Conditional access system and smartcard allowing such access

Abstract: The invention relates to a conditional access system allowing a service provider to supply services only to those users who have acquired entitlements to these services. The services supplied by a service provider consist of an item scrambled by control words. In order to keep the control words secret, they are supplied after having been encrypted with an algorithm with key K. The entitlements of each user are forwarded in messages commonly denoted EMM (the abbreviation EMM standing for "Entitlement Management Messages"). According to the invention, the key K of the control words encryption algorithm is contained in the EMMs.

Description: The present invention relates to a conditional access system. A conditional access system allows a service provider to supply services only to those users who have acquired entitlements to these services. Such is the case, for example, for pay television systems. As is known to those skilled in the art (cf. eg. EP-A-0 506 435, EP-A- 0 461 029, EP-A- 0 375 539), the service supplied by a service provider consists of an item scrambled by control words. The scrambled item can only be descrambled, and hence read by the user, at the level of the entitlements allocated to this user. The scrambled item will hereafter be denoted IE(ECG), where ECG represents the unscrambled item (the abbreviation ECG standing for "Electronically Coded Good"). In order to descramble the item, the service provider supplies each user with the control words which served for scrambling the item. To keep the control words secret, they are supplied after having been enciphered with an algorithm with key K. The various enciphered control words are forwarded to the various users in messages commonly denoted ECM (the abbreviation ECM standing for "Entitlement Control Messages"). In order to grant access to his service only to authorized users alone, the service provider supplies a smartcard and a decoder to each of the users. The smartcard makes it possible, on the one hand, to validate and record the entitlements which the user has to the service delivered and, on the other hand, to decipher, with the aid of the key K, the enciphered control words. For this purpose, the smartcard therefore contains the key K of the algorithm which allowed encipherment of the control words. The decoder, for its part, makes it possible to descramble the scrambled item on the basis of the item consisting of the deciphered control words emanating from the smartcard. The entitlements of each user are forwarded in messages commonly denoted EMM (the abbreviation EMM standing for "Entitlement Management Messages"). According to the known art, the EMM dedicated to a user contains three main items: a first item giving the address of the user's card; a second item giving the description of the user's entitlements; a third item making it possible to validate the EMM and to verify that the user's entitlements contained in the EMM are indeed the entitlements reserved for the user. When a user's decoder recognizes the address of the card associated with him from among the various addresses dispensed by the service provider, the EMM corresponding to the recognized address is analysed. The analysis of the EMM is performed with the aid of an analysis algorithm which depends on the key K for enciphering the control words. The key K of the algorithm for enciphering the control words is contained in each user card. It follows that piracy in relation to a single card may lead to the ascertaining of the key K. Illicit user entitlements may then be created and recorded on all the other cards supplied by the service provider and containing the same key K. It is also possible to copy over onto these other cards the user entitlements contained in the pirated card. The service supplied by the provider is then no longer protected. In order to alleviate these drawbacks, it is known for the service provider to modify, at regular time intervals, the key of the algorithm for enciphering the control words. The service provider must then supply each user with a new card containing a new key K. This represents a drawback, especially in terms of costs, since the number of user cards is often very high. This number may in fact frequently reach several hundred thousand, or even several million. The invention does not have this drawback. The present invention relates to a novel conditional access system. More particularly, the invention relates to a novel definition of the EMMs as well as to a novel definition of the various functions contained in the user card. An object of the invention is a method for descrambling a service scrambled with the aid of a control word, said method comprising the step of : supplying a first message containing access conditions associated with a user and said control word enciphered using a first key; characterized by the steps of: supplying a second message containing entitlements associated with the user and said first key; validating and verifying said access conditions with respect to the entitlements using a second key, said second key being different from said first key and being individual to the user or group of users. Another object of the invention is a smart card providing a control word for descrambling a received scrambled service, said service being scrambled with the aid of a control word, said smart card comprising: a first circuit for receiving and validating a first message, said first message containing data corresponding to access conditions associated with a user to the service, and said control word associated with the scrambled service, said control word being ciphered using a first key; a second circuit for receiving and validating a second message, said second message containing data corresponding to entitlements associated with the user; a circuit for deciphering the control word in response to validations of said first and second messages characterized in that said second message further contains said first key and in that said first circuit is adapted to validate said first message using a third key, said third key being different from said first key; and said second circuit is adapted to validate the second message using a second key, wherein said second key and said first key are different. Yet another object of the invention is a conditional access system for selectively supplying services to a user, comprising: a service provider providing a service scrambled using a control word, first data containing the user's entitlements, and second data containing access conditions to the service and the control word scrambled using a first key; a decoder for descrambling the scrambled service; a smart card for receiving said first and second data, for deciphering the control word using the first key and for providing said control word to the decoder in response to the validation of said first and second data, characterized in that the first key (K) is contained in said first data (EMM) and in that the validation of the first data is carried out using a second key, different from the first key, said second key being individual to one of said user or group of users. An advantage of the invention is considerably to strengthen the protection of the services supplied by the provider. Piracy in relation to one or more user cards then offers practically no benefit to a would-be pirate any more. Other characteristics and advantages of the invention will emerge on reading a preferred embodiment given with reference to the appended figures in which: Figures 1a and 1b represent respectively a first and a second EMM format according to the prior art; Figure 2 represents the format of an ECM according to the prior art; Figure 3 represents the schematic of a user card according to the prior art; Figures 4a and 4b represent respectively a first EMM format and a second EMM format according to the invention; Figure 5 represents the schematic of a user card according to the invention. In all the figures, the same labels designate the same elements. Figure 1a represents a first EMM format according to the prior art. The EMM represented in Figure 1a is composed of a body Cla containing the three main items mentioned earlier, and of a header 4, the content of which (H1) gives, among other things, the type and size of the items contained in the body C1a. The body Cla consists of a first item 1 containing the address (AD) of the user's card, of a second item 2 containing a description of the user's entitlements, and of a third item 3 containing a cue HASH K . The cue HASH K depends on the key K and makes it possible to perform the analysis of the EMM mentioned earlier. Figure 1b represents a second EMM format according to the prior art. The EMM consists of a header 4 and of a body Clb. The body Clb consists of the items 5 and 6 containing respectively the address AD of the user card and the description of the user's entitlements enciphered with the algorithm with key K and relating to the address AD (E (user's entitlements ) K,AD ). According to this EMM format, the validation and verification of the entitlements contained in the EMM are performed by the operation of deciphering the enciphered entitlements. Figure 2 represents the format of an ECM according to the prior art. The ECM consists of a body C2 and of a header 7, the content (H2) of which gives, among other things, the type and size of the items contained in the body C2. The body C2 comprises, among other things, a first item 8 containing the set of access conditions associated with the service supplied by the service provider, a second item 9 containing a control word Cwi enciphered with the algorithm with key K (E(Cwi) K ) and a third item 10 containing a cue HASH K depending on the key K and making it possible to validate and verify the content of the access conditions. The control word Cwi represents the current control word, that is to say the control word making it possible to descramble that part of the program which is currently being read. As is known to those skilled in the art, generally the ECM which contains Cwi also contains a second control word. This second control word is the control word of the next descrambling period, that is to say the current control word of the ECM which has to follow the ECM which contains Cwi as current control word. This second control word has not been represented in Figure 2 so as not to fruitlessly encumber the drawing. As is known to those skilled in the art, the ECMs are forwarded by the service provider together with the scrambled item IE(ECG). The ECM format described in Figure 2 is merely one example of an ECM format. In particular, the order of the various blocks (7, 8, 9, 10) making up the ECM described in Figure 2 can be modified. Figure 3 represents the schematic of a user card according to the prior art. The user card 11 contains five main circuits: a circuit 12 for validating the user's entitlements; a circuit 13 for storing the user's validated entitlements; a circuit 14 for controlling the access; a circuit 15 for validating the ECMs; a circuit 27 for deciphering the enciphered control words. Regardless of the format of the EMM (cf. Figures 1a and 1b), the validation circuit 12 makes it possible to perform on the EMMs the operations mentioned earlier of user address recognition and analysis of the user's entitlements. For this purpose, the validation circuit 12 contains the key K of the encipherment algorithm. If the EMM is validated, the user's entitlements contained in the EMM are stored in the circuit 13 for storing the validated entitlements. The circuit 15 for validating the ECMs makes it possible to perform on the access conditions 8 contained in the ECMs, operations identical to those performed by the validation circuit 12 on the user's entitlements. The validation circuit 15 contains the key K. The deciphering circuit 27 makes it possible to decipher the control words. For this purpose, the deciphering circuit 27 also contains the key K of the algorithm for enciphering the control words. The access control circuit 14 compares the validated access conditions with the validated entitlements of the user. If the validated access conditions correspond to the validated entitlements of the user, a signal S, emanating from the access control circuit 14 and applied to the deciphering circuit 27, authorizes the deciphering of the enciphered control words E(Cwi) K originating from the validation circuit 15. In the contrary case, the signal S does not authorize deciphering. On completion of the various steps of the deciphering procedure, the deciphered control words Cwi are generated by the deciphering circuit 27 in such a way as to allow the descrambling of the scrambled item IE(ECG). As mentioned earlier, piracy in relation to a single user card, thereby allowing access to the key K, leads to destruction of the protection of the set of services supplied by the provider. Figure 4a represents a first EMM format according to the invention. The body C3a of the user's EMM is here composed of four main items: the items 1 and 2 constituting respectively the user's address and the description of the user's entitlements; an item 16 containing the key K of the algorithm for enciphering the control words; an item 17 containing a hash cue HASH KC , where KC is a different key from the key K. According to the preferred embodiment of the invention, the key KC is individual to each user and therefore different from one card to another. According to other embodiments, the key KC is individual to a group of user cards. Figure 4b represents a second EMM format according to the invention. The body C3b of the EMM comprises three main items: the items 18 and 19 constituting respectively the address AD of the user card and the description of the user's entitlements encrypted with the algorithm with key KC and relating to the address AD (E (user's entitlements) KC,AD ). The key KC differs from the key K. According to the preferred embodiment of the invention, the key KC is individual to each user card and therefore different from one card to another. According to other embodiments, the key KC is individual to a group of user cards. According to this EMM format, the validation and verification of the entitlements contained in the EMM are performed by the operation for deciphering the enciphered entitlements. an item 20 containing the key K for enciphering the control words enciphered with the algorithm with key KC (E(K) KC ). Advantageously, regardless of the format of the EMM, the key K for enciphering the control words is not contained in the user's card so long as the EMMs have not been transmitted to the user. Figure 5 represents the schematic of a user card according to the invention as well as the ECMs and the EMMs according to the invention. The user card 21 contains five main circuits: a circuit 22 for validating the user's entitlements; a circuit 23 for storing the user's validated entitlements; a circuit 24 for controlling the access; a circuit 25 for validating the ECMs; a circuit 26 for deciphering the enciphered control words. The EMM of Figure 5 is of the type represented in Figure 4a. The user card according to the invention can however operate with EMMs such as those represented in Figure 4b. According to the invention, the EMMs are analysed with the aid of a validation algorithm controlled by the key KC. The key KC is contained in the validation circuit 22. The ECMs are, for their part, analysed with the aid of a validation algorithm controlled by a key KSP. For this purpose, within the framework of the invention, the ECMs contain an item 28 containing a cue HASH KSP dependent on the key KSP. The key KSP is contained in the validation circuit 25. The key KSP differs from the key K. According to the preferred embodiment of the invention, the key KSP is individual to the service provider. The access control circuit 24 compares the validated access conditions with the validated entitlements of the user. If the validated access conditions correspond to the validated entitlements of the user, a signal Y(K) emanating from the access control circuit 24 and applied to the deciphering circuit 26 authorizes the deciphering of the control words. The signal Y(K) contains the key K so as to transmit the latter to the deciphering circuit 26. The enciphered control words E(Cwi) K are forwarded from the validation circuit 25 to the deciphering circuit 26. The deciphering of the control words is then performed. On completion of the various steps of the deciphering procedure, the deciphered control words Cwi are generated by the deciphering circuit 26 so as to allow the descrambling of the scrambled item. If the validated access conditions do not correspond to the validated entitlements of the user, the deciphering of the control words is not authorized. According to the invention, validation of a user's entitlements is controlled by a key KC individual to the user or to a group of users. It follows that piracy in relation to a user card can lead only to the jeopardizing of the pirated card itself as well as the user cards of the same group of users if the key KC is shared by one and the same group of users. Advantageously, all the other user cards remain protected. According to the above-described embodiment of the invention, the key K is the same for all the services supplied by the provider. The invention allows the implementation of embodiments for which the various services supplied by the provider are scrambled with control words enciphered with an algorithm whose enciphering key differs from one service to another or from one group of services to another. This is particularly advantageous in the case of systems commonly referred to as "off-line" systems for which the scrambled item IE(ECG) and the ECMs are contained on stand-alone data media such as, for example, CDs ("Compact Discs"), DVDs ("Digital Video Discs") or else CD-ROMs ("Compact-Disc Read Only Memories"). Advantageously, piracy in relation to a user card is then even more devoid of benefit than in the case in which all the services of the provider are scrambled with control words enciphered with the same key K. Thus, piracy in relation to a user card then leads to only very partial access in respect of the various services supplied by the provider. Scrambling various services, such as for example films, with an algorithm whose keys differ from one service to another cannot be envisaged within the framework of prior art conditional access systems for which the key of the algorithm for enciphering the control words of a service and the key associated with the algorithm for validating the user's entitlements are identical. Thus, the service provider would then have to supply each user with a card individual to each service or group of services. Such a proliferation of cards is unrealistic, both for practical reasons and for cost reasons. Generally, regardless of the embodiment of the invention, that is to say whether the various services supplied by the provider are associated with a single key for enciphering the control words K or with different enciphering keys K j (j = 1, 2, ..., m), the invention relates equally well to conditional access systems of the "off-line" type as to conditional access systems of the "on-line" type for which the scrambled item IE(ECG) is an item consisting of a signal dispensed simultaneously to the various customers of the service provider from a single source.

Claims: Method for descrambling a service scrambled with the aid of a control word (Cwi), said method comprising the step of: supplying a first message (ECM) containing access conditions associated with a user and said control word enciphered using a first key (K); characterized by the steps of: supplying a second message (EMM) containing entitlements associated with the user and said first key (K); validating and verifying said access conditions with respect to the entitlements using a second key (KC), said second key (KC) being different from said first key (K) and being individual to the user or group of users. Smart card (21) providing a control word (CWi) for descrambling a received scrambled service, said service being scrambled with the aid of a control word, said smart card comprising: a first circuit (25) for receiving and validating a first message (ECM), said first message containing data corresponding to access conditions associated with a user to the service, and said control word associated with the scrambled service, said control word being ciphered using a first key (K); a second circuit (22) for receiving and validating a second message (EMM), said second message containing data corresponding to entitlements associated with the user; a circuit (26) for deciphering the control word in response to validations of said first and second messages, characterized in that said second message further contains said first key (K) and in that : said first circuit is adapted to validate said first message (ECM) using a third key (KSP), said third key (KSP) being different from said first key (K); and said second circuit is adapted to validate the second message (EMM) using a second key (KC), wherein said second key (KC) and said first key (K) are different. Smart card according to claim 2, wherein the second key (KC) is individual to one of an individual smart card or a group of smart cards. Smart card according to one of the claims 2 or 3, wherein the third key (KSP) is individual to the provider of the service. Conditional access system for selectively supplying services to a user, comprising: a service provider providing a service scrambled using a control word (CWi), first data (EMM) containing the user's entitlements, and second data (ECM) containing access conditions to the service and the control word scrambled using a first key (K); a decoder for descrambling the scrambled service; a smart card for receiving said first (EMM) and second (ECM) data, for deciphering the control word using the first key (K) and for providing said control word to the decoder in response to the validation of said first and second data, characterized in that the first key (K) is contained in said first data (EMM) and in that the validation of the first data is carried out using a second key (KC), different from the first key (K), said second key (KC) being individual to one of said user or group of users. System according to Claim 5, characterized in that the system is of the "on-line" type. System according to Claim 5, characterized in that the system is of the "off-line" type.

Inventors: CAMPINOS ARNALDO, FISCHER JEAN-BERNARD, CAMPINOS, ARNALDO, FISCHER, JEAN-BERNARD
Applicants: THOMSON MULTIMEDIA SA, THOMSON MULTIMEDIA
Application year: 1997
Main classification: H04N7
IPC codes: H04N7, H04L9, G07F7