Patent EA-004194-B1 (EA)
Title: Method and system for transmission of decrypting information
Inventor: KUDELSKI ANDRE
IPC: H04N21/4623
Filed: 2001-01-24
Abstract: 1. A multi-channel transmission system of encrypted information for Pay TV, comprising a management centre and at least one subscriber unit, the management centre transmitting encrypted signals and mono-channel authorization messages (ECM) encrypted for each channel, characterized in that it includes multi-channel authorization messages (MECM) common to a group of channels, these messages being combined with the mono-channel authorization messages (ECM) for the channel currently received in order to decrypt the same. 2. A multi-channel transmission system according to claim 1, characterized in that the multi-channel authorization messages (MECM) are encrypted by an algorithm different to the algorithm used to encrypt the mono-channel authorization messages (ECM). 3. A multi-channel transmission system according to claims 1 and 2, characterized in that the multi-channel authorization messages (MECM) are modified according to a period different to the period of the mono-channel authorization messages (ECM). 4. A multi-channel transmission system according to claims 1 to 3, characterized in that the information contained in the multi-channel authorization messages (MECM) is combined with the information contained in the mono-channel authorization messages (ECM) by operations such as addition, subtraction, or exclusive (XOR), multiplication or coding. 5. A multi-channel transmission system according to claims 1 to 3, characterized in that the subscriber unit includes a cryptographic unit (CU) determining control-words (CW) from mono-channel authorization messages (ECM), allowing the subscriber unit to decrypt the encrypted signals, the content of the multi-channel authorization messages (MECM) being combined with the parameters (P1, P2... Pn) of cryptographic calculation of the cryptographic unit (CU). 6. A transmission method of multi-channel encrypted signals for Pay-TV consisting of: -transmitting multi-channel encrypted signals to the subscriber unit, -transmitting mono-channel authorization messages (ECM) encrypted for each channel, -decrypting the authorization messages (ECM) for the channel currently received by a cryptographic unit (CU), the decrypted information representing control-words (CW) necessary to decrypt the signals suitable for the channel currently received, characterized in that it consists in: -transmitting multi-channel authorization messages (MECM) common to a group of channels, -decrypting these multi-channel authorization messages (MECM) and combining the decrypted information with the information necessary for the obtainment of the control-words (CW). 7. A transmission method of multi-channel encrypted signals according to claim 6, characterized in that the combination is done on the entry parameters (P1, P2,.. Pn) of the cryptographic unit (CU). 8. A transmission method of multi-channel encrypted signals according to claim 6, characterized in that the combination is done on the results obtained by the cryptographic unit (CU). 9. A transmission method of multi-channel encrypted signals according to claims 6 to 8, characterized in that it consists in modifying the multi-channel authorization messages (MECM) according to a period different to the modification period of the mono-channel authorization messages (ECM). 10. A transmission method of multi-channel encrypted signals according to claims 6 to 9, characterized in that it consists in encrypting the multi-channel authorization messages (MECM) according to an algorithm different to the algorithm used to encrypt the mono-channel authorization messages (ECM).