CA2406329C - Decoding and decryption of partially encrypted information - Google Patents

Abstract

An encryption arrangement for multiple encryption of television programs. A system according to embodiments of the present invention multiple encrypts only a portion of the data required for full presentation of a television program to permit coexistence of multiple conditional access encryption systems associated with multiple manufacturer's set-top boxes within a single system. By only encrypting a portion of the program, dramatically less bandwidth is consumed than the alternative of multiple encryption of all program data, thus permitting a larger number of programs to be carried over the same bandwidth while permitting coexistence of multiple conditional access systems in a single cable television system.

Description

DECODING AND DECRYPTION OF PARTIALLY

12 A portion of the disclosure of this patent document contains material which 13 is subject to copyright protection. The copyright owner has no objection to the 14 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 16 reserves all copyright rights whatsoever.

19 This invention relates generally to the field of encryption systems. More particularly, this invention relates to systems, methods and apparatus for providing 21 partial encryption and decryption of digital of television signals.

24 Television is used to deliver entertainment and education to viewers. The source material (audio, video, etc.) is multiplexed into a combined signal which is 26 then used to modulate a carrier. This carrier is commonly known as a channel. (A
27 typical channel can carry one analog program, one or two high definition (HD) 28 digital program(s), or several (e.g. nine) standard definition digital programs.) In a 29 terrestrial system, these channels correspond to government assigned frequencies 1 and are distributed over the air. The program is delivered to a receiver that has a 2 tuner that pulls the signal from the air and delivers it to a demodulator, which in turn 3 provides video to a display and audio to speakers. In a cable system the 4 modulated channels are carried over a cable. There may also be an in-band or out-of-band feed of a program guide indicating what programs are available and the 6 associated tuning information. The number of cable channels is finite and limited 7 by equipment/cable bandwidth. Cable distribution systems require a significant 8 capital investment and are expensive to upgrade.
9 Much of television content is valuable to its producers, therefore copyright holders want to control access and restrict copies. Examples of typically protected 11 material include feature films, sporting events, and adult programming.
Conditional 12 access (CA) systems are used to control availability of programming in content 13 delivery systems such as cable systems. CA systems come as matched sets -14 one part is integrated into the cable system headend and encrypts premium content, the other part provides decryption and is built into the set-top boxes (STB) 16 installed in user's homes. Several CA systems are used in the cable industry 17 including those provided by NDS (Newport Beach, CA), Motorola (Schaumberg, IL) 18 and Scientific Atlanta (Atlanta, GA). This matched set aspect of CA systems has 19 the effect that the "legacy" vendor is locked in as the supplier of additional STBs.
Since the various technologies for conditional access are not mutually compatible 21 (and are often proprietary), any new potential supplier is forced to license the 22 legacy CA. Thus, the cable operator finds itself unable to acquire newer technology 23 or competing technology from other set-top box manufacturers since the technology 24 owners are often unwilling to cooperate, or charge reasonable license fees.
This inflexibility can be especially troublesome when cable companies with.
disparate.
26 CA systems are merged. Service providers would like more than one source for 27 STBs for any number of reasons.
28 Once a cable operator picks an encryption scheme, it is difficult to change 29 or upgrade the content encryption scheme without introducing a backward compatible decoding device (e.g. set-top box). Providing multiple mode capability 1 in new set-top boxes to handle multiple encryption systems can add substantial 2 cost to any new set-top box, providing that the technology can be made available 3 to the STB vendor to provide the multiple decryption capability.
4 The only known current option to avoiding domination by the legacy vendor (short of wholesale replacement) is using "full dual carriage". Full dual carriage 6 means that transmission is duplicated for each encrypted program - once for each 7 type of CA encryption to be used. To provide full dual carriage, the headend is 8 enhanced to provide each form of CA simultaneously. Legacy STBs should not be 9 impacted and should continue to perform their function despite any change.
However, full dual carriage often comes at an unpalatable price because of the 11 bandwidth impact, thus reducing the number of unique programs available.
12 Generally, the number of premium channels suffers so that the number of options 13 available to the viewer are limited and the value that can be provided by the cable 14 operator is restricted.
A conventional cable system arrangement is depicted in FIGURE 1. In such 16 a system, the cable operator processes audio/video (AN) content 14 with CA
17 technology from manufacturer A (system A) using CA encryption equipment 18 18 compliant with system A at the cable system -headend 22. The encrypted AN
19 content along with system information (SI) 26 and program specific information (PSI) 27 is multiplexed together and transmitted over the cable system 32 to a 21 user's STB 36. STB 36 incorporates decrypting CA equipment from system A
22 (manufacturer A) 40 that decrypts the AN content. The decrypted AN content can 23 then be supplied to a television set 44 for viewing by the user.
24 In a cable system such as that of FIGURE 1, digital program streams are broken into packets for transmission. Packets for each component.of a program 26 (video, audio, auxiliary data, etc.) are tagged with a packet identifier or PID. These 27 packet streams for each component of all programs carried within a channel are 28 aggregated into one composite stream. Additional packets are also included to 29 provide decryption keys and other overhead information. Otherwise unused 1 bandwidth is filled with null packets, Bandwidth budgets are usually adjusted to 2 utilize about 95% of the available channel bandwidth.
3 Overhead information usually includes guide data describing what programs 4 are available and how to locate the associated channels and components. This guide data is also known as system information or SI. SI may be delivered to the 6 STB in-band (part of the data encoded within a channel) or out-of-band (using a 7 special channel dedicated to the purpose). Electronically delivered SI may be 8 partially duplicated in more traditional forms - grids published in newspapers and 9 magazines.
In order for a viewer to have a satisfying television experience, it is generally 11 desirable that the viewer have clear access to both audio and video content. Some 12 analog cable systems have used various filtering techniques to obscure the video 13 to prevent an unauthorized viewer from receiving programming that has not been 14 paid for. In such a system, the analog audio is sometimes sent in the clear. In the Motorola VideoCipher 2 Plus system used in C-band satellite transmissions, strong 16 digital audio encryption is used in conjunction with a relatively weak protection of 17 the analog video (using sync inversion). In airline in-flight movie systems, the 18 availability of audio only through rental of headphones has been used to provide the 19 full audio and video only to paying customers.

22 The features of the invention believed to be novel are set forth with 23 particularity in the appended claims. The invention itself however, both as to 24 organization and method of operation, together with objects and advantages thereof, may be best understood by reference to the following detailed description 26 of the invention, which describes certain exemplary embodiments of the invention, 27 taken in conjunction with the accompanying drawings in which:
28 FIGURE 1 is a block diagram of a conventional conditional access cable 29 system.

I FIGURE 2 is a block diagram of a system consistent with one embodiment 2 of the present invention in which dual encrypted audio is transmitted along with 3 clear video.
4 FIGURE 3 is a block diagram of a system consistent with an embodiment of the present invention in which portions of programming are dual encrypted 6 according to a time slice mechanism.
7 FIGURE 4 is a flow chart of a dual encryption process consistentwith certain 8 embodiments of the present invention.
9 FIGURE 5 is a flow chart of a decryption process consistent with certain embodiments of the present invention.
11 FIGURE 6 is a block diagram of a system consistent with an embodiment 12 of the present invention in which portions of programming are dual encrypted on a 13 packet basis.
14 FIGURE 7 is a flow chart of a dual encryption process consistent with certain embodiments of the present invention.
16 FIGURE 8 is a flow chart of a decryption process consistent with certain 17 embodiments of the present invention.
18 FIGURE 9 is a block diagram of a system consistent with an embodiment 19 of.the present invention in which system information is encrypted and programming is sent in the clear.
21 FIGURE 10 is a block diagram of a generic system consistent with various 22 embodiments of the present invention.
23 FIGURE 11 is a block diagram of a first embodiment of implementation of 24 an encryption system consistent with embodiments of the present invention in a cable system headend.
26 FIGURE 12 is a block diagram of a second embodiment of implementation 27 of an encryption system consistent with embodiments of the present invention in 28 a cable system headend.
29 FIGURE 13 is a flow chart of an overall encryption process used to 1 implement certain embodiments of the present invention in a cable system 2 headend.
3 FIGURE 14 is a block diagram of a first embodiment of a set-top box 4 implementation of a decoding system consistent with embodiments of the present invention.

6 FIGURE 15 is a block diagram of a second embodiment of 7 implementation of a decoding system consistent with embodiments of the 8 present invention in a cable system STB.
.9 FIGURE 16 is a block diagram of a third embodiment of implementation of a decoding system consistent with embodiments of the present invention in a 11 cable system STB.
12 FIGURE 17 illustrates the PID remapping process carried out in one 13 embodiment of a set-top box PID re-mapper.
14 FIGURE 18 is a block diagram of an exemplary decoder chip that can be utilized in a television set-top box consistent with the present invention.

18 While this invention is susceptible of embodiment in many different forms, 19 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 21 considered as an example of the principles of the invention and not intended to limit 22 the invention to the specific embodiments shown and described. In the description 23 below, like reference numerals are used to describe the same, similar or 24 corresponding parts in the several views of the drawings. The terms "scramble"
and "encrypt" and variations thereof are used synonymously herein. Also, the term 26 "television program" and similar terms can be interpreted in the normal 27 conversational sense, as well as a meaning wherein the term means any segment 28 of A/V content that can be displayed on a television set or similar monitor device.

I OVERVIEW
2 Modern digital cable networks generally use CA systems that fully encrypt 3 digital audio and video to make programming inaccessible except to those who 4 have properly subscribed. Such encryption is designed to thwart hackers and non-subscribers from receiving programming that has not been paid for. However, as 6 cable operators wish to provide their subscribers with set-top boxes from any of 7 several manufacturers, they are frustrated by the need to transmit multiple copies 8 of a single program encrypted with multiple encryption technologies compliant with 9 the CA systems of each STB manufacturer.
This need to carry multiple copies of the programming (called "full dual 11 carriage") uses up valuable bandwidth that could be used to provide the viewer with 12 additional programming content. Certain embodiments of the present invention 13 address this problem in which the bandwidth requirements to provide an equivalent 14 to multiple carriage are minimized. The result could be described as "Virtual Dual Carriage" since the benefits of full dual carriage are provided without the full 16 bandwidth cost. Several embodiments of the present invention are presented 17 herein to accomplish effective partial scrambling. These embodiments vary by the 18 criteria used to select the portion to encrypt. The portion selected in turn affects the 19 additional bandwidth requirements and the effectiveness of the encryption.
It may be desirable to use one encryption process or several processes in combination in 21 a manner consistent with embodiments of the present invention.
22 Certain of the implementations of partial dual encryption described herein 23 utilize an additional (secondary) PID for each duplicated component. These 24 secondary PIDs are used to tag packets that carry duplicated content with an additional encryption method. The PSI is enhanced to convey information about 26 the existence these new PIDs in such a way that inserted PIDs are ignored by 27 legacy STBs but can be easily extracted by new STBs.
28 Some implementations of partial dual encryption involve duplicating only 29 certain packets tagged with a given PID. Methods for selecting which packets to encrypt are detailed hereinafter. The original (i.e. legacy) PID continues to tag the 1 packets encrypted with legacy encryption as well as other packets sent in the clear.
2 The new PID is used to tag packets encrypted by the second encryption method.
3 Packets with the secondary PID shadow the encrypted packets tagged with the 4 primary PID. The packets making up the encrypted pairs can occur in either order but, in the preferred implementation, maintain sequence with the clear portion of 6 the PID stream. By use of the primary and secondary PIDs, the decoder located 7 in the set-top box can readily determine which packets are to be decrypted using 8 the decryption method associated with that set-top box, as will be clear upon 9 consideration of the following description. The processes used to manipulate PIDs will be described later in greater detail.
11 The encryption techniques described herein can be broadly categorized 12 (according to one categorization) into three basic variations - encrypting just a 13 major portion (i.e. audio), encrypting just the SI, and encrypting just selected 14 packets. In general, each of the encryption techniques used in the embodiments disclosed herein seek to encrypt portions of the an AN signal or associated 16 information while leaving other portions of the AN signal in the clear to conserve 17 bandwidth. Bandwidth can be conserved because the same clear portion can be 18 sent to all varieties of set-top boxes. Various methods are used to select the 19 portions of information to be encrypted. By so doing, the various embodiments of this invention eliminate the traditional "brute force" technique of encrypting the 21 entire content in one specific scrambling scheme, which predicates the redundant 22 use of bandwidth if alternate scrambling schemes are desired. In addition, each 23 of the partial dual encryption schemes described herein can be used as a single 24 partial encryption scheme without departing from embodiments of the present invention.
26 The various embodiments of the invention use several processes, alone or 27 in combination, to send substantial portions of content in the clear while encrypting 28 only a small amount of information required to correctly reproduce the content.
29 Therefore the amount of information transmitted that is uniquely encrypted in a particular scrambling scheme is a small percentage of the content, as opposed to 1 the entire replication of each desired program stream. For purposes of the 2 exemplary systems in this document, encryption system A will be considered the 3 legacy system throughout. Each of the several encryption techniques described 4 above will now be described in detail.
The various embodiments of the invention allow each participating CA
6 system to be operated independently. Each is orthogonal to the other. Key sharing 7 in the headend is not required since each system encrypts its own patents.
8 Different key epochs may be used by each CA system. For example, packets 9 encrypted with Motorola's proprietary encryption can use fast changing encryption keys using the embedded security ASIC, while packets encrypted with NDS' smart 11 card based system use slightly slower changing keys. This embodiment works 12 equally well for Scientific Atlanta and Motorola legacy encryption.

Turning now to FIGURE 2, one embodiment of a system that reduces the 16 need for additional bandwidth to provide multiple carriage is illustrated as system 17 100. In this embodiment, the system takes advantage of the fact that viewing 18 television programming without audio is usually undesirable. While there are 19 exceptions (e.g., adult programming, some sporting events, etc.), the typical viewer is unlikely to accept routine viewing of television programming without being able 21 to hear the audio. Thus, at headend 122, the video signal 104 is provided in the 22 clear (unencrypted) while the clear audio 106 is provided to multiple CA
systems 23 for broadcast over the cable network. In the exemplary system 100, clear audio 24 106 is provided to an encryption system 118 that encrypts audio data using encryption system A (encryption system A will be considered the legacy system 26 throughout this document). Simultaneously, clear audio 106 is provided to 27 encryption system 124 that encrypts the audio data using encryption system B.
28 Clear video is then multiplexed along with encrypted audio from 118 (Audio A) and 29 encrypted audio from 124 (Audio B), system information 128 and program specific information 129.

1 After distribution through the cable system 32, the video, system information, 2 program specific information, Audio A and Audio B are all delivered to set-top 3 boxes 36 and 136. At legacy STB 36, the video is displayed and the encrypted 4 audio is decrypted at CA system A 40 for play on television set 44.
Similarly, at new STB 136, the video is displayed and the encrypted audio is decrypted at CA
6 system B 140 for play on television set 144.
7 Audio has a relatively low bandwidth requirement compared with a complete 8 AN program (or even just the video portion). The current maximum bit rate for 9 stereophonic. audio at 384 Kb/second is approximately 10% of a 3.8Mb/second television program. Thus, for dual carriage of only encrypted audio (with video 11 transmitted in the clear) in a system with ten channels carried with 256 QAM
12 (quadrature amplitude modulation), a loss of only about one channel worth of 13 bandwidth would occur.. Therefore, approximately nine channels could be carried.
14 This is a dramatic improvement over the need to dual encrypt all channels, which would result in a decrease in available channels from ten to five. Where deemed 16 necessary, e.g., sporting events, pay per view, adult programming, etc., dual 17 encryption of both audio and video can still be carried out, if desired.
18 Both legacy and new set-top boxes can function in a normal manner 19 receiving video in the clear and decrypting the audio in the same manner used for fully decrypting encrypted AN content. If the user has not subscribed to the 21 programming encrypted according to the above scheme, at best the user can only 22 view the video without an ability to hear the audio. For enhanced security over the 23 video, it possible to employ other embodiments of the invention (as will be 24 described later) here as well. (For example, the SI may be scrambled to make it more difficult for a non-authorized set-top box to tune to the video portion of the 26 program.) Unauthorized set-top boxes that have not been modified by a hacker, will 27 . blank the video as a result of receipt of the encrypted audio.
28 Authorized set-top boxes receive Entitlement Control Messages (ECM) that 29 are used to get access criteria and descrambling keys. The set-top box attempts to apply the keys to video as well as the audio. Since the video is not scrambled, 1 it simply passes through the set-top boxes' descrambler unaffected. The set-top 2 boxes do not care that the video is in-the-clear. The un-modified and un-subscribed 3 set-top boxes behave as being un-authorized for the scrambled audio as well as the 4 clear video. The video, as well as the audio which was actually scrambled, will be blanked. An on-screen display may appear on the TV stating that the viewer needs 6 to subscribe to programming. This desirably totally inhibits the casual viewer from 7 both hearing and viewing the content.
8 In one embodiment of the present invention, the encrypted audio is 9 transmitted as digitized packets over the AN channel. Two (or more) audio streams are transmitted encrypted according to the two (or more) encryption 11 systems in use by the system's set-top boxes. In order for the two (or more) STBs 12 to properly decrypt and decode their respective audio streams, SI (system 13 information) data are transmitted from the cable system's headend 122 that 14 identifies the particular channel where the audio can be found using a transmitted Service Identifier to locate the audio. This is accomplished by assigning the audio 16 for system A is a first packet identifier (PID) and assigning the audio for system B
17 a second packet identifier (PID). By way of example, and. not limitation, the 18 following program specific information (PSI) can be sent to identify the location of 19 the audio for two systems, one using NDS conditional access and one using Motorola conditional access. Those skilled in the art will understand how to adapt 21 this information to the other embodiments of partial encryption described later 22 herein.
23 The SI can be separately delivered to both legacy and non-legacy set-top 24 boxes. It is possible to send SI information so that the legacy and non-legacy set-top boxes operate essentially without interference. In the SI delivered to legacy set-26 top boxes, the VCT (virtual channel table) would state that the desired program, e.g.
27 HBO referenced as program number 1, is on Service ID "1" and that the VCT
28 access control bit is set. The network information table (NIT) delivered to that first 29 STB would indicate that Service ID "1" is at frequency = 1234. In the SI
delivered to non-legacy set-top boxes, the VCT would state that the desired program, e.g.

1 HBO referenced as program number 1001, is on Service ID "1001" and that the 2 VCT access control bit is set. The network information table delivered to the non-3 legacy STB would indicate that the Service ID "1001" is at frequency 1234.
The 4 following exemplary program association Table PSI data are sent to both legacy and non-legacy set-top boxes (in MPEG data structure format):

2 PAT sent on PID=0x0000 3 PAT 0x0000 4 - Transport Stream ID
- PAT version 6 - Program Number I
7 - PMT 0x0010 8 - Program Number 2 9 - PMT 0x0020 - Program Number 3 11 - PMT 0x0030 12 - Program Number 4 13 - PMT Ox0040 14 - Program Number 5 - PMT 0x0050 16 - Program Number 6 17 - PMT 0x0060 18 - Program Number 7 19 - PMT Ox0070 - Program Number 8 21 - PMT 0x0080 22 - Program Number 9 23 - PMT 0x0090 24 - Program Number 1001 - PMT 0x1010 26 - Program Number 1002 27 - PMT 0x1020 28 - Program Number 1003 29 - PMT 0x1030 - Program Number 1004 31 - PMT 0x1040 32 - Program Number 1005 33 - PMT 0x1050 34 - Program Number 1006 - PMT 0x1060 36 - Program Number 1007 37 - PMT 0x1070 38 - Program Number 1008 39 - PMT 0x1080 - Program Number 1009 41 - PMT 0x1090 43 The following exemplary program map table PSI data are selectively 44 received by legacy and non-legacy set-top boxes (in MPEG data structure format):

2 PMT sent on PID=0x0010 3 PMT 0x0010 4 - PMT Program number I
- PMT Section Version 10 6 - PCR PID 0x0011 7 - Elementary Stream 8 - Stream Type (Video 0)(02 or 0x80) 9 - Elementary PID (0x0011) - Descriptor 11 - CA Descriptor (ECM) for CA provider #1 12 - Elementary Stream 13 - Stream Type (Audio 0x81) 14 - Elementary PID (0x0012) - Descriptor 16 - CA Descriptor (ECM) for CA provider #1 18 PMT sent on PID=Oxl 010 19 PMT Oil 010 - PMT Program number 1010 21 - PMT Section Version 10 22 - PCR AID 0x0011 23 - Elementary Stream 24 - Stream Type (Video 0x02 or 0x80) - Elementary PID (0x0011) 26 - Descriptor 27 - CA Descriptor (ECM) for CA provider #2 28 - Elementary Stream 29 - Stream Type (Audio 0x81) - Elementary PID (0x0013) 31 - Descriptor 32 - CA Descriptor (ECM) for CA provider #2 36 Considering an example wherein it is desired to deliver programming in a 37 system using either Motorola or Scientific Atlanta as well as NDS CA, the above 38 communications are consistent with the PSI delivered by both Motorola and 39 Scientific Atlanta in their CA systems, with only minor changes. The program association table (PAT) is changed to reference an additional program map table 41 (PMT) for each program. Each program in this embodiment has two program 42 numbers in the PAT. In the table above, program number I and program-number 43 1001 are the same program except that they will reference different audio PIDs and 1 CA descriptors. Changes in the system to create multiple PMTs and to multiplex 2 new PAT and PMT information with the data stream can be made to appropriately 3 modify the cable system headend equipment. Again, those skilled in the art will 4 understand how to adapt these messages to other partial encryption schemes.
described herein. An advantage of this approach is that no special hardware or 6 software is required for headend or for legacy and non-legacy set-top boxes to 7 deliver audio that is both legacy and non-legacy encrypted using this scheme.
8 This technique deters the user from use of premium programming which has 9 not been paid for by rendering it inaudible, but a hacker may attempt to tune the video. To combat this, the mechanisms employed in other encryption techniques 11 consistent with the present invention (as will be described later) can be employed 12 simultaneously, if desired. Since closed captioning is generally transmitted as a 13 part of the video data, the user can still obtain readable audio information in 14 conjunction with clear. video. Thus, although adequate for some applications, the present technique alone may not provide adequate protection in all scenarios.
In 16 another embodiment, video packets containing closed captioning information as 17 a part of the payload can additionally be scrambled.
18 In an alternative embodiment, only the video may be dual encrypted with 19 separate PIDs assigned to each set of encrypted video. While this may provide a more secure encryption for general programming (since video may be more 21 important than audio), the amount of bandwidth savings compared with full dual 22 carriage is only approximately ten percent, since only the audio is shared amongst 23 all the set-top boxes. However, this approach might be used for certain content, 24 e.g. adult and sports, and help reduce the bandwidth overhead for that content . while the audio encryption approach may be used for other content types. In the .26 Digital Satellite Service (DSS) transport standard used for the DirecTVTm service, 27 the ardio packets can be identified for encryption by use of the service channel 28 identifier (SCID) which is considered equivalent.

2 Another embodiment consistent with the present invention is referred to 3 herein as time slicing and is illustrated in FIGURE 3 as system 200. In this 4 embodiment, a portion of each program is encrypted on a time dependent basis in a manner that disrupts viewing of the program unless the user has paid for the 6 programming. This embodiment of the invention can be implemented as partially 7 encrypted video and clear audio, clear video and partially encrypted audio or 8 partially encrypted video and audio. The duration of the time slice that is encrypted, 9 taken as a percentage of the total time, can be selected to meet any suitable desired balance of bandwidth usage, security against hackers. In general, under 11 any of the embodiments described herein, less than 100 percent of the content is 12 encrypted to produce a desired partial encryption. . The following example details 13 partially encrypted video and audio.
14 By way of example, and not limitation, consider a system which has nine programs that are to be dual partially encrypted according to the present exemplary 16 embodiment. These nine channels are fed to the cable headend as a multiplexed 17 stream of packets and are digitally encoded using packet identifiers (PID) to identify 18 packets associated with a particular one of the nine programs. In this example, 19 assume that those nine programs have video PIDs numbered 101-109 and audio PIDs numbered 201-209. The partial encryption, according to this embodiment is 21 time multiplexed among the programs so that only packets from a single program 22 are encrypted at any given time. The method does not need to be content aware.
23 With reference to TABLE 1 below, an exemplary embodiment of a time slice 24 dual encryption scheme consistent with an embodiment of the invention is illustrated. Forprogram 1 having primary video PID 101 and primary audio PID
201, 26 during the first time period, packets having PID 101 and PID201 are encrypted 27 using encryption system A, while the others representing the other programs are 28 sent in the clear. In this embodiment, secondary PIDs are also assigned to both 29 the video and the audio. The secondary PlDs are PID 111 for video and PID
211 for 1 audio respectively for program 1. The packets with the secondary PIDs are 2 encrypted using encryption system B during the first time period. The next eight 3 time periods are sent in the clear. Then for time period 10, packets having any of 4 the above four PIDs are again encrypted followed by the next eight time periods being sent in the clear. In a similar manner, during the second period of program 6 2 having primary video PID 102 and primary audio PID 201 are encrypted using 7 encryption system A and. packets with their associated secondary PIDs are 8 encrypted using encryption system B, and during the next eight time periods are 9 sent in the clear, and so on. This pattern can be seen clearly in TABLE 1 by examination of the first nine rows. Both audio and video packets, or audio 11 alone or video alone can be encrypted according to this technique, without 12 departing from the invention. Also, the audio and video can have their own 13 individual encryption sequence. In TABLE 1, P1 indicates time period number 1, 14 P2 indicated time period number 2 and so on. EA indicates that the information is encrypted using CA system A and EB indicates that the information is encrypted 16 using CA encryption system B.

1 PROG. IDEO PID AUDIO PID P1 P2 P3 P4 P5 P6 P7 P8 P9 NO P11 P12 ...
2 1 PID 101 PID 201 EA clear clear clear clear clear dear clear clear EA dear clear ...
3 2 PID 102 PID 202 clear EA clear clear clear clear clear clear clear clear EA clear ...
4 3 PID 103 PID 203 dear dear EA clear dear clear dear dear dear clear clear EA , , 4 PID 104 PID 204 dear dear dear EA clear dear clear clear dear dear clear clear ...
6 5 PID 105 PID 205 dear clear clear clear EA clear clear clear clear dear clear clear ...
7 6 PID 106 PID 206 clear clear clear dear clear EA dear clear clear dear dear dear .,, 8 7 PID 107 PID 207 clear clear clear clear clear clear EA clear clear clear dear clear .., 9 8 PID 108 PID 208 clear clear clear clear clear clear clear EA clear clear dear clear .., 9 PID 109 PID 209 clear dear clear clear clear clear dear clear EA clear clear dear .., 12 2 PID 112 PID 212 EB EB .
13 3 PID 113 PID 213 EB EB .

5 PID 115 PID 215. ES
16 8 PID 116 PID 216 ES , TABLE I

22 In order to retain compatibility with an established legacy encryption system 23 (encryption system A), the encrypted periods for each of programs one through 24 nine are encrypted using encryption system A. Legacy STB equipment will accept such partially encrypted AN data streams passing unencrypted packets and 26 decrypting encrypted packets transparently. However, it is desired to obtain dual 27 encryption using both encryption system A and encryption system B. In order to 28 achieve this, a specified program is assigned both primary PIDs (e.g., for program 29 1, video PID 101 and audio PID 201) and a secondary PID (e.g., for program 1, video PID 111 and audio PID 211) to carry the elementary data streams for a given 31 premium channel.
32 With reference to FIGURE 3, system 200 generally depicts the functionality 33 of the cable system headend 222 wherein N channels of clear video 204 at the 34 headend 222 are provided to an intelligent switch 216 (operating under control of a programmed processor) which routes packets that are to be transmitted in the 36 clear to be assigned a primary PID at 220. Packets that are to be encrypted are 1 routed to both conditional access system A encrypter 218 and to conditional 2 access system B encrypter 224. Once encrypted, these encrypted packets from 3 218 and 224 are assigned primary or secondary PIDs respectively at 220.
System 4 information from 228 is multiplexed or combined with the clear packets, the system A encrypted packets and the system B encrypted packets and broadcast over the 6 cable system 32.
7 For discussion purposes, if the period of the time slice is 100 milli-seconds, 8 then as shown in TABLE 1, there are on average one and a fraction encrypted 9 periods totaling 111 milli-seconds each second for all nine-programs. If the period is 50 milli-seconds, then there are on average two and a fraction encrypted periods 11 totaling 111 milli-seconds. A non-subscribing box attempting to tune video would 12 obtain a very poor image if it could maintain any sort of image lock and the audio 13 would be garbled.
14 The PSI for a partially scrambled stream is handled slightly differently from the dual audio encryption example above. Essentially, the same SI and PAT PSI
16 information can be sent to both legacy and non-legacy set-top boxes. The 17 difference lies with the PMT PSI information. The legacy set-top box parses the 18 PMT PSI and obtains the primary video and audio PIDs as before. The non-legacy 19 set-top box obtains the primary PIDs like the legacy set-top box but must look at the CA descriptors in the PMT PSI to see if the stream is partially scrambled. The 21 secondary PID is scrambled specifically for a particular CA provider, consequently 22 it makes sense to use the CA descriptor specific to a particular CA
provider to 23 signal that PID. The invention can allow more than two CA providers to co-exist by 24 allowing more than one secondary PID. The secondary PID shall be unique to a particular CA provider. The set-top box know the CA ID for the CA it has, and can 26 check all CA descriptors for the relevant one for it.
27 While it is possible to send the secondary PID data as private data in the 28 same CA descriptor used for the ECM, the preferred embodiment uses separate 29 CA descriptors. The secondary PID is placed in the CA PID field. This allows headend processing equipment to "see" the PID without having to parse the private 1 data field of the CA descriptor. To tell the difference between the ECM and 2 secondary PID CA descriptor, a dummy private data value can be sent.

PMT sent on P I D=0x0010 6 PMT 0x0010 7 - PMT Program number 1 8 - PMT Section Version 10 9 - PCR PID 0x0011 - Elementary Stream 11 - Stream Type (Video 0x02 or 0x80) 12 - Elementary PID (0x0011) .
13 - Descriptor 14 - CA Descriptor (ECM) for CA provider #1 - CA Descriptor (ECM) for CA provider #2 16 - CA Descriptor (Secondary PID) for CA provider #2 17 - Elementary Stream 18 - Stream Type (Audio 0x81) 19 - Elementary PID (0x0012) - Descriptor 21 - CA Descriptor (ECM) for CA provider #1 22 - CA Descriptor (ECM) for CA provider #2 23 - CA Descriptor (Secondary PID) for CA provider #2 26 CA Descriptor for CA Provider #2 (ECM) 29 Descriptor - Tag: Conditional Access (0x09) 31 - Length: 4 Bytes 32 - Data 33 - CA System ID: 0x0942 (2nd CA provider) 34 - CA PID (0x0015) 39 CA Descriptor for CA Provider #2 (Secondary PID) Descriptor 41 - Tag: Conditional Access (0x09) 42 - Length: 5 Bytes 43 - Data 44 - CA System ID: 0x1234 (2"d CA provider) - CA PID (0x0016) 46 - Private Data 2 Legacy STB 36 operating under CA system A receives the data, ignores 3 the secondary PIDs, decrypts the packets encrypted under CA system A and 4 presents the program to the television set 44. New or non-legacy STB 236 receives the SI 228. It receives PSI 229 and uses the PMT to identify the 6 primary and secondary PID, called out in the second CA descriptor, associated 7 with the program being viewed. The packets encrypted under CA system A are 8 discarded and the packets encrypted under CA system B with the secondary 9 PID are decrypted by CA system B 240 and inserted into the clear data stream for decoding and display on television set 244.
11 FIGURE 4 illustrates one process for encoding at the cable system headend 12 that can be used to implement an embodiment of the present invention wherein CA
13 system A is the legacy system and CA system B is the new system to be 14 introduced. As a clear packet is received, at 250 for a given program, if the packet (or frame) is not to be encrypted (i.e., it is not the current time slice for encryption 16 for this program), the clear packet (C) is passed on to be inserted into the output 17 stream at 254. If the current packet is to be encrypted by virtue of the current 18 packet being a part of the encryption time slice, the packet is passed for encryption 19 to both packet encryption process A 258 and packet encryption process B
262.
The encrypted packets from encryption process A at 258 (EA) are passed on to 21 for insertion into the output stream. The encrypted packets from encryption 22 process B at 262 (EB) are assigned a secondary PID at 264 for insertion into the 23 output stream at 254. This is repeated for all packets in the program.

24 FIGURE 5 illustrates a process used in the STB 236 having the newly introduced CA system B for decrypting and decoding the received data stream 26 containing C, EA and EB packets having primary and secondary PIDs as 27 described. When a packet is received at 272, it is inspected to see if it has a the 28 primary PID of interest. If not, the packet is examined to see if it has the secondary 29 PID of interest at 274. If the packet has neither the primary or secondary PID, it is I ignored or dropped at 278. Any intervening packets between the EA and EB
2 packets that are not the primary or secondary PID are discarded. It is an 3 implementation and mainly a buffering issue whether a decoder can receive 4 multiple EA or EB in a row before receiving the replacement matched EA or EB
packet. Also, just as easy to detect for secondary packets that come before and 6 not after the primary packet. It is also possible to design a circuit where either 7 case can happen - the secondary packet can before or after the primary packet.
8 If the packet has the primary PID of interest, the packet is examined at 284 to 9 determine if it is encrypted. If not, the packet (C) is passed directly to the decoder at 288 for decoding. If the packet is encrypted at 284, it is deemed to be an EA
11. packet and is dropped or ignored at 278. In some implementations, the primary 12 packet's encryption does not get ' checked at 284. Rather, its simple position 13 relative to the secondary packet can ' be checked at 284 to identify it for 14 replacement.
If the packet has the secondary PID at 274, the PID is remapped to the 16 primary PID at 292 (or equivalently, the primary PID is remapped to the secondary 17 PID value). The packet is then decrypted at 296 and sent to the packet decoder at 18 288 for decoding. Of course, those skilled in the art will recognize that many 19 variations are possible without departing from the invention, for example, the order of 292 and 296 or the order of 272 and 274 can be reversed. As mentioned earlier, 21 284 can be replaced with a check of primary packet position with respect to the 22 secondary packet. Other variations will occur to those skilled in the art.
23 Legacy STB 36 operating under the encryption system A totally ignores the 24 secondary PID packets. Packets with the primary PID are decrypted, if necessary, and passed to the decoder without decryption if they are clear packets. Thus, a so 26 called "legacy" STB operating under encryption system A will properly decrypt and 27 decode the partially encrypted data stream associated with the primary PID
and 28 ignore the secondary PID without modification. STBs operating under the 29 encryption system B are programmed to ignore all encrypted packets associated I with the primary PID and to use the encrypted packets transmitted with the 2 secondary PID associated with a particular channel.
3 Thus, each dual partially encrypted program has two sets of PIDs associated 4 therewith. If, as described, the encryption is carried out on a period-by-period basis, for the system shown with an appropriate time slice interval, the picture will 6 be essentially unviewable on a STB with neither decryptipn.
7 In order to implement this system in the headend 322 of FIGURE 6, the SI
8 and PSI can be modified for inclusion of a second set of CA descriptor information.
9 Legacy set-top boxes may not be able to tolerate unknown CA descriptors.
Consequently, alternatively, in the set-top box, it may be possible to "hard code"
11 offsets from the legacy CA PIDs for both the content PIDs and/or the SI/PSI
and 12 ECM PIDs. Alternatively, parallel PSI may be sent. For example, an auxiliary PAT
13 can be delivered on PID 1000 instead of PID 0 for the non-legacy set-top boxes. It 14 can reference auxiliary PMTs not found in the legacy PAT. The auxiliary PMTs can contain the non-legacy CA descriptors. Since auxiliary PMTs would not be known 16 to the legacy set-top boxes, there would not be any interoperation issue.
17 In systems where system A corresponds to legacy set-top boxes 18 manufactured by Motorola or Scientific Atlanta, no modifications to the STBs are 19 required. For the system B compliant STBs, for dual carriage of partially encrypted programs as described herein, the video and audio decoder are adapted to listen 21 to two PIDs each (a primary and a secondary PID) instead of just one. There may 22 be one or more secondary shadow PIDs, depending on the number of non-legacy 23 CA systems in use, however a specific set-top box only listens to one of the 24 secondary PIDs as appropriate for the CA method being used by that specific STB.
In addition, ideally the encrypted packets from the PID carrying the mostly clear 26 video or audio are ignored. Since ignoring "bad packets" (those that cannot be 27 readily decoded as is) may already be a function that many decoders perform, thus 28 requiring no modification. For systems with decoders that do not ignore bad 29 packets, a filtering function can be used. It should be understood that the time slice encryption technique could be applied to just the video or the audio.
Also, the 1 video may be time slice encrypted while the audio is dual encrypted as in the 2 earlier embodiment. The time slice technique may be applied to multiple programs.
3 concurrently. The number of programs that encrypted during a period of time is 4 mainly an issue of bandwidth allocation, and although the example discusses scrambling a single program at a time, the invention is not limited by that.
Other 6 combinations of encryption techniques described in this document will also occur 7 to those skilled in the art.

MT" AND N PACKET ENCRYPTION
11 Another embodiment consistent with the present invention is referred to 12 herein as Mth & N packet encryption. This is a variation of the embodiment 13 illustrated in FIGURE 3 as system 200. In this embodiment, packets of each PID
14 representing a program are encrypted in a manner that disrupts viewing of the program unless the user has paid for the programming. In this embodiment, M
16 represents the number of packets between the start of an encryption event.
N
17 represents the number of packets that are encrypted in a row, once encryption 18 takes place. N is less than M. If M=9 and N=1, then every nine packets there is an 19 encryption event lasting 1 packet. If M=16 and N=2, then every sixteen packets there is an encryption event lasting two packets. Each packet to be dual partially 21 encrypted is duplicated and processed using CA system A 218 and CA system B
22 224 as in the previous embodiment. The difference in operation between this 23 embodiment and the time slicing technique previously is in the operation of switch 24 216 to effect the selection of packets to encrypt under control of a programmed processor.
26 By way of example, and not limitation, consider a system which has nine 27 channels of programming that are to be dual encrypted according to the present 28 exemplary embodiment. These nine channels are digitally encoded using packet 29 identifiers (PID) to identify packets associated with a particular one of nine programs. In this example, assume that those nine programs have video PIDs 1 numbered 101-109 and audio PIDs numbered 201-209. The encryption, according 2 to this embodiment is random program-to-program 'so that packets from other 3 programs may be encrypted at the same time. This is illustrated in TABLE 2 below 4 in which M=6 and N=2 and in which only video is encrypted, but this should not be considered limiting. The method does not need to be content aware. In TABLE 2, 6 PK1 indicated packet number 1, PK2 indicates packet number 2, and so on.

8 PROD. VIDEO PK1 PK2 PK3 PK4 PK5 PK8 PK7 PK8 PK9 PK10 PK11 PK12 ...
9 1 PID 101 EA EA clear clear clear dear EA EA dear clear clear clear ...
2 PID 102 clear clear clear EA EA clear clear clear clear EA EA clear ...
11 3 PID 103 clear clear EA EA clear clear dear dear EA EA clear clear ...
,12 4 PID 104 clear clear clear EA EA clear dear clear clear EA EA clear 13 5 PID 105 clear clear EA EA clear clear dear clear EA EA clear clear ...
14 6 PID 106 EA clear clear clear clear EA EA clear clear dear clear EA ...
7 PID 107 EA EA dear clear clear clear EA EA clear clear dear clear 16 8 PID 108 dear EA EA clear clear clear clear EA EA clear clear clear 17 9 P1D 109 EA clear clear clear clear EA EA clear clear clear dear EA ...
18 1 P10111 EB EB EB EB ...

3 PID 113 EB EB EB EB ...

24 7 PID 117 EB ED EB EB ...
8 PID 118 EB ED EB ED ...
26 9 AID 19 EB EB EB EB ...

29 In the example of TABLE 2, each program is encrypted fully independently of the others using the M=6 and N=2 encryption scheme. Again, the illustrated 31 example encrypts only the video, but audio could also be encrypted according to 1 this or another arrangement. If applied to just the video, audio may be dual 2 scrambled or time slice encrypted as in earlier embodiments. Alternatively, if 3 applied to just the audio, the video may be time sliced as in the earlier 4 embodiment.
Those skilled in the art will recognize that many variations of the technique 6 can be devised consistent with the partial scrambling concepts disclosed herein.
7 For example, a pattern of five clear followed by two encrypted followed by two'clear 8 followed by one encrypted (CCCCCEECCECCCCCEECCE...) is consistent with 9 variations of the present partial encryption concept, as are random, pseudo-random and semi-random values for M and N may be used for selection of packets to 11 encrypt. Random, pseudo-random or semi-random (herein collectively referred to 12 as "random" herein) selection of packets can make it difficult for a hacker to 13 algorithmically reconstruct packets in a post processing attempt to recover 14 recorded scrambled content. Those skilled in the art will understand how to adapt this information to the other embodiments of partial encryption described later 16 herein. Some of the embodiments can be used in combination to more effectively 17 secure the content.

Another partial encryption method consistent with embodiments of the 21 present invention uses a data structure as a basis for encryption. By way of 22 example and not limitation, one convenient data structure to use for encryption is 23 an MPEG video frame. This is illustrated (again with video only) in TABLE 3 below 24 in which every tenth video frame is encrypted. In this embodiment, each program's ten frame encryption cycle is distinct from each other channel, but this should not 26 be considered limiting. This concept can be viewed as a variation of the time slice 27 or Mt' and N partial encryption arrangement (or other pattern) based upon video or 28 audio frames (or some other data structure) with the exemplary embodiment having 29 M=10 and N=1. Of course, other values of M and N can be used in a similar 1 embodiment. In TABLE 3, F1 represents frame number 1, F2 represents frame 2 number 2 and so on.

4 PROG. VIDEO F1 F2 F3 F4 F5 F6 F7 F8 F9 NO F11 F12 1 PlD 101 EA clear clear clear clear dear clear clear clear dear EA clear 6 2 PID 102 clear clear clear EA dear dear dear dear clear dear clear clear 7 3 PID 103 clear clear EA clear clear clear clear clear clear clear clear clear ...
8 4 PID 104 clear clear clear clear EA clear clear clear clear clear clear clear .,.
9 5 PID 105 clear clear clear EA clear clear dear clear clear clear clear clear 6 PID 106 EA dear clear clear clear clear clear clear clear clear EA clear 11 7 PID 107 clear EA clear dear clear dear dear clear dear dear dear EA ...
12 8 PID 108 clear EA clear clear clear clear clear clear dear clear clear EA
...
13 9 PID 109 EA dear clear clear clear dear clear clear dear clear EA dear ...
14 1 PID 111 EB EB ...

19 6 PID 116 EB ES ,,, 7 PID 117 EB EB ,,, Thus, again each encrypted program has two sets of PIDs associated 26 therewith. If, as described, the encryption is carried out on a period-by-period 27 basis, for the system shown, the picture will be essentially unviewable.
For a nine 28 program system at 30 frames per second as depicted, approximately three frames 29 per second wilt be encrypted. For viewers who are not entitled to view the program, their STB will be unable to capture much more than an occasional frozen frame as 31 the STB constantly attempts to synchronize and recover. Viewers who have I subscribed to the programming will be able to readily view the programming.
The 2 bandwidth cost for such an encryption arrangement depends upon the frequency 3 with which the encryption is applied, In the above example, an extra factor of 1 /9 4 of data are transmitted for each program. In this example, approximately one program's worth of bandwidth is used. With a greater number of programs, fewer 6 packets per program are encrypted and the security of the encryption system may 7 degrade somewhat. As in the randomized M and N method, random frames may 8 be selected. Choosing random frames, in the video case, would help guarantee 9 that all frame types would be affected - intra-coded frames (I frames), predictive-coded (P frames), Bi-directional-coded (B frames) and DC frames.
11 In a variation of the invention, it may be possible to encrypt fewer packets to 12 achieve an acceptable level of security, That is, perhaps in a system of nine 13 programs, only one frame per second may need to be encrypted to achieve 14 acceptable levels of security. In such a system, the overhead becomes one encrypted period per second per program or approximately 1/30 of data transmitted 16 in overhead. This level of overhead is a dramatic improvement over the 50%
loss 17 of bandwidth associated with full dual carriage of encryption under two encryption 18 systems. In another variation of the invention, it may be possible to encrypt only 19 certain video frames to achieve an acceptable level of security. For example, for MPEG content, only intra-coded frames (I frames) may be scrambled to further 21 reduce the bandwidth overhead and still maintain an acceptable level of security.
22 These offer significant improvement over the bandwidth required for -full dual 23 carriage.

27 Substantial efficiency in bandwidth utilization can be achieved by use of a 28 selective packet-by-packet dual encryption technique. In this technique, packets 29 are selected for encryption based upon their importance to the proper decoding of the audio and/or video of the program content.

I This embodiment can reduce the bandwidth requirement compared with full 2 dual carriage of encrypted content by only scrambling a small.fraction of the 3 packets. Clear packets are shared between the two (or more) dual carriage PIDs.
4 In one preferred embodiment, as will be disclosed, less that about one percent of the total content bandwidth is used. In a system with a legacy encryption scheme, 6 clear program content packets can be received by both legacy and new set-top 7 boxes. As mentioned before, encrypted packets are dual carried and processed 8 by the respective set-top boxes with the appropriate CA. Each CA system is 9 orthogonal. Key sharing is not required and different key epochs may be used by each CA system. For example, a system with Motorola's proprietary encryption can 11 generate fast changing encryption keys using the embedded security ASIC, while 12 an NDS smart card based system can generate slightly slower changing keys.
13 This embodiment works equally well for Scientific Atlanta and Motorola legacy 14 encryption.
Referring now to FIGURE 6, a block diagram of a system consistent with an 16 embodiment of the present invention in which portions of programming are dual 17 encrypted on a packet-by-packet basis is illustrated as system 300. In this system, 18 packets of each program are dual encrypted using, for example, legacy CA
system 19 A and CA system B. The packets that are encrypted are selected based upon their importance to the proper decoding of the video and/or audio stream.
21 In the system illustrated in FIGURE 6, the cable system headend 322 22 selects AN content 304 packets at a packet selector 316 for encryption.
Packets 23 selected for encryption are chosen so that their non-receipt (by a non-paying 24 decoder) would severely affect the real-time decoding of a program, and any possible post processing of recorded content. That is, only critical packets are 26 encrypted. For the video and audio, this can be accomplished by encrypting "start 27 of frame" transport stream packets containing PES (packetized elementary stream) 28 headers and other headers as part of the payload, since without this information, 29 the STB decoder cannot decompress the. MPEG compressed data. MPEG2 1 streams identify "start of frame" packets with the "Packet Unit Start Indicator in the 2 transport header. Generally, packets carrying a payload that contains a group of 3 pictures header or a video sequence header can be used to effect the present 4 scrambling technique.
MPEG (Moving Pictures Expert Group) compliant compressed video 6 repackages the elementary data stream into the transport stream in somewhat 7 arbitrary payloads of 188 bytes of data. As such, the transport stream packets 8 containing a PES header can be selected for encryption at selector 316 and dual 9 encrypted by both the CA system A encrypter 318 and the CA system B
encrypter 324. Packets to be dual partially encrypted are duplicated and the PIDs of 11 duplicate packets encrypted by encrypter 324 are remapped at 330 to a secondary 12 PID as in the previous embodiment. The remaining packets are passed in the 13 clear. The clear packets, system A encrypted packets, system B encrypted 14 packets and system information 328 are multiplexed together for broadcast over the cable system 32.
16 As with the previous system, the legacy STB 36 receives clear data and data 17 encrypted under CA encryption system A and transparently passes unencrypted 18 data combined with data decrypted by CA decryption A 40 to its decoder. In the 19 new STB 336, the program is assigned to both a primary and a secondary PID.
The clear packets with the primary PID are received and passed to the decoder.
21 The encrypted packets with the primary PID are discarded. Encrypted packets with 22 . the secondary PID are decrypted and then recombined with the data stream (e.g., 23 by remapping the packets to the primary PID) for decoding.
24 Using video is used as an example, each sample is known as a frame and the sample rate is typically 30 frames per second. If the samples are encoded to .
26 fit into 3.8 Mbps, each frame would occupy 127K bits of bandwidth. This data is 27 sliced for MPEG transport into packets of 188 bytes with the first packet(s) of each 28 frame containing the header used for instructions to process the body of the frame 29 data. Dual encrypting just the first header packet (1504 additional bits) requires 1 only 1.2% (1504/127K) of additional bandwidth. For high definition (19 Mbps) 2 streams the percentage is even less.
3 As previously stated, transport stream packets containing a PES header are 4 the preferred target for encryption according to the present embodiment.
These packets contain sequence headers, sequence extension headers, picture headers, 6 quantization and other decode tables that also fall within the same packet.
If these 7 packets cannot be decoded (i.e., by a hacker attempting to view unauthorized 8 programming without paying the subscription charges), not even small portions of 9 the program can be viewed. In general, any attempt to tune to the program will likely be met with a blank screen and no audio whatsoever since known decoder 11 integrated circuits use the PES header to sync up to an elementary stream such 12 as video and audio in real-time. By encrypting the PES header, the decoding 13 engine in an un-authorized set-top box cannot even get started. Post processing 14 attacks, e.g. on stored content, are thwarted by critical dynamically changing information in the packet containing the PES header. Those skilled in the art will 16 appreciate that for implementation of this embodiment of the invention, other critical 17 or important packets or content elements may also be identified for encryption that 18 could severely inhibit unauthorized viewing without departing from the present 19 invention. For example, MPEG intra-coded or I frame picture packets could be encrypted to inhibit viewing of the video portion of the program. Embodiments the 21 present invention may be used in any combination with other embodiments, e.g.
22 scrambling the packet containing the PES header as well as random, Mth and N, 23 or data structure encryption of the other packets. Critical packet encryption may 24 be applied to video encryption, while a different method may be applied to audio.
Audio could be dual encrypted, for instance. Other variations within the scope of 26 the present invention will occur to those skilled in the art.
27 FIGURE 7 is a flow chart depicting an exemplary encoding process such as 28 that which would be used at headend 322 of FIGURE 6: When a transport stream 29 packet is received at 350, the packet is examined to determine if it meets a 1 selection criteria for encryption. In the preferred embodiment, this selection criteria 2 is the presence of a PES header as a portion of the packet payload. If not, the 3 packet is passed as a clear unencrypted packet (C) for insertion into the output 4 data stream at 354. If the packet meets the criteria, it is encrypted under CA
encryption system A at 358 to produce an encrypted packet EA. The packet is 6 also duplicated and encrypted under CA encryption system B at 362 to produce 7 an encrypted packet. This encrypted packet is mapped to a secondary PID at 8 to produce an encrypted packet EB. Encrypted packets EA and EB are inserted 9 into the output data stream along with clear packets C at 354. Preferably, the EA
and EB packets are inserted at the location in the data stream where the single 11 original packet was obtained for encryption so that the sequencing of the data 12 remains essentially the same.
13 When the output data stream from 354 is received at an STB compliant with 14 CA encryption system B such as 336 of FIGURE 6, a process such as that of FIGURE 8 (which is similar to that of FIGURE 5) can be utilized to decrypt and 16 decode the program. When a packet is received having either the primary or the 17 secondary PID at 370, a determination is made as to whether the packet is clear 18 (C) or encrypted under system A (EA) at 370 or encrypted under system B
(EB) at 19 374. If the packet is clear, it is passed directly to the decoder 378. In some embodiments, the relative position of the primary packet, before or after, to the 21 secondary packet may be used to signal a primary packet for replacement in the 22 stream. A check of the scrambling state of the primary packet is not specifically 23 required. If the packet is an EA packet, it is dropped at 380. If the packet is an EB
24 packet, it is decrypted at 384. At this point, the secondary PID packets and/or the primary PID packets are remapped to the same PID at 388. The decrypted and 26 clear packets are decoded at 378.
27 The dual partial encryption arrangement described above can greatly reduce 28 the bandwidth requirements over that required for full dual carriage.
Encrypting the 29 PES header information can be effective in securing video and audio content, while 1 allowing two or more CA systems to independently "co-exist on the same cable 2 system. Legacy system A'set-top boxes are un-affected, and system B set-top 3 boxes require only an minor hardware, firmware, or software enhancement to listen 4 for two PIDs each for video and audio. Each type of STB, legacy and non-legacy, retains its intrinsic CA methodology. Headend modification is limited to selecting 6 content for encryption, introducing the second encrypter, and providing a means to 7 mix the combination into a composite output stream.
8 In one embodiment, the headend equipment is configured to 9 opportunistically scramble as much of the content as the bandwidth will allow, and not just the critical, PES headers. These additional scrambled packets would be 11 either in the PES payload or other packets throughout the video/audio frame to 12 provide even further security of the content.

14 SI ENCRYPTION.
Turning now to FIGURE 9, one embodiment of a system that minimizes 16 the need for any additional bandwidth is illustrated as system 400. In this 17 embodiment, the system takes advantage of the fact that system information (SI) 18 428 is required for a set-top box to tune programming. In a cable system, SI is sent 19 in the out-of-band, a frequency set aside from the normal viewing channels.
It is possible to also sent it in-band. If sent in-band, the SI 428 is replicated and sent 21 with each stream. For discussion purposes, assume that the SI delivered to 22 "legacy" set-top boxes from previous manufacturers, is separate from the SI
23 delivered to set-tops from new manufacturers, such as STB 436.
Consequently, 24 each version of the SI can be independently scrambled as illustrated using conditional access system A 418 and conditional access system B 424. The clear 26 video 404 and clear audio 406 are delivered in the clear, but in order to understand 27 how to find them, the SI information 428 is needed.
28 The Sl delivers information about channel names and program guide 29 information such as program names and start'times, etc. ... as well as the frequency tuning information for each channel. Digital channels are multiplexed I together and delivered at particular frequencies. In the embodiment of the 2 invention, the St information is encrypted, and only made available to authorized 3 set-top boxes. If the SI information is not received to allow knowledge of the 4 location of all ,the A/V frequencies in the plant, then tuning cannot take place.
To frustrate a hacker who might program a set-top box to trial or scan 6 frequencies, the frequencies for the channels can be offset from the standard 7 frequencies. Also, the frequencies can be dynamically changed on a daily, weekly 8 or other periodic or random basis. A typical cable headend may have roughly 9 frequencies in use. Each frequency is typically chosen to avoid interference between, among other things, each other, terrestrial broadcast signals, and 11 frequencies used by clocks of the receiving equipment. Each channel has at least 12 1 independent alternate frequency that if used would not could not cause 13 interference, or cause the frequency of adjoining channels to be changed.
The 14 actual possible frequency maps are therefore 230 or 1.07 x 109. However, a hacker might simply quickly try both frequencies on each tune attempt for each of the 16 channels or so. If successful in locating a frequency with content, the hacker's set-17 top box can then parse the PSI 429 to learn about the individual PIDs that make up 18 a program. The hacker will have difficulty learning that "program 1" is "CNN", and 19 that "program 5" is "TNN", and so on. That information is sent with the SI, which as stated above is scrambled and otherwise unavailable to the un-authorized set-top 21 box. However, a persistent hacker might yet figure those out by selecting each one 22 and examining the content delivered. So in order to frustrate the identification of 23 channels, the assignment of a program within a single stream can move around, 24 e.g. program 2 and program 5 swapped in the example above so that "program is "TNN" and "program 5" is "CNN". Also, it is possible to move programs to 26 entirely different streams with entirely new program groupings. A typical digital 27 cable headend can deliver 250 programs of content including music. Each can be .28 uniquely tuned. The possible combinations for re-ordering are 250!
(factorial).
29 Without a map of the content provided by either the delivered SI or by a hacker, the 1 user is faced with randomly selecting each program in a stream to see if it is the 2 one interest.
3 Thus, at headend 422, the video signal 404 and the audio signal 406 are.
4 provided in the clear (unencrypted) while the SI 428 is provided to multiple CA
systems for delivery over the cable network. Thus, in the exemplary system 400, 6 clear St 428 is provided to an encryption system 428 that encrypts Sl data using 7 encryption system A. Simultaneously, clear SI 428 is provided to encryption 8 system 424 that encrypts the SI data using encryption system B. Clear video and 9 audio are then multiplexed along with encrypted SI from 418 (SI A) and encrypted audio from 424 (SI B) out of band system information 428.
11 After distribution through the cable system 32, the video, the audio, system 12 information A and system information B are all delivered to set-top boxes 36 and 13 436. At STB 36, the encrypted SI is decrypted at CA system A 40 to provide tuning 14 information to the set-top box. The set-top box tunes a particular program to allow it to be displayed on television set 44. Similarly, at STB 436, the encrypted SI is 16 decrypted at CA system B 440 to provide tuning information for the set-top box, 17 allow a particular program to be tuned and displayed on television set 444.
18 An advantage of this approach is that no additional A/V bandwidth is 19 required in the content delivery system, e.g. cable system. Only the SI is dual carried. No special hardware is required. Any offset frequencies from the standard 21 ones can be easily accommodated by most tuners. SI decryption can be performed 22 in software or can be aided by hardware. For example, legacy Motorola set-top 23 boxes have an ability to descramble the SI delivered in the Motorola out-of-band 24 using a hardware decrypter built into the decoder IC chip.
A determined hacker can potentially use a spectrum analyzer on the coax 26 cable to learn where the AN channels are located. Also, it may be possible for the 27 hacker to program a set-top box to auto-scan the frequency band to learn where the 28 AN channels are - a relatively slow process. If the A/V channel frequencies 29 changed dynamically, then that could foil the hackers, since they would need to be constantly analyzing or scanning the band. Also, the program numbers and 1 assigned PIDs can vary. However, dynamically changing frequencies, program 2 numbers, and PIDs might create operational difficulties to a service provider, e.g.
3 cable operator.

GENERALIZED REPRESENTATION
6 Each of the above techniques can be represented generically by the system 7 500 of FIGURE 10. This system 500 has a cable system headend 522 with clear 8 video 504, clear audio 506, SI 528, and PSI 529 any of which can be selectively 9 switched through an intelligent processor control led switch 518, which also serves to assign PIDs (in embodiments requiring PID assignment or reassignment), to 11 conditional access system A 504 or conditional access system B 524 or passed 12 in the clear to the cable system 32. As previously, the program or SI
encrypted 13 according to the legacy CA system A can be properly decoded by SIB 36. The CA
14 system B encrypted information is understood by STBs 536 and decrypted and decoded accordingly, as described previously.

18, The PID mapping concepts described above can be generally applied to the 19 dual partial encryption techniques described herein, where needed. At the cable headend, the general concept is that a data stream of packets is manipulated to 21 duplicate packets selected for encryption.. Those packets are duplicated and 22 encrypted under two distinct encryption methods. The duplicated packets are 23 assigned separate PIDs (one of which matches the legacy CA PID used for clear 24 content) and reinserted in the location of the original selected packet in the data stream for transmission over the cable system. At the output of the cable system 26 headend, a stream of packets appears with the legacy encrypted packets and clear 27 packets having the same PID. A secondary PID identifies the packets that are 28 encrypted under the new encryption system. In addition to the PID remapping that 29 takes place at the headend, MPEG packets utilize a continuity counter to maintain the appropriate sequence of the packets. In order to assure proper decoding, this 1 continuity counter should be properly maintained during creation of the packetized 2 data stream at the headend. This is accomplished by assuring that packets with 3 each PID are assigned continuity counters sequentially in a normal manner.
Thus, 4 packets with the secondary PID will carry a separate continuity counter from those of the primary PID. This is illustrated below in simplified form where PID 025 is the 6 primary PID and PID 125 is the secondary PID, E represents an encrypted packet, 7 C represents a clear packet, and the end number represents a continuity counter.

9 f 025C04 025E05 125E11 025C06 025C07 025008 025C09 125E12 11 In this exemplary segment of packets, packets with PID 025 are seen to 12 have their own sequence of continuity counters (04, 05, 06, 07, 08, 09, ...).
13 Similarly, the packets with secondary PID 125 also have their own sequence of 14 continuity counters (11, 12, ...).
At the STB, the PIDs can be manipulated in any number of ways to correctly 16 associate the encrypted packets with secondary PID with the correct program. In 17 one implementation, the packet headers of an input stream segment illustrated 18 below:

22 are manipulated to create the following output stream segment:

26 The primary PIDs (025) in the input stream are replaced with the secondary PID
27 (125) for the clear packets (C). For the encrypted packets, the primary PID
and 28 secondary PID are retained, but the continuity counters are swapped., Thus, the 29 stream of packets can now be properly decrypted and decoded without errors 1 caused by loss of continuity using the secondary PID. Other methods for 2 manipulation of the PIDs, e.g. mapping the PID (125) on the scrambled legacy 3 packet to a NOP PID (all ones) or other PID value not decoded, and the continuity 4 counters can also be used in embodiments consistent with the present invention.
The primary and secondary PIDs are conveyed to the STBs in the program 6 map table (PMT) transmitted as a part of the program system information (PSI) 7 data stream. The existence of a secondary PID can be established to be ignored 8 by the STB operating under CA encryption system A (the "legacy" system), but new 9 STBs operating under CA encryption system B are programmed to recognize that secondary PIDs are used to convey the encrypted part of the program associated 11 with the primary PID. The set-top boxes are alerted to the fact that this encryption 12 scheme is being used by the presence of a CA descriptor in the elementary PID "for 13 loop" of the PMT. There typically would be a CA descriptor for the video 14 elementary PID "for loop", and another one in the audio elementary PID "for loop".
The CA descriptor uses a Private Data Byte to identify the CA PID as either the 16 ECM PID or the secondary PID used for partial scrambling, thus setting up the STB
17 operating under system B to look for both primary and secondary PIDs associated 18 with a single program. Since the PID field in the transport header is thirteen bits 19 in length, there are 213 or 8,192 PIDs available for use, any, spare PIDs can be utilized for the secondary PIDs as required.
21 In addition to the assignment of a PID for each program component or 22 selected portion thereof, a new PID may be assigned to tag ECM data used in the 23 second encryption technique. Each PID number assigned can be noted as a user 24 defined stream type to prevent disrupting operation of a legacy STB. MPEG
defines a reserved block of such numbers for user defined data stream types.
26 While conceptually the PID mapping at the cable headend is a simple 27 operation, in practice the cable headend equipment is often already established 28 and is therefore modified to accomplish this task in a manner that is minimally 29 disruptive to the established cable system while being cost effective.
Thus, the details of the actual implementation within the cable system, headend are 1 somewhat dependent upon the actual legacy hardware present in the headend, 2 examples of which are described in greater detail below.

Headend IMPLEMENTATIONS
6 Those skilled in the art will appreciate that the above descriptions as related 7 to FIGURES 2, 3, 6, 9 and 10 are somewhat conceptual in nature and are used to 8 explain the overall ideas and concepts associated with the various embodiments 9 of the present invention.. In realizing a real world implementation of the present invention, those skilled in the art will recognize that a significant real world issue 11 to contend with is providing a cost effective implementation of the various partial 12 encryption methods within existing legacy headend equipment at established cable 13 providers. Taking two of the primary legacy cable systems as examples, the 14 following describes how the above techniques can be implemented at a cable headend.
16 First, consider a cable system headend using a Motorola brand conditional 17 access system. In such a system the modifications shown 'in FIGURE 11 can be 18 done to provide a cost effective mechanism for partial dual encryption 19 implementation. In a typical Motorola system, a HITS (Headend In The Sky) or similar data feed is provided from a satellite. This feed provides aggregated 21 digitized content that is supplied to cable providers and is received by a receiver I
22 descrambler I scrambler system 604 such as the Motorola Integrated Receiver 23 Transcoder (IRT) models IRT 1000 and IRT 2000, and Motorola Modular Processing 24 System (MPS). A clear stream of digitized television data can be obtained from the satellite descrambler functional block 606 of the receiver! descrambler l scrambler 26 604. This clear stream can be manipulated by a new functional block shown as 27 packet selector ! duplicator 610. This new block 610 may be implemented as a 28 programmed processor or may be otherwise implemented in hardware, software 29 or a combination thereof.

1 Packet selector /.duplicator 610 selects packets that are to be dual 2 encrypted under any of the above partial dual encryption methods. Those packets 3 are then duplicated with new PIDs so that they can be later identified for encryption.
4 For example, if packets at the input of 610 associated with a particular program have PID A, then packet selector I duplicator 610 identifies packets to be encrypted 6 and duplicates those packets and remaps them to PIDs B and C respectively, so 7 that they can be identified later for encryption under two different systems.
8 Preferably, the duplicate packets are inserted into the data stream adjacent one 9 another in the location of the originally duplicated packet now with PID C
so that they remain in the same order originally presented (except that there are two 11 packets where one previously resided in the data stream). Assume, for the 12 moment, that the new CA system to be added is NDS encryption. In this case, PID
13 A will represent clear packets, PID B will represent NDS encrypted packets and 14 PID C will represent Motorola encrypted packets. The packets having PID B
may be encrypted under the NDS encryption at this point in 610 or may be encrypted 16 later.
17 The packets with PIDs B and C are then returned to the system 604 where 18 packets with PID C are encrypted under Motorola encryption at cable scrambler 19 612 as instructed by the control system 614 associated with the Motorola equipment. The output stream from cable scrambler 612 then proceeds to another 21 new device - PID remapper and scrambler 620, which receives the output stream 22 from 612 and now remaps the remaining packets with PID A to PID C and encrypts 23 the PID B packets under the NDS encryption algorithm under control of control 24 system 624. The output stream at 626 has clear unencrypted packets with PID
C
and selected packets which have been duplicated and encrypted under the 26 Motorola encryption system with PID C along with encrypted packets under the 27. NDS encryption system with PID B. This stream is then modulated (e.g., 28 Quadrature Amplitude Modulated and RF modulated) for distribution over the cable 29 system. The preferred embodiment maps the unencrypted packets on PID A to match the scrambled packets on PID C because the audio and video PIDs called 1 out in legacy program specific information (PSI) is correct that way. The control 2 computer, the scrambler, and legacy set-top boxes only know about PID C.
3 Alternatively, the scrambled packets on PID C could be mapped back to PID A, but 4 this would likely mean editing the PSI, that was automatically generated, to map the PID numbers from PID C back to PID A in the PID remapper and scrambler 6 620.
7 In the above example, the PID remapper and scrambler 620 may also be 8 used to demultiplex PSI information, modify it to reflect the addition of the NDS
9 encryption (through the use of CA descriptors in the ' PMT) and multiplex the modified PSI information back into the data stream. The ECMs to support NDS
11 encryption may also be inserted into the data stream at PID remapper and 12 scrambler 620 (or could be inserted by packet selector / duplicator 610).
13 Thus, in order to add NDS encryption (or another encryption system) to a 14 cable system headend using Motorola equipment, packets are duplicated and PIDs are remapped in the data stream from the satellite descrambler. The remapped 16 PlDs are then used to identify packets that are to be scrambled under each CA
17 system. Once the legacy system encryption has taken place, the clear PID is then 18 remapped so that both clear and encrypted packets in the legacy system share the 19 same PID (or PIDs). PID remapping as in 620 and packet selection and duplication as in 610 can be implemented using a programmed processor or using custom or 21 semi-custom integrated circuitry such as an application specific integrated circuit 22 or a programmable logic device or field programmable gate array. Other 23 implementations are also possible without departing from the present invention.
24 FIGURE 12 depicts a similar equipment configuration such as that used in implementing the partial dual encryption of the present invention in a Scientific 26 Atlanta based cable headend. In this embodiment, the HITS feed or similar is 27 received at IRD 704 which incorporates a satellite descrambler 706. This may be 28 a Motorola IRT or MPS with only the satellite descrambler function enabled.
The 29 output of the satellite descrambler 706 again provides a clear data stream that can be manipulated by a new packet selector/ duplicator 710 which selects packets 1 to be encrypted, duplicates them and maps the PIDs of the duplicate packets to 2 new PIDs. Again, for example, packets to remain in the clear are assigned PID A, 3 packets to be encrypted under the new system (e.g., NDS) are assigned PID B
and 4 packets to be encrypted under the Scientific Atlanta encryption system are assigned PID C. The packets with PID B may be encrypted at this point under the 6 NDS encryption system.
7 The stream of packets is then sent to a multiplexer 712 (e.g., a Scientific 8 Atlanta multiplexer) where the packets having PID C are encrypted under the 9 Scientific Atlanta encryption system at 714 under control of control system associated with multiplexer 712. The stream of data is then supplied internal to 11 multiplexer 712 to a QAM modulator 720. In order to properly remap the packets, 12 the QAM modulated signal at the output of multiplexer 712 is provided to a new 13 processor system 724 where the QAM modulated signal is demodulated at a QAM
14 demodulator 730 and the clear PID A packets are remapped to PID C at PID
remapper 734 under control of a control system 738. Encryption under the NDS
16 encryption algorithm can also be carried out here rather than in 710. The data 17 stream with remapped PIDs and dual partial encryption is then QAM and RI=
18 modulated at 742 for distribution over the cable system.
19 In the above example, the PID remapper and scrambler 734 may also be used to demultiplex PSI information, modify it to reflect the addition of the NDS
21 encryption (adding the CA descriptors to the PMT) and multiplex the modified PSI
22 information back into the data stream. The ECMs to support NDS encryption may 23 also be inserted into the data stream at PID remapper and scrambler 734 (or could 24 be inserted by packet selector/ duplicator 710). PID remapping and or scrambling as in 734 along with QAM demodulation and QAM modulation as in 730 and 742 26 respectively, and packet selection and duplication as in 710 can be implemented 27 using a programmed processor or using custom or semi-custom integrated circuitry 28 such as an application specific integrated circuit or a programmable logic device 29 or field programmable gate array. Other implementations are also possible without departing from the present invention.

1 The above embodiments of the present invention allow legacy scrambling 2 equipment to scramble only the packets desired in an elementary stream instead 3 of the entire elementary stream. The scrambling of certain packets of an 4 elementary stream is accomplished by using a PID number for packets that are not going to be scrambled, e.g., PID A. Packets that will be scrambled will be placed 6 on PID C. The scrambling equipment will scramble the packets on PID C (the ones 7 that have been selected for scrambling). After the scrambling has taken place, the 8 unscrambled packets have the PID number mapped to the same as the scrambled 9 packet - PID A becomes PID C. The legacy set-top boxes will receive an elementary stream with both scrambled and un-scrambled packets.
11 The packets in these embodiments are handled as a stream. The entire 12 stream is sent to the legacy scrambling equipment for scrambling. This keeps all 13 of the packets in exact time synchronous order. If packets were extracted from a 14 stream and sent to the legacy scrambling equipment, time jitter might be introduced. The present embodiment avoids that problem by keeping all the 16 packets in a stream. The embodiment does not require cooperation from the 17 legacy scrambling equipment provider because that equipment is not involved in 18 the remapping of packets- from PID A to PID C. This remapping is preferable 19 because the PID called out by the PSI generated by the legacy scrambling system does not need to change. The legacy system knows about PID C, but not PID A.
21 The entire elementary stream to be scrambled by the legacy scrambling equipment 22 is found on a single PID that the scrambling system has been instructed to 23 scramble.
24 In the above examples, the use of NDS as the second encryption system should not be considered limiting. Moreover, although two widely used systems -26 Motorola and Scientific Atlanta have been depicted by way of example, similar 27 modifications to legacy systems to permit PID remapping and dual partial 28 encryption can be used. In general, the technique described above involves the 29 process generally described as 800 in FIGURE 13. A feed is received at 806 which is descrambled as it is received at 810 to produce a clear data stream of packets.

1 At 814,. packets are selected according to the desired partial dual encryption 2 technique (e.g., audio only, packets containing PES header, etc.). At 818, the 3 selected packets are duplicated and the duplicate pairs are remapped to two new 4 PIDs (e.g., PID B and PID C). The duplicated packets are then encrypted based upon PID (that is, PID C is encrypted according to legacy encryption and PID B
is 6 encrypted according to the new encryption system) at 822. The clear packets (e.g., 7 PID A) are then remapped to the same PID as the legacy encrypted PID (PID C) at 8 826.
9 The order in which some of the elements of the process of FIGURE 13 are carried out can vary according to the particular legacy system being modified to 11 accommodate the particular dual encryption arrangement being used. For 12 example, encryption under a new encryption system can be carried out either at the 13 time of duplication or later at the time of remapping the legacy packets, as 14 illustrated in FIGURE 11 and 12. Additionally, , various demodulation and re-modulation operations can be carried out as needed to accommodate the particular 16 legacy system at hand (not shown in FIGURE 13).

19 Several set-top box implementations are possible within the scope of the present invention. The method used at the headend to select packets for 21 encryption is irrelevant to the STB.
22 One such implementation is illustrated in FIGURE 14. In this embodiment, 23 packets from a tuner and demodulator 904 are provided to a decoder circuit 908's 24 demultiplexer 910. The packets are buffered into a memory 912 (e.g., using a unified memory architecture) and processed by the STB's main CPU 916 using 26 software stored in ROM memory 920.
27 Selected PIDs can be stripped from the incoming transport via the STB's PID
28 filter, decrypted and buffered in SDRAM, similar to the initial processing required 29 in preparation for transfer to an HDD in a PVR application. The host CPU
916 can 1 then "manually" filter the buffered data in SDRAM for elimination of the packets 2 containing unneeded PIDs. There are some obvious side effects to this process, 3 The host overhead is estimated to be about 1 % of the bandwidth of the CPU.
4 In the worst case, this is equivalent to 40K bytes/Second for a 15 Mbit/S
video stream. This reduction is possible since at most only 4 bytes of each packet is 6 evaluated and the location is on 188 byte intervals so the intervening data does not 7 have to be considered. Each packet header in SDRAM can therefore be directly 8 accessed through simple memory pointer manipulation. Additionally, Packets are 9 cached in blocks and evaluated en masse to reduce task switching of the host.
This would eliminate an interrupt to other tasks upon the reception of each new 11 packet. This may produce a increased latency for starting decode of a stream upon 12 channel change to allow time for cache fill. This may be negligible depending upon 13 the allocated SDRAM cache buffer size.
14 The host filtered packets in the SDRAM buffer are then transferred to the AN
Queue through existing hardware DMA processes and mimics a PVR
16 implementation. The filtered packets are then provided to the decoder 922 for 17 decoding.
18 A second technique for implementation in a set-top box is illustrated in 19 FIGURE 15. Since RISC processor AN decoder module in 930 processes the partial transport PIDs and strips/concatenates for decode, the firmware within 21 decoder IC 930 can be altered to exclude individual packets in a partial transport 22 stream based upon criteria in each packet header. Alternatively, the demultiplexer 23 910 can be designed to exclude the packets. Legacy scrambled packet(s) pass 24 through the CA module still encrypted. By using the decoder IC 930 to perform the removal of the legacy scrambled packets and assuming that the packets encrypted 26 under the new encryption algorithm (e.g., NDS) is immediately adjacent the legacy 27 encrypted packet (or at least prior to next primary stream video packet) then the 28 pruning of the legacy packet in effect accomplishes the merging of a single, clear 29 stream into the header strip and video queue.

1 A third technique for implementation of partial decryption in a set-top box is 2 illustrated in FIGURE 16.. In this embodiment, the PID remapping is carried out 3 either within a circuit such as an ASIC, Field Programmable Gate Array-(FPGA), 4 or a programmable logic device (PLD) 938 or other custom designed circuit placed between the tuner and demodulator 9.04 and the decoder IC 908. In a variation of 6 this embodiment, the decoder IC 908 can be modified to implement the PID
7 remapping within demultiplexer 940. In either case, the legacy encrypted packets -8 are dropped and the non-legacy packets re-mapped either in circuit 938 or 9 demultiplexer 940.
This third technique can be implemented in one embodiment using the PLD
11 depicted in FIGURE 17. This implementation assumes that there will be not be 12 more than one encrypted packet of a particular PID appearing in a row, thus, the 13 implementation could be modified to accommodate bursts of encrypted packets 14 such as with the M and Nth encryption arrangement described above (as will be explained later). The input stream passes through a PID identifier 950 which 16 serves to demultiplex the input stream based upon PID. Primary PID packets are 17 checked for continuity at 958. If a continuity error is detected, the error is noted and 18 the counter is reset at 960.
19 The original input packet stream contains packets tagged with many PIDs.
The PID identifier 950 separates packets with the two PIDs of interest (primary and 21 secondary PIDs) from all other packets. This capability can be scaled to process 22 multiple PID pairs. These other packets are bypassed directly to the revised output 23, stream. This processing results in a three or four byte clocking delay.
24 Packets with the secondary PID are routed by the PID identifier 950 to a continuity count checker 954 which verifies sequence integrity for this PID.
Any 26 errors are noted at 956, but specific handling of errors is not relevant to 27 understanding the present invention. The packet's continuity value is preserved for 28 use in checking the sequence of packets to follow. A corresponding continuity 1 check 958 is done for packets with the primary PID using the independent primary 2 counter, and again any errors are noted at 960.
3 The secondary packet is checked for a secondary flag at 962. This Boolean 4 indicator is used to remember if a secondary packet has been processed since the last clear packet. More than one secondary packet between clear packets is an 6 error in this embodiment and is noted at 964. Presence of a secondary packet is 7 remembered by setting the secondary flag at 966.
8 The continuity counter of the secondary packet is changed at 968 to fit into 9 the sequence of the clear packets. Data for this substitution comes from the value used to verify continuity of the primary stream at 958. The revised packet is sent 11 out from 968 and merged into the revised stream forming the output stream.
12 After packets with primary PIDs have had their continuity checked at 958, 13 they are differentiated at 970 by the scrambling flags in the header. If the packet 14 is scrambled, the primary flag is queried at 974. This primary flag Boolean indicator is used to remember if a primary encrypted packet has been processed 16 since the last clear packet. More than one encrypted primary packet between clear 17 packets is an error in this embodiment and is noted at 976 before the packet is 18 discarded at 978. Presence of a encrypted primary packet is remembered by 19 setting the primary flag at 980. If there is no downstream consumer for the primary encrypted packet, it can be discarded at 978. In some cases it may be necessary 21 for the packet to continue on (in which case its continuity counter can use the 22 discarded secondary continuity value).
23 If the primary PID scramble test at 970 detects a clear packet, the state of 24 the secondary and primary flags is tested at 984. Valid conditions are neither set and both set, since encrypted packets should come in matched pairs. A sequence 26 of one without the other should be noted as an error at 988. However, the order of 27 appearance is inconsequential in this embodiment. It should be noted that there 28 may be other ways to flag a primary packet for deletion other than the scrambling 29 bits in the transport header, e.g. the transport priority bit. Also, it is possible not I to use any bits what-so-ever, e.g. using the primary packet's simple positional 2 information, before or after the secondary packet, as an indicator for replacement.
3 Clear packets with the primary PID then have their PID value changed at 992 4 to the secondary PID before being output in the revised output stream.
Alternatively, the secondary PID packets can be remapped to the primary PID
6 value. The content can be decoded when the decoder is provided with the correct 7 PID for decoding the content (whether the primary or secondary PID).
Presence of 8 a clear packet also clears the primary and secondary Boolean flags.
9 In all the embodiments proposed, the secondary packet can be inserted adjoining the primary packet to be replaced even when a series of primary packets 11 are tagged for replacement. However, in some instances, it may facilitate headend 12 partial scrambling if multiple encrypted packets can be inserted into the stream 13 without the intervening secondary packets. In order to accommodate multiple 14 consecutive encrypted packets (such as with the M' and N partial encryption method), the use of primary and secondary flags can be replaced with a counter 16 matching test function. Thus, in place of elements 962, 964 and 966, a secondary 17 encrypted packet counter can be incremented. In place of elements 970, 974, 18 and 980, a primary encrypted packet counter can be incremented. Element 984 19 can be replaced with a comparison of the primary and secondary encrypted packet counters to assure that the same number of encrypted packets are received in both 21 the primary and secondary paths. Instead of clearing flags at 992, the counters are 22 cleared. Using this variation, multiple encrypted packets may be.
consecutively 23 received and the number received are compared to monitor the integrity of the data 24 stream. Other variations will occur to those skilled in the art.
The function described above in connection with FIGURE 17 can be 26 integrated into an AN decoder chip that functions similar. to that of the 27 commercially available Broadcom series 70xx or 71 xx decoder used in commercial 28 set-top boxes. FIGURE 18 illustrates a block diagram for such a decoder chip, 29 where the functions already provided in the commercial chip are essentially 1 unchanged. Normally, commercial decoder chips expect there to be a one-to-one 2 correspondence between the PIDs and program components (e.g., audio or video).
3 The decoder illustrated in FIGURE 18 permits multiple PIDs to be 4 programmed into the decoder via a connection to the STB central. processor so that both primary and secondary PIDs can be handled for main audio, main video and 6 a secondary video used for picture-in-picture (PiP) functions. in this embodiment, 7 the raw data stream is received by a Packet sorter 1002 that provides a function 8 similar to that described in connection with FIGURE 17 above to demultiplex the 9 stream of packets based upon PID. Preferably, the decoder of FIGURE 18 carries out the PID sorting function of 1002 using hard wired logic circuitry rather than 11 programmed software. Program guide and stream navigation information is output 12 for use by an STB's main processor, for example. The packets associated with the 13 main audio program are buffered in a FIFO 1006, decrypted in a decrypter 14 and then buffered at 1014 for retrieval by an MPEG audio decoder 1018 as needed.
Decoded MPEG audio is then provided as an output from the decoder.
16 In a similar manner, packets associated with the main video program are 17 buffered in a FIFO 1024, decrypted in a decrypter 1028 and then buffered at 18 for retrieval by an MPEG video decoder 1036 as needed. Decoded MPEG video 19 for the main channel is then provided to a compositer 1040 and then provided as an output from the decoder. Similarly, packets associated with picture-in-picture 21 video are buffered in a FIFO 1044, decrypted in a decrypter 1048 and then buffered 22 at 1052 for retrieval by an MPEG video decoder 1056 as needed. Decoded MPEG
23 video for the picture-in-picture channel is then provided to the compositer 24 where it is combined with the main channel video and then provided as a decoded video output from the decoder. Other packets not associated with the main or 26 picture-in-picture channel are discarded. Of course, other functions may be 27 incorporated in the decoder chip or deleted without departing from embodiments 28 of the present invention.

2 As previously mentioned, in order to thwart a persistent threat by hackers, 3 several of the above partial encryption arrangements can be combined to further 4 enhance security. For example, the critical packet encryption can be used in any combination with SI encryption, Mth an N, random encryption, time slice and other 6 techniques to further enhance security. In one embodiment, as many packets 7 would be encrypted as bandwidth is available. The amount of encryption might 8 depend on whether the content was a regular program or premium (such as a pay-9 per-view or VOD), whether it was an adult program or a regular movie, and the security level that the various cable operators feel comfortable operating.
Those 11 skilled in the art will appreciate that many other combinations are possible to 12 further enhance the security of the encryption without departing from the present 13 invention.
14 The present invention, as described above in its various embodiments, has been described in terms of a digital AN system using MPEG 2 coding. Thus, the 16 various packet names and protocol specifically discussed is related the 17 coding and decoding. However, those skilled in the art will appreciate that the 18 concepts disclosed and claimed herein are not to be construed in such a limited 19 scope. The same or analogous techniques can be used in any digital cable system without limitation to MPEG 2 protocols. Moreover, the present techniques can be 21 used in any other suitable content delivery scenario including, but not limited to, 22 terrestrial broadcast based content delivery systems, Internet based content 23 delivery, satellite based content delivery systems such as, for example, the Digital .24 Satellite Service (DSS) such as that used in the DirecTVTM system, as well as package media (e.g. CDs and DVDs). These various alternatives are considered 26 equivalent for purposes of this document, and the, exemplary MPEG 2 cable 27 embodiment should be considered to be an exemplary embodiment presented for 28 illustrative purposes.
29 In addition, the present invention has been described in terms of decoding partially encrypted television programs using a television set-top box.
However, the 1 present decoding mechanism can equally be implemented within a television 2 receiver without need for an STB, or music player such as an MP3 player.
Such 3 embodiments are considered equivalent.
4 Also, while the present invention has been described in terms of the use of the encryption techniques described to provide a mechanism for dual partial 6 encryption of a television program, these partial encryption techniques could be 7 used as a single encryption technique or for multiple encryption under more than 8 two encryption systems without limitation. More than two encryption systems 9 would be accommodated with additional duplicated packets that are encrypted.
Alternatively, the encryption key for one of the duplicated packets may be shared 11 amongst the multiple encryption systems. Additionally, although specifically 12 disclosed for the purpose of encryption of television programming, the present 13 inventions can be utilized for single or dual encryption of other content including, 14 but not limited to content for download over the Internet or other network, music content, packaged media content as well as other types of information content.
16 Such content may be played on any number of playback devices including but not 17 limited to personal digital assistants (PDAs), personal computers, personal music 18 players, audio systems, audio / video systems, etc. without departing from the 19 present invention.
Those skilled in the art will recognize that the present invention has been 21 described in terms of exemplary embodiments that can be realized by use of a 22 programmed processor. However, the invention should not be so limited, since the 23 present invention could be implemented using hardware component equivalents 24 such as special purpose hardware and/or dedicated processors which are equivalents to the invention as described and claimed. Similarly, general purpose 26 computers, microprocessor based computers, micro-controllers, optical computers, 27 analog computers, dedicated processors and/or dedicated hard wired logic may be 28 used to construct alternative equivalent embodiments of the present invention.
29 Those skilled in the art will appreciate that the program steps and associated data used to implement the embodiments described above can be implemented 1 using disc storage as well as other forms of storage such as for example Read 2 Only Memory (ROM) devices, Random Access Memory (RAM) devices; optical 3 storage elements, magnetic storage elements, magneto-optical storage elements, 4 flash memory, core memory and/or other equivalent storage technologies without departing from the present invention. Such alternative storage devices should be 6 considered equivalents.
7 The present invention, as described. in embodiments herein, can be 8 implemented using a programmed processor executing programming instructions 9 that are broadly described above in flow chart form that can be stored on any suitable electronic storage medium or transmitted over any suitable electronic 11 communication medium. However, those skilled in the art will appreciate that the 12 processes described above can be implemented in any number of variations and 13 in many suitable programming languages without departing from the present 14 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 16 departing from the invention. Error trapping can be added and/or enhanced and 17 variations can be made in user interface and information presentation without 18 departing from the present invention. Such variations are contemplated and.
19 considered equivalent.
While the invention has been described in conjunction with specific 21 embodiments, it is evident that many alternatives, modifications, permutations and 22 variations will become apparent to those skilled in the art in light of the foregoing 23 description. Accordingly, it is intended that the present invention embrace all such 24 alternatives, modifications and variations as fall within the scope of the appended claims.

Claims (74)

1. A method of decoding partially encrypted digital video content, comprising:

receiving partially encrypted digital video content comprising unencrypted data, first data encrypted under a first encryption system and second data encrypted under a second encryption system, wherein the first and second data are identical when unencrypted;
decrypting the second encrypted data;
decoding the unencrypted data and the decrypted second data to decode the partially encrypted digital video content; and outputting decoded digital video content comprising the unencrypted data and the decrypted second data.

2. The method according to claim 1, wherein the receiving, decrypting and decoding are carried out in a television device.

3. The method according to claim 2, wherein the television device comprises a television set-top box.

4. The method according to claim 1, wherein the receiving, decrypting and decoding are carried out in an integrated circuit.

5. The method according to claim 1, wherein the receiving, decrypting and decoding are carried out in one of an application specific integrated circuit and a field programmable gate array.

6. A method of decoding a partially encrypted digital television signal, comprising:
receiving a message identifying a primary packet identifier (PID) for a television program and a secondary PID for the television program;

receiving multiple selectively encrypted digital video content in which the primary PID identifies unencrypted packets of data as well as selected packets of data that are encrypted under a first encryption method, and wherein the digital video content further comprises a duplicate of the selected packets of data encrypted under a second encryption method that are identified by the secondary PID;
decrypting packets of data having the secondary PID; and combining the decrypted packets of data with unencrypted packets of data having the primary PID to form an output data stream representing the television program.

7. The method according to claim 6, further comprising decoding the decrypted packets of data and the packets of data having the primary PID.

8. The method according to claim 6, further comprising mapping the decrypted packets of data to the primary PID.

9. The method according to claim 8, wherein the mapping is carried out in an integrated circuit device.

10. The method according to claim 8, wherein the mapping is carried out in one of an application specific integrated circuit device, a programmable logic device, and a field programmable gate array.

11. The method according to claim 6, wherein packets of data having the primary PID comprise unencrypted packets of data and encrypted packets of data and further comprising:
discarding the encrypted packets of data having the primary PID.

12. The method according to claim 6, carried out in a television receiver device.

13. The method according to claim 6, carried out in a television set-top box.

14. A method of decrypting a partially multiple encrypted digital television program, comprising:

receiving multiple selectively encrypted digital video data in which a primary packet identifier (PID) identifies unencrypted packets of digital video data as well as selected packets of digital video data that are encrypted under a first encryption method, and wherein the digital video data further comprises a duplicate of the selected packets of digital video data that are encrypted under a second encryption method and identified by a secondary PID;
identifying the digital television program by unencrypted packets of digital video data associated with the primary PID and encrypted packets of digital video data associated with the secondary PID;
decrypting packets of digital video data having the secondary PID in order to provide a fully unencrypted digital television program; and outputting the fully unencrypted digital television program comprising the decrypted packets of digital video data and the unencrypted digital video data.

15. The method according to claim 14, further comprising decoding the decrypted packets of digital video data having the secondary PID along with decrypted packets of digital video data having the primary PID to produce a decoded partially encrypted digital television program as an output.

16. The method according to claim 14 further comprising discarding encrypted packets of digital video data having the primary PID.

17. The method according to claim 14, carried out in a television set-top box.

18. The method according to claim 14, wherein the encrypted packets of digital video data comprise transport stream packets carrying an MPEG packetized elementary stream (PES) header as a portion of a payload thereof.

19. The method according to claim 14, wherein the encrypted packets further comprise digital audio data packets.

20. The method according to claim 14, wherein the encrypted packets of digital video data comprise time sliced samples of the television program.

21. The method according to claim 14, wherein the encrypted packets of digital video data contain information critical to decoding the television program.

22. The method according to claim 14, wherein the television program is compressed and wherein the encrypted packets of digital video data comprise packets containing information used for decompression of the television program.

23. The method according to claim 14, wherein the encrypted packets of digital video data comprise N packets out of every M packets where N is less than M.

24. The method according to claim 14, further comprising remapping packets of digital video data having the secondary packet identifier to have the primary packet identifier.

25. An electronic storage medium storing instructions which, when executed on a programmed processor, carry out the method of decoding a television program according to claim 14.

26. An electronic transmission medium carrying a sequence of instructions for carrying out a method of decoding a television program by the method according to claim 14.

27. A digital television receiver device, comprising:
means for receiving a multiple partially encrypted digital television signal, the television signal being identified by packets of digital video data associated with either a primary packet identifier or a secondary packet identifier;
wherein the multiple partially encrypted digital television signal comprises unencrypted packets of digital video data identified by the first packet identifier, packets of digital video data encrypted under a first encryption method, and packets of digital video data encrypted under a second encryption method identified by the second packet identifier, wherein the packets of digital video data encrypted under the first and second encryption methods represent identical data when unencrypted;
a decrypter that decrypts packets of digital video data having the secondary packet identifier; and a decoder that decodes the decrypted packets of digital video data having the secondary packet identifier along with unencrypted packets of digital video data having the primary packet identifier to decode the partially encrypted digital television signal as an output thereof.

28. The apparatus according to claim 27, further comprising means for discarding encrypted packets of digital video data having the primary packet identifier.

29. The apparatus according to claim 27, further comprising discarding encrypted packets of digital video data having the first packet identifier.

30. The apparatus according to claim 27, wherein the encrypted packets of digital video data further comprise transport stream packets carrying an MPEG
packetized elementary stream (PES) header as a portion of a payload thereof.

31. The apparatus according to claim 27, wherein the encrypted packets of digital video data further comprise audio packets.

32. The apparatus according to claim 27, wherein the encrypted packets of digital video data comprise time sliced samples of the television signal.

33. The apparatus according to claim 27, wherein the digital television receiver device comprises a digital television set-top box.

34. A digital audio visual content player, comprising:
means for receiving digital multiple partially encrypted audio visual content, the content being identified by packets of audio visual data associated with either a primary packet identifier or a secondary packet identifier;
wherein the digital multiple partially encrypted audio visual content comprises unencrypted packets of audio visual data identified by the first packet identifier, packets of audio visual data encrypted under a first encryption method, and packets of audio visual data encrypted under a second encryption method identified by the second packet identifier, wherein the packets of audio visual data encrypted under the first and second encryption methods represent identical audio visual data when unencrypted;
a decrypter that decrypts packets of audio visual data having the secondary packet identifier; and a decoder that decodes the decrypted packets of audio visual data having the secondary packet identifier along with certain packets of audio visual data having the primary packet identifier to produce the digital multiple partially encrypted audio visual content as an output thereof.

35. The apparatus according to claim 34, further comprising means for discarding encrypted packets of audio visual data having the primary packet identifier.

36. The apparatus according to claim 34, wherein certain of the packets of audio visual data associated with the primary packet identifier are encrypted according to a first encryption method, and wherein the packets of audio visual data having a secondary packet identifier are encrypted according to a second encryption method.

37. The apparatus according to claim 34, wherein the encrypted packets of audio visual data comprise transport stream packets carrying an MPEG packetized elementary stream (PES) header as a portion of a payload thereof.

38. The apparatus according to claim 34, wherein certain of the encrypted packets of audio visual data comprise audio packets.

39. The apparatus according to claim 34, wherein certain of the encrypted packets of audio visual data comprise video packets.

40. The apparatus according to claim 34, wherein the encrypted packets of audio visual data comprise time sliced samples of the television program.

41. The apparatus according to claim 34, wherein content player comprises one of a television device, a PDA, a music player and a personal computer.

42. A circuit that processes a stream of packetized audio visual data, comprising:
an input that receives an input stream of audio visual packets of data, the input stream of packets comprising:
unencrypted packets of data having a first packet identifier, encrypted packets of data having the first packet identifier, encrypted packets of data having a second packet identifier, wherein the encrypted packets of data having the first and second packet identifiers represent identical data when unencrypted;
a packet identifier reader that reads the packet identifiers of the packets in the input stream of packets, and that discards the encrypted packets having the first packet identifier;
a packet identifier re-mapping circuit that re-maps the second packet identifier to the first packet identifier to produce re-mapped packets; and a multiplexer that multiplexes the re-mapped packets with the unencrypted packets having the first packet identifier to produce an output stream of audio visual data packets.

43. The apparatus according to claim 42, wherein the encrypted packets having the first packet identifier are encrypted according to a first encryption technique; and wherein the encrypted packets having the second packet identifier are encrypted according to a second encryption technique.

44. The apparatus according to claim 42, further comprising an MPEG decoder receiving the output stream of packets.

45. The apparatus according to claim 42, wherein the circuit is embodied in an integrated circuit.

46. The apparatus according to claim 42, wherein the circuit is embodied in one of a field programmable gate array, a programmable logic device and an application specific integrated circuit.

47. The apparatus according to claim 42, further comprising a demultiplexer that demultiplexes the output stream of packets based upon the packet identifiers.

48. A circuit that processes an input stream of audio visual data packets, comprising:
input means for receiving an input stream of audio visual data packets, the input stream of packets comprising:
unencrypted packets of data having a first packet identifier, encrypted packets of data having the first packet identifier, encrypted packets of data having a second packet identifier, wherein the encrypted packets of data having the first and second packet identifiers represent identical data when unencrypted;
packet identifier reading means for reading the packet identifiers of the packets of data in the input stream of packets, and for discarding the encrypted packets of data having the first packet identifier;
packet identifier re-mapping means for re-mapping the second packet identifier to the first packet identifier to produce re-mapped packets of data; and multiplexer means for multiplexing the re-mapped packets of data with the unencrypted packets of data having the first packet identifier to produce an output stream of audio visual data packets.

49. The apparatus according to claim 48, wherein the encrypted packets of data having the first packet identifier are encrypted according to a first encryption technique;
and wherein the encrypted packets of data having the second packet identifier are encrypted according to a second encryption technique.

50. The apparatus according to claim 48, further comprising an MPEG decoder receiving the output stream of packets of audio visual data.

51. The apparatus according to claim 48, wherein the circuit is embodied in an integrated circuit.

52. The apparatus according to claim 48, wherein the circuit is embodied in one of a field programmable gate array, a programmable logic device and an application specific integrated circuit.

53. The apparatus according to claim 48, further comprising a demultiplexer that demultiplexes the output stream of packets based upon the packet identifiers.

54. A method of processing packets of audio visual data, comprising:
receiving an input stream of packets of audio visual data, the input stream of packets of audio visual data comprising:
unencrypted packets of audio visual data having a first packet identifier, encrypted packets of audio visual data having the first packet identifier, encrypted packets of audio visual data having a second packet identifier, wherein the encrypted packets of audio visual data having the first and second packet identifiers represent identical data when unencrypted;
reading the packet identifiers of the packets of audio visual data in the input stream of packets of audio visual data;
discarding the encrypted packets of audio visual data having the first packet identifier;
re-mapping the second packet identifier to the first packet identifier to produce re-mapped packets; and multiplexing the re-mapped packets of audio visual data with the unencrypted packets of audio visual data having the first packet identifier to produce an output stream of packets of audio visual data.

55. The method according to claim 54, wherein the encrypted packets of audio visual data having the first packet identifier are encrypted according to a first encryption technique; and wherein the encrypted packets of audio visual data having the second packet identifier are encrypted according to a second encryption technique.

56. The method according to claim 54, carried out in an integrated circuit.

57. The method according to claim 54, carried out in one of a field programmable gate array, a programmable logic device and an application specific integrated circuit.

58. The method according to claim 54, carried out in a main central processor of a television set-top box.

59. The method according to claim 54, carried out in a decoder circuit of a television set-top box.

60. The method according to claim 54, further comprising demultiplexing the output stream of packets of audio visual data based upon the packet identifiers.

61. A method of processing packets of audio visual data, comprising:
receiving an input stream of packets of audio visual data, the input stream of packets of audio visual data comprising:
unencrypted packets of audio visual data having a first packet identifier, encrypted packets of audio visual data having the first packet identifier, encrypted packets of audio visual data having a second packet identifier, wherein the encrypted packets of audio visual data having the first and second packet identifiers represent identical data when unencrypted;
reading the packet identifiers of the packets of audio visual data in the input stream of packets of audio visual data;

discarding the encrypted packets of audio visual data having the first packet identifier; and re-mapping packets of audio visual data that have not been discarded so that they have the same packet identifier to produce output audio visual data.

62. The method according to claim 61, further comprising multiplexing the packets of audio visual data that have not been discarded with each other to produce an output stream of packets of audio visual data.

63. The method according to claim 61, wherein the encrypted packets of audio visual data having the first packet identifier are encrypted according to a first encryption technique; and wherein the encrypted packets of audio visual data having the second packet identifier are encrypted according to a second encryption technique.

64. The method according to claim 61, carried out in an integrated circuit.

65. The method according to claim 61, carried out in one of a field programmable gate array, a programmable logic device and an application specific integrated circuit.

66. The method according to claim 61, carried out in a main central processor of a television set-top box.

67. The method according to claim 61, carried out in a decoder circuit of a television set-top box.

68. The method according to claim 61, further comprising demultiplexing the output stream of packets of audio visual data based upon the packet identifiers.

69. A circuit that processes a stream of digital video data packets, comprising:

an input that receives an input stream of digital video packets of data, the input stream of digital video packets of data comprising:
unencrypted packets of data having a first packet identifier, encrypted packets of data having the first packet identifier, encrypted packets of data having a second packet identifier, wherein the encrypted packets of data having the first and second packet identifiers represent identical data when unencrypted;
a packet identifier reader that reads the packet identifiers of the packets of data in the input stream of digital video packets of data, and that discards the encrypted packets of data having the first packet identifier;
a packet identifier re-mapping circuit that re-maps at least one of the second packet identifier and the first packet identifier so that the packets of data that have not been discarded have the same packet identifier to produce an output of digital video data packets having the same packet identifier.

70. The circuit according to claim 69, further comprising a multiplexer that multiplexes the re-mapped packets of data with the unencrypted packets of data having the first packet identifier to produce an output stream of digital video packets of data.

71. The circuit according to claim 69, wherein the encrypted packets of data having the first packet identifier are encrypted according to a first encryption technique; and wherein the encrypted packets of data having the second packet identifier are encrypted according to a second encryption technique.

72. The circuit according to claim 69, further comprising an MPEG decoder receiving the output stream of digital video packets.

73. The circuit according to claim 69, wherein the circuit is embodied in an integrated circuit.

74. The circuit according to claim 69, wherein the circuit is embodied in one of a field programmable gate array, a programmable logic device and an application specific integrated circuit.