Patent ID: 8520856
Filing Date: 2013-08-27
Classification: H04H,H04L,H04N

Abstract:
1. A method for controlling a validity of a decryption key in a broadcast system comprising a server system and a data source arranged to broadcast encrypted data to a client device, the server system being arranged to provide the decryption key to a client device, the method comprising: generating in the server system a first timestamp indicating a start time from which the decryption key is valid and a second timestamp indicating an end time until which the decryption key is valid; transmitting a first message comprising the first timestamp and the second timestamp from the server system to the client device; generating in the server system a third timestamp indicating a time to be compared with the first timestamp and the second timestamp; and transmitting a second message comprising the third timestamp from the server system to the client device, wherein the first timestamp and the second timestamp are defined on a first timescale and the third timestamp is defined on a second timescale, and wherein the first timescale is defined as the second timescale multiplied by a first factor larger than one so that the third timestamp advances slower in time relative to the first timescale during an event associated with the first timestamp and the second timestamp, wherein the first, second and third timestamp enable the client device to decrypt the encrypted data with the decryption key, in response to determining that the third timestamp is greater than or equal to the first timestamp and less than or equal to the second timestamp, and further comprising: in the server system, multiplying the third timestamp by a second factor larger than zero to obtain the third timestamp to be transmitted to the client device.