TECHNICAL FIELD 
       [0001]    The present invention relates to a data processing apparatus capable of encrypting subject data in plain text to render it as encrypted data and then recording it on a predetermined recording medium and also decrypting the encrypted data read from the recording means, and applications thereof. 
       BACKGROUND OF THE INVENTION 
       [0002]    Nowadays, security relating to information is becoming increasingly important, and there is significantly growing demand for the above-mentioned data processing apparatus capable of encrypting the data of which contents should not desirably be known to a third party (referred to as “subject data” in this specification) and recording it on a recording medium. While various encryption techniques are proposed and put into practical use for the sake of keeping the subject data secret, it is difficult to prevent code breaking completely. 
         [0003]    In general, the subject data is encrypted and recorded on the recording medium by cutting the subject data by a predetermined number of bits and recording encrypted data having pieces of the cut data encrypted respectively bound therein on a predetermined recording medium. 
         [0004]    In the case of encrypting each piece of the cut data of the subject data, predetermined algorithm and key are generally used. This algorithm is rendered very complicated to prevent the code breaking, and the key is also strictly managed so as not to be known to the outside. No matter how complicated the algorithm is rendered or even if the key is changed, however, it is relatively easy, once the algorithm and key are known, to break the encrypted data by using the algorithm and key. 
         [0005]    The inventors hereof studied encryption technology for many years and previously invented a data processing apparatus for successively generating at least one of the algorithm and key for performing the encryption and decryption. 
         [0006]    This technique successively generates at least one of the algorithm and key for performing the encryption and decryption. Even in the case where the algorithm or the key is known once, the algorithm or the key or both of them change thereafter. Therefore, strength thereof is much higher than conventional encryption technology. 
         [0007]    As for this technique, however, there is a weakness that, if some of the past algorithms or keys are known, it may be predictable how the algorithm or the key or both of them change from now on. Thus, a possibility of being broken by a third party is not absolutely zero. 
         [0008]    An object of the present invention is to improve the data processing apparatus for encrypting the subject data in plain text to render it as encrypted data and recording it on a predetermined recording medium so as to reduce the possibility of having communication broken by a third party. 
       DISCLOSURE OF THE INVENTION 
       [0009]    To achieve the object, the inventors hereof propose a first invention, a second invention and a third invention described below. 
         [0010]    The first invention of the present invention is as follows. 
         [0011]    The first invention is a data processing apparatus including encrypting means for encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data, recording means for recording the encrypted data, and decrypting means for decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, comprising: solution generating means for sequentially generating new solutions in predetermined timing by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; algorithm generating means for sequentially generating new algorithms in predetermined timing by using the generated solutions; and specific information recording means for recording specific information for identifying the algorithm used when encrypting the subject data in predetermined recording means by associating it with the encrypted data, and wherein: the solution generating means holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0012]    The algorithm generating means of the data processing apparatus generates the algorithms in predetermined timing, such as each time the subject data is encrypted or the encrypted data is decrypted. And the solution generating means of the data processing apparatus uses a predetermined solution obtained by assigning at least one of the past solutions to the solution generating algorithm in the case of generating the solution and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0013]    In other word, the data processing apparatus successively generates the algorithms used for encryption and decryption by the algorithm generating means. The algorithm generating means uses the “solutions” in the case of generating the algorithms. As described above, the solutions are generated by using the past solutions. Furthermore, these solutions are erased once they become unnecessary to generate new solutions. 
         [0014]    Therefore, the data processing apparatus has the past solutions erased one after another. For this reason, even if the solutions at this point in time can be known by a third party, a third party cannot know the route which the solution has traced thereof. 
         [0015]    For the above reason, there is only a little possibility that encrypted communication by this data processing apparatus may be broken by the third party. 
         [0016]    The above-mentioned solutions may be pseudo-random numbers as a result. 
         [0017]    The data processing apparatus of the above-mentioned first invention changes the algorithms. However, it may also change the keys. The same effects as in the above-mentioned case can thereby be obtained. 
         [0018]    For instance, this is exemplified by a data processing apparatus including encrypting means for encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data, recording means for recording the encrypted data, and decrypting means for decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, comprising: solution generating means for sequentially generating new solutions in predetermined timing by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; key generating means for sequentially generating new keys in predetermined timing by using the generated solutions; and specific information recording means for recording specific information for identifying the key used when encrypting the subject data in predetermined recording means by associating it with the encrypted data, and wherein: the solution generating means holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0019]    The data processing apparatus of the first invention may also be the one wherein: it comprises cutting means capable of cutting the subject data by a predetermined number of bits into multiple pieces of plain text cut data and also cutting the encrypted data into multiple pieces of encrypted cut data by the same number of bits by which the encrypted data is cut when encrypted; the encrypting means adapted to encrypt the processing subject data by encrypting each piece of the plain text cut data cut the subject data by the cutting means to render it as the encrypted cut data, and the decrypting means adapted to decrypt by decrypting each piece of the encrypted cut data to render it as the plain text cut data; and it also comprises connecting means for connecting multiple pieces of the encrypted cut data encrypted by the encrypting means into a series of the encrypted data and also connecting multiple pieces of the plain text cut data decrypted by the decrypting means into a series of the subject data. 
         [0020]    In the data processing apparatus of the first invention comprising the algorithm generating means, the algorithm may be generated in any timing whatsoever. 
         [0021]    For instance, the algorithm generating means may generate the algorithms each time the subject data is encrypted. Thus, different algorithms are generated each time the processing subject data is encrypted, and so it is difficult for the third party to know the algorithms by analogy. 
         [0022]    The algorithm generating means may generate the algorithms each time the plain text cut data is encrypted. Thus, the algorithms are generated more frequently, and so it is more difficult for the third party to know the algorithms by analogy. 
         [0023]    In the data processing apparatus of the first invention comprising the key generating means, the key may be generated in any timing whatsoever. 
         [0024]    For instance, the key generating means may generate the keys each time the subject data is encrypted. Thus, different keys are generated each time the processing subject data is encrypted, and so it is difficult for the third party to know the keys by analogy. 
         [0025]    The key generating means may generate the keys each time the plain text cut data is encrypted. Thus, the keys are generated more frequently, and so it is more difficult for the third party to know the keys by analogy. 
         [0026]    The solution generating means generates the new solutions from the past solutions. It may acquire the solutions by assigning multiple past solutions to the solution generating algorithm. To be more specific, either one past solution or multiple past solutions may be assigned to the solution generating algorithm in order to generate the new solutions. 
         [0027]    The solution generating means may hold an initial solution to be assigned to the solution generating algorithm first on initially generating the solutions. 
         [0028]    The specific information used on the data processing apparatus of the first invention comprising the algorithm generating means may be any information as long as it can identify the algorithm used when encrypting the subject data. 
         [0029]    For instance, the specific information may be the algorithm itself, the solutions used by the algorithm generating means on generating the algorithm or information indicating what number generated solutions are the solutions used by the algorithm generating means on generating the algorithm. 
         [0030]    The specific information used on the data processing apparatus of the first invention comprising the key generating means may be any information as long as it can identify the key used when encrypting the subject data. 
         [0031]    For instance, the specific information may be the key itself, the solutions used by the key generating means on generating the key or information indicating what number generated solutions are the solutions used by the key generating means on generating the key. 
         [0032]    The same effects as the data processing apparatus of the first invention comprising the algorithm generating means may be obtained by the following method for instance. 
         [0033]    This method is the one performed in a data processing apparatus for performing steps of: encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data; recording the encrypted data in predetermined recording means; and decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data. 
         [0034]    And the data processing apparatus performs the steps of: sequentially generating new solutions in predetermined timing by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; sequentially generating new algorithms in predetermined timing by using the generated solutions; and recording specific information for identifying the algorithm used when encrypting the subject data in predetermined recording means by associating it with the encrypted data, and the data processing apparatus holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0035]    The same effects as the data processing apparatus of the first invention comprising the key generating means may be obtained by the following method for instance. 
         [0036]    This method is the one performed in a data processing apparatus for performing steps of: encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data; recording the encrypted data in predetermined recording means; and decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data. 
         [0037]    And the data processing apparatus performs the steps of: sequentially generating new solutions in predetermined timing by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; sequentially generating new keys in predetermined timing by using the generated solutions; and recording specific information for identifying the key used when encrypting the subject data in predetermined recording means by associating it with the encrypted data, and the data processing apparatus holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0038]    The second invention of this application is as follows. 
         [0039]    The second invention of this application is a data processing apparatus including encrypting means for encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data, recording means for recording the encrypted data, and decrypting means for decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, which encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof, the apparatus comprising: solution generating means for sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; first algorithm generating means for sequentially generating new algorithms each time the subject data is encrypted by using the generated solutions; second algorithm generating means for sequentially generating the same new algorithms as those generated by the first algorithm generating means each time the encrypted data is decrypted by using the generated solutions, and wherein: the solution generating means holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0040]    The above-mentioned second invention changes the algorithms. However, there are also the cases where it changes the keys as with the first invention. 
         [0041]    The second invention in this case is a data processing apparatus including encrypting means for encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data, recording means for recording the encrypted data, and decrypting means for decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, which encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof, the apparatus comprising: solution generating means for sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; first key generating means for sequentially generating new keys each time the subject data is encrypted by using the generated solutions; second key generating means for sequentially generating the same new keys as those generated by the first key generating means each time the encrypted data is decrypted by using the generated solutions, and wherein: the solution generating means holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0042]    The data processing apparatus of the second invention is similar to that of the first invention. However, it does not use the specific information for identifying the algorithm or the key used when encrypting the subject data. This is related to it that the data processing apparatus of the second invention encrypts multiple pieces of the subject data to render it as encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof. 
         [0043]    The algorithm generating means and the key generating means of the data processing apparatus of the second invention generate the algorithms and keys each time the subject data is encrypted respectively. When performing the decryption, the data processing apparatus of the second invention generates the same algorithms and keys as those used when performing the encryption. 
         [0044]    Therefore, the data processing apparatus of the second invention sequentially generates the same algorithms or keys as those generated in the past. For that reason, it is not necessary to use the above-mentioned specific information if only the multiple pieces of the encrypted data are decrypted in the same order as the order of encryption thereof. 
         [0045]    The two data processing apparatuses of the second invention have one solution generating means common between the first algorithm generating means and second algorithm generating means or the first key generating means and second key generating means provided thereto. It is also possible, however, to provide two solution generating means corresponding to the first algorithm generating means and second algorithm generating means respectively or the first key generating means and second key generating means respectively. 
         [0046]    As an example of the former, there is a data processing apparatus including encrypting means for encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data, recording means for recording the encrypted data, and decrypting means for decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, which encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof, the apparatus comprising: first solution generating means for sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; first algorithm generating means for sequentially generating new algorithms each time the subject data is encrypted by using the solutions generated by the first solution generating means; second solution generating means for sequentially generating the same new solutions as those generated by the first solution generating means each time the encrypted data is decrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; second algorithm generating means for sequentially generating the same new algorithms as those generated by the first algorithm generating means each time the encrypted data is decrypted by using the solutions generated by the second solution generating means, and wherein: the first solution generating means and the second solution generating means hold at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0047]    As an example of the latter, there is a data processing apparatus including encrypting means for encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data, recording means for recording the encrypted data, and decrypting means for decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, which encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof, the apparatus comprising: first solution generating means for sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; first key generating means for sequentially generating new keys each time the subject data is encrypted by using the solutions generated by the first solution generating means; second solution generating means for sequentially generating the same new solutions as those generated by the first solution generating means each time the encrypted data is decrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; second key generating means for sequentially generating the same new keys as those generated by the first key generating means each time the encrypted data is decrypted by using the solutions generated by the second solution generating means, and wherein: the first solution generating means and the second solution generating means hold at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew. 
         [0048]    The data processing apparatus of the second invention may be the one wherein: it comprises cutting means capable of cutting the subject data by a predetermined number of bits into multiple pieces of plain text cut data and also cutting the encrypted data into multiple pieces of encrypted cut data by the same number of bits by which the encrypted data is cut when encrypted; the encrypting means adapted to encrypt the processing subject data by encrypting each piece of the plain text cut data cut the subject data by the cutting means to render it as the encrypted cut data, and the decrypting means adapted to decrypt by decrypting each piece of the encrypted cut data to render it as the plain text cut data; and it also comprises connecting means for connecting multiple pieces of the encrypted cut data encrypted by the encrypting means into a series of the encrypted data and also connecting multiple pieces of the plain text cut data decrypted by the decrypting means into a series of the subject data. 
         [0049]    The second invention may also be implemented by the following method. 
         [0050]    A first example of the second invention is a method performed in a data processing apparatus for performing steps of: encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data; recording the encrypted data in predetermined recording means; and decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data. According to this method, the data processing apparatus performs: a step of sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; a first algorithm generating step of sequentially generating new algorithms each time the subject data is encrypted by using the generated solutions; and a second algorithm generating step of sequentially generating the same new algorithms as those generated in the first algorithm generating step each time the encrypted data is decrypted by using the generated solutions, and the data processing apparatus holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew, encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof. 
         [0051]    A second example is a method performed in a data processing apparatus for performing steps of: encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data; recording the encrypted data in predetermined recording means; and decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data. According to this method, he data processing apparatus performs: a step of sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; a first key generating step of sequentially generating new keys each time the subject data is encrypted by using the generated solutions; and a second key generating step of sequentially generating the same new keys as those generated in the first key generating step each time the encrypted data is decrypted by using the generated solutions, and the data processing apparatus holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew, encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof. 
         [0052]    A third example is a method performed in a data processing apparatus for performing steps of: encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data; recording the encrypted data in predetermined recording means; and decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data. According to this method, the data processing apparatus performs: a first solution generating step of sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; a first algorithm generating step of sequentially generating new algorithms each time the subject data is encrypted by using the solutions generated in the first solution generating step; and a second solution generating step of sequentially generating the same new solutions as those generated in the first solution generating step each time the encrypted data is decrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; a second algorithm generating step of sequentially generating the same new algorithms as those generated in the first algorithm generating step each time the encrypted data is decrypted by using the solutions generated in the second solution generating step, and the data processing apparatus holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew, encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof. 
         [0053]    A fourth example is a method performed in a data processing apparatus for performing steps of: encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data; recording the encrypted data in predetermined recording means; and decrypting the encrypted data read from the recording means by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, wherein: the data processing apparatus performs: a first solution generating step of sequentially generating new solutions each time the subject data is encrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; a first key generating step of sequentially generating new keys each time the subject data is encrypted by using the solutions generated in the first solution generating step; and a second solution generating step of sequentially generating the same new solutions as those generated in the first solution generating step each time the encrypted data is decrypted by assigning past solutions to a predetermined solution generating algorithm capable of generating a new solution by assigning at least one of the past solutions thereto; a second key generating step of sequentially generating the same new keys as those generated in the first key generating step each time the encrypted data is decrypted by using the solutions generated in the second solution generating step, and the data processing apparatus holds at least one of the past solutions and also erases the past solutions when it is no longer necessary to assign them anew, encrypts multiple pieces of the subject data to render them as the encrypted data and decrypts multiple pieces of the encrypted data in the same order as the order of encryption thereof. 
         [0054]    The inventors hereof also propose the following third invention. 
         [0055]    The third invention is a data processing system comprising: multiple first data processing apparatuses; and second data processing apparatuses and third data processing apparatuses of the same number as the first data processing apparatuses, pairing up with the multiple first data processing apparatuses respectively, and communication between the first data processing apparatus is performed in encrypted data having encrypted subject data in plain text, and communication between the second data processing apparatus and the third data processing apparatus is performed in the subject data. 
         [0056]    It is a data processing system wherein both the first data processing apparatus and second data processing apparatus comprise: cutting means for cutting the subject data by a predetermined number of bits into multiple pieces of plain text cut data and also cutting the encrypted data into multiple pieces of encrypted cut data by the same number of bits by which the encrypted data is cut when encrypted; solution generating means for sequentially generating solutions common between the first data processing apparatuses and the second data processing apparatuses as pairs and different from the other first data processing apparatuses and second data processing apparatuses; encrypting and decrypting means for encrypting the plain text cut data with the algorithm common between the first data processing apparatus and the second data processing apparatus generated based on the solution received from the solution generating means to render it as the encrypted cut data and decrypting the encrypted cut data with the algorithm used when encrypting the encrypted cut data to render it as the plain text cut data; connecting means for connecting the decrypted plain text cut data to render it as the subject data; and transmitting and receiving means for transmitting and receiving the encrypted data, and the third data processing apparatus is one of the data processing apparatuses described in the first invention and the second invention for encrypting the subject data generated by the second data processing apparatus by decrypting the encrypted data encrypted by the first data processing apparatus, recording the encrypted data in the recording means, and decoding the encrypted data read from the recording means and transmitting it to the second data processing apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0057]      FIG. 1  is a diagram showing an overall configuration of a data processing system according to a first embodiment; 
           [0058]      FIG. 2  is a diagram showing a hardware configuration of a first data processing apparatus included in the data processing system shown in  FIG. 1 ; 
           [0059]      FIG. 3  is a block diagram showing a configuration of a communication apparatus included in the first data processing apparatus shown in  FIG. 2 ; 
           [0060]      FIG. 4  is a block diagram showing the configuration of an encryption apparatus included in the first data processing apparatus shown in  FIG. 2 ; 
           [0061]      FIG. 5  is a diagram showing the hardware configuration of a second data processing apparatus included in the data processing system shown in  FIG. 1 ; 
           [0062]      FIG. 6  is a block diagram showing the configuration of the encryption apparatus included in the second data processing apparatus shown in  FIG. 5 ; 
           [0063]      FIG. 7  is a block diagram showing the configuration of another encryption apparatus included in the second data processing apparatus shown in  FIG. 5 ; 
           [0064]      FIG. 8  is a block diagram showing the configuration of the communication apparatus included in the second data processing apparatus shown in  FIG. 5 ; 
           [0065]      FIG. 9  is a flowchart showing a flow of a process executed in the data processing system shown in  FIG. 1 ; 
           [0066]      FIG. 10  is a flowchart showing the flow of a process executed in S 110  shown in  FIG. 9 ; 
           [0067]      FIG. 11  is a flowchart showing the flow of a process executed in S 130  shown in  FIG. 9 ; 
           [0068]      FIG. 12  is a flowchart showing the flow of a process executed in S 140  shown in  FIG. 9 ; 
           [0069]      FIG. 13  is a flowchart showing the flow of a process executed in S 150  shown in  FIG. 9 ; 
           [0070]      FIG. 14  is a diagram showing the hardware configuration of the encryption apparatus included in the data processing apparatus of a second embodiment; 
           [0071]      FIG. 15  is a flowchart showing the flow of an encryption process executed in the data processing apparatus of the second embodiment; 
           [0072]      FIG. 16  is a flowchart showing the flow of a decryption process executed in the data processing apparatus of the second embodiment; and 
           [0073]      FIG. 17  is a diagram showing the hardware configuration of the encryption apparatus included in a deformed example of the data processing apparatus of the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0074]    Hereunder, a first preferred embodiment and a second preferred embodiment of the present invention will be described in detail by referring to the drawings. The descriptions of the first embodiment and second embodiment will use common symbols as to common portions and omit overlapping descriptions. 
       First Embodiment 
       [0075]    A data processing system of this embodiment will be configured in outline as shown in  FIG. 1 . 
         [0076]    The data processing system includes multiple first data processing apparatuses  11  and one second data processing apparatus  12  mutually connected via a network  13 . The network  13  is an LAN (Local Area Network) according to this embodiment. 
         [0077]    The multiple first data processing apparatuses  11  and the second data processing apparatus  12  mutually perform encrypted communication. 
         [0078]    The network  13  may have another configuration if capable of data exchange between the first data processing apparatuses  11  and the second data processing apparatus  12 . 
         [0079]    The configurations of the first data processing apparatus  11  and the second data processing apparatus  12  will be described. First, the configuration of the first data processing apparatus  11  will be described. 
         [0080]      FIG. 2  shows a hardware configuration of the first data processing apparatus  11 . 
         [0081]    The first data processing apparatus  11  has configurations including a CPU (central processing unit)  21 , an ROM (read only memory)  22 , an HDD (hard disk drive)  23 , an RAM (random access memory)  24 , an input apparatus  25 , a display apparatus  26 , an encryption apparatus  27 , a communication apparatus  28  and a bus  29 . The CPU  21 , ROM  22 , HUD  23 , RAM  24 , input apparatus  25 , display apparatus  26 , encryption apparatus  27  and communication apparatus  28  can exchange data via the bus  29 . 
         [0082]    The ROM  22  or the HDD  23  has a predetermined program and predetermined data (the predetermined data may include subject data as in the case of this embodiment, and includes the data necessary to execute the program) recorded therein. The CPU  21  controls the entire first data processing apparatuses  11 , and performs the process described later based on the program and data stored in the ROM  22  or the HDD  23 . The RAM  24  is used as a storage area for work for performing the process on the CPU  21 . 
         [0083]    The input apparatus  25  is configured by a keyboard, a mouse and so on, and is used to input a command and data. The display apparatus  26  is configured by an LCD (liquid crystal display), a CRT (cathode ray tube) and so on, and is used to display the command, inputted data, a processing status described later and so on. 
         [0084]    The encryption apparatus  27  encrypts the subject data and decrypts encrypted data as will be described later. 
         [0085]    The communication apparatus  28  performs communication with the second data processing apparatuses  12  via the network  13 . The communication apparatus  28  of the second data processing apparatuses  12  performs communication with the first data processing apparatuses  11  via the network  13 . 
         [0086]    Next, the configuration of the communication apparatus  28  will be described.  FIG. 3  shows a block diagram of the communication apparatus  28 . 
         [0087]    The communication apparatus  28  is configured by an interface portion  281 , an authentication data generating portion  282  and a communication portion  283 . 
         [0088]    The interface portion  281  exchanges the data between the bus  29  and the communication apparatus  28 . The interface portion  281  transmits the encrypted data received from the bus  29  to the authentication data generating portion  282 , and also transmits the encrypted data received from the communication portion  283  to the bus  29 . 
         [0089]    The authentication data generating portion  282  adds authentication data to a header of the transmitted encrypted data, for instance, in the case the encrypted data is transmitted to the second data processing apparatuses  12  as will be described later. The authentication data identifies the first data processing apparatus  11  sending the encrypted data. The authentication data is assigned to each of the first data processing apparatuses  11  by an administrator of the second data processing apparatus  12 , and is recorded on the ROM  22  or the HDD  23  for instance. The authentication data generating portion  282  adds the authentication data read from the ROM  22  or the HDD  23  to the encrypted data. The second data processing apparatus  12  can grasp which first data processing apparatus  11  the received encrypted data is transmitted from by the authentication data added to the encrypted data as will be described later. The authentication data generating portion  282  transmits the encrypted data having the authentication data added thereto to the communication portion  283 . The communication portion  283  transmits the received encrypted data to the second data processing apparatus  12 . 
         [0090]    Next, the configuration of the encryption apparatus  27  will be described.  FIG. 4  shows a block diagram of the encryption apparatus  27 . 
         [0091]    The encryption apparatus  27  is configured by an interface portion  271 , a preprocessing portion  272 , an encrypting and decrypting portion  273 , a solution generating portion  274 , an algorithm generating portion  275 , a key generating portion  276  and a connecting portion  277 . 
         [0092]    The interface portion  271  exchanges data between the bus  29  and the communication apparatus  28 . 
         [0093]    The interface portion  271  receives the subject data from the HDD  23  via the bus  29  and the encrypted data from the communication apparatus  28  via the bus  29  so as to transmit the received subject data or encrypted data to the preprocessing portion  272 . When the interface portion  271  receives the subject data or the encrypted data, it transmits the data indicating reception thereof to the solution generating portion  274 . 
         [0094]    The interface portion  271  receives the subject data or the encrypted data from the connecting portion  277 , and transmits the received subject data or encrypted data to the bus  29  as will be described later. 
         [0095]    The preprocessing portion  272  has a function of cutting the subject data or encrypted data received from the bus  29  via the interface portion  271  by a predetermined number of bits to generate plain text cut data or encrypted cut data and transmitting it to the encrypting and decrypting portion  273 . It will be described later as to how the subject data or the encrypted data is cut. According to this embodiment, the preprocessing portion  272  has a function of including dummy data irrelevant to the subject data in the subject data by a method described later. 
         [0096]    The encrypting and decrypting portion  273  has a function of receiving the plain text cut data or encrypted cut data from the preprocessing portion  272 , encrypting the plain text cut data if received and decrypting the encrypted cut data if received. The encrypting and decrypting portion  273  of this embodiment has a fixed standard number of bits as a processing unit for performing the processing of the encryption and decryption. The standard number of bits of this embodiment is 8 bits although it is not limited thereto. Details of the encryption and decryption processing will be described later. 
         [0097]    The solution generating portion  274  sequentially generates solutions. The solution generating portion  274  of the first data processing apparatus  11  and the solution generating portion  274 A of the second data processing apparatuses  12  described later generate the solutions so that the solutions generated in the same order become the same. The solutions of this embodiment are pseudo-random numbers. The generated solutions are transmitted to the preprocessing portion  272 , algorithm generating portion  275  and key generating portion  276 . 
         [0098]    The algorithm generating portion  275  generates the algorithms based on the solutions received from the solution generating portion  274 . The algorithms are used when performing the encryption process and decryption process in the encrypting and decrypting portion  273 . 
         [0099]    The key generating portion  276  generates the keys based on the solutions received from the solution generating portion  274 . The keys are used when performing the encryption process and decryption process in the encrypting and decrypting portion  273 . 
         [0100]    The connecting portion  277  has a function of connecting the plain text cut data generated by decrypting the encrypted cut data in the encrypting and decrypting portion  273  in original order to render it as a set of the subject data. The subject data is transmitted to the interface portion  271 , and is transmitted as necessary to the HDD  23  or the CPU  21  via the bus  29 . The connecting portion  277  also has a function of connecting the encrypted cut data generated by encrypting the plain text cut data in the encrypting and decrypting portion  273  to render it as a set of the encrypted data. The encrypted data is transmitted to the interface portion  271 , and is transmitted from there to the communication portion  283  of the communication apparatus  28  via the bus  29 , and is further transmitted from the communication portion  283  to the second data processing apparatuses  12 . The connecting portion  277  does not need to have a function of connecting the encrypted cut data generated by encrypting the plain text cut data in the encrypting and decrypting portion  273 . In this case, the encrypted cut data is sequentially transmitted to the communication apparatus at the other end in order in which it is encrypted. In the case where the connecting portion  277  is as described above, the encrypted cut data can be directly transmitted to the communication portion  283  without going through the connecting portion  277 . 
         [0101]    Next, the configuration of the second data processing apparatus  12  will be described. 
         [0102]      FIG. 5  shows the hardware configuration of the second data processing apparatus  12 . 
         [0103]    The hardware configuration of the second data processing apparatus  12  is basically the same as that of the first data processing apparatus  11 . It is different from the first data processing apparatuses  11 , however, in that it has two kinds of the encryption apparatus  27  while the first data processing apparatus  11  has only one and there are an encryption apparatus  27 A and an encryption apparatus  27 B provided instead of the encryption apparatus  27 . 
         [0104]    The CPU  21 , ROM  22 , HDD  23 , RAM  24 , input apparatus  25 , display apparatus  26 , and bus  29  of the second data processing apparatus  12  are the same as those of the first data processing apparatus  11 . 
         [0105]    The encryption apparatus  27 A and encryption apparatus  27 B have the functions of encrypting the subject data and decrypting the encrypted data as with the encryption apparatus  27  of the first data processing apparatus  11 . Hereunder, the configurations of both of them will be described. 
         [0106]    There are multiple encryption apparatuses  27 A, that is, as many as the first data processing apparatuses  11 . Each of the encryption apparatuses  27 A is associated with one of the first data processing apparatuses  11 . To be more specific, each of the encryption apparatus  27 A and the first data processing apparatus  11  mutually associated can decrypt the encrypted data generated by the other by encrypting the subject data. Inversely, each of the encryption apparatus  27 A and the first data processing apparatus  11  not mutually associated cannot decrypt the encrypted data generated by the other by encrypting the subject data. 
         [0107]    The encryption apparatus  27 A is configured as shown in  FIG. 6 . 
         [0108]    The encryption apparatus  27 A is configured by an interface portion  271 A, a preprocessing portion  272 A, an encrypting and decrypting portion  273 A, a solution generating portion  274 A, an algorithm generating portion  275 A, a key generating portion  276 A and a connecting portion  277 A. 
         [0109]    The interface portion  271 A receives the subject data from the encryption apparatus  27 B via the bus  29  and the encrypted data from the communication apparatus  28  via the bus  29  so as to transmit the received subject data or encrypted data to the preprocessing portion  272 A. When the interface portion  271 A receives the subject data or the encrypted data, it transmits the data indicating reception thereof to the solution generating portion  274 A. 
         [0110]    The interface portion  271 A receives the subject data or the encrypted data from the connecting portion  277 A, and transmits the received subject data or encrypted data to the bus  29  as will be described later. 
         [0111]    The preprocessing portion  272 A has a function of cutting the subject data or encrypted data received from the bus  29  via the interface portion  271 A by a predetermined number of bits to generate the plain text cut data or the encrypted cut data and transmitting it to the encrypting and decrypting portion  273 A. According to this embodiment, the preprocessing portion  272 A has a function of including the dummy data irrelevant to the subject data in the subject data by a method described later. 
         [0112]    The encrypting and decrypting portion  273 A has a function of receiving the plain text cut data or encrypted cut data from the preprocessing portion  272 A, encrypting the plain text cut data if received and decrypting the encrypted cut data if received. The encrypting and decrypting portion  273 A of this embodiment has a fixed standard number of bits as the processing unit for performing the processing of the encryption and decryption. The standard number of bits of this embodiment is 8 bits although it is not limited thereto. Details of the encryption and decryption processing will be described later. 
         [0113]    The solution generating portion  274 A sequentially generates the solutions. The solutions generated by the solution generating portion  274 A become the same as the solutions generated by the solution generating portion  274  of the first data processing apparatus  11  in the same order. The generated solutions are transmitted to the preprocessing portion  272 A, algorithm generating portion  275 A and key generating portion  276 A. 
         [0114]    The algorithm generating portion  275 A generates the algorithms based on the solutions received from the solution generating portion  274 A. The algorithms are used when performing the encryption process and decryption process in the encrypting and decrypting portion  273 A. The algorithms generated by the algorithm generating portion  275 A of the second data processing apparatus  12  become the same as the algorithms generated by the algorithm generating portion  275  of the first data processing apparatus  11  in the same order. 
         [0115]    The key generating portion  276 A generates the keys based on the solutions received from the solution generating portion  274 A. The keys are used when performing the encryption process and decryption process in the encrypting and decrypting portion  273 A. The keys generated by the key generating portion  276 A of the second data processing apparatus  12  become the same as the keys generated by the key generating portion  276  of the first data processing apparatus  11  in the same order. 
         [0116]    The connecting portion  277 A of the second data processing apparatus  12  has the same function as that of the first data processing apparatus  11 . The connecting portion  277 A connects the plain text cut data generated in the encrypting and decrypting portion  273 A by decrypting the encrypted cut data as a set so as to generate the subject data. The subject data is transmitted to the encryption apparatus  27 B via the bus  29 . The connecting portion  277 A connects the encrypted cut data generated in the encrypting and decrypting portion  273 A by encrypting the plain text cut data as a set so as to generate the encrypted data. The encrypted data is transmitted to the first data processing apparatus  11  via the communication apparatus  28 . 
         [0117]    There is only one encryption apparatus  27 B. 
         [0118]    The encryption apparatus  27 B has a function of re-encrypting the subject data which the encryption apparatus  27 A generated by decrypting encrypted data which is generated by encrypting the first data processing apparatus  11  the subject data. The encryption apparatus  27 B records the generated encrypted data on the HDD  23  in the second data processing apparatus  12 . The encryption apparatus  27 B also has a function of decrypting the encrypted data read from the HDD  23 . 
         [0119]    The encryption apparatus  27 B is configured as shown in  FIG. 7 . 
         [0120]    The encryption apparatus  27 B is configured by an interface portion  271 B, a preprocessing portion  272 B, an encrypting and decrypting portion  273 B, a solution generating portion  274 B, an algorithm generating portion  275 B, a key generating portion  276 B, a connecting portion  277 B and a specific information generating portion  278 B. 
         [0121]    The interface portion  271 B of the encryption apparatus  27 B receives the subject data from the encryption apparatus  27 A via the bus  29  and the encrypted data from the HDD  23  in the second data processing apparatus  12  via the bus  29  so as to transmit the received subject data or encrypted data to the preprocessing portion  272 B. When the interface portion  271 B receives the subject data or the encrypted data, it transmits the data indicating reception thereof to the solution generating portion  274 B. 
         [0122]    The interface portion  271 B receives the subject data from the connecting portion  277 B in the encryption apparatus  27 B and the encrypted data from the specific information generating portion  278 B, and transmits the received subject data or encrypted data to the bus  29  as will be described later. 
         [0123]    The preprocessing portion  272 B has a function of cutting the subject data or encrypted data received from the bus  29  via the interface portion  271 B by a predetermined number of bits to generate the plain text cut data or the encrypted cut data and transmitting it to the encrypting and decrypting portion  273 B. According to this embodiment, the preprocessing portion  272 B has a function of including the dummy data irrelevant to the subject data in the subject data by a method described later. 
         [0124]    The encrypting and decrypting portion  273 B has a function of receiving the plain text cut data or encrypted cut data from the preprocessing portion  272 B, encrypting the plain text cut data if received and decrypting the encrypted cut data if received. The encrypting and decrypting portion  273 B of this embodiment has a fixed standard number of bits as a processing unit for performing the encryption and decryption processing. The standard number of bits of this embodiment is 8 bits although it is not limited thereto. Details of the encryption and decryption processing will be described later. When performing the decryption, the encrypting and decrypting portion  273 B performs the decryption by using the algorithms and keys identified based on the specific information described later. 
         [0125]    The solution generating portion  274 B sequentially generates solutions. The solutions generated by the solution generating portion  274 B are the pseudo-random numbers. The generated solutions are transmitted to the algorithm generating portion  275 B and key generating portion  276 B and to the preprocessing portion  272 B in addition according to this embodiment. 
         [0126]    The algorithm generating portion  275 B generates the algorithms based on the solutions received from the solution generating portion  274 B. The algorithms are used when performing the encryption process and decryption process in the encrypting and decrypting portion  273 B. 
         [0127]    The key generating portion  276 B generates the keys based on the solutions received from the solution generating portion  274 B. The keys are used when performing the encryption process and decryption process in the encrypting and decrypting portion  273 B. The keys generated by the key generating portion  276 B of the second data processing apparatus  12  become the same as the keys generated by the key generating portion  276  of the first data processing apparatus  11  in the same order. 
         [0128]    The connecting portion  277 B of the second data processing apparatus  12  has the function of connecting the plain text cut data generated in the encrypting and decrypting portion  273 B by decrypting the encrypted cut data so as to generate the subject data. The subject data is transmitted to the encryption apparatus  27 A. The connecting portion  277 B connects the encrypted cut data generated in the encrypting and decrypting portion  273 B by encrypting the plain text cut data as a set so as to generate the encrypted data. The encrypted data is recorded on the HDD  23  in the second data processing apparatus  12 . 
         [0129]    The encryption apparatus  27 B includes the specific information generating portion  278 B. 
         [0130]    The specific information generating portion  278 B adds the specific information to the encrypted data generated by the connecting portion  277 B. The specific information is the information for identifying the algorithm and key used when encrypting the encrypted data to which the specific information is added. To be more precise, it is the information indicating the algorithm itself used when encrypting the encrypted data, the key itself used when encrypting the encrypted data, the solution itself used on generating the algorithm or the key used when encrypting the encrypted data or the information indicating what number generated solution is the solution. According to this embodiment, both the algorithm and the key change, and so the specific information must specify both the algorithm and key or the solution used to generate the algorithm and the key or the order in which the solution was generated. When only one of the algorithm and the key changes, however, the specific information needs to specify only the algorithm or the key that changes. 
         [0131]    According to this embodiment, the specific information generating portion  278 B adds the specific information to the encrypted data. However, the specific information may also be stored at a different location from the encrypted data while being associated with the encrypted data. 
         [0132]    The configuration of the communication apparatus  28  of the second data processing apparatus  12  is approximately the same as the configuration of the communication apparatus  28  of the first data processing apparatus  11 . The functions of the interface portion  281  and the communication portion  283  are not different from those of the communication apparatus  28  of the first data processing apparatus  11 . The communication apparatus  28  of the second data processing apparatus  12  is different from the communication apparatus  28  of the first data processing apparatus  11  in that it has an authentication portion  284  instead of the authentication data generating portion  282  of the first data processing apparatus  11 . 
         [0133]    The authentication portion  284  reads authentication data of the encrypted data received from the first data processing apparatus  11  included in the header according to this embodiment, and determines which first data processing apparatus  11  the encrypted data comes from. The encrypted data is transmitted to the encryption apparatus  27 A associated with the first data processing apparatus  11  as its transmission source via the interface portion  281 . 
         [0134]    Next, a description will be given as to a flow of the processing performed in this data processing system. 
         [0135]    The flow of the processing performed in this data processing system is as follows if described roughly by using  FIG. 9 . 
         [0136]    First, the encryption apparatus  27  of one first data processing apparatus  11  out of the multiple first data processing apparatuses  11  encrypts the subject data so as to generate the encrypted data (S 110 ). 
         [0137]    Next, the first data processing apparatus  11  transmits the encrypted data to the second data processing apparatus  12  (S 120 ). 
         [0138]    Next, of the multiple encryption apparatuses  27 A in the second data processing apparatus  12  having received the encrypted data, the one associated with the first data processing apparatus  11  having transmitted the encrypted data decrypts the encrypted data and changes it back to the subject data (S 130 ). 
         [0139]    Next, the encryption apparatus  27 B encrypts the decrypted subject data and records it on the HDD  23  in the second data processing apparatus  12  (S 140 ). 
         [0140]    Next, the encryption apparatus  27 B decrypts the encrypted data in the HDD  23  and changes it back to the subject data according to a request from the first data processing apparatus  11  for instance (S 150 ). 
         [0141]    Next, the encryption apparatus  27 A encrypts the subject data and renders it as the encrypted data (S 160 ). 
         [0142]    Next, the second data processing apparatus  12  transmits the encrypted data to the first data processing apparatus  11  (S 170 ). Next, the encryption apparatus  27  in the first data processing apparatus  11  decrypts the encrypted data and changes it back to the original subject data (S 180 ). 
         [0143]    First, a detailed description will be given by referring to  FIG. 10  as to the above-mentioned step S 110  in which the encryption apparatus  27  of one first data processing apparatus  11  out of the multiple first data processing apparatuses  11  encrypts the subject data so as to generate the encrypted data. 
         [0144]    First, the subject data is read (S 1101 ). The subject data may be any data whatsoever as long as it is the data necessary to be transmitted from the first data processing apparatus  11  to the second data processing apparatus  12 . According to this embodiment, the subject data is stored on the HDD  23 . The subject data may also be the data read from another recording medium such as an external recording medium to the first data processing apparatus  11 . 
         [0145]    For instance, if a command ordering to transmit the subject data from the input apparatus  25  to the second data processing apparatus  12  is input, the CPU  21  reads the subject data from the HDD  23  and stores it temporarily in the RAM  24 . The subject data is transmitted from the HDD  23  to the encryption apparatus  27  via the bus  29 . To be more precise, the subject data is transmitted to the preprocessing portion  272  via the interface portion  271 . 
         [0146]    The subject data is cut by a predetermined number of bits into the plain text cut data in the preprocessing portion  272  (S 1102 ). The preprocessing portion  272  includes the dummy data in the plain text cut data as required. 
         [0147]    There may be just one method of generating the plain text cut data from the subject data. According to this embodiment, however, the plain text cut data is generated from the subject data by one of the following three methods. 
         [0148]    A) The case of cutting the subject data into the plain text cut data by a predetermined number of bits shorter than the standard number of bits, and including the dummy data at respective fixed positions of pieces of the plain text cut data all of which have the number of bits shorter than the standard number of bits. 
         [0149]    B) The case of cutting the subject data into the plain text cut data by a predetermined number of bits shorter than the standard number of bits, and including the dummy data at different positions of pieces of the plain text cut data all of which have the number of bits shorter than the standard number of bits. 
         [0150]    C) The case of cutting the subject data into the plain text cut data by the number of bits the same as or shorter than the standard number of bits, and including the dummy data in respective pieces of the plain text cut data having the number of bits shorter than the standard number of bits. 
         [0151]    It is decided by the solutions generated by the solution generating portion  274  as to which of the above-mentioned three methods should be used to generate the plain text cut data from the subject data. 
         [0152]    A description will be given first as to how the solution generating portion  274  generates the solutions. 
         [0153]    When the interface portion  271  receives the subject data from the bus  29 , the solution generating portion  274  receives that information from the interface portion  271 . 
         [0154]    The solution generating portion  274  takes this opportunity to start generating the solutions. According to this embodiment, the solution generating portion  274  generates the solutions each time the subject data is received by the interface portion  271 . The solution of this embodiment is a matrix (X) with 8 rows and 8 columns although it is not limited thereto. 
         [0155]    According to this embodiment, the solution generating portion  274  generates the solutions successively as if in nonlinear transition though it does not always have to be the case. The solutions consequently become the pseudo-random numbers. 
         [0156]    To generate the solutions successively as if in nonlinear transition, there are thinkable techniques, such as (1) including exponential calculation of the past solutions in the process of generating the solutions, (2) including multiplication of two or more past solutions in the process of generating the solutions, or a combination of (1) and (2). 
         [0157]    According to this embodiment, the solution generating portion  274  has a 01 st  solution (X 01 ) and a 02 nd  solution (X 02 ) predetermined as initial matrixes (for instance, the 01 st  solution and 02 nd  solution are recorded in a predetermined memory such as the HDD  23  or the ROM  22 ). The initial matrixes each first data processing apparatuses  11  has are different from one another, and so the solutions generated by the first data processing apparatuses  11  are different from one another. 
         [0158]    Each of the multiple encryption apparatuses  27 A of the second data processing apparatus  12  has the same initial matrix as that of the first data processing apparatus  11  associated with each of the multiple encryption apparatuses  27 A. 
         [0159]    The solution generating portion  274  assigns the initial matrixes to the solution generating algorithm and generates a 1 st  solution (X 1 ) as follows. 
         [0000]      1 st  solution ( X   1 )= X   02   X   01 +α (α=matrix with 8 rows and 8 columns) 
         [0160]    This is the solution generated first. 
         [0161]    Next, when the interface portion  271  receives the subject data from the bus  29 , the solution generating portion  274  generates a 2 nd  solution (X 2 ) as follows. 
         [0000]      2 nd  solution ( X   2 )= X   1   X   02 +α 
         [0162]    Similarly, each time the interface portion  271  receives the subject data from the bus  29 , the solution generating portion  274  generates 3 rd , 4 th , . . . N th  solutions as follows. 
         [0000]      3 rd  solution ( X   3 )= X   2   X   1 +α 
         [0000]      4 th  solution ( X   4 )= X   3   X   2 +α       .   .         
         [0000]      N th  solution ( X   N )= X   N−1   X   N−2 +α 
         [0165]    The solutions thus generated are transmitted to the preprocessing portion  272 , the algorithm generating portion  275 , the key generating portion  276  and are also held in the solution generating portion  274 . To generate the N th  solution (X N ), this embodiment uses an (N−1) th  solution (X N−1 ) and an (N−2) th  solution (X N−2 ), that is, the two solutions generated immediately before then. Therefore, to generate the new solution, the solution generating portion  274  must hold the two nearest preceding solutions generated in the past (or else, the two solutions must be held by some other portion than the solution generating portion  274 ). Inversely, the solutions older than the two nearest preceding solutions generated in the past are not to be used to generate the new solution from now on. Thus, this embodiment always holds the two past solutions in the solution generating portion  274 . However, this embodiment erases the solution which is now the third nearest preceding solution due to the generation of the new solution but was the second nearest preceding solution till then from the predetermined memory or the like in which it was recorded. 
         [0166]    The solutions thus generated are chaotic in nonlinear transition, and are also the pseudo-random numbers. 
         [0167]    To cause the nonlinear transition, it is thinkable, when acquiring the N th  solution, to use the following formulas other than the above-mentioned formula: N th  solution (X N )=X N−1 X N−2 +α. 
         [0168]    For instance: 
         [0000]      (a)  N   th  solution ( X   N )=( X   N−1 ) P   
         [0000]      (b)  N   th  solution ( X   N )=( X   N−1 ) P ( X   N−2 ) Q ( X   N−3 ) R ( X   N−4 ) S   
         [0000]      (c)  N   th  solution ( X   N )=( X   N−1 ) P +( X   N−2 ) Q   
         [0169]    P, Q, R and S are predetermined constants respectively. The solution generating portion  274  has two initial matrixes in the case of using the formula (a) or (c), and has four initial matrixes in the case of using the formula (b). 
         [0170]    The above-mentioned α is a constant. However, it may also be specific changing environmental information. The environmental information is the information naturally generated in sequence as time elapses and commonly obtainable at distant places, such as the information determined based on weather of a specific region, information determined based on the contents of a TV broadcast of a TV station broadcasted at a specific time and information determined based on a result of a specific sport. 
         [0171]    It is possible to further improve confidentiality of the communication by creating the above-mentioned α in series and generating common information. 
         [0172]    It is also possible, as a matter of course, to add α (may be generated from the environmental information) to right sides of the formulas (a) to (c). 
         [0173]    As described above, the preprocessing portion  272  having received the solutions (that is, the above-mentioned solutions) decides which of the above-mentioned methods of A), B) and C) should be used to generate the plain text cut data. According to this embodiment, the plain text cut data is generated by the method A) in the case where, in dividing the sum of adding up the numbers configuring the matrix with 8 rows and 8 columns as the solutions by 3, a remainder thereof is 0, by the method B) in the case where the remainder is 1, and by the method C) in the case where the remainder is 2, though it does not always have to be the case. 
         [0174]    In the case of generating the plain text cut data by the method A), the preprocessing portion  272  cuts the subject data received from the interface portion  271  by the predetermined number of bits (7 bits in this embodiment) shorter than the standard number of bits in order from the head to generate the plain text cut data. The preprocessing portion  272  embeds the dummy data at a fixed position of the plain text cut data. The positions of the plain text cut data for embedding the dummy data may be either variable or fixed. In the latter case, the position at which the dummy data is embedded may be the head or the end of the plain text cut data or a predetermined intermediate position such as a second bit or a third bit. The dummy data may be any data as long as it is irrelevant data to the subject data. For instance, there are thinkable processes, such as constantly embedding the data of 0 or the data of 1, or alternately embedding the data of 1 and 0. As a further example, it is possible to decide what dummy data is to be embedded based on the above-mentioned solutions. For instance, if the sum of the numbers configuring the matrix with 8 rows and 8 columns as the solutions added up is divided by 9 and the remainder thereof is 0, it is possible to continue 0, such as 0, 0, 0, 0 . . . If the remainder is 1, it is possible to put in 1 alternately, such as 0, 1, 0, 1 . . . If the remainder is 2, it is possible to put in 1 at every third place, such as 0, 0, 1, 0, 0, 1 . . . Likewise, it is possible to put in 1 at every fourth place if the remainder is 3, put in 1 at every fifth place if the remainder is 4, and put in 1 at every tenth place if the remainder is 9. 
         [0175]    In the case of generating the plain text cut data by the method B), the preprocessing portion  272  cuts the subject data by the predetermined number of bits (7 bits for instance) shorter than the standard number of bits to render it as the plain text cut data, and includes the dummy data at different positions of respective pieces of the plain text cut data all of which have the number of bits shorter than the standard number of bits. In this case, the positions at which the dummy data is embedded may be fixed or regularly changing, such as moving in order of the first bit, second bit, third bit . . . eighth bit, first bit, second bit, . . . eighth bit, or randomly changing as to each piece of the plain text cut data. If the positions at which the dummy data is embedded randomly change, the positions may be decided based on the solutions for instance. 
         [0176]    As for the method of deciding the positions at which the dummy data is embedded by means of the solutions, it is possible to perform the following process for instance. If the sum of the numbers configuring the matrix with 8 rows and 8 columns as the solutions added up is divided by 8 and the remainder thereof is 0, the dummy data is embedded alternately at the head and the end of the pieces of the plain text cut data. If the remainder is 1, the plain text cut data having the dummy data embedded at the head and the plain text cut data having the dummy data embedded at the end are arranged to be at every third place. If the remainder is 2, the plain text cut data having the dummy data embedded at the head and the plain text cut data having the dummy data embedded at the end are arranged to be at every fourth place. If the remainder is 7, the plain text cut data having the dummy data embedded at the head and the plain text cut data having the dummy data embedded at the end are arranged to be at every ninth place. It is also possible to further move the positions at which the dummy data is embedded rather than fixing the positions such as the head and end. 
         [0177]    In the case of generating the plain text cut data by the method C), the subject data is cut to be the standard number of bits or the number of bits shorter than the standard number of bits. This cutting can be performed by cutting the subject data to a random length shorter than 8 bits. For instance, if the sum of the numbers configuring the matrix with 8 rows and 8 columns as the solutions added up is divided by 8 and the remainder thereof is 0, the head of the subject data at that point in time can be cut by 8 bits. If the remainder is 1, the head of the subject data at that point in time can be cut by 1 bit. If the remainder is 2, the head of the subject data at that point in time can be cut by 2 bits. If the remainder is 7, the head of the subject data at that point in time can be cut by 7 bits. Of the plain text cut data thus generated, the preprocessing portion  272  embeds the dummy data in each piece of the plain text cut data of which number of bits is shorter than the standard number of bits. In this case, an embedding position of the dummy data may be a same position such as the head or the end or a predetermined changing position specified by the solutions for instance. 
         [0178]    In any case, the plain text cut data thus generated is transmitted to the encrypting and decrypting portion  273  as a stream in order of generation. 
         [0179]    In parallel with the generation of the plain text cut data, the algorithm generating portion  275  generates the algorithm used on encrypting the plain text cut data. 
         [0180]    According to this embodiment, the algorithm generating portion  275  generates the algorithm based on the solutions. 
         [0181]    According to this embodiment, the algorithm generating portion  275  generates the algorithm as follows. 
         [0182]    The algorithm of this embodiment is defined as “in the case where the plain text cut data as 8-bit data is considered as a matrix Y with 1 row and 8 columns, it is acquired by multiplying by Y the matrix X with 8 rows and 8 columns as the solutions raised to the a-th power and turned clockwise by n×90°.” 
         [0183]    Here, there are the cases where a is a predetermined constant. According to this embodiment, however, a is a number changing based on the solutions. To be more specific, the algorithm of this embodiment changes based on the solutions. For instance, a can be defined as the remainder in the case of dividing by 5 the number acquired by adding up all the numbers as elements of the matrix included in the solutions which are the matrix with 8 rows and 8 columns (provided that it is a=1 in the case where the remainder is 0). 
         [0184]    The above-mentioned n is a predetermined number defined by the key. If the key is a constant number, n is fixed. As described below, however, the key changes based on the solutions. To be more specific, this n also changes based on the solutions according to this embodiment. 
         [0185]    It is also possible to decide on another algorithm. 
         [0186]    According to this embodiment, the algorithm generating portion  275  generates the algorithm each time it receives the solutions from the solution generating portion  274 , and transmits it to the encrypting and decrypting portion  273 . 
         [0187]    In parallel with the generation of the plain text cut data, the key generating portion  276  generates the key used on encrypting the plain text cut data. 
         [0188]    The key generating portion  276  generates the key based on the solutions. 
         [0189]    According to this embodiment, the key generating portion  276  generates the key as the following. 
         [0190]    The key of this embodiment is the number acquired by adding up all the numbers as the elements of the matrix included in the solutions which are the matrix with 8 rows and 8 columns. Therefore, the key changes based on the solutions according to this embodiment. 
         [0191]    It is also possible to decide on another key. 
         [0192]    According to this embodiment, the key generating portion  276  generates the key each time it receives the solutions from the solution generating portion  274 , and transmits it to the encrypting and decrypting portion  273 . 
         [0193]    The encrypting and decrypting portion  273  encrypts the plain text cut data received from the preprocessing portion  272  based on the algorithm received from the algorithm generating portion  275  and the key received from the key generating portion  276  (S 1103 ). 
         [0194]    As described above, the algorithm is defined as “in the case where the plain text cut data as 8-bit data is considered as a matrix Y with 1 row and 8 columns, it is acquired by multiplying by Y the matrix X with 8 rows and 8 columns as the solutions raised to the a-th power and turned clockwise by n×90°,” and n as the key is the above-mentioned number. 
         [0195]    If a is 3 and n is 6 for instance, the encryption is performed by multiplying by the plain text cut data the matrix with 8 rows and 8 columns acquired by turning the matrix with 8 rows and 8 columns acquired by cubing X clockwise by 6×90°=540°. 
         [0196]    The data thus generated is the encrypted cut data. 
         [0197]    The encrypted cut data is transmitted to the connecting portion  277 . The connecting portion  277  connects the encrypted cut data as one, and generates the encrypted data (S 1104 ). Sorting order of the encrypted cut data in this case is corresponding to the sorting order of the original plain text cut data. 
         [0198]    Thus, the step S 110  in which the first data processing apparatus  11  encrypts the subject data to generate the encrypted data is finished first. 
         [0199]    The encrypted data thus generated is transmitted to the communication apparatus  28  in the first data processing apparatus  11  via the bus  29 . The encrypted data is received by the interface portion  281  in the communication apparatus  28  to be transmitted to the authentication data generating portion  282 . The authentication data generating portion  282  adds the authentication data to the header of the encrypted data, and transmits the encrypted data to the communication portion  283 . 
         [0200]    The communication portion  283  transmits the encrypted data to the second data processing apparatus  12  via the network  13 . The above-mentioned step S 120  is thereby performed. 
         [0201]    In the second data processing apparatus  12  having received the encrypted data, the step S 130  of decrypting the encrypted data and changing it back to the subject data is performed. 
         [0202]    Hereunder, this decryption step will be described in detail by referring to  FIG. 11 . 
         [0203]    The encrypted data transmitted to the second data processing apparatus  12  is received by the communication portion  283  of the communication apparatus  28  of the second data processing apparatus  12  (S 1201 ). 
         [0204]    The communication portion  283  transmits the encrypted data to the authentication portion  284 . The authentication portion  284  determines which first data processing apparatus  11  the encrypted data comes from based on the authentication data added to the encrypted data (S 1202 ). 
         [0205]    After such a determination is made by the authentication portion  284 , the encrypted data is transmitted to the interface portion  281 . The interface portion  281  transmits the encrypted data to the encryption apparatuses  27 A associated with the first data processing apparatus  11  determined to be the transmission source of the encrypted data by the authentication portion  284 . 
         [0206]    The preprocessing portion  272 A in the encryption apparatus  27 A receives the encrypted data via the interface portion  271 A. 
         [0207]    The preprocessing portion  272 A cuts the received encrypted data by a predetermined number of bits, and generates the encrypted cut data (S 1203 ). 
         [0208]    In the case of cutting the encrypted data and generating the encrypted cut data, the preprocessing portion  272 A performs a process reverse to the process performed by the connecting portion  277  of the first data processing apparatus  11 . To be more specific, the encrypted data is cut by 8 bits from the head to be divided into multiple pieces of the encrypted cut data. 
         [0209]    Next, the encrypted cut data is transmitted to the encrypting and decrypting portion  273 A, where it is decrypted and rendered as the plain text cut data (S 1204 ). 
         [0210]    The decryption is performed as a process reverse to the process performed by the encrypting and decrypting portion  273  of the first data processing apparatus  11 . For that reason, the second data processing apparatus  12  requires the algorithm and key required on performing the encryption on the first data processing apparatus  11 . 
         [0211]    The algorithm and key used for the decryption are generated inside the encryption apparatus  27 A. Working thereof will be described. 
         [0212]    The information that the interface portion  271 A of the encryption apparatus  27 A received the encrypted data is transmitted to the solution generating portion  274 A. The solution generating portion  274 A having received this information takes this opportunity to generate the solutions each time it receives this information. 
         [0213]    The generation of the solutions performed by the solution generating portion  274 A in the encryption apparatus  27 A of the second data processing apparatus  12  is performed through the same step as the step performed by the solution generating portion  274  of the first data processing apparatus  11 . As described above, the solution generating portion  274 A has the same initial matrix and solution generating algorithm as those of the solution generating portion  274  of the first data processing apparatus  11  associated with the encryption apparatus  27 A including the solution generating portion  274 A. Therefore, the solutions generated in the encryption apparatus  27 A of the second data processing apparatus  12  are the same as the solutions generated in the corresponding encryption apparatus  27 A of the first data processing apparatus  11  if the data in the same order of generation is compared. 
         [0214]    The generated solutions are transmitted from the solution generating portion  274 A to the preprocessing portion  272 A, algorithm generating portion  275 A and key generating portion  276 A. 
         [0215]    The algorithm generating portion  275 A generates the algorithm based on the received solution each time it receives the solutions. The step in which the algorithm generating portion  275 A of the second data processing apparatus  12  generates the algorithm is the same as the step in which the algorithm generating portion  275  of the first data processing apparatus  11  generates the algorithm. The generated algorithm is transmitted from the algorithm generating portion  275 A to the encrypting and decrypting portion  273 A. 
         [0216]    The key generating portion  276 A generates the key based on the received solutions each time it receives the solutions. The step in which the key generating portion  276 A of the second data processing apparatus  12  generates the key is the same as the step in which the key generating portion  276  of the first data processing apparatus  11  generates the key. The generated key is transmitted from the key generating portion  276 A to the encrypting and decrypting portion  273 A. 
         [0217]    As for this data processing system, new solutions are generated on the first data processing apparatus  11  each time the encryption is performed on the first data processing apparatus  11 , and new solutions are also generated on the second data processing apparatus  12  each time the solutions generated on the first data processing apparatus  11  are decrypted on the second data processing apparatus  12 . As described above, the solutions generated by the encryption apparatus  27 A of the second data processing apparatus  12  are the same as the solutions generated by the corresponding encryption apparatus  27  in the first data processing apparatus  11  if the data in the same order of generation is compared. Therefore, all the solutions generated when encrypting certain subject data on the first data processing apparatus  11  and the algorithms and keys generated based on those solutions constantly match with the solutions generated by the encryption apparatus  27 A of the second data processing apparatus  12  and the algorithms and keys generated based on those solutions when decrypting the encrypted data generated on the first data processing apparatus  11  by using the algorithms and keys generated based on the solutions. These circumstances are the same even when the encryption is performed on the second data processing apparatus  12  and the decryption is performed on the first data processing apparatus  11 . 
         [0218]    As described above, the encrypting and decrypting portion  273 A performs the decryption process by using the algorithm received from the algorithm generating portion  275 A. To be more precise, the encrypting and decrypting portion  273 A performs the decryption process by generating the algorithm for performing the decryption process (defined as “in the case where the encrypted cut data is considered as a matrix Z with 1 row and 8 columns, the plain text cut data is acquired by multiplying by Y an inverse matrix of the matrix X with 8 rows and 8 columns as the solution raised to the a-th power and turned clockwise by n×90°”) based on the algorithm received from the algorithm generating portion  275 A (defined as “in the case where the plain text cut data as 8-bit data is considered as a matrix Y with 1 row and 8 columns, the encrypted cut data is acquired by multiplying by Y the matrix X with 8 rows and 8 columns as the solution raised to the a-th power and turned clockwise by n×90°”) and performing calculation according to the above-mentioned definition by using the key. Thus, the encrypting and decrypting portion  273 A decrypts the encrypted cut data provided as a stream from the preprocessing portion  272 A one after another so as to generate the plain text cut data. 
         [0219]    Next, the encrypting and decrypting portion  273 A removes the dummy data from the plain text cut data as required (S 1205 ). As described above, the solutions generated by the solution generating portion  274 A are transmitted to the preprocessing portion  272 A. These solutions were used when determining how the dummy data was embedded in the plain text cut data in the preprocessing portion  272  of the first data processing apparatus  11 . To be more specific, the solutions held by the preprocessing portion  272 A of the encryption apparatus  27 A at that point in time indicate how the dummy data was embedded in the encrypted cut data (to be more precise, the plain text cut data before the encrypted cut data was encrypted) of which decryption is finished (or being performed or just to be performed) by the encrypting and decrypting portion  273 A of the second data processing apparatus  12 . 
         [0220]    The preprocessing portion  272 A transmits to the encrypting and decrypting portion  273 A the information on where in the plain text cut data decrypted by the encrypting and decrypting portion  273 A the dummy data is embedded. 
         [0221]    The encrypting and decrypting portion  273 A removes the dummy data from the plain text cut data by using the information. 
         [0222]    The plain text cut data thus generated is transmitted to the connecting portion  277 A. The connecting portion  277 A connects the received plain text cut data as one and changes it back to the subject data in the original state before being encrypted on the first data processing apparatus  11  (S 1206 ). 
         [0223]    Thus, the step S 130  in which the second data processing apparatus  12  decrypts the encrypted data and changes it back to the subject data is finished. 
         [0224]    The generated subject data is transmitted from the connecting portion  277 A to the interface portion  271 A, and is then transmitted to the encryption apparatus  27 B via the bus  29 . 
         [0225]    Here, the encryption apparatus  27 B performs the process of the above-mentioned step S 140  of re-encrypting the decrypted subject data to render it as the encrypted data. 
         [0226]    The encryption process of the encryption apparatus  27 B is performed in approximately the same flow as that of the first data processing apparatus  11  ( FIG. 12 ). 
         [0227]    The subject data transmitted to the encryption apparatus  27 B is received by the interface portion  271 B (S 1301 ). 
         [0228]    The interface portion  271 B transmits it to the preprocessing portion  272 B. 
         [0229]    The preprocessing portion  272 B cuts the received subject data by a predetermined number of bits, and generates the plain text cut data (S 1302 ). The method of cutting the subject data in this case does not have to be the same as that of the encryption apparatus  27  and encryption apparatus  27 A. According to this embodiment, however, the same process as that described about the encryption apparatus  27  and encryption apparatus  27 A is performed to cut the subject data. The preprocessing portion  272 B performs the same process as that described about the encryption apparatus  27  so as to include the dummy data in the plain text cut data as required. 
         [0230]    Next, the plain text cut data is transmitted to the encrypting and decrypting portion  273 B. The encrypting and decrypting portion  273 B encrypts it to rendered as the encrypted cut data (S 1303 ). 
         [0231]    Here, the algorithm and key to be used for the encryption are generated as in the case of the encryption apparatus  27 . The solutions are also generated before this as in the case of the encryption apparatus  27 . The flow from the generation of the solutions to the generation of the algorithm and key will be described hereunder. 
         [0232]    When the interface portion  271 B receives the subject data from the bus  29 , the solution generating portion  274 B receives that information from the interface portion  271 B. The solution generating portion  274 B should generate the solutions in appropriate timing. If the solution generating portion  274 B of this embodiment receives the information on reception of the subject data from the interface portion  271 B, it takes that opportunity to generate the solutions. Details of the generation of the solutions are the same as those described about the encryption apparatus  27 . 
         [0233]    The generated solutions are transmitted to the algorithm generating portion  275 B and key generating portion  276 B. 
         [0234]    The algorithm generating portion  275 B and key generating portion  276 B generate the algorithm and key by performing the same process as that performed by the algorithm generating portion  275  and key generating portion  276  of the encryption apparatus  27 . The generated algorithm and key are transmitted to the encrypting and decrypting portion  273 B from the algorithm generating portion  275 B or the key generating portion  276 B. 
         [0235]    The encrypting and decrypting portion  273 B receives the algorithm from the algorithm generating portion  275 B and the key from the key generating portion  276 B respectively, and sequentially encrypts the plain text cut data received from the preprocessing portion  272 B (S 1303 ). 
         [0236]    Details of the encryption are the same as those described about the encryption apparatus  27 . 
         [0237]    The generated encrypted cut data is sequentially transmitted to the connecting portion  277 B. 
         [0238]    The connecting portion  277 B connects the encrypted cut data as one to render it as the encrypted data (S 1304 ). The encrypted data is transmitted to the specific information generating portion  278 B. 
         [0239]    The specific information generating portion  278 B adds the above-mentioned specific information to the header, for instance, of the received encrypted data (S 1305 ). 
         [0240]    The encrypted data having the specific information added thereto is transmitted to the bus  29  via the interface portion  271 B to be recorded on the HDD  23  in the second data processing apparatus  12 . 
         [0241]    Next, when the first data processing apparatus  11  sends the second data processing apparatus  12  an instruction to send back the encrypted data recorded on the HDD  23  in the second data processing apparatus  12  to the first data processing apparatus  11  for instance, the second data processing apparatus  12  performs the following process. 
         [0242]    First, the encryption apparatus  27 B reads the encrypted data from the HDD  23  and decrypts the encrypted data to change it back to the subject data, thereby performing the above-mentioned process of S 150 . Details of this process will be described by referring to  FIG. 13 . 
         [0243]    To be more precise, the interface portion  271 B of the encryption apparatus  27 B of the second data processing apparatus  12  reads the encrypted data from the HDD  23  via the bus  29  (S 1401 ). 
         [0244]    The interface portion  271 B transmits the encrypted data to the preprocessing portion  272 B. The preprocessing portion  272 B cuts the received encrypted data by a predetermined number of bits to generate the encrypted cut data (S 1402 ). 
         [0245]    In the case of generating the encrypted cut data by cutting the encrypted data, the preprocessing portion  272 B performs the same process as the above-mentioned process performed by the preprocessing portion  272 A of the encryption apparatus  27 A on performing the decryption. To be more specific, the encrypted data is cut by 8 bits from the head to be divided into multiple pieces of the encrypted cut data. 
         [0246]    Next, the encrypted cut data is transmitted to the encrypting and decrypting portion  273 B.The encrypting and decrypting portion  273 B decrypts it to rendered as the plain text cut data (S 1403 ). 
         [0247]    The decryption is performed as the same process as the above-mentioned process performed by the encrypting and decrypting portion  273 A of the encryption apparatus  27 A on performing the decryption. To perform such decryption, the second data processing apparatus  12  requires the algorithm and key. 
         [0248]    The algorithm and key are generated as follows. 
         [0249]    The interface portion  271 B of this embodiment can read the specific information added to the encrypted data. The specific information is the information for identifying the algorithm and key used when encrypting the encrypted data for having the specific information added thereto. 
         [0250]    For instance, in the case where the specific information is the algorithm and key themselves used when encrypting the encrypted data, the interface portion  271 B reads the algorithm and key from the encrypted data and transmits them to the encrypting and decrypting portion  273 B via the preprocessing portion  272 B for instance. The encrypting and decrypting portion  273 B decrypts the encrypted cut data based on the algorithm and key. 
         [0251]    In the case where the specific information is the solutions used to generate the algorithm and key used when encrypting the encrypted data, the interface portion  271 B reads the solutions from the encrypted data so as to transmit them to the algorithm generating portion  275 B and the key generating portion  276 B. In this case, the algorithm generating portion  275 B and the key generating portion  276 B generate the algorithm and key based on the received solutions respectively. The algorithm and key match with the algorithm and key used when encrypting the encrypted data having the solutions added thereto. The algorithm generating portion  275 B and the key generating portion  276 B transmit the generated algorithm and key to the encrypting and decrypting portion  273 B. The encrypting and decrypting portion  273 B decrypts the encrypted cut data based on the algorithm and key. 
         [0252]    In the case where the specific information is the information indicating what number generated solutions are the solutions used on generating the algorithm and key used when encrypting the encrypted data, the interface portion  271 B reads the information from the encrypted data so as to transmit it to the solution generating portion  274 B. The solution generating portion  274 B having received the information generates the solutions up to the indicated order. The solutions match with those used when encrypting the encrypted data having the above-mentioned information added thereto. In this case, at least the initial matrixes should be held without being erased so that the solutions generated in the same order are always the same. The solution generating portion  274 B transmits the generated solutions to the algorithm generating portion  275 B and the key generating portion  276 B. The algorithm generating portion  275 B and the key generating portion  276 B generate the algorithm and key based on the received solutions respectively. The algorithm and key match with the algorithm and key used when encrypting the encrypted data having the solutions added thereto respectively. The algorithm generating portion  275 B and the key generating portion  276 B transmit the generated algorithm and key to the encrypting and decrypting portion  273 B. The encrypting and decrypting portion  273 B decrypts the encrypted cut data based on the algorithm and key. 
         [0253]    The encrypted cut data is changed back to the plain text cut data as described above. 
         [0254]    Next, the encrypting and decrypting portion  273 B removes the dummy data from the plain text cut data as required (S 1404 ). 
         [0255]    Here, if the dummy data included in the plain text cut data is included at an appropriate position based on the solutions, the encrypting and decrypting portion  273 B requires the solutions used on encrypting the plain text cut data last time when removing the dummy data. In the case where the specific information is the solutions used when the plain text cut data was encrypted last time, the interface portion  271 B transmits the solutions to the encrypting and decrypting portion  273 B. In the case where the specific information is the information indicating what number generated solutions are the solutions used when the plain text cut data was encrypted last time, the solution generating portion  274 B transmits the generated solutions to the encrypting and decrypting portion  273 B. The encrypting and decrypting portion  273 B removes the dummy data included at the appropriate position based on the solutions by using the solutions. 
         [0256]    In the case of including the dummy data included in the plain text cut data at an appropriate position based on the solutions, it is not desirable to render the specific information as the algorithm and key used when encrypting the encrypted data. It is because, if rendered so, the encrypting and decrypting portion  273 B cannot obtain the solutions so that the dummy data cannot be removed. 
         [0257]    The plain text cut data from which the dummy data has been removed is transmitted to the connecting portion  277 B. The plain text cut data is connected as one by the connecting portion  277 B to be changed back to the subject data (S 1405 ). 
         [0258]    The plain text cut data is transmitted to the bus  29  via the interface portion  271 B, and is then transmitted to the encryption apparatus  27 A associated with the first data processing apparatus  11  which requested transmission of the encrypted data as a source of the plain text cut data. 
         [0259]    On receiving this, the encryption apparatus  27 A performs the above-mentioned process of S 160  of encrypting the subject data to render it as the encrypted data. 
         [0260]    The encryption apparatus  27 A performs this process as the same one as the process described in S 110  performed by the encryption apparatus  27  of the first data processing apparatus  11  on rendering the subject data as the encrypted data. 
         [0261]    The encrypted data generated on the encryption apparatus  27 A is transmitted to the communication apparatus  28  of the second data processing apparatuses  12  via the bus  29 , and is transmitted from there to the communication apparatus  28  of the first data processing apparatus  11  which requested transmission of the encrypted data via the network  13 . This corresponds to the above-mentioned process of S 170 . 
         [0262]    The encrypted data is decrypted on the encryption apparatus  27  in the first data processing apparatus  11 . This is the above-mentioned process of S 180 . The encryption apparatus  27  performs this process as the same process as the process described in S 130  performed by the encryption apparatus  27 A of the second data processing apparatus  12  on decrypting the encrypted data as the subject data. 
         [0263]    In short, the encryption apparatus  27  built into each of the first data processing apparatuses  11  of this embodiment and the encryption apparatus  27 A in the second data processing apparatuses  12  associated with that first data processing apparatus  11  are capable of mutually decrypting the encrypted data encrypted by the other. 
         [0264]    The subject data decrypted and generated on the encryption apparatus  27  in the first data processing apparatus  11  is the same as the data which was on the HDD  23  in the first data processing apparatus  11  before the process of S 110  was performed. The subject data is recorded on the HDD  23  in the first data processing apparatus  11  for instance. The first data processing apparatus  11  can use it as appropriate. 
       Second Embodiment 
       [0265]    There is only one data processing apparatus according to the second embodiment. 
         [0266]    The hardware configuration of the data processing apparatus of the second embodiment is the same as that of the first data processing apparatus  11  of the first embodiment. However, the data processing apparatus of the second embodiment does not need to communicate, and so it does not have the communication apparatus  28  provided to the first data processing apparatus  11 . 
         [0267]    To be more specific, the data processing apparatus of the second embodiment includes a CPU  21 , an ROM  22 , an HDD  23 , an RAM  24 , an input apparatus  25 , a display apparatus  26 , an encryption apparatus  27  and a bus  29 . The functions thereof basically match with the functions of the CPU  21 , ROM  22 , HDD  23 , RAM  24 , input apparatus  25 , display apparatus  26 , encryption apparatus  27  and bus  29  of the first data processing apparatus  11 . 
         [0268]    The configuration of the encryption apparatus  27  of the data processing apparatus of the second embodiment is almost the same as the configuration of the encryption apparatus  27  built into the first data processing apparatus  11  of the first embodiment (shown in  FIG. 4 ). However, it is different from the encryption apparatus  27  of the first embodiment in that the algorithm generating portion  275  is replaced by a first algorithm generating portion  275 X and a second algorithm generating portion  275 Y, and the key generating portion  276  is replaced by a first key generating portion  276 X and a second key generating portion  276 Y ( FIG. 14 ). 
         [0269]    The data processing apparatus of the second embodiment performs the processes of encrypting the subject data recorded on the HDD  23  with the encryption apparatus  27 , recording the encrypted data generated by the encryption on the HDD  23 , decrypting the encrypted data recorded on the HDD  23  with the encryption apparatus  27  and recording the subject data generated by the decryption on the HDD  23  as will be described later. According to the second embodiment multiple pieces of the encrypted data are decrypted, and the order of decrypting the encrypted data matches with the order in which the encrypted data was encrypted from the subject data. 
         [0270]    There arise the differences, in conjunction with this point, between the encryption apparatus  27  of the data processing apparatus of the second embodiment and the encryption apparatus  27  built into the first data processing apparatus  11  of the first embodiment. 
         [0271]    The encryption apparatus  27  of the data processing apparatus of the second embodiment has the configuration shown in  FIG. 14  as described above. 
         [0272]    The encryption apparatus  27  in the data processing apparatus of the second embodiment has an interface portion  271 , a preprocessing portion  272 , an encrypting and decrypting portion  273 , a solution generating portion  274  and a connecting portion  277 , which have basically the same functions as those in the encryption apparatus  27  of the first data processing apparatus  11  of the first embodiment. The interface portion  271  exchanges the data between the bus  29  and the communication apparatus  28 . 
         [0273]    The preprocessing portion  272  cuts the subject data or encrypted data received from the bus  29  via the interface portion  271  by a predetermined number of bits to generate the plain text cut data or the encrypted cut data and transmits them to the encrypting and decrypting portion  273 . The preprocessing portion  272  may include the dummy data in the plain text cut data. 
         [0274]    The encrypting and decrypting portion  273  receives the plain text cut data or encrypted cut data from the preprocessing portion  272 , encrypts the plain text cut data if received and decrypts the encrypted cut data if received. The encrypting and decrypting portion  273  has the standard number of bits as the processing unit for performing the processing of the encryption and decryption fixed at 8 bits according to this embodiment. 
         [0275]    The solution generating portion  274  sequentially generates the solutions. According to this embodiment, the solutions are generated each time the preprocessing portion  272  receives the subject data. The solutions are pseudo-random numbers. 
         [0276]    The connecting portion  277  has a function of connecting the plain text cut data generated by decrypting the encrypted cut data in the encrypting and decrypting portion  273  in original order to render it as a set of the subject data. The connecting portion  277  also has a function of connecting the encrypted cut data generated by encrypting the plain text cut data in the encrypting and decrypting portion  273  to render it as a set of the encrypted data. 
         [0277]    The first algorithm generating portion  275 X generates the algorithm based on the solutions received from the solution generating portion  274 . The algorithm is used when performing the encryption. The second algorithm generating portion  275 Y generates the algorithm based on the solutions received from the solution generating portion  274 . The algorithm is used when performing the decryption. The first algorithm generating portion  275 X and the second algorithm generating portion  275 Y generate the same algorithm in the case of generating the algorithm by using the same solutions. 
         [0278]    The first key generating portion  276 X generates the key based on the solutions received from the solution generating portion  274 . The key is used when performing the encryption. The second key generating portion  276 Y generates the key based on the solutions received from the solution generating portion  274 . The key is used when performing the decryption. The first key generating portion  276 X and the second key generating portion  276 Y generate the same key in the case of generating the key by using the same solutions. 
         [0279]    According to this embodiment, the first algorithm generating portion  275 X and the first key generating portion  276 X generate the algorithm and key each time the preprocessing portion  272  receives the subject data. And the second algorithm generating portion  275 Y and the second key generating portion  276 Y generate the algorithm and key each time the preprocessing portion  272  receives the encrypted data. 
         [0280]    Operations of the data processing apparatuses of the second embodiment will be described by using  FIG. 15 . 
         [0281]    First, the subject data is read (S 1501 ). The subject data is read from the HDD  23  according to this embodiment. The subject data is transmitted to the encryption apparatus  27  from the HDD  23  via the bus  29 . To be more precise, the subject data is transmitted to the preprocessing portion  272  via the interface portion  271 . 
         [0282]    The subject data is cut by a predetermined number of bits to be rendered as the plain text cut data in the preprocessing portion  272  (S 1502 ). The preprocessing portion  272  includes the dummy data in the plain text cut data as required. 
         [0283]    The method of generating the plain text cut data from the subject data is the same as that described in S 1102  of the first embodiment. 
         [0284]    On receiving the information on reception of the subject data from the interface portion  271 , the solution generating portion  274  takes the opportunity to generate the solutions. The solutions may be generated each time the subject data is cut in the preprocessing portion  272 . In this case, the generation of the subject data in the preprocessing portion  272  is synchronized with the generation of the solutions in the solution generating portion  274 . 
         [0285]    The method of generating the solutions of this embodiment is the same as the method performed by the solution generating portion  274  when the first data processing apparatus  11  of the first embodiment performed the encryption. 
         [0286]    The generated solutions are transmitted to the first algorithm generating portion  275 X, second algorithm generating portion  275 Y, first key generating portion  276 X and second key generating portion  276 Y. 
         [0287]    The first algorithm generating portion  275 X and first key generating portion  276 X having received this generate the algorithm and key respectively. The method of generating the algorithm and key of this embodiment is the same as the method performed by the algorithm generating portion  275  and key generating portion  276  when the first data processing apparatus  11  of the first embodiment generated the algorithm and key. 
         [0288]    The first algorithm generating portion  275 X and first key generating portion  276 X transmit the generated algorithm and key to the encrypting and decrypting portion  273 . 
         [0289]    The encrypting and decrypting portion  273  encrypts the plain text cut data received from the preprocessing portion  272  based on the algorithm received from the first algorithm generating portion  275 X and the key received from the first key generating portion  276 X (S 1503 ). This process is performed as the same process as that of S 1103  described in the first embodiment. 
         [0290]    The encrypted cut data thus generated is transmitted to the connecting portion  277  and connected as one there to be rendered as the encrypted data (S 1504 ). 
         [0291]    The encrypted data generated as above is recorded on the HDD  23  in the data processing apparatus via the bus  29 . 
         [0292]    Such an encryption process is performed a number of times in this embodiment. 
         [0293]    The data processing apparatus decrypts the encrypted data recorded on the HDD  23 . 
         [0294]    Hereunder, the step of the decryption will be described in detail by referring to  FIG. 16 . 
         [0295]    The decryption is started by having the encrypted data recorded on the HDD  23  read by the encryption apparatus  27  (S 1601 ). 
         [0296]    If the preprocessing portion  272  in the encryption apparatus  27  receives the encrypted data from the HDD  23  via the interface portion  271 , the preprocessing portion  272  cuts the received encrypted data by a predetermined number of bits to generate the encrypted cut data (S 1602 ). 
         [0297]    In the case of generating the encrypted cut data by cutting the encrypted data, the preprocessing portion  272  performs a process reverse to the process performed as the above-mentioned encryption process. To be more specific, the encrypted data is cut by 8 bits from the head to be divided into multiple pieces of the encrypted cut data. This process is the same process as that of S 1203  of the first embodiment. 
         [0298]    Next, the encrypted cut data is transmitted to the encrypting and decrypting portion  273 , where it is decrypted and rendered as the plain text cut data (S 1603 ). 
         [0299]    The decryption is performed as a process reverse to the above-mentioned encryption process performed by the encrypting and decrypting portion  273 . For that reason, the encrypting and decrypting portion  273  requires the algorithm and key used on performing the encryption. Here, the second algorithm generating portion  275 Y generates the algorithm and the second key generating portion  276 Y generates the key by using the solutions generated in advance. As the order in which the encrypted data is decrypted matches with the order in which the encrypted data was encrypted from the subject data, the algorithm and key generated by the second algorithm generating portion  275 Y and the second key generating portion  276 Y are generated based on the solutions used when encrypting the encrypted data about to be decrypted. It means that the algorithm generated by the second algorithm generating portion  275 Y and the key generated by the second key generating portion  276 Y match with the algorithm and key used when encrypting the encrypted data about to be decrypted. 
         [0300]    After having the solutions generated by the solution generating portion  274 , the second algorithm generating portion  275 Y and the second key generating portion  276 Y may generate the algorithm and key in any timing before the encrypting and decrypting portion  273  requires the algorithm and key for the sake of performing the decryption. 
         [0301]    The algorithm generated by the second algorithm generating portion  275 Y and the key generated by the second key generating portion  276 Y are transmitted to the encrypting and decrypting portion  273 . The encrypting and decrypting portion  273  uses the algorithm and key to sequentially decrypt the encrypted cut data and render it as the plain text cut data. This process is performed as the same process as the process described in S 1204  of the first embodiment. 
         [0302]    Next, the encrypting and decrypting portion  273  removes the dummy data from the plain text cut data as required (S 1604 ). This process is performed as the same process as the process in S 1205  of the first embodiment. 
         [0303]    The plain text cut data thus generated is transmitted to the connecting portion  277 . The connecting portion  277  connects the received plain text cut data as one and generates the subject data (S 1605 ). 
         [0304]    The generated subject data is transmitted from the connecting portion  277  to the interface portion  271 , and is then recorded on the HDD  23  via the bus  29 . 
       Deformed Example 
       [0305]    The data processing apparatus of the second embodiment may be deformed as follows. 
         [0306]    The data processing apparatus of this deformed example has a configuration of the encryption apparatus  27  slightly different from the data processing apparatus of the second embodiment. Otherwise, it is the same as the above-mentioned data processing apparatus of the second embodiment. 
         [0307]    The encryption apparatus  27  of the deformed example is configured as shown in  FIG. 17 . This encryption apparatus  27  is different from the encryption apparatus  27  of the data processing apparatus of the second embodiment having only one solution generating portion  274  in that it has two solution generating portions of a first solution generating portion  274 X and a second solution generating portion  274 Y. 
         [0308]    Both the first solution generating portion  274 X and second solution generating portion  274 Y generate the solutions as with the solution generating portion  274  of the second embodiment. 
         [0309]    On receiving the information from the interface portion  271  that the interface portion  271  received the subject data, the first solution generating portion  274 X takes the opportunity to generate the solutions. The first solution generating portion  274 X may also generate the solutions each time the subject data is cut in the preprocessing portion  272 . The solutions generated by the first solution generating portion  274 X are transmitted to the first algorithm generating portion  275 X and first key generating portion  276 X. As in the case of the second embodiment, the first algorithm generating portion  275 X and first key generating portion  276 X having received the solutions generate the algorithm and key respectively, and transmit them to the encrypting and decrypting portion  273 . The encrypting and decrypting portion  273  performs the encryption process by using the algorithm and the key received from the first algorithm generating portion  275 X and first key generating portion  276 X. 
         [0310]    On receiving the information from the interface portion  271  that the interface portion  271  received the encrypted data, the second solution generating portion  274 Y generates the solutions. However, the second solution generating portion  274 Y may also generate the solutions each time the encrypted data is cut in the preprocessing portion  272 . The solutions generated by the second solution generating portion  274 Y are transmitted to the second algorithm generating portion  275 Y and second key generating portion  276 Y. As in the case of the second embodiment, the second algorithm generating portion  275 Y and second key generating portion  276 Y having received the solutions generate the algorithm and key respectively, and transmit them to the encrypting and decrypting portion  273 . The encrypting and decrypting portion  273  performs the decryption process by using the algorithm and key received from the second algorithm generating portion  275 Y and second key generating portion  276 Y. 
         [0311]    The solutions generated by the second solution generating portion  274 Y are the same solutions as those generated by the first solution generating portion  274 X if the solutions generated in the same order are mutually compared. On this point, it is the same as the first embodiment wherein the solution generating portion  274  in the encryption apparatus  27  built into the first data processing apparatus  11  and the solution generating portion  274 A in the encryption apparatus  27 A built into the second data processing apparatuses  12  generate the same solutions if the solutions generated in the same order are mutually compared. To be more specific, the second solution generating portion  274 Y and the first solution generating portion  274 X of the deformed example have the same solution generating algorithm and also have the same initial matrix. 
         [0312]    The data processing apparatus of this deformed example performs the same processes as the data processing apparatus of the second embodiment except the processes of generating the solutions and generating the algorithm. 
         [0313]    The encryption apparatuses of the second embodiment and the deformed example thereof may be replaced by the encryption apparatus  27 B of the first embodiment.
To improve a technology of encryption for a data processing apparatus in order to reduce a possibility of having communication broken by a third party. The data processing apparatus encrypts subject data to render it as encrypted data and records it on a predetermined recording medium, and also decrypts the encrypted data recorded on the recording medium to change it back to the subject data. When performing the encryption, an algorithm and a key to be used for the encryption are generated by using solutions which are sequentially generated by assigning past solutions to a solution generating algorithm. The solutions are erased at a stage where it is no longer necessary to assign them to the solution generating algorithm anew.