Methods for the covert transmission of data

Abstract

A method for determining an identifier of a conditional access card used in a conditional access system, in which the conditional access card autonomously modulates the timing of data packets sent by the conditional access card, to form a timing sequence that corresponds to the identifier of the card. The sequence is generated by a predefined non-linear function stored on the conditional access card, and the predefined non-linear function depends on both the identifier of the conditional access card and a non-linear random sequence that is known to the conditional access card and a monitoring station that receives transmissions from the conditional access card.

What is claimed is: 
     
         1 . A method for an electronic device to communicate data values to a receiving device, the method comprising the steps of:
 performing a predefined function depending on said data values to encode said data values into an encoded sequence of timing modulations;   modulating the timing between transmissions of communications sent from said electronic device to said receiving device corresponding to said encoded sequence of timing modulations, wherein said receiving device is adapted to decode the timing between communications sent from said electronic device to said receiving device to determine said data values.   
     
     
         2 . The method of  claim 1 , further comprising:
 said encoded sequence of timing modulations being generated by a predefined function stored on said electronic device.   
     
     
         3 . The method of  claim 1 , further comprising:
 said modulation of said timing not being in response to a request for a delay.   
     
     
         4 . The method of  claim 1 , wherein:
 said data values are a unique signature of said electronic device, and said receiving device is adapted to decode said encoded sequence of timing modulations to determine said unique signature.   
     
     
         5 . A method for an electronic device to communicate data values to a receiving device, the method comprising the steps of:
 performing a predefined function depending on said data values to encode said data values into an encoded sequence of timing modulations;   modulating the timing between transmissions of communications sent from said electronic device to said receiving device corresponding to said encoded sequence of timing modulations, such that said actual data values are not communicated to said receiving device, wherein said receiving device is adapted to decode the timing between communications sent from said electronic device to said receiving device to determine said data values.   
     
     
         6 . The method of  claim 5 , further comprising:
 said encoded sequence of timing modulations being generated by a predefined function stored on said electronic device.   
     
     
         7 . The method of  claim 5 , further comprising:
 said modulation of said timing not being in response to a request for a delay.   
     
     
         8 . The method of  claim 5 , wherein:
 said data values are a unique signature of said electronic device, and said receiving device is adapted to decode said encoded sequence of timing modulations to determine said unique signature.