Patent ID: 8666072
Filing Date: 2014-03-04
Classification: H04L,H04N

Abstract:
1. A method of receiving a multimedia signal scrambled using a control word, said method comprising: receiving a scrambled multimedia signal by a receiver device, the receiver device comprising a first cryptographic entity and P second cryptographic entities, the first cryptographic entity and one of the P second cryptographic entities being connected within a receiver device for receiving the scrambled multimedia signal, the first cryptographic entity being either a security processor, or a descrambler unit; encrypting the control word or the multimedia signal with the first cryptographic entity using a first cryptographic entity session key and sending the encrypted control word or the encrypted multimedia signal from the first cryptographic entity to the second cryptographic entity; and decrypting the encrypted control word or the encrypted multimedia signal sent from the first cryptographic entity, by the second cryptographic entity using a second cryptographic session key, the first session cryptographic session key and the second cryptographic session keys being obtained by diversifying root keys using a same identifier known to both of the first cryptographic and the second cryptographic entity, wherein only the second cryptographic entities from a group of N second cryptographic entities chosen in the larger set of P second cryptographic entities use a session key obtained by diversifying a common root key identical to the root key used to obtain the first cryptographic entity session key, N being a number of second cryptographic entities strictly less than P and strictly greater than 1; and wherein if the first cryptographic entity is a security processor, then the second cryptographic entity is a descrambler unit, or if the first cryptographic entity is a descrambler unit, then the second cryptographic entity is a scrambled multimedia signal receiver.