Abstract:
Embodiments of the present invention provide a method, apparatus and system for the secure distribution of content such as audiovisual content in a way that prevents users from misusing the content and provides a mechanism for tracking pirated material back to the original location of misappropriation. A security device, in accordance with one embodiment of the present invention, incorporates encryption methods to insure the broadcast encryption key remains secure. A marking device, in accordance with one embodiment of the present invention, incorporates, for example, digital watermarking methods that attach to the content information to identify a location of origin of the misappropriation, such as a Set-top Box (STB) and/or smart card.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to content distribution and, more particularly, to a method, apparatus and system for securely communicating content such as audiovisual content. 
       BACKGROUND OF THE INVENTION 
       [0002]    Content such as audiovisual content, securely stored within a content device, such as a Set-top Box (STB), is often transferred over an unsecured channel (e.g., a home network), to a software player running on, for example, a personal computer (PC). The STB uses a sophisticated conditional access (CA) mechanism to prevent the unauthorized use of the content, however, pirating can easily take place along the unsecured channel. 
         [0003]    As such, what is needed is a method, apparatus and system for the secure distribution of audiovisual content. 
       SUMMARY OF THE INVENTION 
       [0004]    Embodiments of the present invention address these and other deficiencies of the prior art by providing a method, apparatus and system for the secure distribution of content, such as audiovisual content. 
         [0005]    In one embodiment of the present invention, a method for the secure distribution of content includes encrypting the content using a first key, encrypting the first key using a second key, and distributing the encrypted content and the encrypted first key. In such an embodiment of the present invention, the distributed content is decrypted by decrypting the first key using a locally stored copy of the second key and decrypting the content using the decrypted first key. The method can further include the inclusion of identification information intended to identify the original intended user of misappropriated content. That is, the method can further include marking the decrypted content for identification purposes, and re-encrypting the marked content. In addition, the method can further include encrypting the content using a third key, the third key being acquired via a secure channel and communicating the content encrypted using the third key to a source of the third key, wherein the content encrypted using the third key is decrypted using a local copy of the third key. 
         [0006]    In an alternate embodiment of the present invention, an apparatus for the secure distribution of content includes a secure processing module for encrypting and decrypting the content and a smart card for locally storing and decrypting encryption keys. In the apparatus, upon receiving content encrypted with a first key and upon receiving the first key encrypted with a second key, the smart card of the apparatus decrypts the first key using a locally stored copy of the second key, and the secure processing module decrypts the received encrypted content using the decrypted first key. The apparatus of the present invention can further include a marking module for marking the decrypted content. 
         [0007]    In an alternate embodiment of the present invention, a system for the secure distribution of content includes a content source for distributing content, an electronic counter-measure device for encrypting the distributed content using a first key and for encrypting the first key using a second key, an apparatus for receiving the content encrypted with a first key and the first key encrypted with a second key and a storage device for storing the received encrypted content and the first key. The apparatus of the system can include a secure processing module for encrypting and decrypting content and a smart card for locally storing and decrypting encryption keys. In the system of the present invention, upon receiving content encrypted with the first key and upon receiving the first key encrypted with the second key, the smart card of the apparatus decrypts the first key using a locally stored copy of the second key, and the secure processing decrypts the received encrypted content using the decrypted first key. The apparatus of the system of the present invention can further include a marking module for marking the decrypted content. In addition, the system of the present invention can further include a content player for communicating a third key to the apparatus via a secure channel, wherein the apparatus encrypts the decrypted content using the third key and communicates the content encrypted using the third key to the content player and the content player decrypts the content encrypted via the third key using a locally stored copy of the third key. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  depicts a high level block diagram of a system for adding security encryption to content in accordance with an embodiment of the present invention; 
           [0010]      FIG. 2  depicts a high level block diagram of a system including a set-top box as depicted in  FIG. 1  and a software player for receiving and playing the encrypted content of  FIG. 1  in accordance with an embodiment of the present invention; 
           [0011]      FIG. 3  depicts a high level block diagram of a content distribution system in accordance with an embodiment of the present invention; 
           [0012]      FIG. 4  depicts a high level block diagram of a content distribution and watermarking system in accordance with an embodiment of the present invention; and 
           [0013]      FIG. 5  depicts a high level block diagram of a system for receiving and playing encrypted content including an alternate watermarking method in accordance with an alternate embodiment of the present invention. 
       
    
    
       [0014]    It should be understood that the drawings are for purposes of illustrating the concepts of the invention and are not necessarily the only possible configuration for illustrating the invention. To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The present invention advantageously provides a method, apparatus and system for securely communicating content such as audiovisual content in, for example, a home network environment. Although the present invention will be described primarily within the context of audiovisual content in a home network environment including a software player, the specific embodiments of the present invention should not be treated as limiting the scope of the invention. It will be appreciated by those skilled in the art and informed by the teachings of the present invention that the concepts of the present invention can be advantageously applied in substantially any network for the secure transfer of any content (e.g., video, audio, audiovisual, etc.) to be played on substantially any content player. 
         [0016]      FIG. 1  depicts a high level block diagram of a system for adding security encryption to content such as audiovisual content in accordance with an embodiment of the present invention. The system  100  of  FIG. 1  illustratively comprises an audiovisual content transmission device (illustratively a satellite dish)  110 , a Set-top Box  120 , an Electronic Counter-measure device  125  and a content and key storage device  130 . In the system  100  of  FIG. 1 , the Set-top Box  120  includes a smart card  140  and a secure processing and storage module  150 . In the system  100  of  FIG. 1 , the module  150  of the Set-top Box has a secure communications link to the smart card  140 . In addition, the smart card  140  has secure processing and storage capabilities. 
         [0017]    In the system  100  of  FIG. 1 , an electronic counter-measure (ECM) message from the ECM device  125  is communicated to the STB  120  along with the audiovisual content. The ECM message contains, among other things, an encryption key or work key, k w . To prevent interception, the work key, k w , is encrypted with a key to be used by the smart card  140 . The key is denoted herein as the smart card key, k sc  and the encrypted work key as k sc (k w ). The smart card key is stored safely on the smart card  140  and cannot be recovered by someone attempting to intercept or copy the audiovisual content. In the embodiment of  FIG. 1 , the smart card key is a key to a symmetric key cipher. The encryption of the ECM message is not essential to the understanding of the embodiments of the invention presented herein and, as such, will not be described in detail herein. In one embodiment of the present invention, the encryption of the ECM message can be a public key cipher, however any known encryption methods can be applied. 
         [0018]    As previously described, the ECM message is stored along with the encrypted audiovisual content in for example the content and key storage device  130 . Upon playback of the audiovisual content, the ECM is recalled from storage  150  and the encrypted work key is communicated to the smart card  140 . The smart card  140  uses a local copy of k sc  to decrypt and return k w  to the secure processing module  150  of the STB  120 . As such, the STB  120  obtains the necessary key to decrypt the stored audiovisual content. Such decryption can be accomplished in the secure processing module  150 . Although in the embodiment of the system of  FIG. 1  the audiovisual content and ECM is depicted as being communicated to a single STB  120 , in alternate embodiments of the present invention, the audiovisual content and ECM can be broadcast to more than one Set-top box or other receiving device for encryption and processing as described above. For example, each broadcast audiovisual content can be encrypted using a symmetric key cipher. As previously recited, the encryption key or audiovisual work key is herein denoted as k w  and the encrypted audiovisual content as k w (w). The encrypted audiovisual content is received by each STB and stored for later use. 
         [0019]      FIG. 2  depicts a high level block diagram of a set-top box  120  as depicted in  FIG. 1  and a software player for receiving and playing the encrypted audiovisual content of  FIG. 1  in accordance with an embodiment of the present invention. In  FIG. 2 , the software player illustratively comprises a personal computer (PC)  210 . In content distribution systems, it is desirable to allow stored content, such as the audiovisual content stored in the STB  120  and/or the content and key storage device  130  of  FIG. 1  as described above, to be transferred to a personal computer for display. In  FIG. 2 , the software player  210  is provided with a unique private/public key pair and the public key of the STB  120 . The software player  210  encrypts its own public key with the STB public key and communicates this information to the STB. The STB can decrypt this message with its private key. As such, the two devices know each others public key and they can establish a secure communication channel. Through this channel they create and exchange a session key and then terminate the secure channel. The session key will be used to securely transfer the content from the STB to the software player. 
         [0020]    More specifically, in one embodiment of the present invention, stored audiovisual content is communicated directly from STB storage to the PC  210 . As such, the key, k w , needs to be communicated to the PC  210  along with the audiovisual content. In the system of  FIG. 2 , the PC  210  is considered an unsecured platform and poses a risk to the security of the key, k w , which before to the communication to the PC  210  was very secure. 
         [0021]    To maintain the security of k w , a link encryption is implemented. More specifically, the PC  210  and the STB  120  use a public key cipher to establish a secure communications channel, (e.g., a TLS). Public key ciphers, however, are computationally expensive and thus are not often used for large data payloads. Instead, this TLS channel is used to establish and exchange a session key, k s , for a symmetric key cipher. The STB will then decrypt the audiovisual content using the work key, k w , and then immediately encrypt it using the session key, k s . This re-encrypted audiovisual content can then be securely communicated through an unsecured channel, for example a home network, to the PC  210  and decrypted there for display. 
         [0022]    For example,  FIG. 3  depicts a high level block diagram of an audiovisual content distribution system in accordance with an embodiment of the present invention. The audiovisual content distribution system  300  of  FIG. 3  illustratively includes a content and key storage device  130  and a Set-top Box (STB)  120  as depicted in  FIG. 1  and a software player  210  as depicted in  FIG. 2 . In the system of  FIG. 3 , once a session key, k s , has been established, the secure processing device  150  in the STB  120  is used to decrypt the work and re-encrypt it using the symmetric cipher session key, k s . The encrypted content can then be communicated to the PC  210  on an unsecured channel, such as a home network. The player can decrypt the content with its copy of the session key, k s . 
         [0023]    In order to use a public key cipher, the STB  120  and the software running on the PC  210  must each have a public/private key pair. In one embodiment of the present invention, the private key of the STB  120 , k stb   pv , is embedded in the secure processing module  150  during manufacture and the public key, k sb   pu , is stored in a secure database for subsequent distribution. The software player  210  can comprise a proprietary player distributed by a STB owner/operator to its customers upon request. Each copy of the software player  210  will contain a unique private/public key pair, (k pc   pv ,k pc   pu ). A customer request for audiovisual content will include the unique identification of an STB from which the connection is requested. The public key of that STB will be embedded into a respective software player ensuring that the software player can only work with that STB. This also gives an STB operator a record of which STBs have been enabled to communicate with which PCs. 
         [0024]    As such and in accordance with the present invention, the STB  120  has a private key and the software player  210  will have the corresponding public key as well as its own private/public key pair. The software player  210  initiates a connection with the STB  120  over an unsecured channel, for example a home network, and can communicate to the STB  120  information regarding its public key. In such a manner, the STB  120  and the software player  210  are able to establish a secure channel through which they can establish and exchange a symmetric cipher session key as described above with reference to  FIG. 2 . 
         [0025]    Many protocols for establishing a secure channel require that all communication devices have signed digital certificates from a trusted source. Given the proprietary nature of the proposed architecture, these certificates can be generated by, for example, the STB operator (the trusted source) and provided to both the STB  120  and the software player  210 . This ensures that the STB  120  will only establish a secure link with an STB-operator authorized software player. The concepts of the present invention as described above will assist in protecting distributed audiovisual content from being pirated. In various embodiments of the present invention, advanced software security techniques are implemented to protect the software private key and derived session key from being discovered. Unfortunately however, knowledgeable pirates most likely will be successful in discovering these keys. Once discovered, the session key can be used to decrypt the audiovisual content. However, in accordance with an embodiment of the present invention, different audiovisual content will be encrypted with a different session key. As such, while a discovered key is valuable for decrypting corresponding protected audiovisual content on a corresponding STB, the discovered key will not be valuable to anyone else having a different STB nor would it be useful for decrypting other distributed audiovisual content. To do so, another session key would need to be discovered. 
         [0026]    Even further, a software private key can be discovered and used to observe a TLS session, thus learning each session key as the session is established. For example, there can be two groups of individuals who might pursue such unauthorized copying: customers who which to make copies for themselves and their friends and professional thieves. One difference between these two groups is that the misbehaving customers obtain primary value from the content delivery service and only secondary value from the copying. Professional thieves take advantage of the content delivery service for the purpose of generating pirate content. 
         [0027]    Digital watermarking is a technique for modifying digital imagery in order to attach certain identifiable metadata to audiovisual content. The metadata is recoverable from a copy of the watermarked content, even if that content has been re-compressed or has been converted to analog format. The digital watermark in content is also intended to survive the decryption, decoding, and digital-to-analog conversion of content that can be performed in a single secure silicon chip so that the only capturable, clear text content is analog. Such a process is commonly referred to as the “Analog Hole”. 
         [0028]    In various embodiments of the present invention, watermarking can be optionally applied to audiovisual content secured in accordance with the present invention. For example, in a first approach, received audiovisual content is not directly stored in a Set-top Box (STB). Instead, the content is decrypted, watermarked, and re-encrypted prior to storage. The watermark contains information that uniquely identifies the STB and the associated smart card and includes a timestamp indicating a receiving and recording time. 
         [0029]      FIG. 4  depicts a high level block diagram of an audiovisual content distribution and watermarking system in accordance with an embodiment of the present invention. The system  400  of  FIG. 4  illustratively includes a content transmission device (illustratively a satellite dish)  110 , a content and key storage device  130  and a Set-top Box (STB)  120  as depicted in  FIG. 1 . However, in the system of  FIG. 4 , the STB  120  further comprises a watermarking module  175  for applying a watermark to the content received from the content transmission device  110  prior to storage in the content and key storage device  130 . 
         [0030]    In the system  400  of  FIG. 4 , if the security of the STB  120  is compromised and the content is successfully obtained from the STB  120  and is successfully pirated, the watermark applied by the watermarking module  175  will identify the offending STB/customer. The watermarking of the present invention, however, introduces an additional decryption/encryption cycle to the process and this, along with the watermarking, can become computationally expensive for real-time processing in the STB. 
         [0031]    As such, in an alternate embodiment of the present invention, the content is not watermarked during storage, but instead, watermarked as they are transferred to the software player. For example,  FIG. 5  depicts a high level block diagram of a system for receiving and playing encrypted audiovisual content including an alternate watermarking means in accordance with an alternate embodiment of the present invention. The system  500  of  FIG. 5  illustratively includes a content and key storage device  130  and a Set-top Box (STB)  120  as depicted in  FIG. 1  and a software player  210  as depicted in  FIG. 2 . Similar to the embodiment depicted in  FIG. 1 , received content is stored directly in its encrypted form. Upon request, the content is decrypted and re-encrypted with the session key as before, however in the embodiment of  FIG. 5 , a watermark is added by the watermarking module  175  to the content. As previously described, the watermark can include a time stamp identifying at least the time of download and, if available from the STB storage, the time of initial storage as is the case in the first watermarking approach. In addition, a unique ID of the software player  210  is now known at the time of watermarking (i.e., because of the digital signature), and as such, information identifying the particular software player  210  can be included in the watermark information. 
         [0032]    In one embodiment of the present invention, the watermark is added directly into an MPEG-2 bitstream. The marking process can be real-time for the first watermarking embodiment described with respect to  FIG. 4  and can be faster than real-time for the second watermarking embodiment described with respect to  FIG. 5 . In one embodiment, the watermarking process does not introduce any visible or audible artifacts that would tip off a user of its existence. In addition, the watermark data can be recoverable after resizing to a smaller size, transcoding, and a number of other standard television picture processes including de-interlacing, noise reduction, color adjustment, etc. A watermark detector (not shown) does not have any information included in the embedding process. That is, an embedder (not shown) and detector can share a secret, but the detector will not know, apriori, which embedder was used. Detection is a forensic operation and can be slower than real-time. 
         [0033]    Both above described watermarking approaches embed customer identifying information into content that are intended to be viewed and not distributed If a user obtains piracy software that discovers software player keys and if that user uses that piracy software to make unauthorized copies of works stored on the STB, those copies will contain watermarks with identifying information to identify the location of origin of the pirated content. If any of those copies are distributed (i.e., on a P2P network or on a web site for example), each and every unauthorized copy will contain the necessary forensic information (e.g., watermark and identification information) to identify the original intended recipient of that content. After such discovery, an STB operator can take any remedial action deemed appropriate including but not limited to sending a warning letter, to cancellation of service, to the pursuit of legal remedies and the like. 
         [0034]    In accordance with various embodiments of the present invention, an STB includes a private/public key pair. The private key is embedded in the STB and the public key is stored in a secure database by the STB operator. The STB can also include a digital certificate supplied by the STB operator. Subsequently, a customer can contact the STB operator and requests a software player for viewing desired content. The request is accompanied by an STB identifier (this request could be facilitated through the STB). The STB operator recovers the STB public key from the database, creates a digital certificate for the software player, and communicates such information to the customer. Additionally, and as described above, the software player has its own private/public key pair. 
         [0035]    As described above, in a first approach, content to be stored locally at the STB is first decrypted, watermarked, and then re-encrypted. The software player initiates a session with the STB and provides its public key. The software player and the STB negotiate a secure channel using their digital certificates, and establish a session key. In the first approach, stored watermarked content is decrypted on the STB and re-encrypted with the session key before being transferred to the software player. 
         [0036]    In the second approach, stored content is decrypted on the STB, watermarked, and then re-encrypted with the session key before being communicated to the software player. The software player decrypts the content with the session key and plays the content. 
         [0037]    Having described various embodiments for a method, apparatus and system for the secure distribution of content (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. While the forgoing is directed to various embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.