GB2387090A

GB2387090A - A dvb receiver with at least two separate receivers, one of which decrypts encrypted keys which it sends to the others to use them to decrypt programmes

Info

Publication number: GB2387090A
Application number: GB0207498A
Authority: GB
Inventors: Antti Koskela; Kyoesti Koivisto; Antti T Koskela
Original assignee: Nokia Oyj; Nokia Inc
Current assignee: Nokia Oyj; Nokia Inc
Priority date: 2002-03-28
Filing date: 2002-03-28
Publication date: 2003-10-01
Also published as: GB0207498D0

Abstract

The digital video broadcast receiver system comprises a first receiver which receives transmitted data which includes content and control data (an encrypted key which, if decrypted, can be used to decrypt the content data), it then extracts the encrypted key and transmits it to a second receiver (which includes a security module) which is able to decrypt the encrypted key and transmit it back to the first receiver, which in turn uses the decrypted key to decrypt the content data. The receiver system may comprise multiple receivers including a master receiver 2 and a plurality of slave receivers 3, 4 such that the master receiver 2 is able to decrypt control information for the slave receivers 3, 4. The security module may be a smart card.

Description

- 1 - 2387090

Receiver System for Distributing Encryption Control Information Field of the Invention

The present invention relates generally to the field of broadcast and reception,

s particularly but not exclusively to a method of distributing decryption information for decrypting encrypted DVB transmissions at a plurality of receivers, using a single smart card.

Background

10 Conditional access systems are well known and widely used in conjunction with currently available pay television systems, which operate according to standards such as the digital video broadcasting (DVB) standard. At present, such systems are based on the transmission of programmes scrambled with control words which are received by subscribers having a set-top box and a smart card for each subscription 15 package. The smart card for a subscription package from a particular service provider allows the scrambled programmes within the package to be descrambled and viewed. The broadcast stream further contains entitlement management messages and entitlement control messages, which are necessary for the smart card to descramble the broadcast. The terms scrambled and encrypted are used 20 interchangeably in this application.

The conventional model for access to scrambled terrestrial DVB transmissions is that every receiver must have its own conditional access system, including a smart card for descrambling the broadcast service, even when all the receivers are located 2s in close proxnity, for example within a single household.

At present, DVB receivers still form a relatively small proportion of the total number of television receivers. In general terms, the majority of television channels are broadcast in unencrypted form, so that a significant number of households have 30 several TV receivers and/or video recorders that can all be operated independently.

Where a licensing scheme operates, a single licence is generally required per household. If DVB uptake by the population as a whole is to be encouraged, the same level of access to scrambled DVB transmissions needs to be provided. While 3gg25

- 2 all analog equipment requires a new digital receiver to convert it to receiving DVB transmissions, it is highly undesirable for the DVB industry as a whole to force households to buy not only a new receiver, but also a new smart card to replace every existing analog device, simply to maintain the same level of access as those s households currently enjoy.

The present invention aims to provide a way of accessing scrambled DVB transmissions from different receivers using a single set of conditional access resources, for example, a single smart card.

Summary of the Invention

To overcome limitations in the prior art described above and to overcome other

limitations that will be apparent upon reading and understanding the present specification, there is provided, according to the present invention, a method of

15 decrypting an encrypted communication, the communication including encrypted content data and encrypted control information, the control information being capable, once decrypted, of decrypting the encrypted content data, and the encrypted control information being capable of being decrypted by a security module, the method including the steps of receiving the encrypted communication 20 at a first receiver, extracting the encrypted control information from the received communication, transmitting the encrypted control information to a second receiver which includes the security module, receiving the decrypted control information from the second receiver and using said decrypted control information to decrypt the encrypted content data.

2s The security module at the second receiver may be responsible for decrypting the received encrypted control information and can comprise a smart card.

The use of one receiver to decrypt control information from a plurality of other 30 receivers permits a system in which only one receiver within a household, referred to as a master receiver, needs to be equipped with smart card functionality. The other receivers merely need to be equipped to communicate with the master

- 3 - receiver for the purpose of sending encrypted control information to the master receiver and receiving the decrypted control information back.

By transmitting sufficient information to the master receiver to identify the service s for which the control information is required, the master receiver can supply the control information appropriate to the required service to each of a number of other receivers, referred to as slave receivers.

Each of the slave receivers can provide their identity to the master receiver, so that 10 the master receiver sends the decrypted control information to the correct destination, over, for example, a local area network. In addition, the master receiver can provide its identity to the slave receiver making a request for control information, to permit faster future access by the slave receiver.

15 According to the present invention, there is further provided a receiver system for use in decrypting digital transmissions, comprising a plurality of receivers interconnected in a master-slave arrangement, the master receiver being configured to decrypt control information received by each of the slave receivers, on behalf of said slave receivers.

The slave receivers can be configured to communicate only with the master receiver or to communicate with all other available receivers to determine the identity of the master receiver. This latter mode is essentially a 'plug and play' mode, so that no prior configuration is required. Excessive communication between slave receivers 25 can be avoided by storing the identity of the master receiver after each service request by a slave receiver, so that this identity can be communicated between slave receivers during a slave-slave communication.

According to the invention, there is yet further provided a receiver for receiving and 30 decrypting an encrypted transmission, the receiver being svitchable between a master configuration in which it uses a security subsystem within the receiver to decrypt the transmission and a slave configuration in which it communicates with a security sub-system within another receiver to decrypt the received transmission.

The receiver may be configured to switch automatically between said master and slave configurations in response to the presence or absence of the security sub-

system, such as a smart card.

5 According to the invention, there is still further provided a computer program which, when executed on a processor in a communications receiver, is configured to perform the steps of determining the presence or absence of a security system in the receiver for decrypting a communication received at the receiver and in the absence of the security system, initiating transmission of a request to another 10 communications receiver which includes the security system to assist in decrypting the communication.

The program can further comprise the step of initiating transmission of encrypted control information for decrypting the communication, wherein the request for 15 assistance comprises a request to decrypt the encrypted control information.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 20 Figure 1 is a schematic diagram providing an overview of a broadcasting system according to one embodiment of the present invention; Figure 2 is a more detailed view of the system of Figure 1 illustrating the information which is inserted into the broadcast stream; Figure 3 is a detailed schematic diagram of the master and slave receivers shown in 25 Figures 1 and 2; and Figure 4 is a flow diagram illustrating the operation of the system according to one embodiment of the present invention.

Detailed Description

30 In the following description of the various embodiments, reference is made to the

accompanying drawings which form a part hereof and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilised and structural and functional

- 5 modifications may be made without departing from the scope of the present invention. Figure 1 provides an overview of a system according to one embodiment of the s present invention. The system operates according to the digital video broadcasting (I)VB) standard and comprises a broadcast system transmission centre 1 which broadcasts a plurality of services to each of a plurality of receivers 2 - 5, over a broadcasting network 6, for example, a terrestrial transmission network. The receivers 2 - 5 are, for example, located within a single household 7. A first 10 receiver 2 is designated as a master DVB receiver and has a smart card 8 for decrypting broadcast services. The remaining receivers 3 - 5 are designated as slave receivers and are connected to the master receiver 2 by a local area network 9, which can be implemented by any wired or wireless communication system, for example, the Bluetooth_ communication system. None of the slave receivers 3 - 5 15 requires a smart card to operate. Instead, each of the slave receivers 3 - 5 communicates with the master receiver 2 over the communication network 9 to receive the necessary signals to enable it to decrypt a particular broadcast service.

Figure 2 is a more detailed diagram of the system of Figure 1. Content to be 20 broadcast, including, for example, video, audio and data components, is encoded in an encoder 10 using an appropriate coding system, for example MPEG-II for digital broadcasting, as defined in ISO/IEC 13818, the entire contents of which are incorporated herein by reference. The encoded broadcast stream is encrypted or scrambled in a scrambler 11 under the control of a control word CW generated by a 2s control word generator 12 in a manner which is well-known per se. An ECM generator 13 is used to generate an Entitlement Control Message (ECM), which contains the control word encrypted using service keys SK, generated within the broadcast system transmission centre 1, together with access criteria which identify the service and the conditions required to access the service. For example, the 30 access criteria may specify regional limitations on the broadcast. A further type of message, referred to as an Entitlement Management Message (EMM), which carries details of the subscriber and his subscription, is generated by an EMM generator 14.

While an ECM message is associated with a scrambled programme or set of

programmes and carries the information required to decrypt those programmer, an EMM message is a message dedicated to an individual user or group of users and carries the information necessary to determine whether those users have the necessary subscriptions in place to be able to view the programmes.

EMM messages also carry an encrypted version of the service keys SK. These are encrypted using one or more secret keys SCQ held within the transmission centre 1, a copy of which are also securely stored within the smart card 8 for the purpose of decrypting the service keys.

As is well known in the art, each digital broadcast stream is identified by a unique integer value, referred to as a packet identifier (PID), as defined in ISO/IEC 13818 referred to above. Each transmission stream is also associated with a number of other identifying parameters such as a service identifier (SID) and conditional access 15 system identifier (CA id), which identifies the conditional access system being used to encrypt the service.

The scrambled encoded broadcast stream together with the ECM and EMM messages is multiplexed in a multiplexer 15 with other broadcast streams 20 representing other programmes, each having their own ECM and EMM messages and together making up a subscription package from a particular service provider.

The package is sent to a transmitter 16 from which it is transmitted, via a communications channel 17, for example a terrestrial channel, using an appropriate modulation scheme. The scrambled encoded broadcast stream is received at each of 2s the subscriber's receivers 2 - 5.

Figure 3 shows schematic diagrams of each of the master 2 and slave receivers 3, 4, while Figure 4 is a flow chart which provides a more detailed explanation of the way in which the receivers 2 - 5 interoperate according to one embodiment of the 30 present invention to decode different broadcast services, using only the smart card 8 at the master receiver 2. Two slave receivers 3, 4 are shown for the purpose of clarity, but this is representative of any number of receivers connected to the local area network.

- 7 Referring to Figure 4, on receipt of the broadcast stream at one of the receiver 2 - 5 (step s1), the received data is demultiplexed in a demultiplexer 18, to extract the required programme and its associated ECM and EMM messages (step s2). The s receiver's control module 19, for example, a microprocessor 19 running control software stored in memory 20 then checks whether conditional access resources are available internally to decode the incoming broadcast stream. For example, the software determines whether a smart card 8, issued by the service provider, has been inserted (step s3). Where the receiver has been designated as the master 10 receiver 2, a smart card 8 will be present. In this case, the extracted ECM and EMM messages are sent to the plug-in smart card 8 (step s4). The smart card 8 uses the ECM and EMM messages to determine whether the subscriber has the right to view the broadcast (step s5) and if so, decrypts the control word CW (step s6), in a manner which is well known. Essentially, the unique key SCQ stored within the 15 smart card 8 is used to decrypt the service keys SK transmitted within the EMM message. In turn, the service keys SK are used to decrypt the control word CW transmitted within the ECM message.

The decrypted control word CW is input to a descrambler 21 together with the 20 scrambled broadcast stream (step s7) to recover the original MPEGII encoded broadcast stream (step s8). The encoded stream is passed to an MPEG-II decoder 22 (step s9) which produces an output signal comprising audio, video and data components for display on the subscriber's television 23 (step s10).

2s The control word comprises alternating odd and even control words which are alternated at, for example, two second intervals. Each control word is changed at predetermined intervals, for example, every twenty seconds. A continuous stream of ECM messages is therefore required to descramble the scrambled signal. The EMM message can be updated less frequently.

The conventional form of ECM and EMM messages is defined in the international standard ISO/IEC 13818, referred to above.

- 8 - Returning to step s3, if the receiver's control software determines that a smart card is not connected, as illustrated by the reference 8' in Figure 3, this indicates that the receiver has been designated as a slave receiver 3 - 5. In this case, the control module 19 transmits an enquiry over the local area network to locate the master 5 receiver (step sl 1). The enquiry comprises all of the data that is required to identify the digital stream in question, for example the PID, SID and CA id, together with the extracted ECM and EMM messages and the identity of the slave receiver originating the request. The request is made to another receiver via a communications interface 24, for example corresponding Bluetooth_ 10 communications ports, in which case the enquiry includes the Bluetooth_ identifier for the slave receiver 3.

The enquiry is received by another receiver 4 (step sl2) via its communications interface 24, as identified by connection 26 in Figure 3. That receiver in turn 15 checks whether internal conditional access resources are available, for example, whether a smart card is inserted (step sl3). If not, for example, because the receiver is another slave receiver 4, it returns a message to the Inquiring receiver 3 acknowledging the received request and informing the receiver that it does not have the required resources (step sl4). The enquiry message is repeated until every 20 receiver in the system has been contacted. The operation of the system when the receiver 2, which has been designated as the master receiver, is contacted, as designated in Figure 3 by the connection 27, is described below.

As in the case of the service received directly at the master receiver 2, the smart 25 card 8 at the master receiver 2 uses the ECM and EMM messages received from the slave receiver 3 to determine whether the subscriber has the right to view the broadcast (step sl5) and if so, decrypts the control word CW (step s16). The decrypted control word is sent back to the address of the slave receiver 3 originating the request (step sl7), together with the PID, SID and CA id from the request and 30 optionally, the master receiver identity. This information can be used to verify that the slave receiver uses the correct control words.

The master receiver identity can be held at the slave receiver to permit it to identify the master receiver mote quickly in future accesses. The identity of the master receiver can also be communicated between slave receivers during the process of answering resource enquiries, to reduce unnecessary communication between the s slave receivers.

The decrypted control words received from the master receiver 2 are input at the slave receiver 3 to the descrambler 21 together with the scrambled broadcast stream (step s18) to recover the original MPEG-II encoded broadcast stream (step sly).

10 The encoded stream is passed to an MPEG-II decoder 22 (step s20) which produces an output signal comprising audio, video and data components for display on the subscriber's television 25 (step s21).

The descrambling system works in the same way for each of the slave receivers 3-

5 5, enabling each of the slave receivers 3 - 5 to use the smart card 8 at the master receiver 2 to decode different services. Each slave receiver need only identify the service it is interested in to the master receiver and supply the master receiver with the encrypted control word information that it has filtered from the broadcast stream. Identifying each receiver in a unique way within a household can prevent leakage of the control words to another household. Furthermore, the limitation of transmission power or the use of a wire-based solution limits the coverage of the local area network.

2s While the invention has been described in terms of master and slave receivers, it will be apparent from the above description that these two types of receiver may in

fact be identical, and that a receiver can be configured to function either as a master or a slave receiver depending, for example, on whether a smart card is inserted. In 30 an alternative embodiment, system settings enable each receiver to be switched to function as a master or slave receiver. Rather than requiring the slave receivers to send out enquiry messages to other receivers to determine whether conditional access resources are available, the identity of the master receiver can be preset at all

- 10 of the slave receivers for faster access, so that the slave receivers never need to communicate with one another.

It will be apparent to the skilled person that, although a specific communications s protocol has been described, the protocol governing the way in which the master and slave receivers communicate with one another depends on the complexity of the network built between the receivers. As is well known in the art, the communications protocol will deal with all of the control functionality required for the receivers to pass the necessary data to one another, including the opening and 10 closing of sessions, transmission of data and any necessary error handling. The communications protocol is, for example, a client-server protocol in which a server program at the master receiver 2 services the needs of client programs at the slave receivers 3 - 5.

Claims

- 11 Claims

1. A method of decrypting an encrypted communication, the communication including encrypted content data and encrypted control information, the control s information being capable, once decrypted, of decrypting the encrypted content data, and the encrypted control information being capable of being decrypted by a security module, the method including the steps of: receiving the encrypted communication at a first receiver; extracting the encrypted control information from the received 10 communication; transmitting the encrypted control information to a second receiver which includes the security module; receiving the decrypted control information from the second receiver; and using said decrypted control information to decrypt the encrypted content Is data.

2. A method according to claim 1, including decrypting the control information at the second receiver.

20 3. A method according to claim 1 or 2, wherein said security module comprises a smart card.

4. A method according to claim 1, 2 or 3 wherein the control information comprises a stream of control words.

5. A method according to claim 4, wherein the control words are encrypted into entitlement control messages (ECMs) using service keys.

6. A method according to claim 5, wherein the service keys are encrypted into 30 entitlement management messages (EMMs) using one or more keys known to the security module.

- 12 7. A method according to claim 6, comprising sending the entitlement control messages and the entitlement management messages to the second receiver.

8. A method according to claim 7, including determining the control words 5 from the entitlement control messages and the entitlement management messages.

9. A method according to any one of the preceding claims, further including transmitting the identity of the first receiver to the second receiver.

10 10. A method according to any one of the preceding claims, wherein the first receiver is configured as a slave receiver and the second receiver is configured as a master receiver.

11. A method according to any one of the preceding claims, further including 15 transmitting the identity of the second receiver to the first receiver.

12. A method according to any one of the preceding claims, wherein the first receiver transmits to the second receiver sufficient information to identify a service for which the control information is required.

2fi o 13. A method according to any one of the preceding claims, wherein the encrypted communication conforms to the digital video broadcasting standard <)VB).

25 14. A receiver system for use in decrypting digital transmissions, comprising a plurality of receivers interconnected in a master-slave arrangement, the master receiver being configured to decrypt control information received by each of the slave receivers, on behalf of said slave receivers.

30 15. A receiver system according to claim 14, wherein the master receiver includes a security module for decrypting the control information and none of the slave receivers include security modules.

- 13 16. A receiver system according to claim 15, wherein the security module comprises a smart card.

17. A receiver system according to claim 15 or 16, wherein each of the slave 5 receivers is configured to perform an internal check for the presence of a security module,and in the absence of said module, to send a request to at least one of the other receivers in the arrangement.

18. A receiver system according to any one of claims 14 to 17, wherein the 10 master receiver is configured to receive entitlement control messages (ECMs) and entitlement management messages (EMMs) from a slave receiver.

19. A receiver system according to claim 18, wherein the security module is configured to determine the control words from the entitlement control messages 5 and the entitlement management messages.

20. A receiver system according to any one of claims 14 to 17, wherein said receivers are arranged to communicate with one another via a local area network.

20 21. A receiver system according to claim 20, wherein each of said receivers is capable of communicating with one another via the Bluetooth wireless communications protocol.

22. A receiver system according to claim 20 or 21, wherein each of the slave 25 receivers is configured to communicate with the master receiver only.

23. A receiver for receiving and decrypting an encrypted transmission, the receiver being switchable between a master configuration in which it uses a security sub-system within the receiver to decrypt the transmission and a slave configuration 30 in which it communicates with a security sub-system within another receiver to decrypt the received transmission.

- 14 24. A receiver according to claim 23, wherein the receiver switches automatically between said master and slave configurations in response to the presence or absence of the security sub-system.

s 25. A receiver according to claim 23 or 24, wherein the security subsystem comprises a smart card.

26. A computer program which, when executed on a processor in a communications receiver, is configured to perform the steps of: 10 determining the presence or absence of a security system in the receiver for decrypting a communication received at the receiver; and in the absence of the security system, initiating transmission of a request to another communications receiver which includes the security system to assist in decrypting the communication.

27. A computer program according to claim 26, further comprising the step of initiating transmission of encrypted control information for decrypting the communication, wherein the request for assistance comprises a request to decrypt the encrypted control information.