Patent Publication Number: US-6993134-B1

Title: Key exchange via a portable remote control device

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to the field of consumer electronics, and in particular to encryption techniques for copy and display protection for copyright material. 
   2. Description of Related Art 
   Digital recordings have the unique property that copies of the recorded material have the same quality as the original. As such, the need for an effective copy protection scheme is particularly crucial for the protection of copyright material that is digitally recorded. A number of protection schemes have been developed or proposed that rely upon a secure link between electronic devices. These schemes typically rely upon the manufacturers of the electronic devices to comply with an agreed upon standard to make the mass production of protected material economically infeasible. For example, a set top box may communicate a received broadcast to a receiving device, such as a VCR or television, in an encrypted form that is only decryptable by the intended receiving device. In like manner, a playback device, such as a VCR or DVD, communicates the material in an encrypted form that is only decryptable by its intended receiving device, and so on. 
   To effect this one-to-one encryption scheme, the proposed standards often call for the establishment of the encrypted link via a mutual key exchange. One such key exchange system is the “Diffie-Hellman” key-exchange algorithm, common in the art.  FIG. 1  illustrates an example flow diagram for a key-exchange and subsequent encryption of content material using the Diffie-Hellman scheme. At  110 , a first device, Device A, transmits a large prime n, and a number g that is primitive mod n, as a message  111  to a second device, Device B, that receives n and g, at  115 . Each device, at  120  and  125 , generate a large random number, x and y, respectively. At  130 , Device A computes a number X that is equal to g x  mod n; and, at  135 , Device B computes a number Y that is equal to g y  mod n. Device A communicates X to Device B, and Device B communicates Y to Device A, via messages  131 ,  136 , respectively. Note that the determination of x from a knowledge of g and X, and y from a knowledge of g and Y, is computationally infeasible, and thus, an eavesdropper to the exchange of g, n, X, and Y will not be able to determine x or y. Device A computes a key K that is equal to Y x  mod n, at  140 , and Device B computes a key K′ that is equal to X y  mod n, at  145 . Note that both K and K′ are equal to g xy  mod n, and thus Device B knows Device A&#39;s key, and vice versa, while an eavesdropper to the exchange of g, n, X, and Y will not know the key, because the eavesdropper does not know x or y. This exchange of information from which to generate the knowledge of a corresponding key is termed a key exchange. 
   After effecting the key exchange, Device A encrypts the content material M  150  and communicates the encrypted material E k (M) to Device B, at  160 , via communications path  161 . Because Device B&#39;s key K′ is identical to the key K that is used to encrypt the content material M  150 , Device B uses key K′ to decrypt the received encrypted material E k (M) to create a decrypted copy  150 ′ of the content material M  150 , at  165 . An eavesdropper to the communications path  161 , not having a knowledge of the key K, is unable to decrypt the encrypted material E k (M), and thus unable to create a copy of the content material M  150 . 
   Note that the above described key exchange, and virtually all known secure key exchanges, require a bidirectional transfer of information between the devices. Many consumer electronic devices, however, are configured for a unidirectional transfer of content material. For example, as illustrated in  FIG. 2 , a conventional set-top box  210  or DVD player  230  includes a wide-bandwidth transmitter for transmitting  211 ,  212 ,  231 ,  232  the content material to a VCR  260  or display device  250 , but rarely includes a receiver for receiving communications from the VCR or display device. In a device such as the VCR  260  that has bidirectional communications capabilities  251 ,  261 , the key exchange can be effected by multiplexing the key exchange messages  111 ,  131 ,  136  of  FIG. 1  onto the same paths  251 ,  261  that are used to communicate content material. Note, however, that the adoption of this multiplexing scheme for key exchange requires that the receiving device  250  contain receiving equipment that is compatible with the transmission  261  of content material. Thus, a conventional DVD player  230  that transmits  232  wide-bandwidth content material to the VCR  260  will be required to also contain a wide-bandwidth receiver to receive wide-bandwidth content-compatible transmissions  262  from the VCR to effect a key exchange, even though the DVD player will have no other practical use for this wide-bandwidth communications path  262 . Note, also, that a switching means will be required at the VCR to redirect the wide-bandwidth output, from the conventional connection  261  to a display device  250 , to the DVD player via this newly required communications path  262 . Alternatively, additional transmitters, receivers, and communications connectors can be added to each consumer component  210 ,  220 ,  250 ,  260 , etc. to effect the key exchange. Each of these options requires additional material and manufacturing costs to add the required communications and connection equipment. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of this invention to provide a method and system for effecting a cryptographic key exchange between consumer electronic components that utilizes communications devices and paths that are common to most consumer electronic components. It is a further object of this invention to provide an inexpensive system for effecting a cryptographic key exchange between consumer electronic components. It is a further object of this invention to provide a method and system for effecting a cryptographic key exchange between consumer electronic components that is substantially independent of the physical location of the components. 
   These objects and others are effected by utilizing the communications means that are commonly provided for the remote control of electronic components to effect a key exchange. As more sophisticated capabilities are provided for the remote control of equipment, most state of the art consumer electronic devices are being configured with bidirectional infrared transceivers for receiving commands from, and providing feedback to, the remote control device. In accordance with this invention, these bidirectional remote control transceivers are configured to communicate the parameters required to effect the cryptographic key exchange between consumer devices. The principles presented in this invention may also be used to transfer other parameters and information among consumer electronic devices. In a preferred embodiment of this invention a remote control device contains the control means to effect the transfer of these parameters between the consumer devices. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein: 
       FIG. 1  illustrates an example flow diagram of a prior art cryptographic key exchange technique. 
       FIG. 2  illustrates an example block diagram of a prior art system of consumer electronic devices. 
       FIG. 3  illustrates an example block diagram of a system of consumer electronic devices with bidirectional remote control capabilities in accordance with this invention. 
       FIG. 4  illustrates an example block diagram of a pair of consumer electronic devices and a remote control device in accordance with this invention. 
       FIG. 5  illustrates an example flow diagram of a key exchange via a remote control device in accordance with this invention. 
   

   Throughout the drawings, same reference numerals indicate similar or corresponding features or functions. 
   DETAILED DESCRIPTION OF THE INVENTION 
   With the increasing use of convenience features for home automation and integrated audio-visual systems, the traditional function of a remote control device has expanded to include feedback from the device being controlled. Copending U.S. patent application “REMOTE CONTROL PROGRAM SELECTION BY GENRE”, U.S. Ser. No. 09/282,319, filed Mar. 31, 1999 for Karen Travato, Dan Pelletier, Paul Rankin, and Jacquelyn Martino, for example, presents a remote control device that receives program information from the television, DVD or set-top box for display on the remote control device to facilitate a user selection among available programs, or to present information about a program currently being viewed, and is incorporated by reference herein. Most state of the art consumer electronic devices contain bidirectional communications means, typically an infrared transceiver, for communicating with a remote control device. The conventional “universal” remote control device includes such a bidirectional transceiver that can be configured to receive infrared codes from sole-appliance remote control devices to “learn” how to control each appliance. 
     FIG. 3  illustrates a collection of consumer electronic devices that are controllable by a remote control device  390 . Each consumer device, the set-top box  310 , the DVD player  330 , the display device  350 , and the VCR  360 , contains a conventional remote control transceiver  320  for receiving commands from, and providing feedback to a corresponding conventional remote control transceiver  320  in the remote control device  390 . In accordance with this invention, the remote control transceiver  320  in each device is also used to effect a cryptographic key exchange by communicating parameters to each other. Note that although this invention is presented in the context of transferring key-exchange parameters, any other parameters or information items may also be communicated among devices via the remote control transceivers  320  in the light of this disclosure. 
   The communication of parameters between consumer electronic devices  310 ,  330 ,  350 , and  360  can be effected via a direct communication between each pair of devices, but in a preferred embodiment, the remote control device  390  effects a relay, or store-and-forward function, to facilitate the parameter exchange. Typically, remote control transceivers  320  use line-of-sight communications means, such as infrared transmissions. Often, consumer electronic devices are placed in close proximity to each other, with each remote control transceiver  320  oriented in the same direction, toward the expected location of a user of the remote control device  390 . As such, adjacent devices are not within the line of sight of each other&#39;s remote control transceiver  320 . Because each of the adjacent devices are, by intent, within the line of sight of the remote control device  390 , the remote control device  390  is well suited to be a relay between the adjacent devices. Also, when the consumer devices are not adjacent to each other, they are often located in physically separate areas. For example, a home may be configured to allow a television in a bedroom to receive content material from a VCR that is located in a family room. By configuring the remote control device  390  as a store and forward relay system, the remote control device  390  can be configured to receive a parameter from a device in one room, then transmit the parameter to another device when it is brought into the proximity of the other device. It can then receive a parameter from the other device, and transmit it to the original device when it is brought into the proximity of original device. Copending U.S. patent application, “REMOTE CONTROL DEVICE WITH LOCATION DEPENDENT INTERFACE”, U.S. Ser. No. 09/210,416, filed Dec. 11, 1998 for Joost Kemink and Yevgeniy Shteyn, presents a remote control device whose operation is dependent upon the physical location of the device, and is incorporated by reference herein. Note that the parameter exchange for a key exchange need only occur once between the devices; thereafter, the encrypted content material is communicated between devices in separate rooms via the aforementioned conventional wide-bandwidth channels, using, for example, coaxial cable between the rooms. 
     FIG. 4  illustrates an example block diagram of a pair of consumer electronic devices  400 ,  500  and a remote control device  390  in accordance with this invention. Each of the devices  400 ,  500 , and  390  includes a remote control transceiver  320  that is illustrated as a transmitter  320 A and a receiver  320 B. The devices  400 ,  500  may be any pair of consumer devices that have a need to transfer parameters, such as the devices  310 ,  330 ,  350 ,  360  of  FIG. 3 . As noted above, an exchange of parameters via the consumer devices  400  and  500  may be effected in accordance with this invention via direct communication paths  401 ,  501 , but often such paths may not be physically practical to establish. In a preferred embodiment of this invention, the remote control device  390  facilitates the parameter transfer via a store-and-forward relay technique. The operation of the devices  400 ,  500 ,  390  to effect the parameter transfer is best explained with reference to the example flow diagram of  FIG. 5 . In the foregoing description, transmissions from each device  400 ,  500 , and  390  are via the transmitter  390 A within each device  400 ,  500 , and  390 , and receptions at each device  400 ,  500 , and  390  are via the receiver  390 B within each device  400 ,  500 , and  390 . The respective controllers  430 ,  530 , and  393  of the devices  400 ,  500 ,  390 , effect the example flow of  FIG. 5 , respectively. 
   At  910  of  FIG. 5 , the controller  393  of the remote control device  390  transmits an alert message  911 ,  913  to each device  400 ,  500 , respectively, to establish the network of communications among the devices  400 ,  500 ,  390 . Methods for communication among different devices are common in the art and traditionally used for commonly available “universal” remote controllers. In a preferred embodiment, the establishment of the network at  910  may be initiated via an entry on the keypad  398 , or via the receipt of a request (not shown) from, for example, device A, signaling that it has content material to communicate to device B, and requesting that the remote device  390  facilitate the parameter transfer required to effect a key exchange between device A and device B. 
   Upon receipt of the alert  911 ,  913  the controllers  430 ,  520  of each device  400 ,  500  prepare for the key exchange, at  912 ,  914 , respectively. Illustrated in the example of  FIG. 5  is a key exchange based on the Diffie-Hellman key exchange technique. The application of the principles of this invention to other key exchange techniques, or other parameter exchange applications, will be evident to one of ordinary skill in the art in light of the principles presented herein. Each device  400 ,  500  generates a large random number x, y via their respective key parameter generators ( 440 ,  540  in  FIG. 4 ). Techniques for generating or selecting random numbers, or pseudo-random numbers, are common in the art. To effect the Diffie-Hellman key exchange, the remote control device  390  transmits, at  930 , a large prime n, and a number g that is primitive mod n, to each device  400 ,  500 , via messages  931 ,  933 , respectively. At  932 ,  934 , each device computes the parameter X, Y that is to be transferred, based on the “secret” random numbers x, y, respectively. In the example Diffie-Hellman key exchange, X is equal to g x  mod n, and Y is equal to gy mod n. 
   Based upon an agreed upon convention, or protocol, one of the devices transmits its parameter first. In a preferred embodiment, the device having content material to send, device A  400  in the illustrated example, transmits its parameter X  941  to the remote device  390 , at  942 . As would be evident to one of ordinary skill in the art, any one of a variety of protocols may be employed to effect this transmission. For example, the remote device  390  may send a prompt to each device whenever it is ready to receive the parameter, or the device  400 ,  500  may repeatedly send the parameter until the remote device  390  sends an acknowledgment that it received the parameter, and so on. Because the encryption and subsequent decryption of the content material is dependent upon an accurate communication of the parameters X, Y, error checking and error correction techniques, common in the art, are employed in a preferred embodiment. The parameter X  941  is received from the device A  400 , at  940 , and subsequently transmitted to device B  500 , at  950 . Device B receives the parameter X  941 , at  954 , and transmits its parameter Y  963  to the remote control device  390 , at  964 . The remote control device  390  receives the parameter Y  963 , at  960 , and, within the locale of device A  400 , transmits the parameter Y  963  to device A  400 . Each device  400 ,  500  subsequently computes a key that is equal to g xy  mod n by raising the received parameter Y, X to the power of the “secret” random number x, y, at  982 ,  984 , respectively. 
   If the devices are in physically separate locales, the remote control device  390  transmits the alert  911 , and parameters g, n  931  to device A  400  and receives the parameter X  941 , at  940 , and is then transported to the locale of device B  500 . At the locale of device B  500 , the control device  390  transmits the alert  913 , the parameters g, n  933 , and the parameter X  941 , at  950 . 
   Returning to  FIG. 4 , having exchanged parameters X, Y, the key parameter generators  440 ,  540  provide the determined key K, K′, each equal to g xy  mod n, to their corresponding encryptor  420  and decryptor  520  devices, respectively. Each of the devices  400 ,  500 , is illustrated as having an appliance function block  410 ,  510 , respectively. These blocks  410 ,  510  represent the convention functions provided by each device, such as the receipt of content material by a set-top box, the recording and playback functions of a VCR, the display and tuning functions of a television, and so on. Note that, in conventional use, the appliance functions  410 ,  510  are controllable by the remote control device  390 , and feedback from the appliance functions  410 ,  510 , or the controllers  430 ,  530 , are provided to the remote control device  390 , via the transmitters  320 A and receivers  320 B of each device  400 ,  500 ,  390 . Feedback messages are displayable on the display  395  of the remote control device  390 , and may include messages and prompts that are applicable to the above described parameter exchange process or other related tasks. 
   When the device A  400  has content material M  411  to communicate securely to device B  500 , the material M  411  is encrypted by the encryptor  420  to provide an encrypted material E k (M)  421 . The encrypted material E k (M)  421  is subsequently communicated to device B  500 , via a wide-bandwidth communications channel  405 . The decryptor  520  decrypts the received encrypted material E k (M)′  421 ′ to produce a copy of the content material M′  411 ′ that is processable by the appliance function  510 , for example, to render a display of the content material M′  411 ′ corresponding to the original material M  411 . 
   The foregoing merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are thus within its spirit and scope. For example, the control flows illustrated in  FIG. 5  may be effected automatically, or via a sequence of operations communicated via the keypad  398  of the remote control device  390  in  FIG. 4 . The particular configurations and sequences of the figures are presented for illustration purposes. The functions illustrated may be effected, for example, in alternative devices. For example, the parameters g and n may be provided by one of the devices  400 ,  500 , rather than the remote device  390 . In other systems, common in the art, one or more of the parameters may be embedded in the devices  400 ,  500 , obviating the need for random number generators. If the parameters X and Y are embedded in the device, certificates verifying the authenticity of these parameters may also be supplied. In like manner, either of the devices  400 ,  500  may be configured to control the parameter exchange, and the remote control may be configured as a relatively “unintelligent” relay device. For example, the messages from the transmitters  320 A may include conventional communications packets having a destination address, and the remote device  390  may be configured to merely receive the packet and retransmit it to the device associated with the destination address. These and other system configuration and optimization features will be evident to one of ordinary skill in the art in view of this disclosure, and are included within the scope of the following claims.