  uses the received MSK to decrypt the content keys that are sent as part of the media content, which allows the MTV client  6  to decrypt the media content. The end user can then view the media content.
 
     It should be noted that content keys may subsequently be refreshed. This is performed by including an MSK encrypted traffic key MTK in the media data sent to the MTV client. 
     The first specific embodiment of the invention allows the MTV AS  6  to receive the BTID associated with a UE and the key material so that the MTV AS can act as a NAF in the GBA architecture. The MTV AS is therefore provided with the BTID which is subsequently used to retrieve Ks_naf from the BSF  3 , which is in turn used to encrypt session keys MSK for use by the MTV client  6 . 
     Turning now to  FIG. 4 , there is illustrated signalling to set up a Video on Demand (VoD) unicast according to a second specific embodiment of the invention. The following numbering corresponds to the numbering in  FIG. 3 : 
     S 22 . The MTV client  6  sends a SIP Invite message to a P-CSCF  7 . The SIP Invite message includes an indication that VoD IPTV delivery is required. The BTID, which has previously been provided to the UE in a GBA bootstrapping procedure, is included in SIP message Proxy-Authorization Header.
 
S 23 . The SIP Invite is forwarded from the P-CSCF  7  to a Serving-Call Session Control Function (S-CSCF)  8  in the IMS network.
 
S 24 . The S-CSCF  8  forwards the SIP invite to the MTV AS  9 .
 
S 25 - 26 . The MTV AS  9  uses the received BTID to authenticate the MTV client  6  with the BSF  3 , and to retrieve Ks_naf and Ks_naf specific attributes from the BSF  3 . Such attributes include Ks_naf life time validity period, a timestamp and so on.
 
S 27 - 28 . The MTV AS  9  and a Content Server  12  for providing the VoD media to the MTV client  6  negotiate content keys.
 
S 29 -S 32 . The MTV AS  9  and the Content Server  12  configures the Content Server  12  regarding content delivery over a RTP/UDP connection by invocation of an RTSP setup procedure for audio and video streams between the Content Server  12  and the terminal.
 
S 33 . The MTV AS  9  encrypts the content keys using the retrieved Ks_naf.
 
S 33   a . A SIP  200  OK message is sent from the MTV AS  9  to the S-CSCF  8 , the  200  OK message including the content keys encrypted using the retrieved Ks_naf.
 
S 34 . The SIP  200  OK message is sent from the S-CSCF  8  to the P-CSCF  7 .
 
S 35 - 36 . IMS Policy and Charging Control (PCC) functionality performs policy control and enforcement and resource reservation. Based on PCC rules the PCRF  11  instructs the GGSN to activate a secondary PDP context for the bearer to carry the VoD stream for the unicast IPTV delivery.
 
S 37 . The SIP  200  OK message is sent from the P-CSCF  7  to the MTV client  6 , providing the MTV client with the content keys, which the MTV client  6  can decrypt using Ks_naf.
 
S 38 -S 41 . IMS PCC functionality is used to assign an appropriate bearer (QoS defined) for the unicast IPTV delivery. These steps show shows a network controlled bearer establishment/PDP context, but a UE controlled bearer establishment would be equally applicable for the invention.
 
S 42 . The MTV client  6  requests the VoD content from the Content Server  12 .
 
S 43 . The Content Server replies with a  200  OK message.
 
S 44 . Encrypted VoD media content is delivered from the Content Server  12  to the MTV client  6 . The MTV client  6  uses the decrypted content keys to decrypt the media content. The end user can then view the media content.
 
     Turning now to  FIG. 6 , there is illustrated signalling to set up a linear TV unicast according to a third specific embodiment of the invention. The following numbering corresponds to the numbering in  FIG. 4 : 
     S 45 . The MTV client  6  sends a SIP Invite message to a P-CSCF  7 . The SIP Invite message includes an indication that unicast linear delivery is required. The BTID, which has previously been provided to the UE in a GBA bootstrapping procedure, is included in SIP message Proxy-Authorization Header.
 
S 46 . The SIP Invite is forwarded from the P-CSCF  7  to a Serving-Call Session Control Function (S-CSCF)  8  in the IMS network.
 
S 47 . The S-CSCF  8  forwards the SIP invite to the MTV AS  9 .
 
S 48 - 49 . The MTV AS  9  uses the received BTID to authenticate the MTV client  6  with the BSF  3 , and to retrieve Ks_naf and Ks_naf specific attributes, such as a Ks_naf lifetime validity period and a timestamp from the BSF  3 .
 
S 50 - 51 . The MTV AS  9  and a Content Server  13  for providing the VoD media to the MTV client  6  negotiate content keys.
 
S 52 -S 55 . The MTV AS  9  and the Content Server  13  negotiate RTSP setup for audio and video.
 
S 56 . The MTV AS  9  encrypts the session keys using the retrieved Ks_naf.
 
S 56   a . A SIP  200  OK message is sent from the MTV AS  9  to the S-CSCF  8 , the  200  OK message including the content keys encrypted using the retrieved Ks_naf.
 
S 57 . The SIP  200  OK message is sent from the S-CSCF  8  to the P-CSCF  7 .
 
S 58 - 59 . IMS Policy and Charging Control (PCC) functionality performs policy control and enforcement and resource reservation. Based on PCC rules the PCRF  11  instructs GGSN to activate secondary PDP context for the bearer to carry the unicast stream for the IPTV delivery.
 
S 60 . The SIP  200  OK message is sent from the P-CSCF  7  to the MTV client  6 , providing the MTV client with the content keys, which the MTV client  6  can decrypt using Ks_naf.
 
S 61 -S 64 . IMS PCC functionality is used to assign an appropriate bearer (QoS defined) for the unicast IPTV delivery. These steps show shows a network controlled bearer establishment/PDP context, but a UE controlled bearer establishment would be equally applicable for the invention.
 
S 65 . The MTV client  6  requests the linear unicast content from the Content Server  13 .
 
S 66 . The Content Server  13  replies with a  200  OK message.
 
S 67 . Encrypted unicast linear IPTV media is delivered from the Content Server  13  to the MTV client  6 . The MTV client  6  uses the decrypted content keys to decrypt the media content. The end user can then view the media content.
 
     Referring now to  FIG. 6 , there is illustrated schematically an Application Server according to an embodiment of the invention. The Application Server is an MTV AS  9 , as described above. The MTV AS  6  is provided with a first receiver  14  for receiving the SIP Invite message from the MTV client  6 . As described above, the SIP Invite message includes the BTID in the Proxy-Authorization header. A first transmitter  15  is provided for sending an authentication request to the BSF  3 , and a second receiver  16  is provided for receiving a response form the BSF  3 . The response includes Ks_naf. A second transmitter  17  is provided for sending a request, which may include a media encryption key such as an MSK+MTK, or an (MSK encrypted MTK)+MTK to a BM-SC  10  or a Content Server  13 , and a third receiver  18  is provided for receiving a response, which may include a media encryption key from the IP television content provider node. A processor  19  is used for encrypting the media encryption key using the received Ks_naf, and a third transmitter  20  is provided for sending a SIP  200  OK to the MTV client  6 , the  200  OK including the Ks_naf encrypted media encryption key. Of course, the transmitters may all be embodied in a single transmitter, and the receivers may all be embodied in a single receiver. A memory  21  is also provided for storing information such as the received BTID and Ks_naf. 
       FIG. 7  is in IPTV receiving node according to an embodiment of the invention. The IPTV receiving node, in an MTV network as described above, is a UE comprising an MTV client  6 . The UE  22  is provided with a memory  23  for storing the BTID and Ks_naf provided in the GBA procedures. The memory also stores information associated with Ks_naf, such as the Ks_naf lifetime validity period. A transmitter  24  is provided for sending a SIP Invite to the MTV AS  9 , the SIP Invite including the BTID in a Proxy-Authorization header. A first receiver  25  is provided for receiving a SIP  200  OK from the MTV AS  9 , the SIP  200  OK including media encryption keys encrypted using Ks_naf. A first processor  26  is provided for decrypting the media encryption keys using Ks_naf retrieved from the memory  23 . A second receiver  27  is provided for subsequently receiving IPTV media content sent from a content server  13  or BM-SC  10 , the content being encrypted using the media encryption keys. A second processor  28  is provided for decrypting the IPTV media content using the decrypted media encryption key. Of course, the two processors may be embodied in a single processor, and the two receivers may be embodied in a single receiver. 
     The invention ensures that an Application Server such as an MTV AS receives the BTID during content access procedures. This allows the MTV AS to retrieve the Ks_naf key from the BSF, and reduces signalling required as the NAF does not need to be involved. Ks_naf is used by the MTV AS to encrypt service keys (MSK), which are part of the content protection. This provides a single common IMS procedure to retrieve the Ks_naf and store it at the MTV AS/IPTV for service and content protection, independent of type of service access. A single SIP session is required to set up the service and to distribute content keys derived from Ks_naf to the MTV client. Furthermore, the BTID provided to the client in the GBA procedure can be re-used for several types of signalling, such as HTTP And SIP signalling. 
     It will be appreciated by the person of skill in the art that various modifications may be made to the above-described embodiments without departing from the scope of the present invention. For example, whilst the above description discusses the invention in the context of a Mobile TV network, it will be appreciated that the invention also applies to fixed access IPTV networks. The invention may find use in services such as multicast/broadcast conferencing services in Push to Talk over Cellular (PoC) networks. 
     The following abbreviations have been used in this specification: 
     BM-SC: Broadcast Multicast Service Centre 
     BSF: Bootstrapping Server Function 
     BTID: Bootstrapping Transaction ID 
     CK: Content Key 
     EPG: Electronic Programme Guide 
     ESG: Electronic Service Guide 
     GAA: Generic Authentication Architecture 
     GBA: Generic Bootstrapping Authentication 
     HSS: Home Subscriber Server 
     HTTP: Hypertext Transfer Protocol 
     IK: Integrity Key 
     IPTV AS: IPTV Application Server 
     Ks_naf: Long-term key generated by BSF as a result of the GBA procedure
 
Linear BC TV: Tv channel distributed over Broadcast bearer
 
     MBMS: Multimedia Broadcast Multicast Service 
     MCF: Media Control Function 
     MDF: Media Delivery Function 
     MSK: MBMS Session Key 
     MTK: MBMS Traffic Key 
     MTV AS: Mobile TV Application Server 
     MUK: MBMS User Key 
     NAF: Network Application Function 
     SRTP: Secure Real Time Transport Protocol 
     STB: Set Top Box 
     UE: User Equipment 
     URI: Uniform Resource Identifier 
     VoD: Video on Demand