CA2709393C - Progressive video refresh slice detection - Google Patents

Abstract

A selective encryption encoder and method of dual selective encryption and detection of intra-coded slices in video content. The selective encryption encoder has a packet identifier that identifies packets of at least one specified packet type, the at least one specified packet type being packets in a set of N consecutive slices in a frame wherein the a second byte after a slice start code is identical in all N consecutive slices. A packet duplicator duplicates the identified packets to produce first and second sets of the identified packets. The packets are sent to and from a primary encryption encoder to encrypt the first set of identified packets under a first encryption method. A secondary encrypter encrypts the second set of identified packets under a second encryption method.

Description

13 This application is related to patent applications docket 14 number SNY-R4646.01 entitled "Critical Packet Partial Encryption" to Unger et al., serial number 101038,217; patent applications docket number SNY-16 R4646.02 entitled "Time Division Partial Encryption" to Candelore et al., serial 17 number 10/038,032; docket number SNY-R4646.03 entitled "Elementary Stream 18 Partial Encryption" to Candelore , serial number 101037,914; docket number 19 SNY-R4646.04 entitled "Partial Encryption and PID Mapping" to Unger et al., serial number 10/037,499; and docket number SNY-R4646.05 entitled 21 "Decoding and Decrypting of Partially Encrypted Information" to Unger et al., 22 serial number 10/037,498 all of which were filed on January 2, 2002.

24 This application is also related to U.S. patent application serial number 10/273,905, filed October 18, 2002 to Candelore et al. entitled 26 "Video Slice and Active Region Based Dual Partial Encryption", docket number 27 SNY-R4854.01.
28 This application is also related to and claims priority benefit of U.S.
29 Provisional patent application serial number 60/409,675, filed September 9, 2002, docket number 50S5152, entitled "Generic PID Remapping for Content 31 Replacement", to Candelore.

2 A portion of the disclosure of this patent document contains material 3 which is subject to copyright protection. The copyright owner has no objection 4 to the facsimile reproduction of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but 6 otherwise reserves all copyright rights whatsoever.

9 This invention relates generally to the field of digital video and encryption thereof. More particularly, this invention relates to an encryption method and 11 apparatus particularly useful for encrypting packetized video content such as 12 that provided by cable and satellite television systems.

The above-referenced commonly owned patent applications describe 16 inventions relating to various aspects of methods generally referred to herein as 17 partial encryption or selective encryption. More particularly, systems are 18 described therein wherein selected portions of a particular selection of digital 19 content are encrypted using two (or more) encryption techniques while other portions of the content are left unencrypted. By properly selecting the portions 21 to be encrypted, the content can effectively be encrypted for use under multiple 22 decryption systems without the necessity of encryption of the entire selection 23 of content. In some embodiments, only a few percent of data overhead is 24 needed to effectively encrypt the content using multiple encryption systems.
This results in a cable or satellite system being able to utilize Set-top boxes or 26 other implementations of conditional access (CA) receivers from multiple 27 manufacturers in a single system - thus freeing the cable or satellite company 28 to competitively shop for providers of Set-top boxes.

Docket No.. SNY-S5161.01 -2- PATENT

1 The features of the invention believed to be novel are set forth with 2 particularity in the appended claims. The invention itself however, both as to 3 organization and method of operation, together with objects and advantages 4 thereof, may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments 6 of the invention, taken in conjunction with the accompanying drawings in which:
7 FIGURE 1 is a block diagram of an exemplary cable system head end 8 consistent with certain embodiments of the present invention.
9 FIGURE 2 is an illustration of sample transport stream PSI consistent with certain embodiments of the present invention.
11 FIGURE 3 is a further illustration of sample transport stream PSI
12 consistent with certain embodiments of the present invention.
13 FIGURE 4 is a block diagram of an illustrative control processor 100 14 consistent with certain embodiments of the present invention.
FIGURE 5 illustrates the slice structure of a frame of video data 16 consistent with certain embodiments of the present invention.
17 FIGURE 6 is a flow chart of a packet selection and encryption process 18 consistent with certain embodiments of the present invention.
19 FIGURE 7 is a state diagram of a packet selection and encryption process consistent with certain embodiments of the present invention.
21 FIGURE 8 illustrates a television Set-top box that decrypts and decodes 22 in a manner consistent with certain embodiments of the present invention.
23 FIGURE 9 is a flow chart broadly illustrating an encryption process 24 consistent with embodiments of the present invention.

27 While this invention is susceptible of embodiment in many different 28 forms, there is shown in the drawings and will herein be described in detail 29 specific embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and not intended 31 to limit the invention to the specific embodiments shown and described. In the Docket No.: SNY-S5161.01 -3- PATENT

1 description below, like reference numerals are used to describe the same, 2 similar or corresponding parts in the several views of the drawings.
3 The terms "scramble" and "encrypt" and variations thereof are used 4 synonymously herein. Also, the term "television program" and similar terms can be interpreted in the normal conversational sense, as well as a meaning 6 wherein the term means any segment of AN content that can be displayed on 7 a television set or similar monitor device. The term "video" is often used herein 8 to embrace not only true visual information, but also in the conversational sense 9 (e.g., "video tape recorder") to embrace not only video signals but associated audio and data. The term "legacy" as used herein refers to existing technology 11 used for existing cable and satellite systems. The exemplary embodiments 12 disclosed herein are decoded by a television Set-Top Box (STB), but it is 13 contemplated that such technology will soon be incorporated within television 14 receivers of all types whether housed in a separate enclosure alone or in conjunction with recording and/or playback equipment or Conditional Access 16 (CA) decryption module or within a television set itself. The present document 17 generally uses the example of a "dual partial encryption" embodiment, but those 18 skilled in the art will recognize that the present invention can be utilized to 19 realize multiple partial encryption without departing from the invention.
Partial encryption and selective encryption are used synonymously herein.
21 Turning now to FIGURE 1, a head end 100 of a cable television system 22 suitable for use in practicing a dual encryption embodiment of the present 23 invention is illustrated. Those skilled in the art will appreciate that the present 24 invention could also be implemented using more than two encryptions systems without departing from the present invention. The illustrated head end 100 26 implements the dual partial encryption scenario of the present invention by 27 adapting the operation of a conventional encryption encoder 104 (such as those 28 provided by Motorola, Inc. and Scientific-Atlanta, Inc., and referred to herein as 29 the primary encryption encoder) with additional equipment.
Head end 100 receives scrambled content from one or more suppliers, 31 for example, using a satellite dish antenna 108 that feeds a satellite receiver 32 110. Satellite receiver 110 operates to demodulate and descramble the Docket No.: SNY-S5161.01 -4- PATENT

1 incoming content and supplies the content as a stream of clear (unencrypted) 2 data to a selective encryption encoder 114. The selective encryption encoder 3 114, according to certain embodiments, uses two passes or two stages of 4 operation, to encode the stream of data. Encoder 114 utilizes a secondary conditional access system (and thus a second encryption method) in 6 conjunction with the primary encryption encoder 104 which operates using a 7 primary conditional access system (and thus a primary encryption method). A
8 user selection provided via a user interface on a control computer 118 9 configures the selective encryption encoder 114 to operate in conjunction with either a Motorola or Scientific Atlanta cable network (or other cable or satellite 11 network).
12 It is assumed, for purposes of the present embodiment of the invention, 13 that the data from satellite receiver 110 is supplied as MPEG (Moving Pictures 14 Expert Group) compliant packetized data. In the first stage of operation the data is passed through a Special Packet Identifier (PID) 122. Special Packet 16 Identifier 122 identifies specific programming that is to be dual partially 17 encrypted according to the present invention. The Special Packet Identifier 18 signals the Special Packet Duplicator 126 to duplicate special packets. The 19 Packet Identifier (PID) Remapper 130, under control of the computer 118, to remap the PIDs of the elementary streams (ES) (i.e., audio, video, etc.) of the 21 programming that shall remain clear and the duplicated packets to new PID
22 values. The payload of the elementary stream packets are not altered in any 23 way by Special Packet Identifier 122, Special Packet Duplicator 126, or PID
24 remapper 1306. This is done so that the primary encryption encoder 104 will not recognize the clear unencrypted content as content that is to be encrypted.
26 The packets may be selected by the special packet identifier 122 27 according to one of the selection criteria described in the above-referenced 28 applications or may use another selection criteria such as those which will be 29 described later herein. Once these packets are identified in the packet identifier 122, packet duplicator 126 creates two copies of the packet. The first copy is 31 identified with the original PID so that the primary encryption encoder 104 will 32 recognize that it is to be encrypted. The second copy is identified with a new Docket No.: SNY-S5161.01 -5- PATENT

1 and unused PID, called a "secondary PID" (or shadow PID) by the PID
2 Remapper 122; This secondary PID will be used later by the selective 3 encryption encoder 114 to determine which packets are to be encrypted 4 according to the secondary encryption method. FIGURE 2 illustrates an exemplary set of transport PSI tables 136 after this remapping with a PAT 138 6 defining two programs (10 and 20) with respective PID values 0100 and 0200.
7 A first PMT 140 defines a PID=01 01 for the video elementary stream and PIDs 8 0102 and 0103 for two audio streams for program 10. Similarly, a second PMT
9 142 defines a PID=0201 for the video elementary stream and PIDs 0202 and 0203 for two audio streams for program 20.
11 As previously noted, the two primary commercial providers of cable head 12 end encryption and modulation equipment are (at this writing) Motorola, Inc. and 13 Scientific-Atlanta, Inc. While similar in operation, there are significant 14 differences that should be discussed before proceeding since the present selective encryption encoder 114 is desirably compatible with either system.
16 In the case of Motorola equipment, the Integrated Receiver Transcoder (IRT), an 17 unmodulated output is available and therefore there is no need to demodulate 18 the output before returning a signal to the selective encryption encoder 114, 19 whereas no such unmodulated output is available in a Scientific-Atlanta device.
Also, in the case of current Scientific-Atlanta equipment, the QAM, the primary 21 encryption encoder carries out a PID remapping function on received packets.
22 Thus, provisions are made in the selective encryption encoder 114 to address 23 this remapping.
24 In addition to the above processing, the Program Specific Information (PSI) is also modified to reflect this processing. The original, incoming Program 26 Association Table (PAT) is appended with additional Program Map Table (PMT) 27 entries at a PMT inserter 134. Each added PMT entry contains the new, 28 additional streams (remapped & shadow PIDs) created as part of the selective 29 encryption (SE) encoding process for a corresponding stream in a PMT of the incoming transport. These new PMT entries will mirror their corresponding 31 original PMTs. The program numbers will be automatically assigned by the 32 selective encryption encoder 114 based upon open, available program numbers Docket No.: SNY-S5161.01 -6- PATENT

1 as observed from the program number usage in the incoming stream. The 2 selective encryption System 114 system displays the inserted program 3 information (program numbers, etc) on the configuration user interface of control 4 computer 118 so that the Multiple System Operator (MSO, e.g., the cable system operator) can add these extra programs into the System Information (SI) 6 control system and instruct the system to carry these programs in the clear.
7 The modified transport PSI is illustrated as 144 in FIGURE 3 with two 8 additional temporary PMTs 146 and 148 appended to the tables of transport PSI
9 136. The appended PMTs 146 and 148 are temporary. They are used for the primary encryption process and are removed in the second pass of processing 11 by the secondary encryption encoder. In accordance with the MPEG standard, 12 all entries in the temporary PMTs are marked with stream type "user private"
13 with an identifier of OxFO. These PMTs describe the remapping of the PIDs for 14 use in later recovery of the original mapping of the PIDs in the case of a PID
remapping in the Scientific-Atlanta equipment. Of course, other identifiers could 16 be used without departing from the present invention.
17 In order to assure that the Scientific-Atlanta PID remapping issue is 18 addressed, if the selective encryption encoder 114 is configured to operate with 19 a Scientific-Atlanta system, the encoder adds a user private data descriptor to each elementary stream found in the original PMTs in the incoming data 21 transport stream (TS) per the format below (of course, other formats may also 22 be suitable):

Syntax value # of bits private_data_indicator_descriptorO {
descriptor tag OxFO 8 descriptor length 0x04 8 private_data_indicatorO {
orig_pid Ox???? 16 stream_type 0x?? 8 reserved OxFF 8 }
}

Docket No.: SNY-S5161.01 -7- PATENT

1 The selective encryption encoder 114 of the current embodiment also 2 adds a user private data descriptor to each elementary stream placed in the 3 temporary PMTs created as described above per the format below:

Syntax value # of bits private-data _indicator descriptorO {
descriptor tag OxFO 8 descriptor length 0x04 8 private_data_indicatorO {
orig_pid Ox???? 16 stream_type Ox?? 8 reserved OxFF 8 }
}
6 The "???" in the tables above is the value of the "orig_pid" which is a 7 variable while the "??" is a "stream-type" value. The data field for "orig_pid" is 8 a variable that contains the original incoming PID or in the case of remap or 9 shadow PIDs, the original PID that this stream was associated with. The data field "stream-type" is a variable that describes the purpose of the stream based 11 upon the chart below:

14 Stream Type Value Legacy ES Ox00 Remapped ES Ox01 16 Shadow ES 0x02 Reserved 0x03 - OxFF

19 These descriptors will be used later to re-associate the legacy elementary streams, which are encrypted by the Scientific-Atlanta, Inc.
primary 21 encryption encoder 104, with the corresponding shadow and remapped clear 22 streams after PID remapping in the Scientific-Atlanta, Inc. modulator prior to the 23 second phase of processing of the Selective Encryption Encoder. Those skilled 24 in the art will appreciate that the above specific values should be considered Docket No.: SNY-S5161.01 -8- PATENT

1 exemplary and other specific values could be used without departing from the 2 present invention.
3 In the case of a Motorola cable system being selected in the selective 4 encryption encoder configuration GUI, the original PAT and PMTs can remain unmodified, providing the system does not remap PIDs within the primary 6 encryption encoder. The asterisks in FIGURE 1 indicate functional blocks that 7 are not used in a Motorola cable system.
8 The data stream from selective encryption encoder 114 is passed along 9 to the input of the primary encryption encoder 104 which first carries out a PID
filtering process at 150 to identify packets that are to be encrypted. At 152, in 11 the case of a Scientific-Atlanta device, a PID remapping may be carried out.
12 The data are then passed along to an encrypter 154 that, based upon the PID
13 of the packets encrypts certain packets (in accord with the present invention, 14 these packets are the special packets which are mapped by the packet duplicator 130 to the original PID of the incoming data stream for the current 16 program). The remaining packets are unencrypted. The data then passes 17 through a PSI modifier 156 that modifies the PSI data to reflect changes made 18 at the PID remapper. The data stream is then modulated by a quadrature 19 amplitude modulation (QAM) modulator 158 (in the case of the Scientific-Atlanta device) and passed to the output thereof. This modulated signal is then 21 demodulated by a QAM demodulator 160. The output of the demodulator 160 22 is directed back to the selective encryption encoder 114 to a PSI
parser164.
23 The second phase of processing of the transport stream for selective 24 encryption is to recover the stream after the legacy encryption process is carried out in the primary encryption encoder 104. The incoming Program Specific 26 Information (PSI) is parsed at 164 to determine the PIDs of the individual 27 elementary streams and their function for each program, based upon the 28 descriptors attached in the first phase of processing. This allows for the 29 possibility of PID remapping, as seen in Scientific-Atlanta primary encryption encoders. The elementary streams described in the original program PMTs are 31 located at PSI parser 164 where these streams have been reduced to just the 32 selected packets of interest and encrypted in the legacy CA system format in Docket No.: SNY-S5161.01 -9- PATENT

1 accord with the primary encryption method at encoder 104. The elementary 2 streams in the temporary programs appended to the original PSI are also 3 recovered at elementary stream concatenator 168. The packets in the legacy 4 streams are appended to the remapped content, which is again remapped back to the PID of the legacy streams, completing the partial, selective encryption of 6 the original elementary streams.
7 The temporary PMTs and the associated PAT entries are discarded and 8 removed from the PSI. The user private data descriptors added in the first 9 phase of processing are also removed from the remaining original program PMTs in the PSI. For a Motorola system, no PMT or PAT reprocessing is 11 required and only the final secondary encryption of the transport stream occurs.
12 During the second phase of processing, the SE encoder 114 creates a 13 shadow PSI structure that parallels the original MPEG PSI, for example, having 14 at PAT origin at PID 0x0000. The shadow PAT will be located at a PID
specified in the SE encoder configuration as indicated by the MSO from the user 16 interface. The shadow PMT PIDs will be automatically assigned by the SE
17 encoder 114 dynamically, based upon open, available PID locations as 18 observed from PID usage of the incoming stream. The PMTs are duplicates of 19 the original PMTs, but also have CA descriptors added to the entire PMT or to the elementary streams referenced within to indicate the standard CA
21 parameters and optionally, shadow PID and the intended operation upon the 22 associated elementary stream. The CA descriptor can appear in the 23 descriptor) () or descriptor2() loops of the shadow PMT. If found in descri ptorl (), 24 the CA PID called out in the CA descriptor contains the non-legacy ECM PID
which would apply to an entire program. Alternatively, the ECM PID may be 26 sent in descriptor2(). The CA descriptor should not reference the selective 27 encryption elementary PID in the descriptor) () area.

CA PID Definition Secondary CA private data Value ECM PID Ox00 Replacement PID Ox01 Insertion PID 0x02 29 ECM PID undefined (default) Docket No.: SNY-S5161.01 -10- PATENT

2 This shadow PSI insertion occurs regardless of whether the selective 3 encryption operation is for a Motorola or Scientific Atlanta cable network.
The 4 elementary streams containing the duplicated packets of interest that were also assigned to the temporary PMTs are encrypted during this second phase of 6 operation at secondary packet encrypter in the secondary CA format based 7 upon the configuration data of the CA system attached using the DVB (Digital 8 Video Broadcasting) SimulcryptTM standard.
9 The data stream including the clear data, primary encrypted data, secondary encrypted data and other information are then passed to a PSI
11 modifier 176 that modifies the transport PSI information by deletion of the 12 temporary PMT tables and incorporation of remapping as described above. The 13 output of the PSI modifier 176 is modulated at a QAM modulator 180 and 14 delivered to the cable plant 184 for distribution to the cable system's customers.
The control processor 100 may be a personal computer based device 16 that is used to control the selective encryption encoder as described herein. An 17 exemplary personal computer based controller 100 is depicted in FIGURE 4.
18 Control processor 100 has a central processor unit (CPU) 210 with an 19 associated bus 214 used to connect the central processor unit 210 to Random Access Memory 218 and Non-Volatile Memory 222 in a known manner. An 21 output mechanism at 226, such as a display and possibly printer, is provided in 22 order to display and/or print output for the computer user as well as to provide 23 a user interface such as a Graphical User Interface (GUI). Similarly, input 24 devices such as keyboard and mouse 230 may be provided for the input of information by the user at the MSO. Computer 100 also may have disc storage 26 234 for storing large amounts of information including, but not limited to, 27 program files and data files. Computer system 100 also has an interface 238 28 for connection to the selective encryption encoder 114. Disc storage 234 can 29 store any number of encryption methods that can be downloaded as desired by the MSO to vary the encryption on a regular basis to thwart hackers. Moreover, 31 the encryption methods can be varied according to other criteria such as 32 availability of bandwidth and required level of security.

Docket No.: SNY-S5161.01 -1 1- PATENT

1 The partial encryption process described above utilizes any suitable 2 conditional access encryption method at encrypters 154 and 174. However, 3 these encryption techniques are selectively applied to the data stream using a 4 technique such as those described below or in the above-referenced patent applications. In general, but without the intent to be limiting, the selective 6 encryption process utilizes intelligent selection of information to encrypt so that 7 the entire program does not have to undergo dual encryption. By appropriate 8 selection of appropriate data to encrypt, the program material can be effectively 9 scrambled and hidden from those who desire to hack into the system and illegally recover commercial content without paying. The MPEG (or similar 11 format) data that are used to represent the audio and video data does so using 12 a high degree of reliance on the redundancy of information from frame to frame.
13 Certain data can be transmitted as "anchor" data representing chrominance and 14 luminance data. That data is then often simply moved about the screen to generate subsequent frames by sending motion vectors that describe the 16 movement of the block. Changes in the chrominance and luminance data are 17 also encoded as changes rather than a recoding of absolute anchor data.
18 In accordance with certain embodiments of the present invention, a 19 method of dual encrypting a digital video signal involves examining unencrypted packets of data in the digital video signal to identify at least one specified packet 21 type, the specified packet type comprising packets of data as will be described 22 hereinafter; encrypting packets identified as being of the specified packet type 23 using a first encryption method to produce first encrypted packets;
encrypting 24 the packets identified as being of the specified packet type using a second encryption method to produce second encrypted packets; and replacing the 26 unencrypted packets of the specified packet type with the first encrypted 27 packets and the second encrypted packets in the digital video signal to produce 28 a partially dual encrypted video signal.
29 The MPEG specification defines a slice as "... a series of an arbitrary number of consecutive macroblocks. The first and last macroblocks of a slice 31 shall not be skipped macroblocks. Every slice shall contain at least one 32 macroblock. Slices shall not overlap. The position of slices may change from Docket No.: SNY-S5161.01 -12- PATENT
E

1 picture to picture. The first and last macroblock of a slice shall be in the same 2 horizontal row of macroblocks. Slices shall occur in the bitstream in the order 3 in which they are encountered, starting at the upper-left of the picture and 4 proceeding by raster-scan order from left to right and top to bottom...."
By way of example, to represent an entire frame of NTSC information, for 6 standard resolution, the frame (picture) is divided into 30 slices (but in general 7 j slices may make up a full frame). Each slice contains 33 variable length 8 macroblocks (but in general can include k variable length macroblocks) of 9 information representing a 16x16 pixel region of the image. This is illustrated as standard definition frame 250 of FIGURE 5 with each slice starting with a 11 slice header (SH1-SH30) and each slice having 33 macroblocks (MB1-MB33).
12 By appropriate selection of particular data representing the frame, the image 13 can be scrambled beyond recognition in a number of ways as will be described 14 below. By variation of the selection criteria for selective encryption, hackers can be thwarted on a continuing basis. Moreover, the selection criteria can be 16 changed to adapt to bandwidth requirements as well as need for security of 17 particular content (or other criteria).
18 In standard MPEG compliant digital video, the video image is 19 occasionally refreshed with "anchor data". Such anchor data appears in the data stream at various times to provide absolute luminance and chrominance 21 information. This is normally carried out in an MPEG system using an I
Frame.
22 However, some encoders (e. g., those produced by Motorola, Inc.) use P
Frames 23 to encode progressively refreshed intracoded slices. Such systems often 24 refresh three consecutive slices in a P Frame with the following three slices refreshed in the next P Frame. Thus a full refresh takes 30 frames and requires 26 about one second to accomplish. Although typically, three I slices (inter-coded 27 slices) are used for a 30 slice P frame, as many as nine slices may be sent, 28 depending on the configuration of the Motorola encoder. A television set-top 29 box or other receiver tuning to a Motorola encoded program will get a complete screen refresh within about 1 second.
31 Intracoded slices are not based on any previous or future data sent in 32 other frames, but they contain anchor data relied upon by other frames.
This Docket No.: SNY-S5161.01 -13- PATENT

1 anchor data may be advantageously utilized in a selective encryption scheme 2 because if this data were encrypted, then other frames that relied on the data 3 would be detrimentally affected.
4 The slice header has syntax described by the table below:
6 Slice() { No. Mnemonic of bits 7 slice-start-code 32 bslbf 8 If (vertical_size>28000 9 slice-vertical position_extension 3 uimsbf if(<sequence_scalable_extension () is 11 present in bitstream>){

12 if (scalable mode === "data partitioning") 13 priority_breakpoint 7 uimsbf 14 }

quantizer scale_code 5 uimsbf 16 if (nextbits() =='l'){

17 intra_slice_flag 1 bslbf 18 intra slice 1 uimsbf 19 reserved bits 7 uimsbf while (nextbits() =='l' {

21 extra-bit-slice /* with value of '1' */ 1 uimsbf 22 extra-slice-information 8 uimsbf 23 }

24 }

extra-bit-slice /* with value of '0' 26 do{

27 macroblock() 28 } while (nextbits()!='000 0000 0000 0000 29 0000 0000') Docket No.: SNY-S5161.01 -14- PATENT

1 next_start_code() 2 }

4 Slices with all intra-coded macroblocks generally have the intra slice indicator set to 1. This flag may be used not only to signal slices with intra-coded 6 macroblocks which would not only be sent with I Frames, but also with 7 "progressive refresh" P Frames (where a certain number of slices are sent with 8 all intra-coded macroblocks). The intra_slice flag set to "1"maybe used to flag 9 slices with any portion of intra-coded blocks, and might be used to completely eliminate decoding of any intra-coded blocks.
11 As noted above, often, the slice header bits known as intra-slice and 12 intra_slice flag are utilized to signify that the slice is an I slice.
However, the 13 use of these bits is optional. It has been observed that roughly 90% of the HITS
14 (Headend In The Sky) feeds use these flags. This leaves approximately 10%
that do not use these flags. The reason for this is uncertain. The use of the 16 flags may depending on the age of the encoders in use, or possible a setting of 17 the encoders. Consequently, these flags cannot be 100% relied upon to 18 determine whether or not a particular slice is intracoded. While it may be 19 possible to parse each slice to see whether all the macroblocks are intracoded, but this may require processing power which may not be available.
21 It has been observed that in all cases, an unique byte pattern can be 22 identified in the video signal that can be utilized to determine the presence of 23 intra-coded slices. Thus, by looking at particular byte patterns, the presence of 24 an intracoded slice can be ascertained without need for the above-referenced flags. It has been determined that this unique byte pattern in a Motorola 26 encoded progressive refresh system is that the second byte after a slice's Slice 27 Start Code is the same for all three (or in general, N) consecutive slices that are 28 intracoded. Thus, for a thirty slice frame using Motorola's progressive refresh, 29 the second byte after the slice start code is identical for three consecutive slices in each frame. However, other macroblock byte values could equally well be 31 set identical and detected by minor variations of the present invention without 32 departing from the present invention as taught and claimed herein.
Moreover, Docket No.: SNY-S5161.01 -15- PATENT

1 differing numbers of consecutive slices might contain intra-coded data in other 2 embodiments (e.g., high definition or other variations). Again, modifications to 3 the present invention within the scope of the invention will be obvious to those 4 skilled in the art upon consideration of this teaching.
FIGURE 6 is a flow chart depicting one process 300 for detecting the 6 intra-coded slices in accordance with certain embodiments consistent with the 7 present invention starting at 304. At 308 a slice counter N is initialized to 1 and 8 the first (Nth) slice is received at 312. The N+1 slice is received at 316.
The 9 second byte after the slice start code for the N slice and the N+1 slice (referred to in the drawing as byte N and byte N+!) are then read and compared at 320.
11 If these two bytes are the same at 324, it is possible that they are part of a set 12 of intra-coded slices, and control passes to 330. If the next consecutive slice 13 has the same second byte after the slice start code, a possible set of intra-14 coded slices will have been identified. To confirm, the state machine should check subsequent slices in the following frames. In the following frames, the 16 intra-coded slices should incremented, and wrap around after 30. If the 17 subsequent slices are not intra-coded, then the state machine can assume a 18 false start, perhaps a scene change where many slices were intra-coded, and 19 start seeking again.
The next slice (slice N+2) is then received at 330 and at 334, the second 21 byte after the slice start code is read and compared to the second byte after the 22 slice start code of slice N+1 (or equivalently, slice N) at 338. If they are the 23 same at 338, an intra-coded slice group has been identified at 342. These 24 slices can then be encrypted (if that is the objective) at 346 and control passes to 350 where the system awaits the arrival of N is incremented by 3 to begin 26 looking for the next set of intra-coded slices. If only one set of intra-coded slices 27 is present per frame, the process can await the end of the frame (N=30) and 28 then go back to 308 for the next frame. However, if more than one set of intra-29 coded slices is possible per frame, control returns to 350.
After N is incremented by 3, the process checks at 358 to determine if 31 the end of the frame is reached. If N=31 at 358, a new frame is beginning and 32 control passes to 308 where N is reset to 1. If N=31 has not been reached at Docket No.: SNY-S5161.01 -16- PATENT

1 358, control passes to 312 where the process of comparing the next pair of 2 slices begins.
3 In the event, first and second slices do not have an equal second byte 4 after the slice start code at 324, control passes to 350 where the value of N is incremented by three to look for the next set of three consecutive slices.
6 Similarly, if the third consecutive slice at 338 is not equal to the second, N is 7 incremented at 350 and the process proceeds to inspection of the next set of 8 three slices. In light of this disclosure, many variations of this process will occur 9 to those skilled in the art within the scope of the present invention.
Again, it should be noted that the process described is specific to finding 11 three consecutive intra-coded slices in a thirty slice frame. However, those 12 skilled in the art will readily understand how to equivalently extend the method 13 described without departing from the invention upon consideration of the 14 present teaching.
A process for detecting the sets of intra-coded slices as described above 16 can also be implemented using a simple synchronous state machine that can 17 search for three consecutive slices which have the same second byte after the 18 slice start code. With each new frame, a set of three slices are intra-coded.
19 These slices can be 1-3, 4-6, ... 28-30. Generally, the set of three slices progresses from the top of the frame (slices 1-3) to the bottom (slices 28-30).
21 After slice 30, the set of slices that are intra-coded moves to the top of the next 22 frame. The sync state machine 360 as described by the state diagram of 23 FIGURE 7 can verify that that the set of slices move the correct number of slices 24 with each P frame. This state machine assumes a frame of thirty slices (which should not be considered limiting, since high definition images use higher 26 numbers of slices) and assumes three I slices per P frame.
27 State machine 360 starts out in synchronous state 0 where the second 28 byte after the slice start code is inspected for slices N and N+1 (again, the 29 terminology byte N and byte N+1 is used in the drawing). The machine remains in state 0 until two consecutive bytes after the slice start code are identified.
31 When these bytes are equal and MOD3(slice number)=2, that is, the two bytes Docket No.: SNY-S5161.01 -17- PATENT

1 being compared are from slices 1-2, 4-5, ... , 28-29, then the state changes to 2 synchronous state 2.
3 At synchronous state 2, the next slice is read and the second byte after 4 the slice start code is compared in slices N+1 and N+2. If they are the same and MOD3(slice number)=3, then the machine transitions to synchronous state 6 3. The value of a counter LOCK is set to 31. And then the machine transitions 7 to synchronous state 4. State 4 allows transition to the next P frame. A
slice is 8 read, and LOCK is decremented by one. With each read, the second byte after 9 the slice start code is stored. If LOCK = 0, then the machine transitions to synchronous state 1. If the next slice N+31 and N+32 are the same then the 11 state machine can assume that the progressive slice sequence has been 12 correctly found since it spanned across frames. The state machine is in synch.
13 Some implementations might check to see if the progressive slice sequence 14 spans multiple frames before in synch is declared. Once the machine is in synch, then the first slice of progressive refresh sequence can be can be 16 chosen for encryption without receiving the next slice of the sequence for that 17 frame. Also, if there is any noise or drop-outs, the first slice or second slice can 18 be missed, and the machine will still encrypt the other slices.
19 At synchronous state 3, the value of Lock is inspected and if equal to zero, the state machine transitions to synchronous state 1, otherwise the 21 machine remains at synchronous state 4.
22 At synchronous state 1, the next slice (N) is read and the second byte 23 after the slice start code is compared to the following slice. If they are equal, 24 synchronous state 2 is again entered. If they are not equal, synchronous state 0 is entered. Even though, synch may have been "declared", if the byte values 26 do not match, then it can allow the machine to get re-synchronized.
27 In the above-described embodiments, three consecutive intra-coded 28 slices are sought. However, in general, N consecutive slices can be searched 29 for using similar algorithms or state machines, it is possible that the Motorola encoder can create from one to ten intra-coded slices per frame. Thus, the 31 algorithm preferably, but not necessarily provides for a variable or user 32 selectable number of slices to look for.

Docket No.: SNY-S5161.01 -18- PATENT

1 As in the previous explanation in connection with the flow chart of 2 FIGURE 6, when three (or in general N) consecutive intra-coded slices are 3 identified, they can be encrypted if this is the objective of identification of the 4 intra-coded slices. However, there may be other reasons for identification of these slices.
6 Once it is determined that a particular slice is an I slice, a selective 7 encryption encoder can be utilized to select packets containing I slice data for 8 encryption. Such slices can be encrypted by any suitable means including, but 9 not limited to, any or all of encryption of the slice headers, encryption of all data in the slice, encryption of the slice header plus the first macroblock following the 11 slice header, or any other encryption scheme for encryption of all or part of the 12 I slice data.
13 By encryption of a slice header, the corresponding slice cannot be 14 properly displayed. Moreover, a relatively low amount of bandwidth is required in a dual encryption scenario for encryption of packets with secondary PIDs 16 when the encrypted packets are those containing the slice header. As a 17 practical matter, encryption of a packet containing the slice header likely 18 involves encryption of additional information including at least a portion of the 19 first macroblock following each slice header, rendering the slice all the more difficult to decode.
21 Security can be further enhanced if in addition to the slice header, the 22 first macroblock is encrypted in each slice. Since the first macroblock of each 23 slice contains anchor data in the form of absolute chrominance and luminance 24 values, encryption of the first macroblock of each slice reduces the amount of absolute data available to a hacker to work backwards from in order to decypher 26 the image. Using this technique adds little to the overhead of encryption of slice 27 headers alone. Owing to the variable length of the macroblocks, somewhat 28 more data may be encrypted according to this scheme, since a packet may 29 carry portions of multiple macroblocks. Those skilled in the art will also appreciate that the first macroblock of each slice can also be encrypted without 31 encryption of the slice headers to distort the video. This is also a viable 32 encryption scheme.

Docket No.: SNY-S5161.01 -19- PATENT

1 Several techniques are described above for encryption of the selected 2 data. In each case, for the current embodiment, it will be understood that 3 selection of a particular type of information implies that the payload of a packet 4 carrying such data is encrypted. However, in other environments, the data itself can be directly encrypted. Those skilled in the art will appreciate that such 6 variations as well as others are possible without departing from the present 7 invention. Moreover, those skilled in the art will appreciate that many variations 8 and combinations of the encryption techniques described hereinafter can be 9 devised and used singularly or in combination without departing from the present invention.
11 Numerous other combinations of the above encryption techniques as well 12 as those described in the above-referenced patent applications and other partial 13 encryption techniques can be combined to produce a rich pallette of encryption 14 techniques from which to select. In accordance with certain embodiments of the present invention, a selection of packets to encrypt can be made by the 16 control computer 118 in order to balance encryption security with bandwidth and 17 in order to shift the encryption technique from time to time to thwart hackers.
18 An authorized set-top box such as 380 illustrated in FIGURE 8 operating 19 under the secondary CA system decrypts and decodes the incoming program by recognizing both primary and secondary PIDs associated with a single 21 program. The multiplexed video data stream containing both PIDs is directed 22 to a demultiplexer 384. When a program is received that contains encrypted 23 content that was encrypted by any of the above techniques, the demultiplexer 24 directs encrypted packets containing encrypted content and secondary PIDS
to a secondary CA decrypter 388. These packets are then decrypted at 388 and 26 passed to a PID remapper 392. As illustrated, the PID remapper 392 receives 27 packets that are unencrypted and bear the primary PID as well as the decrypted 28 packets having the secondary PID. The PID remapper 392 combines the 29 decrypted packets from decrypter 388 with the unencrypted packets having the primary PID to produce an unencrypted data stream representing the desired 31 program. PID remapping is used to change either the primary or secondary PID
32 or both to a single PID. This unencrypted data stream can then be decoded Docket No.: SNY-S5161.01 -20- PATENT

1 normally by decoder 396. Some or all of the components depicted in FIGURE
2 8 can be implemented and/or controlled as program code running on a 3 programmed processor, with the code being stored on an electronic storage 4 medium.
FIGURE 9 is a flow chart 400 that broadly illustrates the encryption 6 process consistent with certain embodiments of the present invention starting 7 at 404. At 408 the packet type that is to be encrypted is specified. In 8 accordance with certain embodiments consistent with the present invention, the 9 selected packet type may be any packet containing I slice data. Packets are then examined at 412 to identify packets of the specified type. At 416, the 11 identified packets are duplicated and at 420 one set of these packets is 12 encrypted under a first encryption method. The other set of identified packets 13 is encrypted at 424 under a second encryption method. The originally identified 14 packets are then replaced in the data stream with the two sets of encrypted packets at 430 and the process ends at 436.
16 While the above embodiments describe encryption of packets containing 17 the selected data type, it is also possible to encrypt the raw data prior to 18 packetizing without departing from this invention and such encryption is 19 considered equivalent thereto.
Those skilled in the art will recognize that the present invention has been 21 described in terms of exemplary embodiments based upon use of a 22 programmed processor (e.g., processor 118, processors implementing any or 23 all of the elements of 114 or implementing any or all of the elements of 380).
24 However, the invention should not be so limited, since the present invention could be implemented using hardware component equivalents such as special 26 purpose hardware and/or dedicated processors which are equivalents to the 27 invention as described and claimed. Similarly, general purpose computers, 28 microprocessor based computers, micro-controllers, optical computers, analog 29 computers, dedicated processors and/or dedicated hard wired logic may be used to construct alternative equivalent embodiments of the present invention.
31 Those skilled in the art will appreciate that the program steps and 32 associated data used to implement the embodiments described above can be Docket No.: SNY-S5161.01 -21- PATENT

1 implemented using disc storage as well as other forms of storage such as for 2 example Read Only Memory (ROM) devices, Random Access Memory (RAM) 3 devices; optical storage elements, magnetic storage elements, magneto-optical 4 storage elements, flash memory, core memory and/or other equivalent storage technologies without departing from the present invention. Such alternative 6 storage devices should be considered equivalents.
7 The present invention, as described in embodiments herein, is 8 implemented using a programmed processor executing programming 9 instructions that are broadly described above form that can be stored on any suitable electronic storage medium or transmitted over any suitable electronic 11 communication medium or otherwise be present in any computer readable or 12 propagation medium. However, those skilled in the art will appreciate that the 13 processes described above can be implemented in any number of variations 14 and in many suitable programming languages without departing from the present invention. For example, the order of certain operations carried out can 16 often be varied, additional operations can be added or operations can be 17 deleted without departing from the invention. Error trapping can be added 18 and/or enhanced and variations can be made in user interface and information 19 presentation without departing from the present invention. Such variations are contemplated and considered equivalent.
21 Software code and/or data embodying certain aspects.of the present 22 invention may be present in any computer readable medium, transmission 23 medium, storage medium or propagation medium including, but not limited to, 24 electronic storage devices such as those described above, as well as carrier waves, electronic signals, data structures (e.g., trees, linked lists, tables, 26 packets, frames, etc.) optical signals, propagated signals, broadcast signals, 27 transmission media (e.g., circuit connection, cable, twisted pair, fiber optic 28 cables, waveguides, antennas, etc.) and other media that stores, carries or 29 passes the code and/or data. Such media may either store the software code and/or data or serve to transport the code and/or data from one location to 31 another. In the present exemplary embodiments, MPEG compliant packets, 32 slices, tables and other data structures are used, but this should not be Docket No.: SNY-S5161.01 -22- PATENT

1 considered limiting since other data structures can similarly be used without 2 departing from the present invention.
3 While the invention has been described in conjunction with specific 4 embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those skilled in the art in light of the 6 foregoing description. Accordingly, it is intended that the present invention 7 embrace all such alternatives, modifications and variations as fall within the 8 scope of the appended claims.

Docket No.: SNY-S5161.01 -23- PATENT

Claims (29)

What is claimed is:

1. A selective encryption decoder, for decrypting and decoding a selectively encrypted digital video signal, comprising:
a demultiplexer that receives packets of digital video, certain of the packets being unencrypted and certain of the packets being encrypted, wherein certain of the encrypted packets comprise packets in a set of N consecutive slices in a frame wherein a second byte after a slice start code is identical in all N
consecutive slices;
the unencrypted packets having a first packet identifier (PID) and the encrypted packets having a second packet identifier (PID);
a decrypter receiving the encrypted packets having the second PID and decrypting the encrypted packets using a first encryption method to produce decrypted packets;
a PID remapper that changes at least one of the first and second PIDs so that the unencrypted packets and the decrypted packets have the same PID; and a decoder that decodes the unencrypted and decrypted packets to produce a decoded video signal.

2. The selective encryption decoder according to claim 1, wherein N is between 1 and 10.

3. A method of decrypting and decoding a selectively encrypted digital video signal, comprising:
receiving packets of digital video, certain of the packets being unencrypted and certain of the packets being encrypted, wherein certain of the encrypted packets comprise packets in a set of N consecutive slices in a frame wherein a second byte after a slice start code is identical in all N consecutive slices;
the unencrypted packets having a first packet identifier (PID) and the encrypted packets having a second packet identifier (PID);

decrypting the encrypted packets having the second PID to produce decrypted packets;
remapping at least one of the first and second PIDs so that the unencrypted packets and the decrypted packets have the same PID; and decoding the unencrypted and decrypted packets to produce a decoded video signal.

4. A computer readable medium carrying instructions which, when executed on a programmed processor, carry out the method of decoding and decrypting a digital video signal according to claim 3.

5. The method according to claim 3, wherein N is between 1 and 10.

6. A computer readable medium that carries instructions that when executed on a programmed processor to facilitate operation of a video receiver device to decrypt and decode a selectively encoded digital video signal wherein the instructions comprise:
a code segment that controls a demultiplexer that receives packets of digital video, certain of the packets being unencrypted and certain of the packets being encrypted, wherein certain of the encrypted packets comprise packets in a set of N consecutive slices in a frame wherein a second byte after a slice start code is identical in all N consecutive slices, the unencrypted packets having a first packet identifier (PID) and the encrypted packets having a second packet identifier (PID);
a code segment that controls decryption of the encrypted packets to produce decrypted packets;
a code segment that controls remapping at least one of the first and second PIDs so that the unencrypted packets and the decrypted packets have the same PID;
and a code segment that controls decoding the unencrypted and decrypted packets to produce a decoded video signal.

7. The computer readable medium according to claim 6, wherein N is between 1 and 10.

8. A method of detecting intra-coded slices in a progressive refresh frame of video data, comprising:
reading a value of a predetermined byte in each of a plurality of adjacent slices of a frame of video data;
comparing the byte values read from the plurality of adjacent slices, each other; and determining that the adjacent slices are intra-coded slices if the byte values are the same in the plurality of adjacent slices.

9. The method according to claim 8, embodied in a synchronous state machine.

10. The method according to claim 8 or 9, wherein the plurality of adjacent slices comprises N adjacent slices.

11. The method according to any one of claims 8 to 10, wherein the predetermined byte comprises a macroblock byte.

12. The method according to claim 11, wherein the macroblock byte value comprises a second byte after a slice start code.

13. The method according to claim 8, further comprising:
duplicating the intra-coded slices to create duplicate intra-coded slices; and dual encrypting the duplicate intra-coded slices under first and second encryption methods.

14. The method according to claim 13, wherein the dual encrypting comprises dual encrypting packets containing slice headers intra-coded slices.

15. The method according to claim 13, wherein the dual encrypting comprises dual encrypting packets containing infra-coded macroblocks intra- coded slices.

16. The method according to claim 13, wherein the dual encrypting comprises dual encrypting packets containing data from a first macroblock following the video slice header in the intra-coded slices.

17. The method according to claim 8, further comprising encrypting the intra-coded slices.

18. The method according to claim 17, wherein the encrypting comprises encrypting packets containing slice headers intra-coded slices.

19. The method according to claim 17, wherein the encrypting comprises encrypting packets containing intra-coded macroblocks intra-coded slices.

20. The method according to claim 17, wherein the encrypting comprises encrypting packets containing data from a first macroblock following the video slice header in the intra-coded slices.

21. The method according to claim 10, wherein N is between 1 and 10.

22. A computer readable medium storing instructions which, when executed on a programmed processor, carry out the method of encrypting a digital video signal according to any one of claims 8 to 21.

23. A method of detecting intro-coded slices in a progressive refresh frame of video data, comprising:
reading a second byte following a slice start code in a plurality of adjacent slices of a frame of video data;
comparing the second byte following the slice start code values in N adjacent slices;
and determining that the N adjacent slices are intro-coded slices if the values are the same in the N adjacent slices.

24. The method according to claim 23, embodied in a synchronous state machine.

25. The method according to claim 23, wherein N=3.

26. The method according to claim 25, wherein the N adjacent slices begin with slice number 1, 4, 7,..., 28 in a thirty slice frame.

27. The method according to claim 23, further comprising:
duplicating the infra-coded slices to create duplicate intra-coded slices; and dual encrypting the duplicate intra-coded slices under first and second encryption methods.

28. The method according to claim 23, further comprising encrypting the intra-coded slices.

29. The method according to claim 23, wherein N is between 1 and 10.