Method for secure transfer of messages

Abstract

The present invention may be deployed in a system for broadcast of conditional access content where it is desirable to detect and take action against receiver equipment which has been used in a control word sharing activity. By requiring that receiver equipment used in the system send a message to a broadcaster of conditional access content at a precise time, the invention provides a method for the server to detect receiver equipment involved in control word sharing activity and to inhibit that receiver's ability to further access the content.

1 . A method for securely receiving a key for decrypting content in a receiver for receiving and decrypting content, the receiver comprising a security module comprising a slave time counter for keeping track of a slave time and being configured to receive or calculate a value of a predetermined calling time, the method comprising:
 providing, for authentication at a device external to the receiver, a verification message when a value of the slave time counter is reached, wherein said value of the slave time counter, when subject to a predetermined function, is equal to the value of the predetermined calling time;   receiving the key for decrypting the content only if the verification message is authenticated, by a party external to the receiver, as having been provided at a time corresponding, within a predetermined calling time window, to the predetermined calling time.   
     
     
         2 . The method according to  claim 1 , wherein the verification message is sent to the device external to the receiver when the security module detects that the value of the slave time counter is equal to the value of the predetermined calling time. 
     
     
         3 . The method according to clam  1 , wherein the predetermined calling time corresponds to the receiver in that it allows for the receiver to be positively identified. 
     
     
         4 . The method according to  claim 1 , wherein the external party authenticates the sent message, said authentication involving consulting a reference time counter, the reference time counter having been synchronized with the slave time counter. 
     
     
         5 . The method according to  claim 1 , wherein the verification message cannot be authenticated as having been provided at a time corresponding to within a predetermined calling time window of the predetermined calling time, the method further comprising:
 receiving a key message, said key message comprising inhibit key information to disallow the decryption of the content at least for a predetermined exclusion period;   extracting, by the security module, the inhibit key information from the key message.   
     
     
         6 . The method according to  claim 5 , wherein the predetermined exclusion period varies as a function of a number of times a verification message cannot be authenticated as having been provided at a time corresponding to within a predetermined calling time window of the predetermined calling time. 
     
     
         7 . In a server, a method for providing a key, the server comprising a reference time counter for keeping track of a reference time, the method comprising:
 receiving, at a calling time according to the reference time counter, a verification message, the verification message comprising an identifier;   providing the key only if the calling time is equal, within a predetermined calling time window, to a predetermined calling time corresponding to the identifier.   
     
     
         8 . A method for securely transferring a key from a server to a receiver, the server comprising a reference time counter for keeping track of a reference time, the receiver comprising a security module and a slave time counter for keeping track of a slave time and being configured to receive or calculate a value of a predetermined calling time, the method comprising:
 sending a verification message from the security module to the server when a value of the slave time counter is reached, wherein said value of the slave time counter, when subject to a predetermined function, is equal to the value of the predetermined calling time;   defining, by the server, a reception time for receiving the verification message, according to a value of the reference time counter when the verification message is received;   transferring the key to the receiver only if the reception time is equal, to within the predetermined calling time window, to the predetermined calling time.   
     
     
         9 . The method according to  claim 8 , wherein the sending of the verification message is done when the security module detects that the value of the slave time counter is equal to the value of the predetermined calling time. 
     
     
         10 . The method according to clam  8 , wherein the predetermined calling time corresponds to the receiver in that it allows for the receiver to be positively identified. 
     
     
         11 . The method according to  claim 8 , wherein the authentication involves consulting a reference time counter, the reference time counter having been synchronized with the slave time counter. 
     
     
         12 . The method according to  claim 8 , wherein the verification message cannot be authenticated as having been provided at a time corresponding to within a predetermined calling time window of the predetermined calling time, the method further comprising:
 receiving a key message, said key message comprising inhibit key information to disallow the decryption of the content at least for a predetermined exclusion period;   extracting, by the security module, the inhibit key information from the key message.   
     
     
         13 . The method according to  claim 12 , wherein the predetermined exclusion period varies as a function of a number of times a verification message cannot be authenticated as having been provided at a time corresponding to within a predetermined calling time window of the predetermined calling time.