# Patent

## Title
System and method for partially encrypted multimedia stream

## Abstract

A multimedia stream head end includes a legacy conditional access (CA) device that fully encrypts the stream using legacy keys. A copy of the stream is sent to a secondary CA device that encrypts only critical packets in the stream using secondary keys to render a partially encrypted stream. The critical packets in the fully encrypted stream from the legacy CA device are obtained and inserted next to the corresponding critical packets in the partially encrypted stream. Thus, only critical packets are encrypted, with encrypted versions being generated by both the legacy CA and secondary CA without the legacy CA knowing which of the packets that it encrypts are “critical”.

## Background
RELATED APPLICATIONS
This application is a continuation-in-part of patent application entitled “Critical Packet Partial Encryption” to Unger et al., Ser. No. 10/038,217; patent application entitled “Time Division Partial Encryption” to Candelore et al., Ser. No. 10/038,032; application entitled “Elementary Stream Partial Encryption” to Candelore, Ser. No. 10/037,914; application entitled “Partial Encryption and PID Mapping” to Unger et al., Ser. No. 10/037,499; and application entitled “Decoding and Decrypting of Partially Encrypted Information” to Unger et al., Ser. No. 10/037,498 all of which were filed on Jan. 2, 2002 and are hereby incorporated by reference herein; this application is also related to and claims priority benefit of U.S. Provisional patent application Ser. No. 60/429,011, filed Nov. 22, 2002, entitled “Critical Packet Selection in an Encrypted Transport Stream Through Referenced Offset”, to Pedlow; this application is also related to and claims priority benefit of U.S. Provisional patent application Ser. No. 60/409,675, filed Sep. 9, 2002, entitled “Generic PID Remapping for Content Replacement”, to Candelore; this application is also related to and claims priority benefit of U.S. Provisional patent application Ser. No. 60/372,870 filed Apr. 16, 2002, entitled “Generic PID Remapping for Content Replacement Applications”, to Candelore. This application is also related to U.S. patent applications Ser. No. 10/273,905, filed Oct. 18, 2002 to Candelore et al., entitled “Video Slice and Active Region Based Dual Partial Encryption”; Ser. No. 10/273,903, filed Oct. 18, 2002 to Candelore et al., entitled “Star Pattern Partial Encryption”; Ser. No. 10/274,084, filed Oct. 18, 2002 to Candelore et al., entitled “Slice Mask and Moat Pattern Partial Encryption”; and Ser. No. 10/274,019, filed Oct. 18, 2002 to Candelore et al., entitled “Video Scene Change Detection”. Each of the above applications are hereby incorporated by reference herein.


FIELD OF THE INVENTION
The present invention relates generally to encrypted multimedia streams.
BACKGROUND OF THE INVENTION
Multimedia streams that are sought to be protected (e.g., pay-per-view sporting events, movies, and the like) can be encrypted at the transmitter (colloquially referred to as the “head end”) with keys in a way that receiving television set-top boxes (STBs) that have complementary keys can decrypt the content for viewing. Accordingly, cable service providers must use head end conditional access (CA) devices that encrypt multimedia streams in accordance with the capabilities of the set-top boxes of the viewers. Many of these capabilities, including decryption capabilities, are proprietary to the makers of the set-top boxes.
It happens that only a very few “incumbent” companies sell most of the set-top boxes. Accordingly, competitors seeking to enter the cable television set-top box market must license the proprietary keys from the incumbents, often at high prices. This reduces competition.
A straightforward alternative way to permit competitive STB makers to enter the market without paying licensing fees to the incumbents would be to encourage the cable service providers, at their head ends, to completely encrypt each stream with as many CA devices (using respective sets of keys) as there are set-top box providers. This, however, would plainly undesirably multiply the amount of bandwidth necessary to carry a program. Accordingly, Sony has developed an encryption scheme whereby only “critical” portions, such as I-frames or headers, of a stream are encrypted, with the remainder of the stream being sent in the clear but being useless without being able to decrypt the “critical” portions. In this way, only the critical portions need be duplicated in encrypted form, not the entire stream. With more specificity, only the critical portions are encrypted both by the existing (“legacy”) CA devices using the incumbents' keys and by a secondary conditional access process using a competitor's keys. Published U.S. patent application Ser. No. 10/038,217, filed Jan. 2, 2002 and incorporated herein by reference, discloses such a scheme.
As understood herein, the legacy CA components that are made by the incumbent providers can be programmed by the incumbent providers to detect that the above-mentioned process is ongoing. Consequently, the legacy components might be programmed by the incumbents to defeat the process and, thus, to maintain a de facto monopoly. Having recognized this possibility, the solution below is provided.
SUMMARY OF THE INVENTION
A method for multimedia transmission includes generating a copy of a multimedia stream to render first and second clear streams having identical predetermined portions. The method also includes sending the first clear stream to a first conditional access (CA) component, which can be a legacy component provided by an incumbent, to encrypt the entire first clear stream to render a completely encrypted stream without the legacy component knowing about the second clear stream. Encrypted versions of the predetermined portions are obtained from the completely encrypted stream. The second clear stream is used to encrypt the predetermined portions using a second CA component to render a partially encrypted stream. The method then contemplates inserting the encrypted predetermined portions obtained from the completely encrypted stream into the partially encrypted stream for transmission thereof.
In a preferred embodiment, the partially encrypted stream with two encrypted versions of each critical packet is sent to plural set-top boxes over cable. Or, the partially encrypted stream can be wirelessly broadcast to plural receivers.
Preferably, the method includes determining locations of the predetermined portions using corresponding offsets from at least one packet identifier (PID). The offsets can be in integral numbers of packets from at least one PID. In a preferred embodiment, the offsets are used for identifying the locations of the encrypted predetermined portions in the completely encrypted stream for obtaining them and inserting them into the partially encrypted stream, e.g., adjacent to the predetermined portions that were generated by the second CA component.
In another aspect, a system for dual partial encryption of a digital data stream includes means for copying the stream to render first and second streams, and first conditional access (CA) means for encrypting only critical portions of the first stream to render a partially encrypted stream. Legacy CA means encrypt the entire second stream to render a substantially fully encrypted stream. Means are provided for combining only critical portions from the fully encrypted stream with the partially encrypted stream.
In still another aspect, a system for use in a digital stream transmitter head end having a legacy conditional access (CA) device includes a system CA device that encrypts at least predetermined portions, and preferably only the predetermined portions, of a first version of a stream. A reconstitution component combines, into a stream such as the first version of the stream, the predetermined portions from the system CA device with the predetermined portions obtained from a full encryption of a second version of the stream generated by the legacy CA device.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an architectural block diagram; and
FIG. 2 is a flow chart of the present logic.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIG. 1, a system is shown, generally designated 10, that includes a source 12 of digital data streams, such as multimedia streams. The streams are sent to a critical packet locator and offset detector 14 which determines which packets in the stream are “critical”. The critical packet locator and offset detector 14 also determines the offset (in integer numbers of packets from one or more packet identifiers (PID)) of each critical packet from a reference packet, e.g., the start of frame packet. The above-referenced patent application discusses critical packet selection. For clarity and completeness, critical packets may be information frames (“I-frames”) in MPEG streams, or packetized elementary stream (PES) headers, or “action zones” of video, or other key packets that contain information which is essential to the successful recovery of picture and/or audio data. Preferably, packets containing references to program clock references (PCR) in the picture data (including presentation timestamp (PTS) and decoding timestamp (DTS) information) are never designated as “critical” packets.
As shown in FIG. 1, the offsets of the critical packets are stored in a critical packet offset table 16 or other data structure. Also, the stream is sent from the locator 14 to a stream copier 18 that makes a copy of the data stream. It is to be understood that the stream could be copied before critical packets and their offsets are identified.
As can be appreciated in reference to FIG. 1, one version of the stream is sent to a legacy conditional access (CA) device 20. The legacy CA device 20 can be considered to be a device provided by an incumbent that can process the stream by, e.g., encoding the stream with encryption keys, in accordance with the incumbent's proprietary CA scheme. The legacy CA device 20 completely encrypts the stream in accordance with conventional incumbent CA principles to render a fully encrypted stream.
Additionally, a version of the stream is sent from the stream copier to a buffer, preferably a circular first in first out (FIFO) buffer 22. The length of the buffer 22 should be of sufficient length (potentially a fixed length) to account for the delay caused by the processing time of the legacy CA device 20 in accordance with principles discussed below. The length of the FIFO buffer 22 may be established in increments of frame/picture or sequence/GOP for management purposes.
FIG. 1 shows that a secondary CA and reconstitution device 24 receives the clear stream from the FIFO buffer and the fully encrypted stream from the legacy CA device 20. The secondary CA and reconstitution device 24 includes a CA component, which encrypts only the critical packets in the clear stream received from the buffer 22, leaving the remaining portions of the stream unencrypted to render a partially encrypted stream. The secondary CA device 24 uses encryption keys that are different from those used by the legacy CA device 20. If desired, the pass through the secondary CA device 24 may slave to a new PCR value output by the legacy CA device 20, with the resulting corresponding value generated by the secondary CA device 24 differing by a fixed offset.
Also, the secondary CA and reconstitution device 24 includes a reconstitution component, which copies or strips or otherwise obtains only the now-encrypted critical packets from the fully encrypted stream received from the legacy CA device 20 and inserts the packets into the partially encrypted stream in accordance with principles below. The partially encrypted stream, now with two encrypted versions of each critical packet (one generated by the legacy CA device 20 and one generated by the secondary CA device 24) can be transmitted by a transmission system 26 over, e.g., cable, or terrestrial broadcast, or satellite broadcast.
It is to be understood that the functions of the secondary CA and reconstitution device 24 can be undertaken by separate components. It is to be further understood that the functions of the components 16, 18, 22, and 24 can be executed by a single secondary CA computing device or system or by separate devices/systems, and that the principles set forth herein apply to an overall system 10 that can have plural secondary CA systems.
The logic that is implemented by the system 10 shown in FIG. 1 can be seen in FIG. 2. Commencing at block 28, critical packets in the stream are identified, along with their offsets from a predetermined packet or packets, in accordance with principles set forth above. The offsets are stored (e.g., in the offset table 16) at block 30, and the stream is copied at block 32 by the stream copier 18.
A first clear version of the stream is sent to the legacy CA device 20 at block 34. At block 36, the legacy CA device 20 fully encrypts the stream in accordance with incumbent CA principles. In parallel, a second clear version of the stream is buffered at block 38 and then partially encrypted at block 40 by the secondary CA device 24. As mentioned above, the secondary CA device 24 encrypts only the critical packets.
Block 42 represents the reconstitution function. The encrypted critical packets from the legacy CA device 20 are obtained by accessing the critical packet offset table 16, obtaining the offsets, and counting through the fully encrypted stream using the offsets from the reference PID or PIDs. At each indicated critical packet offset location, the encrypted packet at that location is obtained by, e.g., copying the packet from the stream. The critical packets are then inserted into the partially encrypted stream immediately next to the corresponding preexisting critical packets in the stream that were generated by the secondary CA device 24. The partially encrypted stream with two encrypted versions of each critical packet, one from the legacy CA device 20 and one from the secondary CA device 24, is transmitted at block 44.
While the particular SYSTEM AND METHOD FOR PARTIALLY ENCRYPTED MULTIMEDIA STREAM as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention. For example, in a less elegant solution, the secondary CA device 24 could completely encrypt the stream, and the critical packets from the fully encrypted versions from the legacy and secondary CA devices could be copied and inserted into a third clear version of the stream from which the unencrypted critical packets have been removed. The scope of the present invention thus fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited as a “step” instead of an “act”. Absent express definitions herein, claim terms are to be given all ordinary and accustomed meanings that are not irreconciliable with the present specification and file history.

## Claims

1. A method for multimedia transmission, comprising:
generating a copy of a multimedia stream to render first and second clear streams having identical predetermined portions;
sending the first clear stream to a first conditional access (CA) component to encrypt the entire first clear stream to render a completely encrypted stream;
obtaining encrypted versions of the predetermined portions from the completely encrypted stream;
using the second clear stream, encrypting substantially only the predetermined portions using a second CA component to render a partially encrypted stream; and
inserting the encrypted predetermined portions obtained from the completely encrypted stream into the partially encrypted stream to render a transmission stream that is only partially encrypted for transmission thereof.

2. The method of claim 1, comprising transmitting the transmission stream to plural set-top boxes over cable.

3. The method of claim 1, comprising wirelessly broadcasting the transmission stream to plural receivers.

4. The method of claim 1, wherein the first CA component is a legacy component provided by an incumbent.

5. The method of claim 1, comprising determining locations of the predetermined portions at least in one of the streams using corresponding offsets from at least one packet identifier (PID).

6. The method of claim 5, wherein the offsets are in integral numbers of packets from at least one PID.

7. The method of claim 5, wherein the offsets are used for identifying the locations of the encrypted predetermined portions in the completely encrypted stream for obtaining them and inserting them into the partially encrypted stream to render the transmission stream.

8. The method of claim 1, wherein the encrypted predetermined portions obtained from the completely encrypted stream are inserted adjacent to the predetermined portions encrypted using the second CA component in the partially encrypted stream to render the transmission stream.

9. A system for use in a digital stream transmitter head end having a legacy conditional access (CA) device, comprising:
at least a system CA device encrypting at least predetermined portions of a first version of a stream; and
a reconstitution component combining, into a stream, the predetermined portions from the system CA device and the predetermined portions obtained from a full encryption of a second version of the stream to render a partially encrypted stream having a first encryped version of the predetermined portions and a second encrypted version of the predetermined portions and having substantially no other encrypted data therein, the full encryption being generated by the legacy CA device.

10. The system of claim 9, wherein the predetermined portions obtained from the full encryption generated by the legacy CA device represent the same information as the predetermined portions encrypted by the system CA device, and the stream into which the predetermined portions are combined is the first version of the stream.

11. The system of claim 10, wherein the head end transmits the partially encrypted stream over cable.

12. The system of claim 10, wherein the head end wireless broadcasts the partially encrypted stream.

13. The system of claim 10, comprising at least one critical packet locator determining offsets of at least some predetermined portions from at least one packet identifier (PID).

14. The system of claim 13, wherein the offsets are in integral numbers of packets from at least one PID.

15. The system of claim 13, wherein the reconstitution component uses the offsets to insert the predetermined portions obtained from the full encryption such that the predetermined portions obtained from the full encryption are adjacent to the predetermined portions of the first version in the partially encrypted stream.

16. The system of claim 9, further comprising at least one buffer temporarily holding the first version of the stream.

17. The system of claim 13, further comprising at least one data structure storing the offsets.