Cryptography – Key management – Having particular key generator
Patent
1990-10-19
1992-07-28
Swann, Tod
Cryptography
Key management
Having particular key generator
380 21, 380 43, 380 50, 380 48, H04N 7167
Patent
active
051346567
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pay-television system or device using a memory card associated with a decoder.
In pay-television systems or devices, the video and audio signal designed to be broadcast is first scrambled according to an ordinary process and is then transmitted by antenna, satellite, or cable. At the end, the signal is received and unscrambled at the home of each subscriber by means of a specific device usually called "decoder".
In advanced pay-television systems known at present, the decoder mainly comprises an electronic device designed to unscramble or decode the video picture. To this decoder is associated a memory card or a card including an integrated circuit, mainly designed to control the access to broadcasts and to manage the credit required to buy those broadcasts or emissions.
In such pay-television systems an arbitrary word or code is emitted during the broadcast; this word is designed for initializing a pseudo-random generator determining a code table. This code table is used for scrambling the video signal. This initialization word is enciphered by a predetermined enciphering key, and the enciphered initialization word is broadcasted with the video signal. In the subscriber's decoder, the enciphered initialization word is deciphered by the same key so as to be reproduced in clear and to be used as an initialization word for a pseudo-random generator which is identical to that of the emission and consequently generates an identical code table. Then, this code table is used for unscrambling the video signal which can then be sent to the television set.
In the following, the "broadcasting company" is to be meant as a person or company having the rights to emit scrambled broadcast (also called coded broadcast) and who rents to its subscribers a specific decoder or a specific card usable with a non specific decoder, the latter being liable to be used to decode the broadcasts issued by other broadcasting companies. In the following, "main card" is to be meant as a card or a device designed to encipher the initialization word by using a specific key of a broadcasting company and "subscriber card" is to be meant as a card or equivalent device rented to the subscriber.
The memory card has numerous advantages among which the advantage of being simultaneously usable by several broadcasting companies. However, this memory card may exhibit some drawbacks, such as piracy, that will be explained hereinafter.
In the case of a memory card designed to be used by several broadcasting companies, a broadcasting company A can write on each card its keys and rights and another broadcasting company B can independently write on the same cards or other cards its keys and rights. In this case, it may happen that a person well informed gets a subscriber's card and uses it for deciphering the initialization word that has been sent enciphered with the video signal emitted by the broadcasting company A. Then, a main card is used for enciphering this initialization word according to the other key used by another broadcasting company, e.g. by the broadcasting company B. Thus, said person sends to his subscribers the broadcasts from the broadcasting company A transferred into the card network of broadcasting company B.
The aim of the invention is to remedy the hereinabove mentioned drawback.
The invention relates to a pay-television system using a memory card associated with a decoder.
According to a characteristic of the invention, on the emission side, a digital generator supplies a random code which is sent to the input of a main card that enciphers this code by using a predetermined key. The so enciphered code is emitted with the video signal. A first device receives at the inputs, on the one hand, the random code and, on the other hand, the code enciphered by the main card and carries out a determined digit combination of those two codes, these combination forming the initialization word of a pseudo-random generator which is intended to supply a code table designed to scramble the video signal. On the r
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patent: 4771458 (1988-09-01), Citta et al.
patent: 4890324 (1989-12-01), Jansen
patent: 5016275 (1991-05-01), Smith
Kudelski S.A. Fabrique d'Enregistruers Nagra
Swann Tod
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