FR2855689A1 - ACCESS CONTROL MODULE WITH SECURED INTERFERENCE KEY - Google Patents

Abstract

The present invention relates to an AC access control module comprising, on the one hand, a MIC control unit provided with a descrambling member operating by means of a descrambling key and, on the other hand, a storage member MEM for memorizing. This descrambling key. In addition, the MIC descrambling and MEM storage members are connected by means of a transmission bus BM within an integrated control circuit CC.

Description

Secure access key access control module

  The present invention relates to a secure access key access control module.

  The field of the invention is that of services with restricted access which can be obtained by any communication network, in particular a cable network or a radio network. Access is restricted in the sense that it is subject to the provision of a secret code which is generally obtained during the subscription of a subscription allowing to benefit from these services.

  By way of example, a digital pay television decoder allows a video sequence which has been scrambled before being broadcast on the network to be scrambled by means of a secret scrambling code.

  Such a decoder essentially comprises a reception module and an access control module. The reception module comprises means for demodulating the signal received from the network in order to transmit it to the access control module 15, this demodulated signal here being the scrambled video sequence. It further comprises means for receiving from the access control module the unscrambled video sequence in order to decode it to provide an appropriate signal to a television set.

  The function of the access control module is therefore to unscramble the video sequence broadcast on the network. This module includes a descrambling member intended to perform this descrambling by means of a descrambling key. It further comprises a storage device for storing this key which must remain confidential. These two bodies which appear on two separate components are connected by a single bond which is not protected. In fact, very often the storage device appears on a smart card issued when subscribing to the services concerned.

  It is quite easy to spy on the data passing over this simple link in order to recover the unscrambling key. Likewise, it is relatively easy to replace the smart card with equipment making it possible to emulate its operation, so that the access control module can unscramble the sequence broadcast on the network.

  This is against the interests of the provider of the restricted access service.

  A first object of the present invention is thus to strengthen the protection of confidential information recorded in the storage device.

  According to the invention, the access control module comprises on the one hand a control unit provided with a descrambling member operating by means of a descrambling key and a storage member for memorizing this descrambling key; in addition, the descrambling and storage devices are connected via a transmission bus within an integrated control circuit.

  Advantageously, the control circuit comprises securing means for securing this transmission bus.

  Optionally, the security means incorporate encryption means.

  The above-mentioned restricted services are often subject to a flat-rate billing. However, certain individualized services are billed individually. One thinks for example of the system known under the English name "Pay Per View" which makes it possible to view a determined film subject to the prior payment of a stipulated amount.

  Access to the individualized service is therefore doubly restricted, on the one hand by selectively distributing the unscrambling key and on the other hand by checking that the stipulated amount has been paid.

  A second object of the present invention is therefore to facilitate the management of this double restriction.

  According to the invention, the control circuit is further provided with a transfer connection intended for the transfer of information with a transfer unit via a transfer interface.

  Thus, the payment can be controlled by using this transfer unit.

  Preferably, this transfer interface appearing in the control circuit, the latter further comprises a transfer bus for connecting the transfer interface to the control unit.

  In addition, the control circuit includes securing means for securing this transfer bus.

  Optionally, these securing means incorporate encryption means.

  According to a preferred embodiment, the access control module 35 further comprises, connected to this transfer interface, a transfer unit.

  This transfer unit will often be a smart card connector.

  Thus, the connector, which according to the state of the art was used for the supply of the unscrambling key, can be used here as a payment terminal. It would indeed be very bulky and very inconvenient to have two card connectors in a single module. There would even be a not insignificant risk that the service user, confusing the two access controls, would introduce the card containing the unscrambling key into the connector provided for payment and vice versa.

  The present invention will now appear in more detail in the context of the description which follows of embodiments given by way of illustration 10 with reference to the single appended figure which represents a diagram of a digital decoder suitable for setting up. work of the invention.

  The invention is presented in relation to a digital video broadcasting network with which a restricted access system is associated. Thus, prior to its broadcasting on the network, a video sequence is the subject of interference which has the effect of rendering the images, the sound and possibly the data it contains unintelligible. In addition, conditional access messages that include the parameters necessary for descrambling are transmitted with the scrambled video sequence.

  For example, two types of conditional access message are used, a command message and an operation message which are both generated from three data, namely a control word, a service key. (which can be common to several users) and a user key (which is specific to a specific user).

  The control message is an encrypted function of the control word using the service key while the operation message is an encrypted function of the service key using the user key.

  On receipt, the service key is obtained by decrypting the operating message using the user key stored in a smart card.

  This service key is then used to decrypt the command message in order to retrieve the control word. It is this control word which makes it possible to initialize the descrambling of the scrambled video sequence.

  It thus appears that the user key is the unscrambling key, a unique key without which unscrambling is impossible.

  Control and operating messages are periodically broadcast over the network.

  We therefore consider here a wireless network although the invention can be applied to any type of network. More specifically, we place ourselves within the framework of the European project "DVB" (for the English expression "Digital Video Broadcasting").

  In this context, with reference to the figure, it is a digital decoder which ensures the reception of the scrambled video sequence and performs the descrambling.

  This decoder essentially comprises a reception module RD and an access control module AC interconnected by means of a common interface C1 ("Common Interface" in English, in the European project 10 "DVB"). It will be noted here that the invention would also apply if the reception module and the access control module were not delimited by this common interface which was developed to facilitate the interchangeability of this latter module.

  The reception module RD comprises a tuner TU for bringing the carrier received on the antenna IN back to baseband. It then comprises a demodulator which demodulates the signal in baseband, thus restoring the scrambled video sequence SS which it transmits to the access control module AC via the common interface C1. It also comprises a demultiplexer MUX which receives the sequence unscrambled video DS of the access control module AC via the common interface C1 to isolate the video signal, the audio signal and possibly the data signal D present in this unscrambled sequence DS.

  A VDEC video decoder decodes the video signal supplied by the MUX demultiplexer, a signal coded here according to the "MPEG" standard (for the English expression "Motion Pictures Expert Group"), in order to deliver a P 25 image signal directly interpretable by a television set. Similarly, an ADEC audio decoder decodes the audio signal supplied by the MUX demultiplexer in order to deliver a sound signal S directly interpretable by this television set.

  The access control module AC first comprises a control circuit CC which is an integrated circuit.

  This CC control circuit comprises a control unit, a microprocessor MIC for example. The primary function of the control unit MIC is that of a descrambling device which descrambles the scrambled sequence SS received from the reception module DR, this in order to restore the scrambled sequence DS to it. The control circuit also comprises a memory storage device MEM in which the user key or unscrambling key necessary for unscrambling the scrambled sequence SS is recorded. This MEM storage member is for example located in a non-volatile memory of the "flash" type.

  The descrambling devices MIC and storage MEM are connected by a transmission bus BM which is buried in the control circuit CC, so that the information conveyed by this transmission bus BM is much better protected than when it was traveling on a simple external link to the control circuit.

  However, the BM transmission bus is not completely secure.

  It is always possible to come and read its content from outside the CC control circuit. The invention therefore proposes to protect this bus and an advantageous solution consists in using encryption means. Preferably, these encryption means are implemented by the control unit MIC which is thus provided with a second function.

  In fact, the data is encrypted before being recorded in the memory storage device MEM and they are decrypted when they are read in this storage device before being processed.

  To do this, we will prefer a private key algorithm because it requires much shorter computation times than a public key algorithm.

  By way of example, the following algorithms will be retained: - AES (abbreviation of the English expression "Advanced Encryption Standard"), working on 128-bit words and offering, at present, maximum security, - DES (abbreviation of the English expression "Data Encryption Standard"), working on 64-bit words, known for its universality in the least demanding systems in terms of security, - 3DES (abbreviation of the English expression "Triple Data Encryption Standard "), or - XDES (abbreviation of the English expression" Extended Data Encryption Standard "), the latter two algorithms being renowned for systems that are more demanding in terms of security while ensuring high encryption rates at low cost. The encryption key used by the algorithm can be stored in an insecure area of the control circuit CC, access to which is done without encryption, preferably in a programmable register only once called "OTP" (for the expression English "One Time Programmable").

  In fact, if the microprocessor MIC detects an operation not provided for on the transmission bus BM, it suffices for it to erase this encryption key immediately, which is a very rapid operation.

  It will also be noted that the storage device MEM can also be used for other purposes by the control circuit CC.

  The access control module AC secondly comprises a transfer unit such as a smart card connector LC which can be used as a payment terminal. This LC connector is connected to a transfer interface IT, itself connected by a transfer link to a transfer connection TC of the control unit MIC.

  Again, if this transfer link is easily accessible, the confidential information contained in a smart card inserted in the LC connector is poorly protected.

  It is therefore proposed therefore to arrange the transfer interface IT inside the control circuit CC. This transfer interface IT is connected to the transfer connection TC of the control unit MIC by a transfer bus BT.

  The transfer bus BT is buried in the control circuit CC so that the information which it conveys is much better protected than if it circulated on a transfer link external to the control circuit CC.

  However, this BT transfer bus, like the BM transmission bus, is not completely secure.

  It is therefore preferable to provide means for securing the transfer bus BT equivalent to the means described above in relation to the transmission bus BM.

  The embodiments of the invention presented above have been chosen having regard to the concrete character which they have in common. However, it would not be possible to exhaustively list all the embodiments covered by this invention. In particular, any means described can be replaced by equivalent means without departing from the scope of the present invention.

Claims (9)

  1) AC access control module comprising on the one hand a control unit MIC provided with a descrambling device operating by means of a descrambling key and on the other hand a memory storage device MEM for storing this key , characterized in that said MIC and MEM storage devices are connected by means of a transmission bus BM within an integrated control circuit CC.   2) Module according to claim 1, characterized in that said control circuit CC comprises securing means MIC for securing said transmission bus BM.   3) Module according to claim 2, characterized in that said MIC security means incorporate encryption means.   4) Module according to claim 1, characterized in that said control circuit CC is further provided with a transfer connection TC provided for the transfer of information with a transfer unit LC via a transfer interface IT.   5) Module according to claim 4 characterized in that, said IT transfer interface appearing in said control circuit CC, this further comprises a transfer bus BT for connecting this IT transfer interface to said control unit MIC .   6) Module according to claim 5, characterized in that said control circuit CC comprises securing means MIC for securing said transfer bus BT.   7) Module according to claim 6, characterized in that said MIC security means incorporate encryption means.   8) Module according to any one of claims 5 to 7, characterized in that it further comprises, connected to said IT transfer interface, an LC transfer unit.   9) Module according to claim 8 characterized in that said transfer unit is an LC card connector.