CA2437086C - Multiple partial encryption using retuning - Google Patents

Abstract

A partial dual encryption encoder, consistent with certain embodiments of the present invention receives video from a source of an unencrypted digital video signal. A first segment of the unencrypted digital video signal is selected for transmission over a first channel. A first encrypter encrypts a second segment of the unencrypted digital video signal under a first encryption method to produce a first encrypted segment and a second encrypter that encrypts the second segment of the unencrypted digital video signal under a second encryption to produce a second encrypted segment. A multiplexer combines the unencrypted digital video signal with the first and second encrypted segments for transmission, so that the first segment is transmitted over a first channel, the first encrypted segment is transmitted over the first channel and the second encrypted segment is transmitted over a second channel. A trigger message generator generates a trigger message indicating that the second encrypted segment of the digital video signal will be encrypted and will be transmitted on a second channel the multiplexer further combines the trigger message with the first segment, the first encrypted segment and second encrypted segment.

Description

27 A portion of the disclosure of this patent document contains material which 28 is subject to copyright protection. The copyright owner has -ho objection to the 29 facsimile reproduction of the patent, document or the patent disclosure, as it 1 appears in the Patent and Trademark Office patent file or records, but otherwise 2 reserves all copyright rights whatsoever.

T his invention relates generally to the field of encryption. More particularly, 6 in certain embodiments, this invention relates to a multiple encryption method and 7 apparatus particularly useful -nor multiple encryption of packetized video content 8 such as that provided by cable and satellite television systems.

BACKGROUND OF THE INVENTION
11 A conventional cable system arrangement is depicted in FIGURE 1. in such 12 a system, the cable operator processes audio/video (.A" ) content 14 with CA
13 technology from manufacturer A (system A) using CA encryption equipment 16 14 compliant with system A at the cable system -headersd22. The encrypted Aa content along with system information (Sl) 26 and program specific information 16 (PSI) 27 is multiplexed together and transmitted over the cable system 32 to a 17 user's Set-top box (STEM) or other receiver 36. STB 36 incorporates decrypting CA
18 equipment from system A (manufacturer A) 40 that decrypts the A/V content.
The 19 decrypted A;V content can then be'supplied to a television set 44 for viewing by the user.

21 In a cable system such as that of FIGURE 1, digital program streams are 22 broken into packets for transmission. Packets for each component of a program 23 (video, audio, auxiliary data, etc.) are tagged with, a packet identifier or Ply. These 24 packet streams for each component of all programs carried within a channel are aggregated into one composite stream. Additional packets are also included to 26 provide decryption keys and other overhead information. Otherwise unused 27 bandwidth is filled with null packets.
28 Overhead information usually includes guide data describing what programs 29 are available and how to locate the associated channeis and components.
This Docket No.: SNY-65158.01 -2- PATENT

I guide data is also known as system information or SI. SI may be delivered to the 2 ST13 in-band (part of the data encoded within a channel) or out-of-band (using a 3 special channel dedicated to the purpose). Electronically delivered Si may be 4 partially duplicated in more traditional forms - grids published in newspapers and magazines.
6 Since the encryption process defined by conditional access system A is 7 proprietary to the manufacturer of the STB 36, it is difficult and expensive for a 8 cable operator to utilize alternative sources for this hardware.
Consequently, the 9 cable or satellite operator may be locked in to a particular supplier for hardware.
The above-referenced commonly owned patent applications address this 11 issue and therein describe inventions relating to various aspects of methods 12 generally referred to herein as partial encryption or selective encryption.
More 13 particularly, systems are described therein wherein selected portions of a particular 14 selection of digital content are encrypted using two (or more) encryption techniques while other portions of the content are left uÃnencrypted'. By properly selecting the 16 portions to be encrypted, the content can effectively be encrypted for use under 17 multiple decryption systems without the necessity of encryption of the entire 18 selection of content. In some embodiments, only a few percent of data overhead 19 is needed to effectively encrypt the content using multiple encryption systems. This results in a cable or satellite system being able to utilize Set-top boxes (STB) or 21 other implementations of conditional access (CA) receivers from multiple 22 manufacturers in a single system - thus freeing the cable or satellite company to 23 competitively shop for providers of Set-top boxes.
24 In each of these disclosures, the content is carried in the clear using a primary Packet Identifier (P1D). A secondar}.! PIO is also assigned to the program 26 content. Selected portions of the content are then encrypted under two (or more) 27 encryption systems and the encrypted content transmitted using both the primary 28 and secondary PIDs. The so-called legacy STBs operate in a normal manner 29 decrypting encrypted packets arriving under the primary PR[). The newer STBs operate by associating both the primary and secondary 'Pis with a single program.

Docket No.: SNY-55158.01 -3- PATENT

1 Packets with a primary PID are decoded normally and packets with a secondary 2 PlO are first decrypted then decoded. The packets associated with both Pips are 3 then assembled together to make up a single program stream.

BRIEF DESCRIPTION OF THE D W I G S
6 The features of the invention believed to be novel are set forth with 7 particularity in the appended claims. The invention itself however, both as to 8 organization and method of operation, together with objects and advantages 9 thereof, may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, 11 taken in conjunction with the accompanying drawings in which:
12 FIGURE 1 is a block diagram of a conventional cable television sys-iem.
13 FIGURE 2 is block diagram of a dual encrypted cable television system 14 consistent with certain embodiments of the present invention.
FIGURE 3 is a flow chart of a head end encryption process consistent with 16 certain embodiments of the present invention.
17 FIGURE 4 illustrates a dual encrypted data stream consistent with 18 certain embodiments of the present invention.
19 FIGURE 5 is a high level block diagram illustrating operation of STS 136 consistent with certain embodiments of the present invention.
21 FIGURE 6 is a high level block diagram illustrating operation of STB 36 22 consistent with certain embodiments of the present invention.
.23 FIGURE 7 is a flow chart of a process for decoding and decrypting 24 content in a manner consistent with certain embodiments of the present invention.
FIGURE 8 is a flow chart of a process for decoding and decryption of A/V
26 content in a legacy STB consistent with certain embodiments of the present 27 invention.

Docket No.: SNY-S5158.0e -4- PATENT

1 DETAILED DESK IPTIC _.F THE INVENTION
2 While this invention is susceptible of embodiment in many different forms, 3 there is shown in the drawings and will herein be described in detail specific 4 embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and not intended to limit 6 the invention to the specific embodiments shown and described. In the description 7 below, like reference numerals are used to describe the same, similar or 8 corresponding parts in the several views of the drawings.
9 The terms "scramble" and "encrypt" and variations thereof are used synonymously herein. Also, the term "television program" and similar terms can 11 be interpreted in the normal conversational sense, as well as a meaning wherein 12 the term means any segment of e content that can be displayed on a television 13 set or similar monitor device. The term "video" is often used herein to embrace not 14 only true visual information, but also in the conversational sense (e.g., "video tape recorder") to embrace not only video signals but associated audio and data.
The 16 term "legacy" as used herein refers to existing technology used for existing cable 17 and satellite systems. The exemplary embodiments disclosed herein are decoded 18 by a television Set-Top Box ( T ), but it is contemplated That such technology will 19 soon be incorporated within television receivers of all types whether housed in a separate enclosure alone or in conjunction with recording and/or playback 21 equipment or within a television set itself. The present, document generally uses 22 the example of a "dual partial encryption" embodiment, but those skilled in the art 23 will recognize that the present invention can be utilized to realize multiple partial 24 encryption without departing from the invention. Partial encryption and selective encryption are used synonymously herein.
26 Turning now to FIGURE 2, a cable television system suitable for use in 27 practicing a dual encryption embodiment of the present invention is illustrated.
28 Those skilled in the art will appreciate that the present invention could also be 29 implemented using more than two encryptions systems without departing from the Docket No.: SNY-55158.01 - - PATENT

1 present invention. The illustrated head end 100 implements the dual partial 2 encryption scenario of the present invention by implementing a retuning to a 3 different channel to accommodate decryption of an encrypted portion of a partially 4 encrypted selection of content.
6 Head end 100 receives scrambled content from one or more suppliers, for 6' example, using a satellite dish antenna that feeds a satellite receiver (not shown).
7 The satellite receiver operates to demodulate and descraimble the incoming content 8 and supplies the content as a stream of clear (unencrypted) data. It is assumed, 9 for purposes of the present embodiment of the invention, that the data from the satellite receiver is supplied as NIPEG (Moving Pictures Expert Group) compliant 11. packetized data. This unencrypted (clear) digital television signal 14 is selectively 12 applied to a first conditional access encryption system A 18 as well as to a second 13 conditional access encryption system B 104. Encryption system 18 can be the 14 legacy encryption system used in the conventional single encryption system of FIGURE 1. Encryption system 104 can be a new encryption system that is to be 16 added to the cable (or equivalently satellite) television system. The clear AN signal 17 14 is also applied to a multip exec 110 for selective transmission over the cable 18 system as will be described shortly. Encrypted portions of the clear signal 14 as 19 produced by encryption systems 18 and 104 are also selectively applied to multiplexer 110 in accordance with the present invention as will be described.
In 21 addition to these signals, system information 26 and program specific information 22. 27 is applied to multiplexer 110.
23 In accordance with the operation of certain embodiments consistent with the 24 present invention, selected segments of the content are encrypted under both encryption systems 18 and 104. In accordance with any suitable algorithm, 26 segments of the clear content are selected for encryption. Any given selected 27 segment that is to be dual encrypted is duplicated and encrypted by both systems 28 18 and 104. These selected segments are then inserted at Multiplexer 110 into the 29 outbound data stream in place of the corresponding original, unencrypted content.
These selected encrypted segments are inserted as content in the same channel Docket No.: >NY-S5158.01 -6- PATENT

1 as the unencrypted content (channel A) as well as in a second channel (channel 2 B).
3 When a segment is selected for encryption, a trigger message is generated 4 (e.g., as a user data message in the Program Specific i form tion (PSI' O, by a trigger message generator 116 and transmitted in advance of the encrypted 6 content. This trigger message is used by a Set-top box 136 as a signal that a 7 portion of the upcoming content will be encrypted and will appear on a second 8 channel. Thus, when the ST 136 receives this message it prepares to retune to 9 the second channel (channel B) at a time or packet number prescribed by the trigger message. Thus, at the prescribed time, STB 13(retunes to channel B and 11 uses a decryptor for conditional access system 140 to decrypt the inc )ming 12 encrypted segment. In this manner, STB 1 36 need not comply with the conc:_-%onal 13 access system A 40 of ST3 36 and can thus be supplied by a different 14 manufacturer (avoiding need for a license to conditional access system A).
The unencrypted and decrypted AN signal is then passed to television set 144, 16 At the legacy STS 36 using conditional access system A 40, a mixture of 1 ? encrypted and unencrypted packets are received. Conditional access system A
1 decrypter 40 on such systems automatically decrypt that which is encrypted and 1 pass that which is not. Thus, STB 36 operates normally with the dual encryption operating transparently.
2 i The operation of the cable system head end I D0 in generating the dual 22 partially encrypted data stream can be described by the process 200 of 23 FIGURE 3 starting at 204. tnencrypted content is seat out on channel A of the 24 head end 100 to the cable system 32 at 208. If the and of the content is not reached at 212, a trigger message is sent to the cable network 32 at 216. This 26 trigger message defines a starting time or packet number (and possibly a stopping 27 time or packet number) for encrypted content to begin and further specifies the 28 channel that the next segment of encrypted content will use. The selected segment 29 of content is then dual encrypted (in this exarnole, but multiply encrypted in general) and transmitted using encryption method A and channel A at 220 and using Docket No.: Si`d`(-55155.01 -7- PATENT

1 encryption method B and channel B at 224. If the end of the content is not reached 2 at 230, another trigger message (according to the current embodiment in which a 3 stop time or packet number is not defined for the encrypted segment at 216) is 4 generated at 236 indicating that clear content is to follow at a prescribed start time or packet number over channel A. When the end of the content is reached at 212 6 or 230, the process stops at 240.
7 In accordance with one embodiment consistent with the present invention, 8 the ; content can be segmented such that several seconds, e.g., ten seconds, 9 of content is encrypted periodically to encrypt, for example, between 10 and percent of the AN content. This, however, should not be considered limiting since 11 any desired segmentation can be used to produce segments of encrypted content.
12 In preferred embodiments, encrypted segments last between several seconds and 13 several tens of seconds, but this should not be considered limiting. Due to the 14 nature of MPEG encoding, encryption of certain data such as I Frames and P
Frames, or any packet containing intra-coded data, will result in a further 16 scrambling effect on the picture beyond the encrypted segment for any hacker 17 attempting to view the A/V content without authorization. Thus, as the STB's 18 MPEG decoder attempts to recover from loss of data following a segment of 19 encryption, there may be several seconds or longer of content that the decoder cannot reconstruct until the next frame or packet of intra-coded data is received.
21 This results in a greater encryption effect than simply loss of the encrypted 22 segments of content.
23 The head end 100, thus, produces a stream of NV data that may resemble 24 data stream 250 shown in FIGURE 4. The data stream 250 may start with either a clear or encrypted data stream without limitation. A segment of clear data 26 254 in the data stream is followed by a trigger message 256 specifying the channel 27 and timing of an encrypted segment to follow. Encrypted segments 262 and 28 follow in any order (but generally intermingled) with encrypted content on 29 channels A and B using encryption methods A and 8 as previously described.
A
trigger message 270 indicates that unencrypted content will follow at a specified Docket No.: SNY-S5158.0i - 3- PATENT

I timing on channel A. This is followed by a segment 2714 of clear content on 2 channel A until such time as a next segment is to be encrypted. The next segment 3 of encrypted content is then s`gnaled by trigger message 280 and so on, 4 Upon receipt of a data stream such as stream 250, STB 136 operates as illustrated in the block diagram of FIGURE S. The multiplexed AN data stream 6 from multiplexer 110 which is generally quadrature amplitude modulated (QAM) is 7 received at a tuner/demodulator 302 that tunes to the appropriate carrier frequency 8 and demodulates the QAM signal into a strew of packets. This stream of packets 9 is delivered to a demultiplexer 306 that selects appropriate: packets for further processing (Note that the strearn of packets may include multiple channels and 11 multiple programs as well as other data packets.) . When, the demuitiplexer detects 12 a trigger message (which may be a part of the Program Specific Information 13 encoded as user private data, this packet is delivered to a control processor that 14 incorporates a trigger message decoder 310 in one ernooodirnent. In other embodiments, the, trigger message decoder may be implemented in any other 16 suitable manner.
17 The trigger message decoder 31 0 decodes the trigger message to determine 18 when the change between encrypted and unencrypted content will occur and what channel will bear each. The) trigger message decoder 310 then instructs the demultiplexer 306 to tune to a specified Packet identifier (PI1)), and if necessary, 21 to tune the tuner/demodulator 302 to a different frequency channel at the 22 appropriate time to receive and decode the next segment of content.
23 The content is delivered to decrypter 140 Which passes unencrypted packets 24 unaltered and decrypts the encrypted packets when they are encountered. The content is then passed to an A/V decoder 316 that decodes the content into 26 decoded A/V data (in either analog or digital form as, desired) to the television 27 receiver 144.
28 The operation of legacy STB 36 is depicted in the block diagram of FIGS

29 6. Tuner/demodulator 330 operates on the multiplexed data stream in a manner Docket No.: SNY-S5158, O1 -9- PATENT

I similar to that of 302 to tune and demodulate the incoming signal. This signal is 2 then dermultiplexed at demultiplexer 334 to select the appropriate channel (channel 3 A). This demultiplexed output is then passed to decrypter 40 which decrypts 4 encrypted packets and passes unencrypted packets undisturbed to the decoder 340. AN decoder 34=:0 operates in a manner similar to that of A/V
decoder 6 316 to produce decoded AN output.
7 Turning now to FIGU 7, a process 350 rsor decoding a data stream at. STS
6 136 consistent with certain embodiments of the invention is depicted in flow chart 9 form starting at 354. At 358 the STB tunes to channel A (which may involve a tuning process in the STB's tuner as well as selection of a particular set of audio 1111, and video PIDs) associated with a particular program. .jnencrypted content is then 12 received at 362 using channel A in the illustrated embodiment (but encrypted 13 content could equally well be received first). If the end the content is not reached 14 at 366,* a trigger message can be received at 370 signaling a switch to a new channel B to receive a segment of encrypted content at a prescribed time or packet 16 number. At an appropriate time, the ST 1 36 'then tunes to channel B at 374 to 17 begin receiving and decrypting the content on channel 3 at 378. if the and of the 18 content is not received at 332, another trigger message may be received to signal 19 a switch to unencrypted content on channel A (or another channel such as channel C) at 386. Control then returns to 358 where the STS 136 tunes to the new channel 21 to receive unencrypted content at the prescribed time. When the and of the content 22 is received at either 366 or 382, control passes to 380 where the process stops.
23 Operation of a legacy STB such as 36 is depicted by process 400 of FIGURE
24 8 starting at 402. At 406, the STS 36 tunes to channel A to receive a selected program and begins receiving content over channel A at 410. Any trigger 26 messages received are ignored at S T 8 36. If the content is encrypted at 414, 27 control passes to 418 where. the content is decrypted. If the content is not.
28 encrypted at 414, the data are passed without alteration at 414 by the decrypter.
29 When the end of the content is reached at 422, the process stops at 428.

Docket No.: SNY-S5158.O1 -10- PATENT

1 While the process 400 depicted in connection with operation of legacy S T B
2 36 is the normally contemplated process, it is also possible to direct trigger 3 messages to the legacy S T 8 36 to cause a channel change for encrypted or 4 unencrypted content, rendering the content more difficult for a hacker to obtain without authorization. Similarly, channel changes for the encrypted and 6 unencrypted content can be made to make reception by a hacker more difficult is 7 _ contemplated in connection withthe operation of STB 135. Also, in a variation of 8 the present invention a return to the primary (i.e., unencrypted) channel could be accomplished by use of a timer such that the trigger signal that signals a channel I change from the first segment to the second segment can incorporate a duration 1 I field that determines when a change back to the primary channel is to occur. Other 12 variations will occur to those skilled in the art upon consideration of the present 13 disclosure.
14 Those skilled in the art will recognize that the present invention has been . described in terms of exemplary embodiments based upon use of a programmed is processor. However, the invention should not be so limited, since the present 17 invention could be implemented using hardware component equivalents such as 18 special purpose hardware and/or dedicated processors which are equivalents to 19 the invention as described and claimed. Similarly, general purpose computers, microprocessor based comp~.uytyers, micro-controllers, optical computtgers,p~anallog 21 co 8n~:. ute , dedicated pr oceesesors a r?d or dedi atedd, haa.I ¾1~j V~OFir ei`d logic G 1 ECa+@1 be used 22 to construct alternative equivalent embodiments of the present invention.
23 Those skilled in the artwill appreciate that the program steps and associated 24 data used to implement the embodiments described above can be implemented using disc storage as well as other forms of storage such as for example Read 26 Only Memory (RO 1) devices, Random Access Memory (RAM) devices; optical 27 storage elements, magnetic storage elements, magneto-optical storage elements, 28 flash memory, core memory and/or other equivalent storage technologies without 29 departing from the present Invention. Such alternative storage devices should be 3 considered equivalents.

Docket No.: SNY-S5158.01 -1 1-- PATENT

I The present invention, as described in embodiments herein, is implemented 2 using a programmed processor executing programming instructions that are 3 broadly described above form that can be stored on any suitable electronic storage 4 medium or transmitted over any suitable electronic communication medium or otherwise be present in any computer readabie or propagation medium. However, 6 those skilled in the art will appreciate that the processes described above can be implemented in any number of variations and in many suitable programming 8 languages without departing from the present invention. For example, the order of 9 certain operations carried out can often be varied, additional operations can be added or operations can be deleted withou departing from the invention. Error 11 trapping can be added and/or enhanced and variations can be made in user 12 interface and information presentation without departing from the present invention.
13 Such variations are contemplated and considered equivalent.
14 Software code and/or data embodying certain aspects of the present invention may be present in any computer readable medium, transmission 16 medium, storage medium or propagation medium including, but not limited to, 17 electronic storage . devices such as those described above, as well as carrier 18 waves, electronic signals, data structures (e.g., trees, linked lists, tables, packets, 19 frames, etc.) optical signals, propagated signals, broadcast signals, trans ission media (e.g., circuit connection, cable, twisted pair, fiber optic cables, waveguides, 21 antennas, etc.) and other media that stores, carries or passes the code and/or data.
22 Such media may either store the software code and/or data or serve to transport 23 the code and/or data from one location to another. in the present exemplary 24 embodiments, IMPEL compliant packets, slices, tables and other data structures are used, but this should not be considered limiting since other data structures can 26 similarly be used without departing from the present invention.
27 While the invention has been described in conjunction with specific 28 embodiments, it is evident that many alternatives, modifications, permutations and 29 variations will become apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace al such Docket No.: SNY-55158.01 -12- PATENT

s alternatives, modifications and variations as faH within the scope of the appended 2 chairs.

Docket No.: SNP"-S5I58.01 -13- PATENT

Claims (71)

1. A method of partially dual encrypting an unencrypted digital video signal, comprising:
transmitting a first segment of the digital video signal as an unencrypted digital video signal using a first channel;
transmitting a trigger message indicating that a second segment of the digital video signal will be encrypted and will appear on a second channel;
duplicating the second segment to produce first and second copies of the second segment;
encrypting the first copy of the second segment under a first encryption method to produce a first encrypted segment;
encrypting the second copy of the second segment under a second encryption method to produce a second encrypted segment;
transmitting the first encrypted segment over the first channel; and transmitting the second encrypted segment over the second channel.

2. The method according to claim 1, wherein the first channel is associated with a first packet identifier (PID) and the second channel is associated with a second packet identifier.

3. The method according to claim 1, wherein the first channel is associated with a first frequency and the second channel is associated with a second frequency.

4. The method according to claim 1, wherein the trigger message comprises a part of a program specific information (PSI) message.

5. The method according to claim 4, wherein the trigger message is encoded as user specific information within the PSI message.

6. The method according to claim 1, wherein the trigger message contains a starting time for the second segment of digital video signal.

7. The method according to claim 1, wherein the trigger message contains a starting packet number for the second segment of digital video signal.

8. The method according to claim 1, further comprising transmitting segments of unencrypted digital video alternating with duplicated segments of encrypted digital video, with the duplicated encrypted digital video being encrypted under the first and second encryption methods.

9. The method according to claim 8, wherein each of the duplicated encrypted digital video comprises between approximately 10% and 35% of the total digital video signal.

10. The method according to claim 1, further comprising transmitting a second trigger message indicating that a third segment of the digital video signal will be unencrypted and will appear on a specified channel.

11. The method according to claim 10, wherein the specified channel comprises the first channel.

12. The method according to claim 10, wherein the specified channel comprises a third channel.

13. A computer readable medium storing instructions which, when executed or a programmed processor, carry out the method of encrypting a digital video signal according to claim 1.

14. A partial dual encryption encoder, comprising:
a source of an unencrypted digital video signal;

means for selecting a first segment of the unencrypted digital video signal for transmission over a first channel;
a first encrypter that encrypts a second segment of the unencrypted digital video signal under a first encryption method to produce a first encrypted segment;
a second encrypter that encrypts the second segment of the encrypted digital video signal under a second encryption to produce a second encrypted segment;
a multiplexer that combines the unencrypted digital video signal with the first and second encrypted segments for transmission, so that the first segment is transmitted over a first channel, the first encrypted segment is transmitted over the first channel and the second encrypted segment is transmitted over a second channel;
a trigger message generator that generates a trigger message indicating that the second encrypted segment of the digital video signal will be encrypted and will be transmitted on a second channel; and wherein, the multiplexer further combines the trigger message with the first segment, the first encrypted segment and second encrypted segment.

15. The partial dual encryption encoder according to claim 14, wherein the first channel is associated with a first packet identifier (PID) and the second channel is associated with a second packet identifier.

16. The partial dual encryption encoder according to claim 14, wherein the first channel is associated with a first frequency and the second channel is associated with a second frequency.

17. The partial dual encryption encoder according to claim 14, wherein the trigger message comprises a part of a program specific information (PSI) message.

18. The partial dual encryption encoder according to claim 17, wherein the trigger message is encoded as user specific information within the PSI message.

19. The partial dual encryption encoder according to claim 14, wherein the trigger message contains a starting time for the second segment of digital video signal.

20. The partial dual encryption encoder according to claim 14, wherein the trigger message contains a starting packet number for the second segment of digital video signal.

21. The partial dual encryption encoder according to claim 14, further comprising transmitting segments of unencrypted digital video alternating with duplicated segments of encrypted digital video, with the duplicated encrypted digital video being encrypted under the first and second encryption methods.

22. The partial dual encryption encoder according to claim 21, wherein each of the duplicated encrypted video comprises between approximately 10% and 35% of the total digital video signal.

23. The partial dual encryption encoder according to claim 14, further comprising transmitting a second trigger message indicating that a third segment of the digital video signal will be unencrypted and will appear on a specified channel.

24. The partial dual encryption encoder according to claim 23, wherein the specified channel comprises the first channel.

25. The partial dual encryption encoder according to claim 23, wherein the specified channel comprises a third channel.

26. A method of partially encrypting an unencrypted digital video signal, comprising:
transmitting a first segment of the digital video signal as an unencrypted digital video signal over a first channel;

transmitting a trigger message indicating that a second segment of the digital video signal will be encrypted;
encrypting the second segment of the digital video signal to produce an second encrypted segment; and transmitting the second encrypted segment over a second channel.

27. The method according to claims 26, wherein the first channel is associated with a first packet identifier (PID) and the second channel is associated with a second packet identifier.

28. The method according to claim 26, wherein the first channel is associated with a first frequency and the second channel is associated with a second frequency.

29. The method according to claim 26, wherein the trigger message comprises a part of a program specific information (PSI) message.

30. The method according to claim 29, wherein the trigger message is encoded as user specific information within the PSI message.

31. The method according to claim 26, wherein the trigger message contains a starting time for the second segment of digital video signal.

32. The method according to claim 26, wherein the trigger message contains a starting packet number for the second segment of digital video signal.

33. The method according to claim 26, further comprising transmitting segments of unencrypted digital video alternating with segment of encrypted digital video.

34. The method according to claim 33, wherein the encrypted digital video comprises between approximately 10% and 35% of the total digital video signal.

35. The method according to claim 26, further comprising transmitting a second trigger message indicating that a third segment of the digital video signal will be unencrypted and will appear on a specified channel.

36. The method according to claim 26, wherein the specified channel comprises the first channel.

37. The method according to claim 26, wherein the specified channel comprises a third channel.

38. A computer readable medium storing instructions which, when executed on a programmed processor, carry out the method of encrypting a digital video signal according to claim 26.

39. A partial encryption encoder, comprising:
a source of an unencrypted digital video signal;
means for selecting a first segment of the unencrypted digital video signal for transmission over a first channel;
an encrypter that encrypts a second segment of the unencrypted digital video signal under a first encryption method to produce a second encrypted segment;
a multiplexer that combines the unencrypted digital video signal with the second encrypted segment for transmission, so that the first segment is transmitted over a first channel and the second encrypted segment is transmitted over a second channel;
a trigger message generator that generates a trigger message indicating that the second encrypted segment of the digital video signal will be encrypted and will be transmitted on a second channel; and wherein, the multiplexer further combines the trigger message with the first segment and second encrypted segment.

40. The partial encryption encoder according to claim 39, wherein the first channel is associated with a first packet identifier (PID) and the second channel is associated with a second packet identifier.

41. The partial encryption encoder according to claim 39, wherein the first channel is associated with a first frequency and the second channel is associated with a second frequency.

42. The partial encryption encoder according to claim 39, wherein the trigger message comprises a part of a program specific information (PSI) message.

43. The partial encryption encoder according to claim 42, wherein the trigger message is encoded as user specific information within the PSI message.

44. The partial encryption encoder according to claim 39, wherein the trigger message contains a starting time for the second segment of digital video signal.

45. The partial encryption encoder according to claim 39, wherein the trigger message contains a starting packet number for the second segment of digital video signal.

46. The partial encryption encoder according to claim 39, further comprising transmitting segments of unencrypted digital video alternating with segments of encrypted digital video.

47. The partial encryption encoder according to claim 46, wherein the encrypted digital video comprises between approximately 10% and 35% of the total digital video signal.

48. The partial encryption encoder according to claim 42, further comprising transmitting a second trigger message indicating that a third segment of the digital video signal will be unencrypted and will appear on a specified channel.

49. The partial encryption encoder according to claim 48, wherein the specified channel comprises the first channel.

50. The partial encryption encoder according to claim 48, wherein the specified channel comprises a third channel.

51. A method of decrypting partially encrypted digital video signal comprising:
receiving a first unencrypted segment of the digital video signal as an unencrypted digital video signal over a first channel;
receiving a trigger message indicating that a second segment of the digital video signal will be encrypted and transmitted over a second channel;
tuning to the second channel;
receiving the second encrypted segment over the second channel; and decrypting the second encrypted segment.

52. The method according to claim 51, wherein the first channel is associated with a first packet identifier (PID) and the second channel is associated with a second packet identifier.

53. The method according to claim 51, wherein the first channel is associated with a first frequency and the second channel is associated with a second frequency.

54. The method according to claim 51, wherein the trigger message comprises a part of a program specific information (PSI) message.

55. The method according to claim 54, wherein the trigger message is encoded as user specific information within the PSI message.

56. The method according to claim 51, wherein the trigger message contains a starting time for the second segment of digital video signal.

57. The method according to claim 51, wherein the trigger message contains a starting packet number for the second segment of digital video signal.

58. The method according to claim 51, further comprising receiving segments of unencrypted digital video alternating with segments of encrypted digital video.

59. The method according to claim 58, wherein the encrypted digital video comprises between approximately 10% and 35% of the total digital video signal.

60. A computer readable medium carrying instructions which, when executed on a programmed processor, carry out the method of decrypting a digital video signal according to claim 51.

61. A partial encryption decoder for decoding and decrypting a partially encrypted digital video signal, comprising:
a receiver that receives a first unencrypted segment of the digital video signal as an unencrypted digital video signal over a first channel and receives a second encrypted segment over a second channel;
a trigger message decoder that receives and decodes a trigger message indicating that a second segment of the digital video signal will be encrypted and transmitted over a second channel, the decoder causing the receiver to tune to the second channel for receipt of the second encrypted segment; and a decrypter that receives and decrypts the second encrypted segment.

62. The partial encryption decoder according to claim 61, wherein the first channel is associated with a first packet identifier (PID) and the second channel is associated with a second packet identifier.

63. The partial encryption decoder according to claim 61, wherein the first channel is associated with a first frequency and the second channel is associated with a second frequency.

64. The partial encryption decoder according to claim 61, wherein the trigger message comprises a part of a program specific information (PSI) message.

65. The partial encryption decoder according to claim 64, wherein the trigger message is encoded as user specific information within the PSI message.

66. The partial encryption decoder according to claim 61, wherein the trigger message contains a starting time for the second segment of digital video signal.

67. The partial encryption decoder according to claim 61, wherein the trigger message contains a starting packet number for the second segment of digital video signal.

68. The partial encryption decoder according to claim 61, further comprising receiving segments of unencrypted digital video alternating with segments of encrypted digital video.

69. The partial encryption decoder according to claim 68, wherein the encrypted digital video comprises between approximately 10% and 35% of the total digital video signal.

70. A television set-top box, comprising:
a receiver receiving a digital television signal comprising:
a plurality of unencrypted packets received over a first channel;
a plurality of encrypted packets received over a second channel; and a trigger message indicating that the plurality of encrypted packets are transmitted over the second channel a decrypter that decrypts the encrypted packets;
a trigger message decoder that receives and decodes the trigger message and causes the receiver to tune to the second channel for receipt of the plurality of encrypted packets; and a decoder that decodes the unencrypted packets and the decrypted packets to produce a signal suitable for play on a television set.

71. A computer readable medium that carries instructions that when executes on a programmed processor to facilitate operation of a video receiver device to decrypt a selectively encoded digital video signal wherein the instructions comprise:
a code segment that controls a receiver that receives a first unencrypted segment of the digital video signal as an unencrypted digital video signal over a first channel and receives a second encrypted segment over a second channel;
a code segment that controls a trigger message decoder that receives and decodes a trigger message indicating that a second segment of the digital video signal will be encrypted and transmitted over a second channel, the decoder causing the receiver to tune to the second channel for receipt of the second encrypted segment; and a code segment that controls a decrypter that receives and decrypts the second encrypted segment.