Authenticated Mode Control

Abstract

Methods and systems for authenticated mode control in controlled devices are disclosed. A method for changing a mode in a controlled device from a current mode includes selecting one of several available key derivation functions based on a target mode, generating a target mode specific root key using a global root key and the selected key derivation function, and the use of that root key to affect a change of the controlled device to a target mode. Corresponding devices and systems are also disclosed. In one embodiment, the methods are applicable to a cable television distribution system and the changing of the operating mode of a set top box from one conditional access provider to another.

1 . A device comprising:
 at least one processor;   a plurality of key derivation functions configured to be executed by the at least one processor, wherein each key derivation function of the plurality of key derivation functions includes an assigned mode value corresponding to one of a plurality of operating modes of the device, and wherein said each key derivation function is configured to take as input a global root key and generate a root key specific to the assigned mode value.   
     
     
         2 . The device of  claim 1 , further comprising:
 a mode controller configured to:
 recover a mode change instruction from an encrypted message using the generated root key; and 
 change an operating mode of the device based upon the recovered mode change instruction. 
   
     
     
         3 . The device of  claim 2 , further comprising:
 a non-volatile memory configured to store the global root key.   
     
     
         4 . The device of  claim 2 , wherein the device is a set-top box. 
     
     
         5 . The device of  claim 2 , wherein the device is a system-on-a-chip for a set-top box. 
     
     
         6 . The device of  claim 1 , further comprising:
 a selector configured to select one key derivation function from the plurality of key derivation functions, wherein the assigned mode value of the one key derivation function matches a received requested mode value.   
     
     
         7 . A method for changing an operating mode of a device from a current mode, comprising:
 selecting a target key derivation function from a plurality of key derivation functions, wherein the target key derivation function corresponds to a target mode, and wherein the target mode is one of a plurality of operating modes of the device;   generating a target root key by providing a global root key as input to the target key derivation function; and   changing the operating mode in the device from the current mode to the target mode using the generated target root key.   
     
     
         8 . The method of  claim 7 , wherein the changing step comprises:
 using the target root key to recover a decryption key from a key distribution message; and   using the recovered decryption key to decrypt a requested mode change message.   
     
     
         9 . The method of  claim 7 , further comprising:
 receiving a mode change request from an entity external to the device, wherein the received mode change request includes the target mode.   
     
     
         10 . The method of  claim 9 , wherein the mode change request is generated by a conditional access provider. 
     
     
         11 . A computer readable storage medium having instructions stored thereon that, when executed by a processor, cause the processor to perform a method for changing an operating mode of a device, wherein the method comprises:
 selecting a target key derivation function from a plurality of key derivation functions, wherein the target key derivation function corresponds to a target mode, and wherein the target mode is one of a plurality of operating modes of the device;   generating a target root key by providing a global root key as input to the target key derivation function; and   changing the operating mode in the device from the current mode to the target mode using the generated target root key.   
     
     
         12 . The computer readable storage module of  claim 11 , wherein the changing step comprises:
 using the target root key to recover a decryption key from a key distribution message; and   using the recovered decryption key to decrypt a requested mode change message.   
     
     
         13 . The computer readable storage module of  claim 11 , wherein the method further comprises:
 receiving a mode change request from an entity external to the device, wherein the received mode change request includes the target mode.