Abstract:
In an authentication communicating semiconductor device to enhance protection against illegal copying, a logic analyzer probe or the like is connected to a CPU bus to suppress possibility in which the authentication process is intercepted and is analyzed to break the mechanism of illegal copy protection and the electronic device is modified to set a tampered encryption key to the CPU bus. The authentication communicating semiconductor device includes a semiconductor chip, a main processing unit formed on the chip for generating a key code according to a predetermined algorithm, for determining approval/non-approval of communication of data with an external device, and for controlling the communication; an encryption unit formed on the chip for encrypting and decoding communication data using the key code generated by the main processing unit, and an interface unit formed on the chip for conducting communication with an upper-layer or a lower-layer according to a predetermined protocol.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a data processing technique and a technique suitably applicable to processing to code and to decode digital data using an encryption key code, for example, to a technique efficiently applicable to a communicating semiconductor device and a system using the device in which data is communicated between electronic apparatuses connected to each other via a serial bus conforming to, for example, the standard of Institute of Electrical and Electronics Engineers 1394 (IEEE1394) while guaranteeing safety of the communication.  
           [0002]    The IEEE1394 standard is a standard to serially transmit digital data of audio and video information between electronic apparatuses such as audiovisual (AV) apparatuses via a cable. Recently, there have been proposed electronic apparatuses in which electronic apparatuses such as an integrated receiver decoder (IRD), a digital video home system (D-VHS), and a digital video (DV) camera recorder (camcoder) are connected to each other via a serial bus of the IEEE1394 standard to communicate digital contents including, for example, digital audio data and/or digital video data therebetween using a packet conforming to, for example, the Moving Picture Experts Group 2 Transport Stream (MPEG2-TS) according to the International standardization Organization/International Electrotechnical Commission (ISO/IEC) 13813 standard and a packet conforming to the IEC61883 standard.  
           [0003]    For media such as a digital video tape and a digital video disk to store copyrighted materials such as a film and reproducing apparatuses to reproduce the materials, a technique to prevent illegal copying of the copyrighted material is indispensable in consideration of protection of copyrights. Recently, to protect copyrights of digital contents, an illegal copy prevention technique is being standardized, for example, by a copy protection technical working group (CPTWG) organized by industrial groups organized by the industry for the electric appliance for family use, personal computers, and films. According to an illegal copy protection technique proposed primarily by CPTWG, a specification of content scrambling system (CSS) of DVD video and a specification of 5 company digital transmission content protection (5C-DTCP) for IEEE1394 have been put to practices at present.  
           [0004]    However, against CSS of the DVD-video copy protection technique, some crackers, i.e., hackers who illegally access computer systems of other person for malicious purposes have already created software to circumvent or to break security provided by CSS. In the U.S.A. and France, the software has been delivered via the internet through worldwide web (www) servers and has caused damages in various fields of the industry.  
           [0005]    Therefore, in a situation in which a large amount of audiovisual apparatuses using an identical security technique such as the standardized CSS or 5C-DTCP are widely spread in the world, highly reliable security is necessary for the audiovisual apparatuses against illegal copy by crackers in consideration of the protection of copyrights for digital contents.  
           [0006]    As a vicious example of the illegal copying of copyrighted materials, an illegal or an authorized game machine has been put to market. The illegal game machine is implemented by illegally modifying hardware of a game machine of a known company to enable the illegal copying of game software stored on a compact disk (CD). The copyright of the game software has been infringed. As above, in the present stage of technique, there possibly occurs software wise and hardware wise attack, that is, not only the illegal copy by software but also the illegal copy by modified hardware of electronic apparatuses are used to attack the illegal copy protection technique.  
           [0007]    On the other hand, 5C-DTCP has been practically applied to a system below. FIG. 13 shows a general configuration of an audiovisual apparatus as an authentication communicating apparatus of the 5C-DTCP specification and a system using the apparatus according to the prior art. The configuration of FIG. 13 includes a communicating semiconductor device (communicating apparatus)  72  of the 5C-DTCP specification and an authentication device  71  including a microcomputer chip to conduct authentication. The authentication device  71  and the communicating device  72  are mounted on audiovisual apparatuses such as a digital video tape recorder and a set-top box.  
           [0008]    As shown in FIG. 13, the communicating device  72  includes a low-layer interface circuit  100  to establish connections to IEEE1394 serial buses  741  to  743 , an upper-layer interface circuit  200  to establish a connection to an external device, and an encryption circuit  300 . The communicating device  72  is connected between a 1394 physical (PHY) layer as a physical layer including ports  711  to  713  to establish connections to cables  730  of the IEEE1394 standard and an external device  90  such as a display including an MPEG2 decoder, a codec, or a DV codec. The communication device  72  has a function which receives encrypted digital data from the IEEE1394 cable  730  to decode the digital data to pass the decoded digital data to the external device  80 . The low-layer interface circuit  100 , the upper-layer interface circuit  200 , and the encryption circuit  300  may be configured as respectively separate chips depending on cases. The authentication device  71  is connected via an internal bus  41  to the communicating device  72 . The authentication device  71  has a function to generate an encryption key code (to be simply referred to as an encryption key herebelow) necessary for the encryption circuit  300  and a function to conduct authentication in response to a request from an audiovisual apparatus which desires to receive data.  
         SUMMARY OF THE INVENTION  
         [0009]    However, in the system of the 5C-DTPC specification (authentication communicating apparatus) of the prior art, the communicating device  71  and the authentication device  72  are configured as respectively separate chips and hence the communicating device  71  is connected via the bus to the authenticating device  71 , a random access memory (RAM)  750 , and an electrically rewritable flash read-only memory (ROM). The interface circuits  100  and  200  in the communicating device  72  include control registers  14  and  24 , respectively. The encryption circuit  300  includes a key register  34 . Control data and a coding/decoding encryption key code are set via the registers  14 ,  24 , and  34  to the authentication device  71  to conduct operations such as the coding or encryption and the decoding operation.  
           [0010]    Consequently, in the authentication communicating apparatus of 5C-DTCP specification of the prior art, there exists a disadvantage. That is, by monitoring a signal at an external terminal  62  at which the encryption circuit  300  is connected to the bus  41 , secret items are known to a third person, for example, an encryption key is known to the third person and an encryption algorithm is analyzed by the third person. Specifically, in the configuration of an audiovisual apparatus shown in FIG. 10, there exists a chance for the third person to make an attack against to the system, for example, to access the secret items of the authenticating device. That is, the third person accesses the system by monitoring the signal at the external terminal  62  of the communicating device  72  and data on the central processing unit (CPU) bus  41  to illegally obtain communication commands, an encryption exchange key, and a random number value for the operation of authentication. This may deteriorate reliability of security of this system.  
           [0011]    Assume that an illegal device is produced as a result of the attack to pass the authentication in an illegal way. For example, as shown in FIG. 14, when an illegal device  75  is connected to the CPU bus  41  and the authentication device  71  in each of audiovisual apparatuses  800 A and  800 B and a connection line such as a jumper wire  46  is disposed between the respective CPU buses  41 . As a result of this illegal modification, communication commands for the authentication are issued from the illegal device  75  to the authentication device  71  associated therewith to form an illegally pass to detour round the legitimate authentication. Consequently, the authentication is granted or satisfied in an illegal way. Thereafter, in a stage to code/decode the pertinent digital content in the encryption circuit, the illegal device  75  issues a bus right request signal to the associated authentication device  71  to acquire the bus right of the CPU bus  41 . After the illegal device  75  obtains the bus right of the CPU bus  41  from the authentication device  71 , the illegal device  75  uses an illegal key, which is shared between the illegal devices  75 , in place of an encryption key to be used after the authentication is legitimately approved. This leads to a problem of possibility that the digital content is illegally sent from the audiovisual apparatus  800 A to the audiovisual apparatus  800 B.  
           [0012]    It is therefore an object of the present invention to provide an authentication communicating apparatus in which an encryption key and control data of the system cannot be obtained even by the monitoring of the external terminal. This prevents a cracker aiming at illegal accesses to the system from analyzing such information as the encryption key and control data and hence from attacking the illegal copy protection technique to protect copyrights of digital contents. The authentication communicating apparatus thereby prevents the illegal copy of digital contents.  
           [0013]    Another object of the present invention is to provide an authentication communicating apparatus in which the illegal copy protection technique withstands any attack using the modification of hardware.  
           [0014]    The other objects, novel features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings.  
           [0015]    In accordance with the present invention, there are provided representative aspects of embodying the invention as follows.  
           [0016]    To achieve the objects, according to one aspect of the present invention, there is provided an authentication communicating semiconductor device comprising a semiconductor chip, a main processing unit formed on the semiconductor chip for generating a key code according to a predetermined algorithm, for determining approval/non-approval of communication of data with an external device, and for controlling the communication; an encryption unit formed on the semiconductor chip for encrypting and decoding communication data using the key code generated by the main processing unit, and an interface unit formed on the semiconductor chip for conducting communication with an upper layer or a lower layer according to a predetermined protocol.  
           [0017]    More specifically, according to another aspect of the present invention, there is provided an authentication communicating semiconductor device comprising a single semiconductor chip, an encryption unit formed on the single semiconductor chip for encrypting, in an encrypting mode, ordinary or nonencrypted statement data into encrypted statement data; for decoding, in a decoding mode, the encrypted statement data into ordinary statement data; and for directly passing data therethrough when neither encryption nor decoding is required. To the device, there are also connected a lower-layer interface unit formed on the single semiconductor chip for the encrypted statement data of the encryption unit for controlling a protocol of communication with a lower layer and an upper-layer interface unit formed on the single semiconductor chip for the ordinary statement data of the encryption unit for controlling a protocol of communication with an upper layer. The lower-layer interface unit comprises at least one lower-layer communication path for communicating encrypted statement data with a lower-layer device controlling a communication signal outside the semiconductor chip. The upper-layer interface unit comprises at least one upper-layer communication path for communicating ordinary statement data with an upper-layer device outside the semiconductor chip. The device also includes a key generation unit formed on the single semiconductor chip for executing authentication processing of communication passing through the lower layer and for executing key generation processing for the encryption unit. The key generation unit comprises a CPU, an ROM, and an RAM. The CPU sets a key register for the encryption unit to keep an encryption key, a control register of the lower-layer interface unit, and a control register of the upper-layer interface unit via a bus connecting the CPU, the encryption unit, the lower-layer interface unit, and the upper-layer interface unit to each other.  
           [0018]    In the configuration above, it is difficult to externally obtain or steal internal signals of the semiconductor chip and a communication command for the authentication process, and an encryption key for the encryption process cannot be tampered to be externally inputted to the authentication communicating device configured in a large scale integration (LSI) chip. It is therefore difficult for the third person to analyze the authentication process to circumvent the illegal copy (unauthorized copying) protection technique. This also makes it difficult to circumvent the illegal copy protection technique by modifying an electronic apparatus. In consequence, there can be implemented an electronic apparatus capable of communicating digital contents requiring copyright protection in quite a safe environment.  
           [0019]    Furthermore, when an electrically rewritable nonvolatile memory is necessary to store inherent information of an electronic device on which the pertinent semiconductor device is mounted, the memory is also formed on the pertinent same chip. This prevents the inherent information of the electronic device from being intercepted or stolen by a third person. Since the electrically rewritable nonvolatile memory is employed, security can be improved at a low cost by writing mutually different inherent information items for the respective devices. The information items can be written in the electrically rewritable nonvolatile memory before the installation of the memory in the system.  
           [0020]    Additionally, the main processing unit which generates a key code, which authenticates an external device, and which controls communication; the encryption unit, and the interface unit are mutually connected via an internal bus. When an electrically rewritable nonvolatile memory is necessary to store inherent information of an electronic device on which the pertinent semiconductor device is mounted, a bus control circuit is disposed between an external terminal connected to the nonvolatile memory and the internal bus to control a bus change-over operation. Therefore, the encryption process and the authentication process cannot be externally intercepted. This also makes it difficult for a third person external with respect to the chip to tamper an encryption key used in the encryption process and a communication control code used in the authentication process. Therefore, neither the encryption key nor the communication control code can be easily inputted to the system in the illegal way. Attack from crackers such as analysis of the encryption and authentication and modification of devices can be resultantly prevented. This improves safety against the illegal copy of digital contents for which the copyright protection is required.  
           [0021]    Moreover, there is further required a host CPU to control the overall system of the electronic apparatus on which the semiconductor device is mounted. The main processing unit of the semiconductor device includes a nonvolatile memory having stored therein a program implementing a key generation algorithm and an authentication algorithm to authenticate an external device requesting data communication and program execution-type control means for generating a key code and for determining approval/non-approval of communication of data with an external device according to the program. In this configuration, there is provided a communication circuit for communication between the control means and the host CPU between a communication port of the host CPU and the internal bus. As a result, this prevents, in a semiconductor device having a communication port to the host CPU, the encryption process and the authentication process from being externally intercepted via the communication port. This also makes it difficult for a third person to externally tamper an encryption key in the encryption process and a communication control code in the authentication process. Therefore, neither the encryption key nor the communication control code can be easily inputted to the system in the illegal way. Attack from crackers such as analysis of the encryption and authentication and modification of devices can be resultantly prevented.  
           [0022]    In this case, the control unit is so configured to accept only restricted and predetermined commands. This prevents illegal intervention in the encryption process and the authentication process and hence improves safety of the system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a block diagram showing a first embodiment including an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0024]    [0024]FIG. 2 is a block diagram showing second first embodiment including an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0025]    [0025]FIG. 3 is a block diagram showing a third embodiment including an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0026]    [0026]FIG. 4 is a block diagram showing fourth first embodiment including an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0027]    [0027]FIG. 5 is a block diagram showing a fifth embodiment including an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0028]    [0028]FIG. 6 is a block diagram showing sixth first embodiment including an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0029]    [0029]FIG. 7 is a diagram for explaining a configuration including an IEEE1394 serial bus connected two audiovisual apparatuses each configured as shown in FIG. 1.  
         [0030]    [0030]FIG. 8 is a diagram for explaining processes of authentication and encryption in an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0031]    [0031]FIG. 9 is a block diagram showing a seventh embodiment including an authentication communicating LSI unit according to the present invention and an audiovisual apparatus including the same.  
         [0032]    [0032]FIG. 10 is a block diagram showing a variation of the embodiment shown in FIG. 9.  
         [0033]    [0033]FIG. 11 is a block diagram showing another variation of the embodiment shown in FIG. 9.  
         [0034]    [0034]FIG. 12 is a block diagram showing a further another variation of the embodiment shown in FIG. 9.  
         [0035]    [0035]FIG. 13 is a block diagram showing an example of an authentication communicating LSI unit of the prior art and an audiovisual apparatus including the same.  
         [0036]    [0036]FIG. 14 is a diagram for explaining an illegal modification in an authentication communicating LSI unit of the prior art and an audiovisual apparatus including the same. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0037]    Description will now be given of embodiments of the present invention by referring to the drawings.  
         [0038]    [0038]FIG. 1 shows a first embodiment of an authentication communicating LSI circuit of the 5C-DTCP specification according to the present invention.  
         [0039]    In this embodiment of an authentication communicating LSI circuit, a key generation &amp; authentication unit  50  which includes a CPU  500 , an RAM  502  to provide a work are, and an ROM  501  to store programs and fixed data and which has functions such as a function to generate an encryption key and a function to conduct the authentication to determine approval/non-approval of communication of data to and from an external device, and a function to control communication; a lower-layer interface unit  10  to establish connection to an IEEE1394 serial bus, an upper-layer interface unit  20  to establish connection to an external device, an encryption unit  30  to execute encryption and decoding of data using an encryption key, and an internal bus  41  to connect the constituent units to each other are formed on one semiconductor chip such as a monocrystalline silicon chip.  
         [0040]    The inner bus  41  is connected to an external nonvolatile memory  740  such as an electrically rewritable flash memory to store data and information, for example, a communication control program to set a communication route and inherent information of devices. The lower-layer interface unit  10  is connected to an IEEE1394 physical layer protocol (1394PHY) chip  700  as a physical layer including ports  711  to  713  to be connected respectively to IEEE1394 cables  730  (which will be described later) of the IEEE1394 standard and the upper-layer interface unit  20  is connected to an external device  90  such as an MPEG2 decoder, a codec, or a DV codec and the external device  90  is connected to a recording and reproducing unit  400 . This resultantly configures an audiovisual apparatus.  
         [0041]    The lower-layer interface unit  10  includes a packet processing circuit  101  to process data for communication thereof in a packet format and a 1394 link circuit  100  as a link layer connected via a lower-layer bus  12  to the 1394PHY chip  700  to control connection to the IEEE1394 cables  730 . The 1394PHY chip  700  is a semiconductor chip to conduct a control operation as a physical layer such as multiplexing and demultiplexing of data. The chip  700  includes, although not limited to, three ports  711 ,  712 , and  713  of the IEEE1394 specification. Specific connection between the ports  711  to  713  and the IEEE1394 cables (to be simply referred to as 1394 cables herebelow)  730  is the same as for the prior art example shown in FIG. 13. That is, the ports  711 ,  712 , and  713  are respectively connected to sockets  721 ,  722 , and  723  of the IEEE1394 specification of a connector unit  720 .  
         [0042]    Referring to FIG. 13, the user connects a 1394 plug  731  as an end of a 1394 cable  741  to the socket  721  available in the IEEE1394 connector unit  720  and connects a 1394-plug  751  of an end of a non-connection side of the 1394 cable  741  to the IEEE1394 connector unit of the audiovisual apparatus. As a result, the user can reserve a 1394-bus  810  as a transmission path to communicate digital contents and communication commands between the audiovisual apparatuses  800 A and  800 B as shown in FIG. 7. By removing the plug  731  of the 1394 cable  741 , the pertinent audiovisual apparatus can be released from the 1394 bus. For simplification of description, the 1394 bus connection is established between two audiovisual apparatuses in FIG. 7. However, in accordance with the present invention, the number of buses stipulated by the lower-layer communication protocol is not topologically limited to two. That is, other electronic apparatuses can be similarly connected to the 1394 bus  810 .  
         [0043]    The upper-layer interface circuit  200  is an interface circuit to pass a digital content from a physical layer of the 1394PHY chip  700  and a link layer of the 1394 link circuit  100  to an upper-layer device. The upper-layer interface circuit  200  is connected via an upper-layer bus  22  to the external device  90  such as an MPEG2 codec (coder/decoder) or a DV codec. The external device is connected to the recording and reproducing apparatus  400 . The apparatus  400  records or reproduces audio and visual digital contents.  
         [0044]    The interface units  10  and  20  respectively include control registers  14  and  24 . The CPU  500  of the key generation &amp; authentication unit  50  sets a control code via the internal bus  41  to the control registers  24  and  14  to set communication paths to the 1394 link circuit  100  and the upper-layer interface circuit  200 . A lower-layer communication control program is stored in an external memory  740 . According to the program, the CPU  500  sets the control register  14  to conduct communication via a lower-layer device to an electronic device on the 1394 bus  810 . Specifically, the CPU  500  issues a communication command to an electronic device on the 1394 bus  810  for a desired function. For example, the CPU  500  controls the recording or reproducing operation of the electronic apparatus, the on/off state of its power source, a browsing operation for information of the electronic device.  
         [0045]    The encryption key processing unit  30  includes a key register  34 . The ROM  501  beforehand stores programs respectively to implement an encryption key generation algorithm and an authentication algorithm. According to the encryption key generation algorithm, the CPU  500  of the key generation &amp; authentication unit  50  generates an encryption key to write the encryption key in the key register  34  of the encryption circuit  300 . The CPU  500  conducts authentication according to the authentication algorithm stored in the ROM  501 .  
         [0046]    Referring next to FIG. 8, description will be given in detail of procedures of authentication and encryption between audiovisual apparatuses each of which includes the authentication communicating LSI chip of the embodiment.  
         [0047]    To transmit a digital content to be accumulated or sent from the audiovisual device  800 A to the recording/reproducing device  400 , the audiovisual device  800 B which desires to receive an encrypted digital content issues a communication command, i.e., an authentication request command with information of its own machine via the 1394 bus to the audiovisual device  800 A to request authentication. Having received the authentication request command, the CPU  500  of the audiovisual device  800 A executes an authentication program recorded on the ROM  51  to conduct authentication for the audiovisual machine  800 B. If the authentication is approved or satisfied, the pertinent electronic apparatus is recognized as an authorized machine.  
         [0048]    After the authentication is successfully finished, the key generation &amp; authentication unit  50  of the audiovisual device  800 A (FIG. 8) generates an encryption exchange key Ksx by executing encryption processing to convert an encryption key Kcont of the digital content into an exchange key Kx using a random number value seed and an authentication key Kauth necessary for the audiovisual device  800 B to generate the encryption key Kcont. The key Ksx is then sent via the CPU bus  41 , the 1394 link circuit, the 1394 physical chip  700 , and the 1394 bus  810  to the audiovisual device  800 B.  
         [0049]    On the other hand, the audiovisual device  800 B receives the communication command from the 1394 bus  810 . In the device  800 B, the command is passed via the 1394 physical chip  700 , the 1394 link circuit  100 , and the CPU bus  41  to the key generation &amp; authentication unit  50 . The unit  50  decodes the random number value seed and the encryption exchange key Ksx received from the audiovisual device  800 A, using an authentication key Kauth kept in the unit  50  to produce an exchange key Kx as a result of the decoding. Using the exchange key Kx, there is obtained an encryption key Kcont which is equal to the encryption key used on the audiovisual device  800 A side. That is, the exchange key Kx is shared between the audiovisual devices  800 A and  800 B.  
         [0050]    Subsequently, audiovisual device  800 A executes a key generation program recorded on the ROM  501  to generate an encryption key Kcont using the exchange key Kx and the random number value seed and then sets the encryption key Kcont to the key register  34  of the encryption circuit  300 . In response thereto, the circuit  300  encrypts a digital content including an ordinary statement data contained in, for example, an MPEG2-TS packet inputted from the external device  90  of the audiovisual device  800 A into encrypted statement data using the encryption key Kcont. The circuit  300  accumulates the encrypted statement data in a buffer, not shown, of the packet processing circuit  101  to configure a packet stipulated by IEEE1394. The buffer keeps the data until it is possible for the 1394 link circuit  100  to transfer data to the 1394 bus  810  to thereby serve a function of a buffer memory to absorb discrepancy between the transmission speed of the upper-layer bus  22  and that of the lower-layer bus  12 .  
         [0051]    When it is possible for the 1394 link circuit  100  to transfer data to the 1394 bus  810 , a 1394 packet data containing the encrypted digital content is outputted from the lower-layer bus  12  to the 1394 physical chip  700 . The chip  700  starts transmitting the digital content via the 1394 bus  810  to the communicating audiovisual device  800 B. Additionally, the audiovisual device  800 A sends the random number value seed as information for the decoding by the audiovisual device  800 B via the 1394 bus  810  thereto. Having received the value seed, the audiovisual device  800 B decodes the encrypted digital contents by the encryption circuit  300 . Specifically, using the random number value seed and the exchange key Kx obtained by decoding the encryption exchange key Ksx using the authentication key Kauth, the encryption circuit  300  decodes the digital content according to a key generation algorithm in the ROM  501  of the key generation &amp; authentication unit  50  of the audiovisual device  800 B. A decoded digital content resultant from the decoding is sent via the external device  90  to be recorded in or reproduced by the recording/reproducing device  400  of the audiovisual device  800 B.  
         [0052]    In the first embodiment of the authentication communication LSI chip, data associated with program accesses to the ROM  501  appearing in the authentication and key generation processes and temporary data stored in the RAM  502  during the CPU operation in the sequence of processing are delivered to the CPU bus  41 . In this connection, an authentication device and an encryption device which are configured in mutually different chips in the prior art are formed on one semiconductor chip. When compared with the directly observation of the external terminal of the encryption device, the external observation of the bus alone cannot easily identify the authentication and the key generation executed by the CPU. Therefore, it is difficult to analyze details of the processes of processing in the chip. That is, since the CPU bus  41  is used for various operations and hence passes various data items therethrough. Consequently, even if data on the CPU bus  41  is observed, it is difficult to identify the authentication and the key generation among the various operations.  
         [0053]    Furthermore, when the authentication communication LSI chip of the embodiment is incorporated in the system (in a real system state), the CPU bus  41  is under control of the CPU  500 . Therefore, in the real system state, only the CPU  500  can set data to the key register  34 . That is, in the real system state, it is impossible to externally input data via the CPU bus  41  to the key register  34  for the setting thereof. This makes it difficult to modify a device on which the authentication communicating LSI chip is mounted. Additionally, since the system is configured in one chip, the system cost is minimized and the number of parts thereof is reduced to increase the mounting or packaging density of the chip.  
         [0054]    [0054]FIG. 2 shows a configuration of a second embodiment of the present invention. The second embodiment is almost the same in the configuration as the first embodiment. Three different points therebetween are as follows. First, the lower-layer interface unit  100  can process different types of packets in the second embodiment. For example, the unit includes a first packet processing circuit  101  to construct an MPEG-TS packet, a second packet processing circuit  102  to construct a digital content such as IEC61883 for which encryption is not required, and a third packet processing circuit  103  to construct a digital data packet such as the serial bus protocol 2 (SBP-2) which is being standardized according to NCITS 325-1998 of the American national Standard Institute (ANSI). In this configuration, the digital content for which encryption is not required is transmitted via transmission lines  211  and  212  directly between the packet processing circuit  102  or  103  and the upper-layer interface unit  20 . Second, the upper-layer interface unit  20  includes an upper-layer interface circuit  201  which selects a packet from the encryption circuit  300  or a packet from the second packet processing circuit  102  to transmit the packet to an upper-layer bus  221  and an upper-layer interface circuit  202  which selects a packet from the second packet processing circuit  102  or a packet from the third packet processing circuit  103  to transmit the packet to an upper-layer bus  222 . Third, a plurality of external devices  90  to  93  can be connected to the upper-layer interface circuits  201  and  202  at the same time. The packet processing circuits  102  and  103  are connected via a bus  111  to the 1394 link circuit  100 . The packet processing circuits  102  is connected via a bus  211  to the upper-layer interface circuits  201  and  202 . The packet processing circuit  103  is connected via a bus  212  to the upper-layer interface circuit  202 . The other configuration, procedures of various processing, and effects of operations are substantially the same as those of the first embodiment and hence description thereof will be avoided.  
         [0055]    [0055]FIG. 3 shows a configuration of a third embodiment of the present invention. The third embodiment is configured almost in the same way as for the first embodiment. Two different points therebetween are as follows. First, the encryption unit  30  includes two encryption circuits  300  and  302 , the lower-layer interface unit  10  includes tow packet processing circuits  101  and  104  to configure, for example, MPEG2-TS packets, and the upper-layer interface unit  20  includes first and second upper-layer interface circuits  200  and  203  respectively corresponding to the encryption processing circuits  300  and  302  so that digital contents for which encryption is required can be transferred through two channels at the same time. Second, a plurality of external devices  91  and  92  can be respectively connected to the upper-layer interface circuits  200  and  203  at the same time. The other configuration, procedures of various processing, and effects of operations are substantially the same as those of the first embodiment and hence description thereof will be avoided.  
         [0056]    [0056]FIG. 4 shows a configuration of a fourth embodiment of the present invention. The fourth embodiment is implemented by disposing an internal nonvolatile memory  503  in place of the electrically rewritable nonvolatile memory  740  disposed as an external device in the first embodiment.  
         [0057]    In each of the authentication communicating LSI chips of the first to third embodiments, the memory  740  outside the chip is connected to the internal bus  41 . In the sequence of processing from the authentication to the key generation, data associated with program accesses to the ROM  501  taking place during the authentication and key generation processes and temporary data stored in the RAM  502  during the CPU operation are fed to the CPU bus  41 . Therefore, the data can be externally observed. However, in the authentication communicating LSI chip  70  of the fourth embodiment, the CPU bus  41  is not connected to an external terminal of the chip  70 , and hence the processes of operations cannot be externally observed. Additionally, in the real system state of the configuration, the CPU bus  41  is controlled such that only the CPU  500  can set the key register  34 . Consequently, data cannot be inputted via the CPU bus  41  to the key register  34 , and hence it is difficult to modify the system.  
         [0058]    [0058]FIG. 5 shows a configuration of a fifth embodiment of the present invention. In the fourth embodiment, the lower-layer device 1394 physical circuit  700  disposing as an external device in the first embodiment is arranged in the authentication communicating LSI chip  70 . The 1-chip configuration including the circuit  700  further enhances cost reduction and minimizes the number of parts and hence increases the packaging density.  
         [0059]    [0059]FIG. 6 shows a configuration of a sixth embodiment of the present invention. In the sixth embodiment, the lower-layer device 1394 physical circuit  700  disposing as an external device in the fourth embodiment is arranged in the authentication communicating LSI chip  70 .According to the sixth embodiment, the advantage of the fourth embodiment and that of the fifth embodiment can be obtained.  
         [0060]    [0060]FIG. 9 shows another embodiment of the authentication communicating LSI chip of the 5C-DTCP specification in accordance with the present invention. This embodiment is implemented by adding to the LSI chip of the first embodiment a host CPU  82  to control the overall system, a communication circuit  80  to conduct serial communication with the host CPU  82 , and a bus control circuit to control a connection change operation for the external memory  740  and the internal bus  41 . As can be seen from FIG. 9, the communication circuit  80  is arranged between the internal bus  41  and the host CPU  82  and is connected via a serial communication line  81  to the host CPU  82 . The external memory  740  is connected via an external bus  61  to a control circuit  60 , and the CPU  500  controls the connection change operation of the bus control circuit  60  to the external memory  740  or the internal bus  41 .  
         [0061]    In the embodiment as above, the internal bus  41  is separated from the external device by the bus control circuit  60  and the communication control circuit  80 . That is, in this configuration, the signal on the internal bus  41  cannot be monitored directly via an external terminal. Therefore, secrecy of data is increased and it is more difficult for the cracker to analyze the authentication algorithm and the key generation algorithm. In the embodiment, the internal CPU  500  accepts only predetermined commands from the host CPU  82 . That is, data of the RAM  502  and the ROM  501  cannot be read therefrom by inputting an illegal command to the CPU  500 .  
         [0062]    [0062]FIG. 10 shows further another embodiment of the authentication communicating LSI chip in accordance with the present invention. In this embodiment, the communication circuit  80  to conduct the serial communication with the host CPU  82  in the LSI chip of the ninth embodiment is removed, and a bus control circuit  60  to control, for example, a bus connection change operation between the external memory  740  and the internal bus  41  is arranged.  
         [0063]    [0063]FIG. 11 shows still another embodiment of the authentication communicating LSI chip in accordance with the present invention. In this embodiment, the communication circuit  80  to conduct the serial communication with the host CPU  82  in the LSI chip of the ninth embodiment is removed, and a bus control circuit  60  to control, for example, a bus connection change operation between the external memory  740  and the internal bus  41  and only the upper-layer external interface circuit  20  are disposed (the lower-layer external interface circuit  10  is not arranged).  
         [0064]    [0064]FIG. 12 shows another embodiment of the authentication communicating LSI chip in accordance with the present invention. In this embodiment, the communication circuit  80  to conduct the serial communication with the host CPU  82  in the LSI chip of the ninth embodiment is removed, and a bus control circuit  60  to control, for example, a bus connection change operation between the external memory  740  and the internal bus  41  and only the lower-layer external interface circuit  10  are disposed (the upper-layer external interface circuit  20  is not arranged).  
         [0065]    Also in the embodiments of FIGS.  10  to  12 , the internal bus  41  is separated by the bus control circuit  60  from the external bus  61 . Therefore, for the protection of the illegal copy, these embodiments have substantially the same advantages as those of the ninth embodiment of the authentication communicating LSI chip. Moreover, when the encryption  6  authentication unit  50 , the encryption unit  30 , and either one of the upper-layer and lower-layer external interface circuits  10  and  20  are formed on one chip, it is not possible to estimate an encryption key by directly comparing the ordinary statement data and encrypted statement data inputted to or outputted from the encryption unit  30 . This consequently increases secrecy of the data.  
         [0066]    Description has been given in detail of particular embodiments of the present invention. However, the present invention is not restricted by the embodiments. It is possible to modify and to change the embodiments in various ways within the scope of the present invention. For example, the embodiments shown in FIGS.  4  to  12  may be configured in the same fashion as for the embodiments shown in FIGS. 2 and 3. That is, a plurality of packet data items are simultaneously transferred by disposing a plurality of packet processing circuits and a plurality of upper-layer interface circuits. The description has been given of cases in which the present invention of the inventors is applied to a background field of the invention, that is, to the authentication communicating LSI chip of the 5C-DTCP specification. However, the present invention is also applicable to a communicating LSI chip of the CSS specification for the DVD video system. Furthermore, the authentication communicating LSI chip according to the present invention can be used not only in audiovisual apparatuses such as a digital video tape recorder and an integrated receiver/recorder (IRD), but also in a personal computer.  
         [0067]    Typical features of the present invention described in the present specification lead to advantages as follows. According to the present invention, the internal signal of the semiconductor chip cannot be externally intercepted or stolen. It is difficult to externally tamper the communication command during the authentication process and the encryption key setting during the encryption process. That is, it is difficult to input a tempered data item to the system, the authentication process cannot be easily analyzed to overcome the illegal copy protection technique. Additionally, the illegal copy protection technique cannot be easily overcome by modifying the electronic device. Resultantly, it is possible to implement an electronic apparatus to communicate digital contents requiring the copyright protection with high safety.  
         [0068]    The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims.