Note: Descriptions are shown in the official language in which they were submitted.
CA 02709393 2010-07-12
1
2
3
4
6
7
8 PROGRESSIVE VIDEO REFRESH SLICE DETECTION
9
11
12 CROSS REFERENCE TO RELATED DOCUMENTS
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.
23
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.
32
-1-
CA 02709393 2010-07-12
1 COPYRIGHT NOTICE
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.
7
8 FIELD OF THE INVENTION
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.
13
14 BACKGROUND OF THE INVENTION
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.
29
31 BRIEF DESCRIPTION OF THE DRAWINGS
Docket No.. SNY-S5161.01 -2- PATENT
CA 02709393 2010-07-12
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.
26 DETAILED DESCRIPTION OF THE 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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
122
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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):
23
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
}
}
24
Docket No.: SNY-S5161.01 -7- PATENT
CA 02709393 2010-07-12
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:
4
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:
12
13
14 Stream Type Value
Legacy ES Ox00
Remapped ES Ox01
16 Shadow ES 0x02
Reserved 0x03 - OxFF
17
18
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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.
28
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
CA 02709393 2010-07-12
1
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
1 next_start_code()
2 }
3
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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
CA 02709393 2010-07-12
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.
9
11
Docket No.: SNY-S5161.01 -23- PATENT
