Progressive video refresh slice detection

[0001] This application is a continuation-in-part of patent applications docket number SNY-R4646.01 entitled Critical Packet Partial Encryption to Unger et al., Ser. No. 10/038,217; patent applications docket number SNY-R4646.02 entitled Time Division Partial Encryption to Candelore et al., Ser. No. 10/038,032; docket number SNY-R4646.03 entitled Elementary Stream Partial Encryption to Candelore, Ser. No. 10/037,914; docket number SNY-R4646.04 entitled Partial Encryption and PID Mapping to Unger et al., Ser. No. 10/037,499; and docket number SNY-R4646.05 entitled Decoding and Decrypting of Partially Encrypted Information to Unger et al., Ser. No. 10/037,498 all of which were filed on Jan. 2, 2002 and are hereby incorporated by reference herein.

[0002] This application is also a continuation-in-part of U.S. patent application Ser. No. 10/273,905, filed Oct. 18, 2002 to Candelore et al. entitled Video Slice and Active Region Based Dual Partial Encryption, docket number SNY-R4854.01, which is hereby incorporated by reference.

[0003] This application is also related to and claims priority benefit of U.S. Provisional patent application serial No. 60/409,675, filed Sep. 9, 2002, docket number 50S5152, entitled Generic PID Remapping for Content Replacement, to Candelore. These applications are also hereby incorporated by reference herein.

[0004] A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection 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 otherwise reserves all copyright rights whatsoever.

[0005] This invention relates generally to the field of digital video and encryption thereof. More particularly, this invention relates to an encryption method and apparatus particularly useful for encrypting packetized video content such as that provided by cable and satellite television systems.

[0006] The above-referenced commonly owned patent applications describe inventions relating to various aspects of methods generally referred to herein as partial encryption or selective encryption. More particularly, systems are described therein wherein selected portions of a particular selection of digital content are encrypted using two (or more) encryption techniques while other portions of the content are left unencrypted. By properly selecting the portions to be encrypted, the content can effectively be encrypted for use under multiple decryption systems without the necessity of encryption of the entire selection of content. In some embodiments, only a few percent of data overhead is 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 other implementations of conditional access (CA) receivers from multiple manufacturers in a single systemthus freeing the cable or satellite company to competitively shop for providers of Set-top boxes.

[0007] The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however, both as to organization and method of operation, together with objects and advantages thereof, may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, taken in conjunction with the accompanying drawings in which:

[0008] FIG. 1 is a block diagram of an exemplary cable system head end consistent with certain embodiments of the present invention.

[0009] FIG. 2 is an illustration of sample transport stream PSI consistent with certain embodiments of the present invention.

[0010] FIG. 3 is a further illustration of sample transport stream PSI consistent with certain embodiments of the present invention.

[0011] FIG. 4 is a block diagram of an illustrative control processor 100 consistent with certain embodiments of the present invention.

[0012] FIG. 5 illustrates the slice structure of a frame of video data consistent with certain embodiments of the present invention.

[0013] FIG. 6 is a flow chart of a packet selection and encryption process consistent with certain embodiments of the present invention.

[0014] FIG. 7 is a state diagram of a packet selection and encryption process consistent with certain embodiments of the present invention.

[0015] FIG. 8 illustrates a television Set-top box that decrypts and decodes in a manner consistent with certain embodiments of the present invention.

[0016] FIG. 9 is a flow chart broadly illustrating an encryption process consistent with embodiments of the present invention.

[0017] While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail 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 to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawings.

[0018] The terms scramble and encrypt and variations thereof are used synonymously herein. Also, the term television program and similar terms can be interpreted in the normal conversational sense, as well as a meaning wherein the term means any segment of AN content that can be displayed on a television set or similar monitor device. The term video is often used herein to embrace not only true visual information, but also in the conversational sense (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 used for existing cable and satellite systems. The exemplary embodiments disclosed herein are decoded by a television Set-Top Box (STB), but it is contemplated that such technology will soon be incorporated within television receivers of all types whether housed in a separate enclosure alone or in conjunction with recording and/or playback equipment or Conditional Access (CA) decryption module or within a television set itself. The present document generally uses the example of a dual partial encryption embodiment, but those skilled in the art will recognize that the present invention can be utilized to realize multiple partial encryption without departing from the invention. Partial encryption and selective encryption are used synonymously herein.

[0019] Turning now to FIG. 1, a head end 100 of a cable television system suitable for use in practicing a dual encryption embodiment of the present invention is illustrated. Those skilled in the art will appreciate that the present invention could also be implemented using more than two encryptions systems without departing from the present invention. The illustrated head end 100 implements the dual partial encryption scenario of the present invention by adapting the operation of a conventional encryption encoder 104 (such as those provided by Motorola, Inc. and Scientific-Atlanta, Inc., and referred to herein as the primary encryption encoder) with additional equipment.

[0020] Head end 100 receives scrambled content from one or more suppliers, for example, using a satellite dish antenna 108 that feeds a satellite receiver 110. Satellite receiver 110 operates to demodulate and descramble the incoming content and supplies the content as a stream of clear (unencrypted) data to a selective encryption encoder 114. The selective encryption encoder 114, according to certain embodiments, uses two passes or two stages of operation, to encode the stream of data. Encoder 114 utilizes a secondary conditional access system (and thus a second encryption method) in conjunction with the primary encryption encoder 104 which operates using a primary conditional access system (and thus a primary encryption method). A user selection provided via a user interface on a control computer 118 configures the selective encryption encoder 114 to operate in conjunction with either a Motorola or Scientific Atlanta cable network (or other cable or satellite network).

[0021] It is assumed, for purposes of the present embodiment of the invention, that the data from satellite receiver 110 is supplied as MPEG (Moving Pictures Expert Group) compliant packetized data. In the first stage of operation the data is passed through a Special Packet Identifier (PID) 122. Special Packet Identifier 122 identifies specific programming that is to be dual partially encrypted according to the present invention. The Special Packet Identifier 122 signals the Special Packet Duplicator 126 to duplicate special packets. The 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 programming that shall remain clear and the duplicated packets to new PID values. The payload of the elementary stream packets are not altered in any way by Special Packet Identifier 122, Special Packet Duplicator 126, or PID 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.

[0022] The packets may be selected by the special packet identifier 122 according to one of the selection criteria described in the above-referenced applications or may use another selection criteria such as those which will be 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 identified with the original PID so that the primary encryption encoder 104 will recognize that it is to be encrypted. The second copy is identified with a new and unused PID, called a secondary PID (or shadow PID) by the PID Remapper 122. This secondary PID will be used later by the selective encryption encoder 114 to determine which packets are to be encrypted according to the secondary encryption method. FIG. 2 illustrates an exemplary set of transport PSI tables 136 after this remapping with a PAT 138 defining two programs (10 and 20) with respective PID values 0100 and 0200. A first PMT 140 defines a PID0101 for the video elementary stream and PIDs 0102 and 0103 for two audio streams for program 10. Similarly, a second PMT 142 defines a PID0201 for the video elementary stream and PIDs 0202 and 0203 for two audio streams for program 20.

[0023] As previously noted, the two primary commercial providers of cable head end encryption and modulation equipment are (at this writing) Motorola, Inc. and Scientific-Atlanta, Inc. While similar in operation, there are significant differences that should be discussed before proceeding since the present selective encryption encoder 114 is desirably compatible with either system. In the case of Motorola equipment, the Integrated Receiver Transcoder (IRT), an unmodulated output is available and therefore there is no need to demodulate the output before returning a signal to the selective encryption encoder 114, 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 encryption encoder carries out a PID remapping function on received packets. Thus, provisions are made in the selective encryption encoder 114 to address this remapping.

[0024] In addition to the above processing, the Program Specific Information (PSI) is also modified to reflect this processing. The original, incoming Program Association Table (PAT) is appended with additional Program Map Table (PMT) entries at a PMT inserter 134. Each added PMT entry contains the new, additional streams (remapped & shadow PIDs) created as part of the selective encryption (SE) encoding process for a corresponding stream in a PMT of the incoming transport. These new PMT entries will mirror their corresponding original PMTs. The program numbers will be automatically assigned by the selective encryption encoder 114 based upon open, available program numbers as observed from the program number usage in the incoming stream. The selective encryption System 114 system displays the inserted program information (program numbers, etc) on the configuration user interface of control 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) control system and instruct the system to carry these programs in the clear.

[0025] The modified transport PSI is illustrated as 144 in FIG. 3 with two additional temporary PMTs 146 and 148 appended to the tables of transport PSI 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 by the secondary encryption encoder. In accordance with the MPEG standard, all entries in the temporary PMTs are marked with stream type user private with an identifier of 0xF0. These PMTs describe the remapping of the PIDs for 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 be used without departing from the present invention.

[0026] In order to assure that the Scientific-Atlanta PID remapping issue is addressed, if the selective encryption encoder 114 is configured to operate with 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 transport stream (TS) per the format below (of course, other formats may also be suitable):

	Syntax	value	of bits
	private_data_indicator_descriptor()
	descriptor_tag	0xF0	8
	descriptor_length	0x04	8
	private_data_indicator()
	orig_pid	0x	16
	stream_type	0x	8
	reserved	0xFF	8

[0027] The selective encryption encoder 114 of the current embodiment also adds a user private data descriptor to each elementary stream placed in the temporary PMTs created as described above per the format below:

	Syntax	value	of bits
	private_data_indicator_descriptor()
	descriptor_tag	0xF0	8
	descriptor_length	0x04	8
	private_data_indicator()
	orig_pid	0x	16
	stream_type	0x	8
	reserved	0xFF	8

[0028] The in the tables above is the value of the orig_pid which is a variable while the is a stream_type value. The data field for orig_pid is a variable that contains the original incoming PID or in the case of remap or 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 upon the chart below:

	Stream Type	Value
	Legacy ES	0x00
	Remapped ES	0x01
	Shadow ES	0x02
	Reserved	0x03 - 0xFF

[0029] These descriptors will be used later to re-associate the legacy elementary streams, which are encrypted by the Scientific-Atlanta, Inc. primary encryption encoder 104, with the corresponding shadow and remapped clear streams after PID remapping in the Scientific-Atlanta, Inc. modulator prior to the second phase of processing of the Selective Encryption Encoder. Those skilled in the art will appreciate that the above specific values should be considered exemplary and other specific values could be used without departing from the present invention.

[0030] In the case of a Motorola cable system being selected in the selective encryption encoder configuration GUI, the original PAT and PMTs can remain unmodified, providing the system does not remap PIDs within the primary encryption encoder. The asterisks in FIG. 1 indicate functional blocks that are not used in a Motorola cable system.

[0031] The data stream from selective encryption encoder 114 is passed along 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 the case of a Scientific-Atlanta device, a PID remapping may be carried out. The data are then passed along to an encrypter 154 that, based upon the PID of the packets encrypts certain packets (in accord with the present invention, 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 program). The remaining packets are unencrypted. The data then passes through a PSI modifier 156 that modifies the PSI data to reflect changes made at the PID remapper. The data stream is then modulated by a quadrature amplitude modulation (QAM) modulator 158 (in the case of the Scientific-Atlanta device) and passed to the output thereof. This modulated signal is then demodulated by a QAM demodulator 160. The output of the demodulator 160 is directed back to the selective encryption encoder 114 to a PSI parser 164.

[0032] The second phase of processing of the transport stream for selective encryption is to recover the stream after the legacy encryption process is carried out in the primary encryption encoder 104. The incoming Program Specific Information (PSI) is parsed at 164 to determine the PIDs of the individual elementary streams and their function for each program, based upon the descriptors attached in the first phase of processing. This allows for the possibility of PID remapping, as seen in Scientific-Atlanta primary encryption encoders. The elementary streams described in the original program PMTs are located at PSI parser 164 where these streams have been reduced to just the selected packets of interest and encrypted in the legacy CA system format in accord with the primary encryption method at encoder 104. The elementary streams in the temporary programs appended to the original PSI are also recovered at elementary stream concatenator 168. The packets in the legacy 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 the original elementary streams.

[0033] The temporary PMTs and the associated PAT entries are discarded and removed from the PSI. The user private data descriptors added in the first 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 required and only the final secondary encryption of the transport stream occurs.

[0034] During the second phase of processing, the SE encoder 114 creates a shadow PSI structure that parallels the original MPEG PSI, for example, having 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 interface. The shadow PMT PIDs will be automatically assigned by the SE encoder 114 dynamically, based upon open, available PID locations as observed from PID usage of the incoming stream. The PMTs are duplicates of 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 parameters and optionally, shadow PID and the intended operation upon the associated elementary stream. The CA descriptor can appear in the descriptor1( ) or descriptor2( ) loops of the shadow PMT. If found in descriptor1( ), 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 sent in descriptor2( ). The CA descriptor should not reference the selective encryption elementary PID in the descriptor1( ) area.

	CA PID Definition	Secondary CA private data Value
	ECM PID	0x00
	Replacement PID	0x01
	Insertion PID	0x02
	ECM PID	undefined (default)

[0035] This shadow PSI insertion occurs regardless of whether the selective encryption operation is for a Motorola or Scientific Atlanta cable network. The elementary streams containing the duplicated packets of interest that were also assigned to the temporary PMTs are encrypted during this second phase of operation at secondary packet encrypter in the secondary CA format based upon the configuration data of the CA system attached using the DVB (Digital Video Broadcasting) Simulcrypt standard.

[0036] The data stream including the clear data, primary encrypted data, secondary encrypted data and other information are then passed to a PSI modifier 176 that modifies the transport PSI information by deletion of the temporary PMT tables and incorporation of remapping as described above. The output of the PSI modifier 176 is modulated at a QAM modulator 180 and delivered to the cable plant 184 for distribution to the cable system's customers.

[0037] The control processor 100 may be a personal computer based device that is used to control the selective encryption encoder as described herein. An exemplary personal computer based controller 100 is depicted in FIG. 4. Control processor 100 has a central processor unit (CPU) 210 with an 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 output mechanism at 226, such as a display and possibly printer, is provided in order to display and/or print output for the computer user as well as to provide a user interface such as a Graphical User Interface (GUI). Similarly, input 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 234 for storing large amounts of information including, but not limited to, program files and data files. Computer system 100 also has an interface 238 for connection to the selective encryption encoder 114. Disc storage 234 can 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, the encryption methods can be varied according to other criteria such as availability of bandwidth and required level of security.

[0038] The partial encryption process described above utilizes any suitable conditional access encryption method at encrypters 154 and 174. However, these encryption techniques are selectively applied to the data stream using a technique such as those described below or in the above-referenced patent applications. In general, but without the intent to be limiting, the selective encryption process utilizes intelligent selection of information to encrypt so that the entire program does not have to undergo dual encryption. By appropriate selection of appropriate data to encrypt, the program material can be effectively scrambled and hidden from those who desire to hack into the system and illegally recover commercial content without paying. The MPEG (or similar format) data that are used to represent the audio and video data does so using a high degree of reliance on the redundancy of information from frame to frame. Certain data can be transmitted as anchor data representing chrominance and luminance data. That data is then often simply moved about the screen to generate subsequent frames by sending motion vectors that describe the movement of the block. Changes in the chrominance and luminance data are also encoded as changes rather than a recoding of absolute anchor data.

[0039] In accordance with certain embodiments of the present invention, a 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 type, the specified packet type comprising packets of data as will be described hereinafter; encrypting packets identified as being of the specified packet type using a first encryption method to produce first encrypted packets; encrypting the packets identified as being of the specified packet type using a second encryption method to produce second encrypted packets; and replacing the unencrypted packets of the specified packet type with the first encrypted packets and the second encrypted packets in the digital video signal to produce a partially dual encrypted video signal.

[0040] The MPEG specification defines a slice as . . . a series of an arbitrary number of consecutive macroblocks. The first and last macroblocks of a slice shall not be skipped macroblocks. Every slice shall contain at least one macroblock. Slices shall not overlap. The position of slices may change from picture to picture. The first and last macroblock of a slice shall be in the same horizontal row of macroblocks. Slices shall occur in the bitstream in the order in which they are encountered, starting at the upper-left of the picture and proceeding by raster-scan order from left to right and top to bottom . . . .

[0041] By way of example, to represent an entire frame of NTSC information, for standard resolution, the frame (picture) is divided into 30 slices (but in general j slices may make up a full frame). Each slice contains 33 variable length macroblocks (but in general can include k variable length macroblocks) of information representing a 1616 pixel region of the image. This is illustrated as standard definition frame 250 of FIG. 5 with each slice starting with a slice header (SH1-SH30) and each slice having 33 macroblocks (MB1-MB33). By appropriate selection of particular data representing the frame, the image can be scrambled beyond recognition in a number of ways as will be described below. By variation of the selection criteria for selective encryption, hackers can be thwarted on a continuing basis. Moreover, the selection criteria can be changed to adapt to bandwidth requirements as well as need for security of particular content (or other criteria).

[0042] In standard MPEG compliant digital video, the video image is occasionally refreshed with anchor data. Such anchor data appears in the data stream at various times to provide absolute luminance and chrominance information. This is normally carried out in an MPEG system using an I Frame. However, some encoders (e.g., those produced by Motorola, Inc.) use P Frames to encode progressively refreshed intracoded slices. Such systems often 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 about one second to accomplish. Although typically, three I slices (inter-coded slices) are used for a 30 slice P frame, as many as nine slices may be sent, depending on the configuration of the Motorola encoder. A television set-top box or other receiver tuning to a Motorola encoded program will get a complete screen refresh within about 1 second.

[0043] Intracoded slices are not based on any previous or future data sent in other frames, but they contain anchor data relied upon by other frames. This anchor data may be advantageously utilized in a selective encryption scheme because if this data were encrypted, then other frames that relied on the data would be detrimentally affected.

[0044] The slice header has syntax described by the table below:

	No. of
Slice()	bits	Mnemonic
slice_start_code	32	bslbf
If (vertical_size>28000
slice_vertical_position_extension	3	uimsbf
if(<sequence_scalable_extension () is present
in bitstream>)
if (scalable_mode data partitioning)
priority_breakpoint	7	uimsbf
quantizer_scale_code	5	uimsbf
if (nextbits() 1)
intra_slice_flag	1	bslbf
intra_slice	1	uimsbf
reserved_bits	7	uimsbf
while (nextbits() 1
extra_bit_slice /* with value of 1 */	1	uimsbf
extra_slice_information	8	uimsbf
extra_bit_slice /* with value of 0 */
do
macroblock()
while (nextbits()000 0000 0000 0000 0000
0000)
next_start_code()

[0045] 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 macroblocks which would not only be sent with I Frames, but also with progressive refresh P Frames (where a certain number of slices are sent with all intra-coded macroblocks). The intra_slice_flag set to 1 may be used to flag slices with any portion of intra-coded blocks, and might be used to completely eliminate decoding of any intra-coded blocks.

[0046] As noted above, often, the slice header bits known as intra-slice and intra_slice_flag are utilized to signify that the slice is an I slice. However, the use of these bits is optional. It has been observed that roughly 90% of the HITS (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 flags may depending on the age of the encoders in use, or possible a setting of the encoders. Consequently, these flags cannot be 100% relied upon to determine whether or not a particular slice is intracoded. While it may be possible to parse each slice to see whether all the macroblocks are intracoded, but this may require processing power which may not be available.

[0047] It has been observed that in all cases, an unique byte pattern can be identified in the video signal that can be utilized to determine the presence of intra-coded slices. Thus, by looking at particular byte patterns, the presence of 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 encoded progressive refresh system is that the second byte after a slice's Slice Start Code is the same for all three (or in general, N) consecutive slices that are intracoded. Thus, for a thirty slice frame using Motorola's progressive refresh, 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 set identical and detected by minor variations of the present invention without departing from the present invention as taught and claimed herein. Moreover, differing numbers of consecutive slices might contain intra-coded data in other embodiments (e.g., high definition or other variations). Again, modifications to the present invention within the scope of the invention will be obvious to those skilled in the art upon consideration of this teaching.

[0048] FIG. 6 is a flow chart depicting one process 300 for detecting the intra-coded slices in accordance with certain embodiments consistent with the present invention starting at 304. At 308 a slice counter N is initialized to 1 and the first (Nth) slice is received at 312. The N1 slice is received at 316. The second byte after the slice start code for the N slice and the N1 slice (referred to in the drawing as byte N and byte N) are then read and compared at 320. If these two bytes are the same at 324, it is possible that they are part of a set of intra-coded slices, and control passes to 330. If the next consecutive slice has the same second byte after the slice start code, a possible set of intra-coded slices will have been identified. To confirm, the state machine should check subsequent slices in the following frames. In the following frames, the intra-coded slices should incremented, and wrap around after 30. If the subsequent slices are not intra-coded, then the state machine can assume a false start, perhaps a scene change where many slices were intra-coded, and start seeking again.

[0049] The next slice (slice N2) is then received at 330 and at 334, the second byte after the slice start code is read and compared to the second byte after the slice start code of slice N1 (or equivalently, slice N) at 338. If they are the same at 338, an intra-coded slice group has been identified at 342. These 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 looking for the next set of intra-coded slices. If only one set of intra-coded slices is present per frame, the process can await the end of the frame (N30) and then go back to 308 for the next frame. However, if more than one set of intra-coded slices is possible per frame, control returns to 350.

[0050] After N is incremented by 3, the process checks at 358 to determine if the end of the frame is reached. If N31 at 358, a new frame is beginning and control passes to 308 where N is reset to 1. If N31 has not been reached at 358, control passes to 312 where the process of comparing the next pair of slices begins.

[0051] In the event, first and second slices do not have an equal second byte 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. Similarly, if the third consecutive slice at 338 is not equal to the second, N is incremented at 350 and the process proceeds to inspection of the next set of three slices. In light of this disclosure, many variations of this process will occur to those skilled in the art within the scope of the present invention.

[0052] Again, it should be noted that the process described is specific to finding three consecutive intra-coded slices in a thirty slice frame. However, those skilled in the art will readily understand how to equivalently extend the method described without departing from the invention upon consideration of the present teaching.

[0053] A process for detecting the sets of intra-coded slices as described above can also be implemented using a simple synchronous state machine that can search for three consecutive slices which have the same second byte after the slice start code. With each new frame, a set of three slices are intra-coded. 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). After slice 30, the set of slices that are intra-coded moves to the top of the next frame. The sync state machine 360 as described by the state diagram of FIG. 7 can verify that that the set of slices move the correct number of slices 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 numbers of slices) and assumes three I slices per P frame.

[0054] State machine 360 starts out in synchronous state 0 where the second byte after the slice start code is inspected for slices N and N1 (again, the terminology byte N and byte N1 is used in the drawing). The machine remains in state 0 until two consecutive bytes after the slice start code are identified. When these bytes are equal and MOD₃(slice number)2, that is, the two bytes being compared are from slices 1-2, 4-5, . . . , 28-29, then the state changes to synchronous state 2.

[0055] At synchronous state 2, the next slice is read and the second byte after the slice start code is compared in slices N1 and N2. If they are the same and MOD3(slice number)3, then the machine transitions to synchronous state 3. The value of a counter LOCK is set to 31. And then the machine transitions to synchronous state 4. State 4 allows transition to the next P frame. A slice is read, and LOCK is decremented by one. With each read, the second byte after the slice start code is stored. If LOCK0, then the machine transitions to synchronous state 1. If the next slice N31 and N32 are the same then the state machine can assume that the progressive slice sequence has been correctly found since it spanned across frames. The state machine is in synch. Some implementations might check to see if the progressive slice sequence 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 chosen for encryption without receiving the next slice of the sequence for that frame. Also, if there is any noise or drop-outs, the first slice or second slice can be missed, and the machine will still encrypt the other slices.

[0056] 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 machine remains at synchronous state 4.

[0057] At synchronous state 1, the next slice (N) is read and the second byte after the slice start code is compared to the following slice. If they are equal, 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 do not match, then it can allow the machine to get re-synchronized.

[0058] In the above-described embodiments, three consecutive intra-coded slices are sought. However, in general, N consecutive slices can be searched 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 algorithm preferably, but not necessarily provides for a variable or user selectable number of slices to look for.

[0059] As in the previous explanation in connection with the flow chart of FIG. 6, when three (or in general N) consecutive intra-coded slices are identified, they can be encrypted if this is the objective of identification of the intra-coded slices. However, there may be other reasons for identification of these slices.

[0060] Once it is determined that a particular slice is an I slice, a selective encryption encoder can be utilized to select packets containing I slice data for encryption. Such slices can be encrypted by any suitable means including, but 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 slice header, or any other encryption scheme for encryption of all or part of the I slice data.

[0061] By encryption of a slice header, the corresponding slice cannot be properly displayed. Moreover, a relatively low amount of bandwidth is required in a dual encryption scenario for encryption of packets with secondary PIDs when the encrypted packets are those containing the slice header. As a practical matter, encryption of a packet containing the slice header likely involves encryption of additional information including at least a portion of the first macroblock following each slice header, rendering the slice all the more difficult to decode.

[0062] Security can be further enhanced if in addition to the slice header, the first macroblock is encrypted in each slice. Since the first macroblock of each slice contains anchor data in the form of absolute chrominance and luminance 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 the image. Using this technique adds little to the overhead of encryption of slice headers alone. Owing to the variable length of the macroblocks, somewhat more data may be encrypted according to this scheme, since a packet may 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 encryption of the slice headers to distort the video. This is also a viable encryption scheme.

[0063] Several techniques are described above for encryption of the selected data. In each case, for the current embodiment, it will be understood that selection of a particular type of information implies that the payload of a packet 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 variations as well as others are possible without departing from the present invention. Moreover, those skilled in the art will appreciate that many variations and combinations of the encryption techniques described hereinafter can be devised and used singularly or in combination without departing from the present invention.

[0064] Numerous other combinations of the above encryption techniques as well as those described in the above-referenced patent applications and other partial encryption techniques can be combined to produce a rich pallette of encryption 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 control computer 118 in order to balance encryption security with bandwidth and in order to shift the encryption technique from time to time to thwart hackers.

[0065] An authorized set-top box such as 380 illustrated in FIG. 8 operating under the secondary CA system decrypts and decodes the incoming program by recognizing both primary and secondary PIDs associated with a single program. The multiplexed video data stream containing both PIDs is directed to a demultiplexer 384. When a program is received that contains encrypted content that was encrypted by any of the above techniques, the demultiplexer directs encrypted packets containing encrypted content and secondary PIDS to a secondary CA decrypter 388. These packets are then decrypted at 388 and passed to a PID remapper 392. As illustrated, the PID remapper 392 receives packets that are unencrypted and bear the primary PID as well as the decrypted packets having the secondary PID. The PID remapper 392 combines the decrypted packets from decrypter 388 with the unencrypted packets having the primary PID to produce an unencrypted data stream representing the desired program. PID remapping is used to change either the primary or secondary PID or both to a single PID. This unencrypted data stream can then be decoded normally by decoder 396. Some or all of the components depicted in FIG. 8 can be implemented and/or controlled as program code running on a programmed processor, with the code being stored on an electronic storage medium.

[0066] FIG. 9 is a flow chart 400 that broadly illustrates the encryption process consistent with certain embodiments of the present invention starting at 404. At 408 the packet type that is to be encrypted is specified. In accordance with certain embodiments consistent with the present invention, the 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 identified packets are duplicated and at 420 one set of these packets is encrypted under a first encryption method. The other set of identified packets is encrypted at 424 under a second encryption method. The originally identified packets are then replaced in the data stream with the two sets of encrypted packets at 430 and the process ends at 436.

[0067] While the above embodiments describe encryption of packets containing the selected data type, it is also possible to encrypt the raw data prior to packetizing without departing from this invention and such encryption is considered equivalent thereto.

[0068] Those skilled in the art will recognize that the present invention has been described in terms of exemplary embodiments based upon use of a programmed processor (e.g., processor 118, processors implementing any or all of the elements of 114 or implementing any or all of the elements of 380). However, the invention should not be so limited, since the present invention could be implemented using hardware component equivalents such as special purpose hardware and/or dedicated processors which are equivalents to the invention as described and claimed. Similarly, general purpose computers, microprocessor based computers, micro-controllers, optical computers, analog computers, dedicated processors and/or dedicated hard wired logic may be used to construct alternative equivalent embodiments of the present invention.

[0069] Those skilled in the art will appreciate that the program steps and associated data used to implement the embodiments described above can be implemented using disc storage as well as other forms of storage such as for example Read Only Memory (ROM) devices, Random Access Memory (RAM) devices; optical storage elements, magnetic storage elements, magneto-optical storage elements, flash memory, core memory and/or other equivalent storage technologies without departing from the present invention. Such alternative storage devices should be considered equivalents.

[0070] The present invention, as described in embodiments herein, is implemented using a programmed processor executing programming instructions that are broadly described above form that can be stored on any suitable electronic storage medium or transmitted over any suitable electronic communication medium or otherwise be present in any computer readable or propagation medium. However, those skilled in the art will appreciate that the processes described above can be implemented in any number of variations and in many suitable programming languages without departing from the present invention. For example, the order of certain operations carried out can often be varied, additional operations can be added or operations can be deleted without departing from the invention. Error trapping can be added and/or enhanced and variations can be made in user interface and information presentation without departing from the present invention. Such variations are contemplated and considered equivalent.

[0071] Software code and/or data embodying certain aspects of the present invention may be present in any computer readable medium, transmission medium, storage medium or propagation medium including, but not limited to, electronic storage devices such as those described above, as well as carrier waves, electronic signals, data structures (e.g., trees, linked lists, tables, packets, frames, etc.) optical signals, propagated signals, broadcast signals, transmission media (e.g., circuit connection, cable, twisted pair, fiber optic cables, waveguides, antennas, etc.) and other media that stores, carries or 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 another. In the present exemplary embodiments, MPEG compliant packets, slices, tables and other data structures are used, but this should not be considered limiting since other data structures can similarly be used without departing from the present invention.

[0072] While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.