Abstract: A secure method for transmitting a control word between a server and a plurality of processing entities so as to respectively produce and utilize the control word. Preferably such a method is applied to the field of conditional access methods and systems for preventing the fraudulent use of compromised decryption keys resulting from a coalition of pirate hackers.

Abstract: The invention relates to a method and a system for conditional access making it possible to prevent the fraudulent use of a subscriber electronic device (1a, 1b, 1m) and to thus effectively combat the fraudulent making available of protected contents. The invention further relates to the adaptation of such a device as well as to a method allowing the revocation of the latter if it is deemed to be illicitly exploited or its possible reinstatement.

Abstract: The invention relates to a method for preventing the fraudulent use of an electronic device and thus for effectively combating the fraudulent dissemination of protected content. The invention further relates to such a device as well as to a method enabling permanent revocation thereof if the device is considered to be unlawfully used or optional reinstatement of the device.

Abstract: The invention relates to a method and a system for conditional access making it possible to prevent the fraudulent use of a subscriber electronic device (1a, 1b, 1m) and to thus effectively combat the fraudulent making available of protected contents. The invention further relates to the adaptation of such a device as well as to a method allowing the revocation of the latter if it is deemed to be illicitly exploited or its possible reinstatement.

Abstract: A secure method for transmitting a control word between a server and a plurality of processing entities so as to respectively produce and utilize the control word. Preferably such a method is applied to the field of conditional access methods and systems for preventing the fraudulent use of compromised decryption keys resulting from a coalition of pirate hackers.

Abstract: The cryptographic scheme subdivides time into periods with an index j=0, 1, 2, etc. A public key indicates elements u and v of a first cyclic group G1 of prime order p and, for each period j, an integer sj between 0 and p?1 and elements g1,j of the group G1 and g2,j, wj and hj of another cyclic group G2 of order p. The private key of a member of the group indicates an integer xi between 0 and p?1 and, for each period j, an element Ai,j of the group G1 such that Ai,n=[Ai,n-1/g1,n-1]1/(xi?sn) for 1?n?j. To sign a message during a period j?0, the member selects two integers ? and ? between 0 and p?1, calculates T1=u?, T2=Ai,j·v?, S1=g2,j? and S2=e(Ai,j, hj)? where e(., .) is a bilinear map of G1×G2 onto GT, and determines according to the message the data that justify the fact that the elements T1, T2, S1 and S2 are correctly formed with knowledge of the private key of the member for the period with index j.

Abstract: The invention relates to a method for preventing the fraudulent use of an electronic device and thus for effectively combating the fraudulent dissemination of protected content. The invention further relates to such a device as well as to a method enabling permanent revocation thereof if the device is considered to be unlawfully used or optional reinstatement of the device.

Abstract: A first entity (1) includes a secret encryption key (g1, ?) of an encryption diagram which can accept a plurality of encryption keys. A plurality of decoders have respective encryption keys, each incorporating a respective key index. The method comprises an encryption operation, wherein a value is taken as a variable element (s) and a ciphertext (C?) is calculated from the data to be transmitted (K) and at least from the value taken as the variable element and the secret encryption key. An operation for revoking a decryption key is integrated into an encryption operation performed with a value of the variable element (s) based on the index key (x?) of one of the decryption keys, which will be used during an operation for tracking illegitimate decoders.

Abstract: The cryptographic scheme subdivides time into periods with an index j=0, 1, 2, etc. A public key indicates elements u and v of a first cyclic group G1 of prime order p and, for each period j, an integer sj between 0 and p?1 and elements g1,j of the group G1 and g2,j, wj and hj of another cyclic group G2 of order p. The private key of a member of the group indicates an integer xi between 0 and p?1 and, for each period j, an element Ai,j of the group G1 such that Ai,n=[Ai,n-1/g1,n-1]1/(xi?sn) for 1?n?j. To sign a message during a period j?0, the member selects two integers ? and ? between 0 and p?1, calculates T1=u?, T2=Ai,j·v?, S1=g2,j? and S2=e(Ai,j, hj)? where e(., .) is a bilinear map of G1×G2 onto GT, and determines according to the message the data that justify the fact that the elements T1, T2, S1 and S2 are correctly formed with knowledge of the private key of the member for the period with index j.

Abstract: A public key (PK) dependent on a secret key is accessible to a sender entity (2) and to recipient entities. A private key that can be associated with a recipient entity depends on the secret key and on an identity parameter (IDj) of said entity. Encryption of a message (M) intended for a set of s recipient entities (s>1) comprises generating a symmetrical encryption key (K) and an associated cryptogram (Hdr), as a function of the public key, from the identity parameters of the s recipient entities and a number chosen by the sender entity. The cryptogram allows access to the associated encryption key by combination with the public key, the identity parameters of the s recipient entities and the private key of an identified recipient entity of the set. The message is encrypted in the sender entity with the generated encryption key and is broadcast in this encrypted form, accompanied by said cryptogram.

Abstract: A first entity (1) includes a secret encryption key (g1, ?) of an encryption diagram which can accept a plurality of encryption keys. A plurality of decoders have respective encryption keys, each incorporating a respective key index. The method comprises an encryption operation, wherein a value is taken as a variable element (s) and a ciphertext (C?) is calculated from the data to be transmitted (K) and at least from the value taken as the variable element and the secret encryption key. An operation for revoking a decryption key is integrated into an encryption operation performed with a value of the variable element (s) based on the index key (x?) of one of the decryption keys, which will be used during an operation for tracking illegitimate decoders.