Patent ID: 7590240
Filing Date: 2009-09-15
Classification: H04L,H04N

Abstract:
1. A cryptographic method for rendering a conditional access system resistant to replay attacks comprising the steps of: generating a set of one or more keys usable for encryption or decryption, said generating caused by an authorization module controlling authorization of access to a plurality of transport streams, said authorization module on or in communication with a receiver among a plurality of receivers in communication with a headend; storing an encrypted transport stream transmitted from said headend, wherein said encrypted transport stream is further encrypted at said receiver, using one or more keys from said set of one or more keys usable for encryption or decryption, so that a doubly encrypted transport stream is stored on a storage medium on or accessible to said receiver; and decrypting said doubly encrypted transport stream by a decryption module on or in communication with said receiver using one or more keys from said set of one or more keys usable for encryption or decryption.