Digital broadcast systems include direct broadcast digital satellite systems, interactive World Wide Web (“Web”) access systems, and digital cable systems. Digital broadcasting provides a number of advantages to subscribers, such as variety and flexibility of programming, useful and comprehensive support services (such as detailed electronic programming guides), and superior audio and video quality.
The Conditional Access (CA) function of a digital broadcast system allows selective access to valuable copyrighted information. Such information includes, for example, pay-per view movies, premium sporting events, etc. The producers of the movies, events, etc., require that access to the premium services be controlled in order to protect and enforce their copyrights, protect copyright ownership, and protect their commercial interests as well. The digital broadcast system operators (also referred to as Multiple System Operators, MSOs) also have a commercial interest in preventing unauthorized use and in limiting access to these premium services to authorized users only.
To prevent unauthorized use, MSOs typically broadcast a scrambled signal. The scrambled signal is then descrambled by a descrambling unit in the transceiver (e.g., using a key provided by the MSO, for example, in the smart card). However, the typical transceiver includes a number of internal components or functional blocks. To provide the copyrighted services to the user, the descrambed signal needs to be coupled to one or more additional internal components of the transceiver for further processing. To prevent pirating of the descrambled signal, various prior art schemes are used to prevent unauthorized access to the audio video content of the descrambled signal. For example, in many cases, certain secure transmission techniques are employed which use encryption and decryption to protect the descrambled signal. In other cases, various encapsulation methods (e.g., epoxy encapsulation) are employed which prevent access to the transceiver circuit board.
Prior Art FIG. 1 is a block diagram showing some of the elements in one embodiment of a prior art transceiver (e.g., a set-top box) that uses both encryption and encapsulation to protect the descrambled signal. It should be noted that for clarity, not all of the elements of the set-top box are shown. Front-end unit 20 of the set-top box comprises a tuner (not shown), as well as other devices known in the art, for receiving a digital broadcast signal 90. Coupled to front-end unit 20 is a point of deployment (POD) 10. POD 10 typically is adapted to receive a smart card (not shown) that, as described above, can be used to provide billing information to the MSO. The smart card also typically contains a key provided by the MSO that is used to descramble digital broadcast signal 90. POD 10 includes a descrambling/encryption unit 40 that uses the key provided by the MSO to descramble broadcast signal 90 (if the signal is scrambled). Descrambling/encryption unit 40 also encrypts the signal (if the signal is not encrypted). It is appreciated that, in other prior art embodiments, descrambling functionality and the encryption functionality of unit 40 may consist of separate elements, one for descrambling and one for encrypting.
Front-end unit 20 also includes decryption unit 50 for decrypting an encrypted broadcast signal before the signal is sent to audio/visual (A/V) decoder 30. A/V decoder 30 is used for demultiplexing the signal and for decoding, for example, MPEG (Moving Picture Experts Group) video signals and/or Dolby AC3 audio signals.
Thus, in this prior art embodiment, digital broadcast signal 90 is received by the set-top box at front-end unit 20 and forwarded to POD 10. Broadcast signal 90 is descrambled by descrambling/encryption unit 40. Once descrambled, broadcast signal 90 is encrypted to prevent unauthorized duplication. Further downstream in the set-top box, broadcast signal 90 is decrypted using decryption unit 50 so that it can be decoded (e.g., MPEG or AC3 decoding) in A/V decoder 30, and subsequently processed so that it can be viewed and/or listened to by an authorized subscriber.
A problem with this prior art embodiment is that, between decryption unit 50 and A/V decoder 30, broadcast signal 90 is transmitted in the clear at point 12 (that is, it is not scrambled nor is it encrypted at this point). Thus, at point 12, broadcast signal 90 can be intercepted and duplicated. As a digital signal, it is possible to make near perfect copies which can be readily distributed to unauthorized parties (e.g., rebroadcast via the Internet, copied onto a compact disk, etc.). While the MSO may receive payment for a one-time use, subsequent use by unauthorized users is made without proper compensation to the MSO or the copyright owners.
With the advent of digital cable, including Internet access, set-top boxes have bi-directional capability, and increased bandwidth requirements, resulting in audio video signals being transported between an increased number of functional modules within the cable set-top box. Unfortunately, this creates new opportunities for theft of the digital audio video content. Thus, while Prior Art FIG. 1 shows a single bus line 12 where broadcast signal 90 can be intercepted and duplicated, the most modern, most complex bi-directional set-top boxes will often have numerous such points of interception, as digital information is transmitted between and among numerous functional modules within the cable set-top box.
To prevent pirating, especially in the case of the more complex, bi-directional set-top boxes, numerous and varied prior art schemes are employed. Such schemes include, for example, “booby trapping” the transceiver housing in order to intentionally disable the transceiver should the housing be tampered with, the encapsulation of the entire circuit board of the transceiver within a thick epoxy layer to prevent access to circuit traces (e.g., intermodule buses), and the like. These methods are employed individually and in unison, all in an attempt to prevent theft of the audio video content of the descrambled signal.
While the above prior art methods are successful to some extent, they have proven unable to stop the more sophisticated pirates. Such individuals, for example, often have detailed technical knowledge of the transceiver which allows them to, for example, determined an exact location at which to “drill” or “tap” a bus trace to obtain access to the descrambled signal, or to disable any housing booby traps. Additionally, the incorporation of such multiple security schemes imposes a significant cost penalty on the design and manufacture of set-top box transceivers. Such schemes often require the incorporation of special-purpose, specially designed, one-of-a-kind type components designed specifically for a single model of transceiver.