Patent Publication Number: US-6990204-B2

Title: Interface security system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit of priority under 35 USC §119 to Japanese Patent Application No. 2000-087390 filed on Mar. 27, 2000, the entire contents of which are incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention pertains to a security technique such as for data in an interface between devices and to, for example, a technique for preventing leakage or the like of the data exchanged between ICs. 
   2. Description of the Related Art 
   Environment of the development and diffusion of multimedia has been prepared through progress in the digitization technique. Since information formed into digital data does not change its quality even in processing such as storing, reproducing, communicating, its application has been steadily expanded. 
   Through an information content compression technique or the like, information such as not only characters and graphics but also voice and video has been able to be processed, stored, and reproduced digitally. 
   In the back of these techniques, infringement of copyright and the like through an illegal copy or the like has become a problem, and thus various technical methodology for preventing reproduction of written materials or the like have been taken. For example, SCMS (Serial Copy Management System) is implemented in the CD, MD, DAT, CD-R, and the like for music, and CGMS (Copy Generation Management System) or the like is implemented in the DVD (Digital Versatile Disk). 
   A typical example of a digital music player in which a memory card is employed is shown in FIG.  1 . 
   Audio data such as in music which is formed into digital data are compressed, for example, by an information content compression technique, and after specific cryptography is incorporated in a specific portion by a copy protection technique, those audio data are recorded in a memory card  111 . 
   The data recorded in the memory card  111  are read by the a card I/F section  121 , cryptography incorporated in the data is decrypted by a decryption section  122 , data compressed are decoded by a compressed signal decode section  131  and are converted into an analog signal by a DAC (Digital-Analog Converter) section  141  so as to be sent to an output device such as a speaker. In the drawing, the parts shown by broken lines show configurational units of the apparatus, and the present digital music player is composed of a card slot  110  holding the memory card  111 , an IC- 120  having the card I/F section  121  and the decryption section  122 , an IC- 130  having the compressed signal decode section  131 , and an IC- 140  having the DAC section  141 . The respective devices or blocks are connected by wiring  151  to  154 . 
   As shown in the drawing, since the data flowing between the card slot  110  and the IC- 120  are encrypted in advance, the confidentiality thereof is maintained. However, on and after the IC- 120 , that is, the data flowing between the IC- 120  and the IC- 130  and between the IC- 130  and the IC- 140  are digital data whose cryptography is released by the decryption section  122  in order to reproduce music data. Specifically, the data flowing between the IC- 130  and the IC- 140  are the data further decoded by the compressed signal decode section  131 . Accordingly, it is not impossible to connect a measuring device such as a probe to the wiring portions  153 ,  154  to absorb data so as to use them wrongly. 
   That is, it is the present situation that although a copy protection technique employed conventionally is applied to an interface section provided in the external of an apparatus such as in between a memory card and a music player, it has not fully covered, for example, an interface between ICs inside a music player apparatus. 
   In order to solve such problem in a digital music player as shown in  FIG. 1 , although a method may be thought wherein the IC- 120 , the IC- 130 , the IC- 140  are formed into one chip, such method is difficult to be realized actually due to problems in a manufacturing cost, a technical problem, and the like. 
   In general, in such interface between ICs, terminals are specified by data, clock, a latch signal, or the like, and by employing a measuring device, a signal flowing between ICs can be surmised, and even the data transferred may be read. In some cases, data may be exchanged between ICs in a state without any cryptography or scrambling depending on the data. 
   Further, since, for example, music data, video data, or the like have only several types of transfer formats, specifying a format is easy, and thus such data are likely to be falsely copied in a state where a copyrighted material is a high grade digital signal. With respect to data having a high concealment property, a protection such as cryptography is given to the data themselves in advance, but an interface between chips inside an apparatus is often in a defenseless state. 
   This type of problem exists not only regarding a reproduction device for music or video software but also similarly regarding an information processing apparatus, for example, for operating a computer program or game software and also is contained in an information transmission means or the like employing a network or a digital broadcast. 
   SUMMARY OF THE INVENTION 
   The present invention is developed to solve the above-described problems, and it is an object of the present invention to provide interface security system and method by which leakage or the like of data and the like exchanged between devices can be prevented by making an interface between devices such as ICs switchable between the devices. 
   In order to solve the above-described problems, the present invention embraces an interface security system between devices connected to each other and transmitting/receiving a signal, characterized in that the interface security system encompassing a first device including a selector selecting a connection pattern between a signal transmitted/received and an external terminal for transmitting/receiving the signal based on a switch signal and a switch switching a connection between the signal and the external terminal in accordance with a connection pattern selected by the selector, and a second device including a selector selecting a connection pattern between a signal transmitted/received and an external terminal for transmitting/receiving the signal based on a switch signal and a switch switching a connection between the signal and the external terminal in accordance with a connection pattern selected by the selector, wherein the selector of the second device inputs a switch signal of the same value as the switch signal that the selector of the first device inputs. 
   According to embodiments of the present invention, since the corresponding relationship between the signal transmitted/received and the external terminal is switched in accordance with a connection pattern set up between the respective devices, specifying a signal, for example, data, flowing between the devices becomes difficult. 
   A second embodiment of the present invention is characterized in that the respective first device and second device have bidirectional buffers connected to the external terminals, and the selectors of the respective devices control the bidirectional buffers, respectively, so as to switch the direction of input/output of the external terminals in accordance with the connection pattern. 
   According to embodiments of the present invention, since not only the corresponding relationship between the signal transmitted/received and the external terminal but also the relationship of the input/output of the terminal are switched in accordance with a connection pattern set up between the respective devices, specifying a signal, for example, data, flowing between the devices becomes further difficult. 
   Other objects, characteristics, and effects of the present invention are made clear further through the detailed explanation described below referring to drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a configuration example of a digital music player in which a memory card is employed. 
       FIG. 2  is a schematic diagram showing an embodiment in which an interface security system according to the present invention is applied to ICs. 
       FIG. 3  is a schematic diagram showing an embodiment of a SEED generation circuit. 
       FIG. 4  is a circuit diagram showing an embodiment of a random number generation circuit. 
       FIG. 5  is a circuit diagram showing another embodiment of a random number generation circuit. 
       FIG. 6  is a circuit diagram showing a configuration example of a selector circuit. 
       FIG. 7  is a circuit diagram showing an embodiment in which input/output control is performed employing bidirectional buffers. 
       FIG. 8  is a circuit diagram showing an example in which the SEED generation circuit is arranged in the external. 
       FIG. 9  is a circuit diagram showing an example in which a cryptography circuit is provided inside the IC-A and a decode circuit inside the IC-B. 
       FIG. 10  is a circuit diagram showing an example in which a physical random number generation circuit is provided inside the IC-A. 
       FIG. 11  is a circuit diagram showing an example in which a counter is provided inside the IC-A and the IC-B. 
       FIG. 12  is a flow chart showing a processing operation example by the interface security system shown in the first embodiment and the second embodiment. 
       FIG. 13  is a flow chart showing a processing operation example by an interface security system shown in the third embodiment. 
       FIG. 14  is a flow chart showing a processing operation example of a case where the connection pattern is switched every time data transmission/reception is performed between the IC-A and B. 
       FIG. 15  is a flow chart showing a processing operation example of a case where the connection pattern is switched. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Embodiments of the present invention are explained below based on drawings. 
   (First Embodiment) 
     FIG. 2  is a schematic diagram showing an embodiment of an interface security system according to the present invention. In the present embodiment, shown is an example in which two ICs, IC-A (first device) and IC-B (second device), are connected by six signal lines of DATA 1 , CLOCK 1 , SIGNAL 1 , DATA 2 , CLOCK 2 , AND SIGNAL 2 . Respective signals of DATA 1 , CLOCK 1 , and SIGNAL 1  are sent from the IC-A to the IC-B, and respective signals of DATA 2 , CLOCK 2 , and SIGNAL 2  are sent from IC-B to IC-A. In a conventional interface between ICs, it is specified that DATA  1  passes on a line  31 , CLOCK 1  a line  32 , SIGNAL 1  a line  33 , DATA 2  a line  34 , CLOCK 2  a line  35 , and SIGNAL 2  a line  36 . 
   The IC-A has a SEED generation circuit  10  generating seeds of random numbers, a first random number generation circuit  20  generating random numbers from the seeds that the SEED generation circuit  10  generates, and a first selector circuit  30  switching the lines  31  to  36  based on the first random numbers that the random number generation circuit  20  generates, and the IC-B has a second random number generation circuit  20  generating random numbers from seeds  13  that the SEED generation circuit  10  generates and a second selector circuit  30  switching the signal lines  31  to  36  employed based on the random numbers that the second random number generation circuit  20  generates. Although the SEED generation circuit  10  can be either in the IC-A or in the IC-B, the present embodiment shows an example in which it is in the IC-A. The first and second random number generation circuits  20  are supposed to have the same hardware structures in the IC-A and IC-B, and the same random numbers are formed from the same seeds in synchronization to each other. The first and second selector circuits  30  in the IC-A and the IC-B switch a corresponding relationship between internal signals and external input/output terminals based on the random numbers that the first and second random number generation circuits  20  generate in synchronization to each other. 
   An operation example of an interface security system according to the present invention is explained further in detail below. 
   First, SEED data that are seeds of random numbers are generated in the SEED generation circuit  10  before communication of signals (data) is performed between the IC-A and the IC-B such as at power on time of the apparatus main body. A specific example of the SEED generation circuit  10  is shown in FIG.  3 . 
   In  FIG. 3 , the SEED generation circuit  10  has an N-bit counter  11  and an N-bit latch circuit  12 . The N-bit counter  11  is a counter counting in synchronization with a clock signal and performs counting of necessary bit numbers (N bits). Even when this type of counter is not prepared specially, if there is a counter of a necessary bit number or more inside the IC, it can be employed. When not a counter but shift registers whose values constantly change are studded, necessary bit numbers of registers are selected and may be employed as data. 
   The N-bit latch circuit  12  generates N-bit data that the N-bit counter  11  generates as seeds of N-bit random numbers in synchronization with a latch signal. Accordingly, by the timing of sending this latch signal the values of SEED data are decided. Although that the timing of sending the latch signal may generally be an initial operation time such as at a time of power on, for example, when the case of a digital music player is taken, pressing down of a play button may be a trigger. A case may be effective in a sense to eliminate repeatability wherein a trigger is not of a certain regular cycle. By setting a trigger at a time when a circumstance of the system changes such as at a time of pressing down a play button, even if the synchronization falls into disorder, the synchronization can be restored. 
   It is set that the SEED data do not become zero. It is necessary to set a sequence in such a manner as to be generated over again when a zero is detected or to provide a circuit for setting a arbitrary value or the like. 
   The SEED data obtained like this are sent to both first and second random number generation circuits  20  of the IC-A and IC-B. Various modes can be devised for the first and second random number generation circuit  20 , and for example, a circuit generating a maximum long period sequence (M-sequence) which is generally popularly employed may be employed. 
   A specific example of a circuit generating 6-bit random numbers is shown in FIG.  4 . As shown in  FIG. 4 , the circuit inputs the 6-bit SEED data being initial values and is comprised of six steps R 0  to R 5  of linear shift registers and respective feedback taps so that 6-bit random numbers Q 0  to Q 5  of maximum 63 cycles can be generated. 
   The circuit generating such random numbers is provided as the first and second random number generation circuits  20  in both IC-A and IC-B. At this time, circuits of the same configurations are installed in both. That is, the same frequencies and phases of clocks of the shift registers are employed. Thus, both input the SEED data from the SEED generation circuit  10  as initial values to generate random numbers so that the random number data outputted from the first random number generation circuit  20  of the IC-A and the random number data outputted from the second random number generation circuit  20  of the IC-B become the same random numbers constantly. 
   As shown in  FIG. 5 , it is possible to provide a selector to form a circuit configuration so as to change the number of bits. In the example shown in  FIG. 5 , it is possible to select either a case where six-dimensional M-sequence is formed or a case where seven-dimensional M-sequence is formed and switch them by the selector. In this case, the number of bits of the SEED data sent from the SEED generation circuit  10  needs the number of bits corresponding to the M-sequence and the selected signal. 
   Then, the data outputted from the first and second random number generation circuits  20  are inputted to the selector circuits  30 , and the first and second selector circuits  30  work so as to connect the internal circuit and the external terminals in accordance with a fixed specific connection pattern.  FIG. 6  shows a specific example of the first and second selector circuit  30  selecting and switching three kinds of signals (DATA 1 , CLOCK 1 , AND SIGNAL 1 ). 
   The decoder circuits  30   b  of the first and second selector circuits  30  generate control signals controlling respective first and second switch circuits  30   a  based on the N-bit random number data generated by the first and second random number generation circuits  20  in the IC-A and IC-B. The first and second decoder circuits  30   b  may utilize, for example, ROM (Read Only Memory) or may be one utilizing a gate circuit. 
   Table 1 shows each value of 3-bit random numbers and a selection example of the switch circuits  30   a  corresponding thereto. The decoder circuits  30   b  generate control signals controlling the switch circuits  30   a  (SW 1  to SW 6 ) of the selector circuits  30  according to the connection pattern (corresponding relationship) regulated by that table, respectively. Since “000” is a value which cannot be taken in M-sequence as a random number value, “no data (−)” is given in the table. 
   
     
       
         
             
             
             
             
             
             
             
           
             
               TABLE 1 
             
             
                 
             
             
               RANDOM 
                 
                 
                 
                 
                 
                 
             
             
               NUMBER 
             
             
               VALUE 
               SW1 
               SW2 
               SW3 
               SW4 
               SW5 
               SW6 
             
             
                 
             
           
          
             
                        000 
               — 
               — 
               — 
               — 
               — 
               — 
             
             
               001 
               A 
               B 
               C 
               A 
               B 
               C 
             
             
               010 
               A 
               C 
               B 
               A 
               C 
               B 
             
             
               011 
               B 
               A 
               C 
               B 
               A 
               C 
             
             
               100 
               B 
               C 
               A 
               B 
               C 
               A 
             
             
               101 
               C 
               A 
               B 
               C 
               A 
               B 
             
             
               110 
               C 
               B 
               A 
               C 
               B 
               A 
             
             
               111 
               A 
               B 
               C 
               A 
               B 
               C 
             
             
                 
             
          
         
       
     
   
   For example, when the random number value is “001”, the decoder circuit  30   b  of the IC-A side gives control signals of SW 1 =A, SW 2 =B, SW 3 =C to the respective switches SW 1  to SW 3 . As a result, SW 1  of the selector circuit  30  is connected to DATA 1 , SW 2  CLOCK  1 , and SW 3  SIGNAL  1 . Similarly, the decoder circuit  30   b  of the IC-B side gives control signals of SW 4 =A, SW 5 =B, SW 6 =C to the respective switches SW 4  to SW 6 , and SW 4  of the selector circuit  30  is connected to DATA 1 , SW 5  CLOCK 1 , and SW 6  SIGNAL 1 . 
   Thus, an interface between the IC-A and the IC-B is established. That is, DATA 1  is transferred through the signal line  31 , CLOCK 1  the signal line  32 , and SIGNAL 1  the signal line  33 . 
   Then, for example, when the random number changes to “101”, the state is changed in such a manner that DATA 1  is transferred through the signal line  31 , CLOCK 1  the signal line  33 , and SIGNAL 1  the signal line  32 . 
   Both of the transmitting side and the receiving side synchronize to perform such switching, whereby exchange of data signals can be performed correctly. 
   By setting in such a manner that the random number values keep changing constantly, when, for example, an external terminal is directed attention, an outputted signal changes every time the random number value changes, whereby it becomes possible to disturb a person trying to exploit data falsely. The timing of generation of a random number and switching of signals is not only at the time of initial setting, and, for example, it may be set at a timing frequently switching such as at each time 1 data are sent, at a time of reference clock input of both ICs, or the like, thereby imparting further effectiveness. 
   Second Embodiment 
   In the first embodiment, explained is an example in which the inputs/outputs of the respective first and second external terminals of both ICs are fixed. In the present embodiment, explained is a mode in which bidirectional buffers are connected to the first and second external terminals, and input/output control of these bidirectional buffers is performed by random numbers that the random number generation circuits generate. A specific example in which the bidirectional buffers are employed is shown in FIG.  7 . 
   In the example shown in  FIG. 7 , its specification is supposed that there are three kinds of signals of DATA 1 , DATA 2 , and DATA 3  as internal signals, and DATA 1  and DATA 2  are sent from the IC-A to the IC-B, and inversely, DATA 3  is sent from the IC-B to the IC-A. first and second Bidirectional buffers IO 1  to IO 6  are installed between the switches SW 1  to SW 6  and the first and second external terminals. 
   The SEED generation circuit  10  and the first and second random number generation circuits  20  are similar to those explained in the first embodiment. 
   The decoder circuits  30   b  generate control signals controlling the switching circuits  30   a  (SW 1  to SW 6 ) of the first and second selector circuits  30  and further control signals controlling the bidirectional buffers IO 1  to IO 6  based on the random numbers that the first and second random number generation circuits  20  generate. 
   Table 2 shows each value of 3-bit random numbers, a selection example of the switch circuits  30   a  (SW 1  to SW 6 ) corresponding thereto, and an input/output switching example of the first and second bidirectional buffers IO 1  to IO 6 . In the table, “OUT” means that a signal from an external terminal of the IC is outputted, and “IN” means that a signal from the external is inputted to that terminal of the IC. 
   
     
       
         
             
             
             
             
             
             
             
             
             
             
             
             
             
           
             
               TABLE 2 
             
             
                 
             
             
               RANDOM 
                 
                 
                 
                 
                 
                 
                 
                 
                 
                 
                 
                 
             
             
               NUMBER 
             
             
               VALUE 
               SW1 
               SW2 
               SW3 
               SW4 
               SW5 
               SW6 
               IO1 
               IO2 
               IO3 
               IO4 
               IO5 
               IO6 
             
             
                 
             
           
          
             
               000 
               — 
               — 
               — 
               — 
               — 
               — 
               — 
               — 
               — 
               — 
               — 
               — 
             
             
               001 
               A 
               B 
               C 
               A 
               B 
               C 
               OUT 
               OUT 
               IN 
               IN 
               IN 
               OUT 
             
             
               010 
               A 
               C 
               B 
               A 
               C 
               B 
               OUT 
               IN 
               OUT 
               IN 
               OUT 
               IN 
             
             
               011 
               B 
               A 
               C 
               B 
               A 
               C 
               OUT 
               OUT 
               IN 
               IN 
               IN 
               OUT 
             
             
               100 
               B 
               C 
               A 
               B 
               C 
               A 
               OUT 
               IN 
               OUT 
               IN 
               OUT 
               IN 
             
             
               101 
               C 
               A 
               B 
               C 
               A 
               B 
               IN 
               OUT 
               OUT 
               OUT 
               IN 
               IN 
             
             
               110 
               C 
               B 
               A 
               C 
               B 
               A 
               IN 
               OUT 
               OUT 
               OUT 
               IN 
               IN 
             
             
               111 
               A 
               B 
               C 
               A 
               B 
               C 
               OUT 
               OUT 
               IN 
               IN 
               IN 
               OUT 
             
             
                 
             
          
         
       
     
   
   For example, when the random number value is “001”, the decoder circuit  30   b  of the IC-A side gives control signals of SW 1 =A, SW 2 =B, SW 3 =C to the respective switches SW 1  to SW 3  and further gives control signals of the first bidirectional buffer IO 1 =OUT, IO 2 =OUT, and IO 3 =IN to the respective buffers IO 1  to IO 3 . As a result, SW 1  of the selector circuit  30  is connected to DATA 1 , SW 2  DATA 2 , and SW 3  DATA 3 , and the bidirectional buffer IO 1  is controlled to do output, IO 2  also to output, and IO 3  to input. Similarly, the decoder circuit  30   b  of the IC-B side gives control signals of SW 4 =A, SW 5 =B, SW 6 =C to the respective switches SW 4  to SW 6 , the switch SW 4  of the selector circuit  30  is connected to DATA 1 , the switch SW 5  DATA  2 , and the switch SW 6  DATA  3 , and the second bidirectional buffer IO 4  is controlled to do input, IO 5  also to output, and IO 6  to output. 
   Thus, an interface between the IC-A and the IC-B is established. That is, DATA  1  is transferred from the IC-A to the IC-B through the signal line  31 , DATA  2  is transferred from the IC-A to the IC-B through the signal line  34 , and DATA  3  is transferred from the IC-B to the IC-A through the signal line  37 . 
   Similarly, when the random number changes to “010”, the state is changed so that DATA 1  is transferred from the IC-A to the IC-B through the signal line  31 , DATA 2  is transferred from the IC-A to the IC-B through the signal line  37 , and DATA 3  is transferred from the IC-B to the IC-A through the signal line  34 . 
   Since variations in combination are likely to be limited if only control of change in a row of signals is performed, by adding control of input/output further, more complex connections can be performed. 
   (Third Embodiment) 
   Although in the first embodiment and the second embodiment, shown is an example in which the SEED generation circuit  10  is installed in the IC-A (or the IC-B), in the present embodiment, shown in  FIG. 8  is an example in which the SEED generation circuit  10  is installed in the external. 
   As shown in the drawing, seeds of random numbers  13  (SEED data) are sent from the SEED generation circuit  10  arranged in the external to the first and second random number generation circuits  20  of the respective ICs (IC-A and IC-B). This SEED generation circuit  10  may be installed as one chip of the external or may be incorporated in a microcomputer section or the like controlling the entire system. When it is incorporated in a microcomputer, a mechanism may be taken wherein the seeds are software-like generated. 
   By configuring like this, shown parts of the IC-A and IC-B can have the same configurations. 
   (Fourth Embodiment) 
   When the SEED data generated inside the IC-A are sent to the IC-B, in order to enhance the concealment property of the sent data, such data may be encrypted and sent. Its example is shown in FIG.  9 . The configuration exemplified in the present embodiment is similar to the configuration example previously shown in  FIG. 6  except that a cryptography circuit  41  is provided inside the IC-A and a decode circuit  42  inside the IC-B. 
   The SEED data that the SEED generation circuit  10  inside the IC-A generates are sent to the first random number generation circuit  20  and the cryptography circuit  41  inside the IC-A. The cryptography circuit  41  gives an encryption process to the inputted SEED data in a predetermined mode and transmits them to the IC-B. 
   The encrypted SEED data are inputted in the decode circuit  42  inside the IC-B, and the decode circuit  42  performs a decode process for restoring the encrypted SEED data in a predetermined mode. The decoded SEED data are inputted to the second random number generation circuit  20  in the IC-B. Processing operations on and after the first and second random number generation circuit  20  are similar to those in the example shown in the first embodiment. Although the present embodiment is shown as a variation example of the first embodiment, it is possible to combine with the second embodiment or the third embodiment. 
   As described above, by encrypting the SEED data so that a third party cannot decrypt, transferring them from the IC-A to the IC-B, and switching the connection pattern between the internal signals and the external input/output terminals in the connection between the devices based on the random numbers generated through the SEED data decoded in the same mode as that employed in the encryption, the concealment property can be further enhanced. 
   A cryptography mode employed in the cryptography circuit  41  and the decode circuit  42  is not specifically limited and may be, for example, an existing cryptography mode such as a public key cryptography such as RSA(Rivest-Shamir-Adleman) cryptography. 
   Other than the method in which the above-mentioned cryptography is employed, a method may be adopted wherein the SEED generation circuit  10  may be set so as to constantly output various values, and the first and second random number generation circuits  20  may acquire the SEED data from them at a specific timing. For example, a prescript may be adopted wherein when a predetermined value is outputted from the SEED generation circuit  10 , m-th data counted from that value are employed. 
   (Fifth Embodiment) 
   Although in the first embodiment to the fourth embodiment, explained is a mode in which so called pseudo-random numbers are employed, in the present embodiment, explained is an example in which physical random numbers generated by utilizing a random phenomenon in the natural world are employed as random numbers whose periodicity, regularity, and repeatability are lower and whose unpredictability is higher. 
   As shown in  FIG. 10 , a physical random number generation circuit  44  is provided inside the IC-A, and this physical random number generation circuit  44  measures the interval of generation or the frequency of generation of random pulses generated from an external noise source  43  and generates physical random numbers. The physical random numbers that the physical random number generation circuit  44  generates are inputted to the first and second selector circuits  30  inside the IC-A and IC-B. Processing operations on and after the first and second selector circuits  30  are similar to those in the example shown in the first embodiment. Although the present embodiment is shown as a variation example of the first embodiment, it is of course possible to combine with the second embodiment, the third embodiment, or the fourth embodiment. 
   For example, electrical noise such as a thermal noise is given as the random pulse generated from the noise source  43 . Other than the mode in which the noise source  43  is provided in the external, for example, a random signal of the thermoelectron in a semiconductor element or the like may be utilized. 
   By employing the physical random number whose unpredictability is high and switching the corresponding relationship between the internal signals and the external input/output terminals in the connection between devices, the concealment property can be further enhanced. 
   (Sixth Embodiment) 
   Although in the first embodiment through the fourth embodiment, shown is an example in which the pseudo-random number generation circuits are employed and in the fifth embodiment the physical random number generation circuit is employed, in the present embodiment, shown is an example in which counters are employed instead of random numbers. 
   As shown in  FIG. 11 , counter values generated in first and second counters  46  inside the IC-A and the IC-B are inputted to the decoder circuits  30   b , respectively, and the decoder circuits  30   b  switch a connection pattern between devices according to the inputted counter values. At this time, when the decoder circuits  30   b  convert the inputted counter values according to a predetermined mode set up between devices in advance and switch the connection pattern between the internal signals and the external input/output terminals in the connection between the devices, employing the values after the conversion, the concealment property can be further enhanced. 
   By a synchronizing signal that a synchronizing signal generation circuit  45  in the IC-A generates at a predetermined timing, the counter values that the first and second counters  46  in the respective ICs generate can be synchronized, and when the counter values are frequently reset, it is possible to disturb a person who is trying to exploit data. 
   The above can be realized only by employing simple counter circuits instead of a complex random number generation circuit, and there is no restriction or the like that, for example, a special process is needed in a case where the SEED data value is zero such as in the M-sequence random number generation circuits explained before. 
   (Processing Operation Example) 
   The first embodiment through the sixth embodiment are explained in detail above, and here, processing operation examples by an interface security system according to the present invention are explained in detail. 
     FIG. 12  is a flow chart showing a processing operation example by the interface security system, for example, shown in the first embodiment and the second embodiment. That is, the processing operation example corresponds to a mode in which seeds of random numbers are generated in the SEED generation circuit  10  inside the IC-A and are utilized in the random number generation circuit inside the IC-A as well as being transferred to the random number generation circuit inside the IC-B. 
   For example, the SEED generation circuit  10  inside the IC-A generates a seed of a random number, n, (Step 02 ) on a predetermined trigger such as at a time of power on or at a time of play button pressing (Step 01 ) and transfers this seed of a random number, n, to the IC-B side (Step 03 ). 
   Then, inside the respective IC-A and IC-B, the following processing is performed. First, the first and second random number generation circuits  20  are initialized by the seed of a random number, n, (Step 11  and Step 21 ), and the random number generation circuits  20  generate pseudo-random numbers (Step 12  and Step 22 ). Further, the first and second selector circuits  30  decide a connection pattern based on pseudo-random numbers generated from the random number generation circuits  20  and switch the corresponding relationship of the connection between the IC-A and B (connection pattern between the internal signals and the external input/output terminals) in synchronization to each other (Step 13  and Step 23 ). After the corresponding relationship of the connection between the IC-A and B is established, sending/receiving data is performed between the IC-A and B (Step 14  and Step 24 ). 
   After the connection pattern is decided and switched at Step 13  and Step 23 , until a predetermined time period (T time) elapses, data transmitting/receiving processing is continuously performed between the IC-A and B (Step  14  and Step  24 ). After the predetermined time period (T time) elapses (Step 15  and Step 25 ), the steps return to Step 12  and Step 22  again, the random number generation circuits  20  generate new pseudo-random numbers, and the first and second selector circuits  30  decide a new connection pattern based on the pseudo-random numbers (Step 13  and Step 23 ). 
   When a predetermined trigger is generated (Step 01 ), the SEED generation circuit  10  inside the IC-A generates a seed of a random number, n, over again (Step 02 ) and transfers this seed of a random number, n, to the IC-B side (Step 03 ). 
     FIG. 13  is a flow chart showing a processing operation example by an interface security system shown, for example, in the third embodiment. That is, the example is a processing operation example of a mode in which a seed of a random number is generated in the SEED generation circuit  10  of the external and is transferred to the first random number generation circuit of the IC-A and the second random number generation circuit of the IC-B. 
   For example, a seed of a random number, n, is generated in the SEED generation circuit  10  installed in the external (Step 32 ) on a predetermined trigger such as at a time of power on or a time of play button pressing (Step 31 ), and this seed of a random number, n, is transferred to both of the IC-A and the IC-B (Step 33 ). 
   Then, the following processing is performed in the respective IC-A and the IC-B. First, the first and second random number generation circuits  20  are initialized by the seed of a random number, n, (Step 41  and Step 51 ), and the first and second random number generation circuits  20  generate pseudo-random numbers (Step 42  and Step 52 ). The first and second selector circuits  30  decide a connection pattern based on the pseudo-random numbers generated from the first and second random number generation circuits  20  and switch a corresponding relationship in the connection between the IC-A and B (connection pattern between the internal signals and the external input/output terminals) in synchronization to each other (Step 43  and Step 53 ). After the connection pattern between the IC-A and B is established, sending/receiving data is performed between the IC-A and B (Step 44  and Step 54 ). 
   After the connection pattern is decided and switched at Step 43  and Step 53 , until a predetermined time period (T time) elapses, data transmitting/receiving processing is continuously performed between the IC-A and B (Step 44  and Step 54 ) After the predetermined time period (T time) elapses (Step 45  and Step 55 ), the steps return to Step 12  and Step 22  again, the random number generation circuits  20  generate new pseudo-random numbers, and the first and second selector circuits  30  decide a new connection pattern based on the pseudo-random numbers (Step 43  and Step 53 ). 
   When a predetermined trigger is generated (Step 31 ), the SEED generation circuit  10  in the external generates a seed of a random number, n, over again (Step 32 ) and transfers this seed of a random number, n, to both of the IC-A and the IC-B (Step 33 ). 
   Although in the processing operation examples shown in FIG.  12  and  FIG. 13 , the connection pattern is switched every predetermined time (T time), by setting the value of T so as to change randomly, a further effectiveness maybe brought about. 
   Although FIG.  12  and  FIG. 13  show the processing operation examples in which switching of the corresponding relationship in the connection between the IC-A and B (connection pattern between the internal signals and the external input/output terminals) is performed every predetermined time (T time), next shown is a processing operation example in which switching of the connection pattern is performed every time data transmission/reception is performed between the IC-A and B. 
     FIG. 14  corresponds to a processing operation example of a case where the connection pattern is switched every time data transmission/reception is performed between the IC-A and B in a mode in which a seed of a random number is generated in the SEED generation circuit  10  inside the IC-A, is utilized in the first random number generation circuit  20  inside the IC-A, and is transferred to the second random number generation circuit  20  inside the IC-B. A difference from the process shown in  FIG. 12  is that after the data transmission/reception is performed between the IC-A and B (Step 14  and Step 24 ), the steps return to Step 12  and Step 22  again unconditionally, the first and second random number generation circuits  20  generate new pseudo-random numbers, and the first and second selector circuits  30  decide a new connection pattern based on the pseudo-random numbers (Step 13  and Step 23 ). 
     FIG. 15  corresponds to a processing operation example of a case where the connection pattern is switched every time data transmission/reception is performed between the IC-A and B in a mode in which a seed of a random number is generated in the SEED generation circuit  10  in the external and is utilized in the first random number generation circuit inside the IC-A and the second random number generation circuit inside the IC-B. A difference from the process shown in  FIG. 13  is that after the data transmission/reception is performed between the IC-A and B (Step 44  and Step 54 ), the steps return to Step 42  and Step 52  again unconditionally, the first and second random number generation circuits  20  generate new pseudo-random numbers, and the first and second selector circuits  30  decide a new connection pattern based on the pseudo-random numbers (Step 43  and Step 53 ). 
   As shown in FIG.  14  and  FIG. 15 , since the connection pattern is switched every time data transmission/reception is performed between the IC-A and B, illegal copy or the like can be prevented further effectively. 
   Additional advantage and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by appended claims and their equivalents. 
   For example, although an interface between ICs is explained as an example in the present embodiments, the present invention is not limited to an interface between ICs and can be applied to various parts between devices which may be an interface. 
   As explained above, in the present invention, since a corresponding relationship between transmitted/received signals and external terminals is switched in accordance with a connection pattern fixed between the respective devices, it becomes difficult for a third party to specify data flowing between the devices, and illegal copy of data or the like can be prevented. 
   When a connection pattern is selected, by utilizing random numbers or the like whose periodicity, regularity, and repeatability are low and whose unpredictability is high, a further effectiveness may be brought about. 
   By switching not only a corresponding relationship between transmitted/received signals and external terminals but also a terminal input/output relationship, specifying data flowing between devices becomes further difficult.