Electrical computers and digital processing systems: support – Multiple computer communication using cryptography
Reexamination Certificate
1999-09-21
2002-05-21
Peeso, Thomas R. (Department: 2767)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
C713S168000, C713S171000, C713S180000, C705S051000, C606S079000
Reexamination Certificate
active
06393562
ABSTRACT:
The present invention relates to a method of and apparatus for preventing fraudulent access in a conditional access system linked to a subscriber's receiver/decoder. The technique may be used in the field of data communication where transmitted encrypted data is received and decrypted by, for example, an authorised subscriber's receivcer/decoder.
The term “receiver/decoder” used herein may connote a receiver for receiving either encoded or non-encoded signals, for example, television and/or radio signals. The term may also connote a decoder for decoding received signals. Embodiments of such receiver/decoders may include a decoder integral with the receiver for decoding the received signals, for example, in a “set-top box” or such a decoder functioning in combination with a physically separate receiver.
The receiver/decoder is stated above as being “linked to” the conditional access system, which includes the possibilities that the receiver/decoder either forms part of or is separate from the conditional access system.
In particular, but not exclusively, the invention may be used in a mass-market broadcast system having some or all of the following preferred features. It may be an information broadcast system, preferably a radio and/or television broadcast system; it may be a satellite system (although it could be applicable to cable or terrestrial transmission); it may be a digital system, preferably using the MPEG, more preferably the MPEG-2, compression system for data/signal transmission; it may afford the possibility of interactivity; and it may use smartcards. Again, the invention may be used in conjunction with a digital audio visual transmission system. In the context of the present invention the term “digital audio visual transmission system” refers to all transmission systems for transmitting or broadcasting primarily audio visual or multimedia digital data. Whilst the present invention is particularly applicable to a broadcast digital television system, the present invention may equally be used in filtering data sent by a fixed telecommunications network for multimedia internet applications etc. As used herein, the term “smartcard” includes, but not exclusively so, any chip-based card device possessing, for example, microprocessor and/or memory storage. Also included in this term are chip devices having alternative physical forms, for example key-shaped devices such as are often used in TV decoder systems.
The term MPEG refers to the data transmission standards developed by the International Standards Organisation working group “Motion Pictures Expert Group” and in particular but not exclusively the MPEG-2 standard developed for digital television applications and set out in the documents ISO 13818-1, ISO 13818-2, ISO 13818-3 and ISO 13818-4. In the context of the present patent application, the term includes all variants, modifications or developments of MPEG formats applicable to the field of digital data transmission.
An aim of the invention is to provide a data communication method, transmitter and receiver/decoder which can be used to provide data to, for example, subscribers or other buyers of reception rights on a secure basis.
In existing broadcasting systems, a smartcard is used by a subscriber to obtain the reception right and it has been found pursuant to the present invention that there is a problem of preventing misuse of the card to defraud the owner of the rights.
For example, in a known MPEG television subscriber system, the rights of different subscribers or groups of subscribers can be checked centrally, for instance on a monthly basis, and an authorising message can be subsequently sent, from a central station, to each subscriber or group of subscribers to authorise (or to block) use of the rights. Suitably, the authorising message is simply a “1” or “0” located in different bitmap positions which have been assigned to respective subscriber identities for the month, only the presence of a “1” authorising use of the right for the subscriber at the respective bitmap position, a “0” denying use of that right. The following problem with this system has been identified pursuant to the present invention. If, for example, the original subscriber ceases payment for the right, after a lapse of time, the system will no longer identify the original subscriber at the previously assigned bitmap position and this position may then be newly assigned to the identity of a “new” subscriber. If the new subscriber has paid for and hence been authorised to use the right, there will be a “1” again in the bitmap position. If, at the “original” subscriber's receiver/decoder, the decoder is disconnected before the next authorising message can update a linked conditional access system (associated with the “original subscriber”) and if the decoder is later reconnected (or if a clock is re-set), the “original” subscriber will then be mistaken for the “new” subscriber who has been authorised to use the right and the “original” subscriber will thereby fraudulently obtain the right.
The present invention seeks to solve this problem and other similar or related problems where subscriber rights may be granted over periods of time which may depend typically, but not exclusively, on settling accounts. For example, rights may be granted for considerations other than payment where different subscribers can be authorised to use a system to gain access to a secure area, or to secure information, or to some other secure service.
In the context of the present invention the terms “EMM” and “ECM” are utilised.
An Entitlement Management Message or EMM is a message designated to one subscriber or to a group of subscribers. It is usually generated by a subscription authorisation system and is multiplexed with an MPEG-2 stream. It is usually encrypted with a so-called “management” key for example for group use. Hence it may be encrypted by a key common to all subscribers in a group of subscribers.
An Entitlement Control Message or ECM is a message sent in relation with one scrambled program. The ECM enables a user to descramble a control word to obtain the right to descramble a television (or similar) programme. A key (termed herein an “ECM key”) is passed through the EMM to a subscriber because the smartcard used by the subscriber needs the ECM key to decipher the ECM. The deciphered ECM is used to descramble the control word and hence to descramble the program.
According to one aspect of the present invention there is provided a method of preventing fraudulent access in a conditional access system which is linked to a subscriber's receiver/decoder for receiving an entitlement management message (EMM) for a group of subscribers to enable said system to provide access for a respective subscriber, the method including the step of:
programming the receiver/decoder only to accept a current EMM of a current calendar period if it has received at least a previous EMM of a previous calendar period.
Hence the problem of preventing fraudulent access can be solved.
The method preferably further comprises the steps of:
transmitting redundant date information with the current EMM; and receiving the current EMM and using redundant date information to check whether said previous EMM has been received.
In a first preferred embodiment, each EMM contains rights date information concerning a current right of access and corresponding check date information concerning a previous right of access, such check date information constituting the redundant date information. This can be a particularly efficient way of putting the invention into practice.
In a second preferred embodiment, the redundant date information is an ECM key of a previous calendar period. This is a convenient alternative way of representing such information.
The subscriber rights may change on a regularly timed basis and the redundant date information may concern an immediately preceding period.
In one illustrative example of the invention, wherein the receiver/decoder is one of a plurality of receiver/decoders in a broadcast s
Jack Todd
Peeso Thomas R.
Sterne Kessler Goldstein & Fox P.L.L.C.
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