KR20060040583A - Method of partially scrambling a data stream - Google Patents

Abstract

A method of partially scrambling a data stream (6) including transport stream packets (7), each transport stream packet (7) having a header (8) and a payload (9), wherein a sequence of transport stream packets (7) has payloads carrying encoded data elements, arranged in units (15), includes: selecting transport stream packets (7) forming a subsequence of the sequence, and scrambling at least part of the payloads (9) of each transport stream packet (7) in the subsequence. The method further includes monitoring the payloads (9) of at least some of the transport stream packets (7) in the sequence for the presence of data (22) indicating a boundary between two subsequent units (15), and, for selected units (15), including at least one of the transport stream packets (7) carrying data forming part of the selected unit (15) in the sub-sequence.

Description

Method of partially scrambling a data stream

The present invention provides a method of partially scrambled a data stream comprising transport stream packets, wherein each transport stream packet has a header and a payload, the sequence of transport stream packets carrying encoded data elements and arranged into units. The scrambling method having payloads includes selecting transport stream packets that form a sub-sequence of the sequence, and scrambled at least some of the payloads of each transport stream packet in the subsequence. To partially scramble the data stream.

The invention also provides a system for partially scrambled a data stream comprising transport stream packets, each transport stream packet having a header and a payload, the sequence of transport stream packets carrying encoded data elements and arranged into units The scramble system, having payloads to be included, includes a port for receiving the data stream, and an apparatus for processing the data in the stream, the system comprising a transport stream forming a sub-sequence of the sequence. A system for partially scrambled a data stream, configured to select packets and scramble at least some of the payloads of each transport stream packet in the sub-sequence.

The invention also relates to a computer program.

The invention also relates to a signal carrying a data stream comprising transport stream packets, each transport stream packet having a header and a payload.

Examples of such methods, systems, computer programs and signals are known from WO 03 / 061289-A1. In known systems, the cable system headend selects A / V content packets in the packet selector for encryption. Packets selected for encryption are selected such that their non-receipt will subsequently have a significant impact on the real-time decoding of the program and any possible processing of the recorded content. That is, only important packets are encrypted. For video and audio, this can be achieved by encrypting "frame start" transport stream packets that contain Packetized Elementary Stream (PES) headers and other headers as part of the payload, because without this information the STB decoder This is because MPEG compressed data cannot be decompressed, and MPEG-2 streams identify "frame start" packets with a "packet unit start indicator" in the transport header. In general, packets carrying a payload that includes a picture header or a video sequence header can be used to implement current scrambling techniques. Other important or critical packets or content elements can also be identified for encryption that can strictly prohibit unauthorized viewing without departing from the present invention. For example, MPEG intra-coded or I frame picture packets are encrypted to prohibit viewing of the video portion of the program.

A problem with the known method is that encryption of all TS packet payloads, including PES packet headers or selected sensitive packets, results in a stream where most of the packets have an encrypted payload. This makes this method unsuitable for broadcasting to devices with limited processing capability for encryption. Encryption of very few TS packets payloads, including PES packet headers or selected important packets, includes packet audiovisual data encoded using advanced compression techniques in which the payloads of the packets are highly resilient to packet loss. If that's not enough. In this case, the unauthenticated recipient can decode the content using the data that remains apparent.

SUMMARY OF THE INVENTION An object of the present invention is a method, system of the above-described kind, which can scramble payloads of only a few selected transport stream packets while maintaining effective content protection in the presence of advanced decoder technologies for processing lost encoded data. And a computer program.

This object is achieved by a method according to the invention, the method comprising: monitoring at least some payloads of transport stream packets in the sequence for the presence of data indicating a boundary between two subsequent units, and For said selected units, including at least one of transport stream packets carrying a data forming part of said selected unit in said sub-sequence.

Since transport stream packets are selected to form a subsequence, that is, a sequence formed less than the entire transport stream packets in the sequence, the descrambling load on the decoder receiving the partially scrambled stream is reduced. Because encoded data elements are composed of units, they are also processed per unit when decoded. Since the entire payload of the transport stream packets monitors for the presence of data indicating a boundary between two subsequent units, it can be ensured that only selected units are unknown. The number and characteristics may depend on the decoding processing. It also takes into account that the data forming the unit can be carried in the payload of a plurality of transport stream packets. Thus, scrambling can be more closely tailored to the encoding technique.

In a preferred embodiment, the data stream is a multiplex of elementary streams, and the method identifies at least one elementary stream comprising the sequence of transport stream packets and only payloads of packets in the identified elementary stream (s). Monitoring the steps.

Thus, a relatively efficient method for partially scrambled transport stream packet payloads is provided.

In a preferred embodiment, the selected units comprise units that include at least a portion of the encoded representation of the picture.

This embodiment has a relatively large impact at the decoder. The pictures contained in each unit hardly change the desired output of the decoder, which can no longer be provided without descrambled transport stream packet payloads containing these selected units.

In a preferred embodiment, each unit comprises an indication of the following type of data and a portion comprising the data, the type of each unit in the monitored payloads is determined from the indication, and the unit is of the type. Corresponding to at least one particular type is included among the selected units.

Thus, while effectively protecting the content, it is achieved to greatly reduce the number of transport stream packets whose payloads are scrambled.

Certain type (s) and other types of units are preferably included randomly between the selected units.

Thus, extra content protection is achieved.

In a preferred variant of the previous two embodiments, these types are defined by an encoding technique that forms encoded data elements.

Thus, these packet payloads containing the units most important to the decoding process can be selected for scrambling. This allows for more effective content protection because it is precisely tailored to the specific codec used.

In a preferred embodiment, the encoded data elements are decodable using predictive decoding techniques, and the specific types include the type of data element such that the prediction is derived from only decoded data belonging to the data element.

Because these data elements allow random access to the stream of encoded data, accessing them has a great impact on the decoding process, and the decoding process generally cannot start without these encoded data elements.

In a preferred embodiment, up to the maximum number of transport stream packets following the first transport stream packet carrying the data forming part of the selected unit is included in the sub-sequence.

This reduces the load on the receiver while maintaining proper protection. The maximum number is selected to disable error correction. In particular, if transport stream packets are of all standard lengths, including up to the maximum number of all transport stream packets carrying the data-forming part of the unit is more than necessary to ineffectively reduce the receiver's technique to handle data loss. Avoid scrambling many payloads. Thus, effective protection is achieved while keeping the burden on the authenticated receiver providing access to the partially scrambled system as low as possible.

According to another feature, the system according to the invention is configured to monitor the payloads of at least some of the transport stream packets in the sequence for the presence of data indicating a boundary between two subsequent units, wherein the selected units And to include in the sub-sequence at least one of the transport stream packets carrying the data forming portion of the selected unit.

The system is well suited for generating a partially scrambled stream where the data elements are well protected against access by unauthorized receivers but do not require much processing capacity of the authenticated receivers.

The system is configured to include up to the number of maximum transport stream packets following the first transport stream packet carrying the data forming portion of the selected unit in the sub-sequence and preferably an arrangement for setting the maximum number is provided.

This reduces the load on the receiver while maintaining proper protection. The maximum number can be set to disable error correction. In particular, if all transport stream packets are of standard length, including up to the maximum number of all transport stream packets carrying the data forming part of the unit is more than necessary to ineffectively reduce the receiver's technique to cope with data loss. Avoid scrambling many payloads. Thus, effective protection is achieved while keeping the burden on the authenticated receiver providing access to the partially scrambled system as low as possible. Since the maximum number can be set, factors such as the profile of typical receivers, the encoding method and the number of selected units can be considered.

According to another feature, the invention provides a computer program adapted to configure a computer to execute a method according to the invention when executed on a computer.

According to yet another aspect, the invention provides a signal for carrying a data stream comprising transport stream packets, each transport stream packet having a header and a payload, the sequence of transport stream packets carrying encoded data elements and unit Each unit is of a particular type, and at least a portion of the payload of each transport stream packet in the subsequence of the sequence is scrambled, and for each unit of a type corresponding to the selected type, The sub-sequence includes at least one of the transport stream packets carrying a data forming portion of the unit, and at least one of the transport stream packets includes data indicating a boundary between two subsequent units.

The signal is suitable for unicast, multicast, or broadcast to receivers equipped with decoders with limited processing capacity to descramble but with high tolerance for data loss. These include in particular wireless devices.

1 is a schematic diagram of a system for partially scrambled a data stream;

2 is a schematic diagram of a data stream including transport stream packets according to the MPEG-2 standard;

3 is a schematic diagram of a configuration of an MPEG-2 transport stream packet header;

4 is a schematic diagram of a configuration of a program elementary stream packet carried in the data stream of FIG. 2;

5 is a schematic diagram of the configuration of a network adaptation layer unit as defined by the H.264 / AVC standard and carried in the data stream of FIG.

The invention will now be described in more detail with reference to the accompanying drawings.

The present invention will be described in an embodiment which partially scrambles a data stream comprising transport stream packets according to the ISO / IEC 13818-1 or MPEG-2 system standard. In this particular embodiment, MPEG-2 is used as the delivery mechanism for audiovisual data encoded according to the H.264 / AVC standard. It will be appreciated that the present invention can be applied to MPEG-2 and other delivery mechanisms. One example is the Internet Protocol (IP), which defines IP datagrams with a header and payload. Similarly, due to the high degree of compression and acceptable quality that can be achieved, using H.264 / AVC as a content encoding technique is a useful example. However, MPEG-2 video coding, which arranges the encoded video into frames, is an alternative.

In the example to be described in detail, the data stream is in MPEG-2 transport stream format. This example may be adapted to the program stream format. Thus, the term transport stream packet does not mean to be defined as the use of a particular format. When the program stream format is used, it has been observed that data is sent in PES packets each having a header, and the PES packets are grouped into packs each having a pack header.

In FIG. 1, video file server 1 provides in particular an MPEG-2 system stream carrying H.264 encoded video. The multiplexer 2 splices Conditional Access (CA) messages into a data stream. CA messages include Entitlement Management Messages (EMM) generated by the EMM generator 3 and Entitlement Control Messages (ECM) generated by the ECM generator 4. The ECM generator 4 generates Control Words (CW). These are provided to the scrambling unit 5 arranged to partially scramble the output data stream of the multiplexer 2. The CWs are encrypted under the service key provided by the EMM generator 3, which packs the service keys into the EEMs. Thus, the CA scheme used substantially corresponds to the Digital Video Broadcasting (DVB) Common Scrambling Algorithm, which is known from ETSI Technical Report 289 and is not described in detail herein. It has been observed that the separation into the elements of Figure 1 is a functional property. Several or all of these may be combined in a single physical device, since the functionality of any of these elements may be provided separately by different devices. In addition, this functionality may be implemented in software or hardware.

2 shows a data stream 6 comprising transport stream (TS) packets 7a-7p. Each TS packet 7 has a TS packet header 8a-8p and a TS packet payload 9a-9p. The data stream 6 is a multiplex of elementary streams. Each elementary stream corresponds to a coded bit stream, eg, a coded audio, video or data stream. For example, ECMs are carried in a separate elementary stream, while at least one elementary stream received by the scrambling unit 5 is a stream of H.264 encoded video.

3 shows the configuration of the TS packet header 8. It comprises a sync byte 10, a payload_unit_start_indicator 11, a packet identifier (PID) field 12, a transmission scrambling control field 13 and optionally, an adaptation field 14. Other parts are described in ISO / IEC 13818-1. Each elementary stream corresponds to a unique PID. Thus, the scrambling unit 5 can identify the H.264 elementary stream or the streams carrying the encoded video. For efficiency, only TS packets 7 belonging to such a stream or streams are processed. As is known from ISO / IEC 13818-1, MPEG-2 transport streams contain program specific information (PSI) that identifies the various elementary streams and their assigned PIDs as well as the type of data carried in the elementary stream. Will include. One type that can be identified in the Program Association Table (PAT) is H.264. The scrambling unit 5 uses the PSI to identify the PID (s) of the elementary stream (s) to be partially scrambled.

In the following, it will be assumed that only one elementary stream will be partially scrambled. TS packets 8 with a PID corresponding to a particular elementary stream are retrieved from the data stream and thus of TS packets 8 with TS packet payloads 9 carrying H.264 encoded data elements. Form a sequence.

The encoded data elements preferably include at least portions of the encoded representations of the pictures. A picture is a frame or field in a video sequence (ie, an entire picture or alternative lines). Macroblocks, blocks of 16 × 16 luma and chroma samples are formed from the data of each picture. This maps a rectangular two-dimensional pattern of macroblocks in the image to a one-dimensional pattern in accordance with a raster scan, resulting in the next row in which the first entries of the one-dimensional pattern are scanned from left to right respectively. From the first top of the two-dimensional pattern, scanned from left to right from the first top row of the two-dimensional pattern, before the macroblocks. This picture is divided into slice groups, ie subsets of macroblocks. A slice contains macroblocks that are contiguous in the raster scan within the slice group but is not necessarily required in the picture. Thus, for example, every other macroblock can be assigned to a separate slice group in a raster scan of an image. A slice is only decoded based on the samples in itself, ie independent of the samples in the other slices. However, when data in one slice is lost in transmission, it can be used to organize the data in another slice to “fill in the blanks” in the decoded picture.

The frequency of the sampled pictures provides time division in addition to the topographical partition provided by the slices. H.264 is an example of a predictive encoding method: the pixel value is encoded as the sum of the predicted value and the difference value, the latter value being reduced as much as possible during encoding. For slices containing data from the first picture and from pictures defined as random access points, the predicted values are not based on the values of the pictures at different points in the transmission order only based on the values in the picture itself. Do not. Such slices are referred to as intra-coded slices. The remaining slices may be coded so that they can only be decoded using the values of other pictures in the order of the sequence of pictures. Thus, one can decode a sequence of encoded pictures by starting with an intra-coded picture but starting with another type of encoded picture.

The description of the relevant parts of H.264 only takes into account the so-called Video Coding Layer (VCL). In order to transmit the encoded slices, they are packaged into so-called Network Adaptation Layer (NAL) units 15a-15x (FIG. 1). Each slice is contained in a single NAL unit 15. The sets of NAL units 15 form access units AU. Each AU always contains the original coded picture, ie all macroblocks of the picture. It will be appreciated that the data size of NAL unit 15 varies with the type of (entropy) coding used to generate the number of slice groups, slices, and the like. Thus, the sequence of TS packets 7 includes NAL units 15 of variable lengths.

Each set of NAL units 15 forming an AU is carried in one program elementary stream (PES) packet 16, after which the PES packet is carried by TS packets 7. The configuration of the PES packet 16 is shown in FIG. The PES packet includes a packet start code pre-fix 17a-d (see also FIG. 2). The packet start code pre-fix 17 is a 24-bit long code. In addition to stream_id 18, this constitutes a packet start code that identifies the start of the PES packet 16. In contrast to the TS packets 7 of standard fixed length, the PES packet 16 is of variable length. This length is indicated in the PES packet length field 19. The field 19 is optionally preceded by the PES header 20. Then, the PES packet payload 21, i.e., the NAL units 15, comes.

Note that stream_id (18) specifies both the type and number of the elementary stream. Thus, alternatively, stream_id 18 may be used to identify the elementary stream to be partially scrambled by the scrambling unit. The start of a new PES packet 16 always immediately follows on the TS packet header 8, in which case the payload_unit_start_indicator 11 has the value 'TRUE'. Two PES packets 16 do not start in the same TS packet 7.

4 shows the configuration of a NAL unit 15 in a format for transmitting in a byte stream. This is ahead of the start code pre-fix 22. The start code pre-fix 22 is a unique sequence of 3 bytes equal to '0x00 0001' that is embedded in the byte stream as a pre-fix in each NAL unit 15. Thus, the start code pre-fix 22 marks the boundary between two subsequent NAL units 15. The start code pre-fix 22 precedes the prohibition_bit 23, nal_storage_idc 24, and nal_unit_type 25.

Ten different types are defined by the encoding technique in which the slice is formed. One of these is the Access Unit Delimiter (AUD) type. The presence of this type of NAL unit 15 marks the boundary between subsequent AUs. The first NAL unit 15 of the AU is always of this type. Another possible type is the Instantaneous Decoder Refresh (IDR) type. This NAL unit 15 comprises an intra coded slice. Thus, the corresponding value of nal_unit_type 25 indicates that the byte-aligned data 26 preceding it is part of the data element representing the intra-coded picture.

Once retrieved from the data stream 6, i. To watch. The scrambling unit 5 can distinguish the start code pre-fix 22 that indicates the boundary between the packet start code pre-fix 17 and the subsequent NAL units 15 of the PES packet 16. It has been observed that the PES packet start code pre-fix 17 always follows immediately on the TS packet header 8. The scrambling unit 5 may monitor the portions of the TS packet payload 9 separated by the TS packet header 8 by elementary stream packets, i.e. elements indicating the start of the PES packet.

Once the end of NAL unit 15 is identified, the system determines the type of NAL unit 15 as indicated by nal_unit_type 25. If at least this type corresponds to IDR, one or more of the TS packets 7 carrying the data forming part of the NAL unit 15 are selected to be included in the subsequence. The TS packet payloads 9 of the TS packets 7 in the sub-sequence are scrambled. The term 'sub-sequence' is observed as a notional one. This is referred to herein as a smaller number of TS packets 7 in the ordered subset, ie the sequence of TS packets 7 forming the elementary stream.

The plurality of additional TS packets 7 following the first TS packet 7 carrying the data forming part of the selected NAL unit 15 are also preferably selected to be included in the sub-sequence to be scrambled. These additional TS packets 7 are selected from the same elementary stream based on the PID determined from the PID field 12. The system includes means for adjusting the number of additional packets selected. Thus, the operator of the conditional access system can achieve a compromise between the level of processing capacity and the level of content protection required to descramble the partially scrambled stream.

The fraction of the scrambled TS packets 7 in the sequence carrying the elementary stream may be relatively low when the selection is based on the presence of NAL units 15 of type IDR. In such cases, additional TS packets 7 may be selected to scramble. In a useful embodiment, the system may be configured or configured to randomly select IDR and other types of units. The TS packet payload 9 of at least one of the TS packets 7 carrying the selected unit is also scrambled. The other types may be a subset or all of the IDR and nine other defined types. In one embodiment, the rate at which additional TS packets 7 are included in the sub-sequence to scramble is continuously adjusted. This is done in such a way as to keep the fraction of the TS packets 7 in a sub-sequence for all the TS packets at a certain level, for example in the sequence representing the elementary stream at or below 5%.

The partially scrambled data stream is modulated by the transmitter 27. In a preferred embodiment, MPEG-2 transport stream packets are modulated into CDMA (code division multiple access) carriers according to the System E variant of the Digital Audio Broadcasting Standard (ETSI 300401). Thus, the transmitter transmits a signal carrying a partially scrambled data stream. By using a wireless transmission technique, the partially scrambled data stream can be used for mobile receiver / decoder devices. These devices are preferably provided with descrambling and decoding capabilities implemented in software. In this case, the method in which the signal, in particular the data stream, is scrambled allows for descrambling and decoding with low processing strength.

It will be apparent that scrambling is performed at the transport stream level, ie by scrambled at least some of the TS packet payloads 9 of the selected TS packets 7. The TS packet header 8, in particular the transport scrambling control field 13, provides a valid way to signal to the receiver whether a particular packet has a scrambled payload. Thus, the receiver does not need to examine the entire content of the payload of each packet to selectively descramble the encoded data. Rather, it may perform descrambling before processing the actual payload contents.

The invention is not limited to the embodiments described herein but may vary within the scope of the appended claims. For example, encoded data elements may be carried in payloads of transport stream packets defined by other protocols for wireless transmission. In addition, scrambling may be carried at the PES level, which indicates that the payload of the PES packet 16 determined to execute a particular type of NAL unit 15 (eg, IDR) is included among the packet payloads to be scrambled. Means that.

Claims (12)

A method of partially scrambled a data stream (6) comprising transport stream packets (7), each transport stream packet (7) having a header (8) and a payload (9), and transport stream packets (7). The scramble method has a payload that carries encoded data elements and is arranged in units 15, Selecting transport stream packets 7 forming a sub-sequence of the sequence, and A method for partially scrambled the data stream, comprising scrambled at least some of the payloads 9 of each transport stream packet 7 in the subsequence. Monitoring at least some of the payloads 9 of the transport stream packets 7 in the sequence for the presence of data 22 indicating a boundary between two subsequent units 15, and Partially scrambled the data stream for the selected units 15, comprising in the sub-sequence at least one of the transport stream packets 7 carrying the data forming part of the selected unit How to. The method of claim 1, wherein the data stream (6) is a multiplex of elementary streams, and the method identifies at least one elementary stream comprising the sequence of transport stream packets and is within the identified elementary stream (s). Monitoring only the payloads of packets. Method according to claim 1 or 2, characterized in that the selected units (15) comprise units comprising at least part of an encoded representation of a picture. 4. The unit according to any one of the preceding claims, wherein each unit (15) comprises an indication (25) of the following type of data and a portion (26) containing said data, wherein said monitored payloads The type of each unit within is determined from the indication, and wherein the unit is included among the selected units if the type corresponds to at least one particular type. 5. The method of claim 4, wherein units of types other than the particular type (s) are randomly included between the selected units. 6. The method of claim 4 or 5, wherein the types are defined by an encoding technique that forms encoded data elements. The data element of claim 4, wherein the encoded data elements are decodable using predictive decoding techniques, and wherein the specific types are such that the data element is derived such that the prediction is derived from only decoded data belonging to the data element. And partially scrambled the data stream. The data stream of claim 1, wherein the data stream is partially included in the sub-sequence up to a maximum number of transport stream packets following the first transport stream packet carrying the data formation portion of the selected unit. How to scramble. A system for partially scrambled a data stream (6) comprising transport stream packets (7), each transport stream packet having a header (8) and a payload (9), a sequence of transport stream packets (7) The scramble system has payloads carrying encoded data elements and arranged in units 15, A port for receiving the data stream, and An apparatus (2-5) for processing said data in said stream, The system is configured to select transport stream packets 7 forming a sub-sequence of the sequence and scramble at least some of the payloads of each transport stream packet 7 in the sub-sequence. In a system that partially scrambles a stream, The system is configured to monitor payloads of at least some of the transport stream packets in the sequence for the presence of data 22 indicating a boundary between two subsequent units 15 and for selected units. And include in the sub-sequence at least one of the transport stream packets carrying a data forming portion of the selected unit. 10. The apparatus of claim 9, configured to include up to a maximum number of transport stream packets following a first transport stream packet carrying a data forming portion of a selected unit in the sub-sequence, wherein an apparatus for setting the maximum number is provided. , A system that partially scrambles the data stream. A computer program adapted to configure the computer, when executed on a computer, for carrying out the method according to any one of claims 1 to 8. As a signal carrying a data stream 6 comprising transport stream packets 7, each transport stream packet 7 has a header 8 and a payload 9, and the transport stream packets 7 The sequence has payloads 9 carrying encoded data elements and arranged into units 15, each unit 15 being of a particular type and of each transport stream packet 7 in the subsequence of the sequence. At least a portion of the payload 9 is scrambled, and for each unit 15 of the type corresponding to the selected type, the sub-sequence is the transport stream packet carrying the data forming part of the unit 15. At least one of said transport stream packets, said at least one of said transport stream packets comprising data (22) indicating a boundary between two subsequent units (15).

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