Patent Publication Number: US-2005135705-A1

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to an image forming apparatus such as a digital copying machine that temporarily stores, for example, image data read by a scanner or image data received from an external device in a storage device such as a hard disk and performs an image forming processing on the basis of the image data stored in the storage device.  
      2. Description of the Related Art  
      In an image forming apparatus such as a digital copying machine of the prior art, image data read by a scanner or image data received from an external device are temporarily stored in a storage device such as a hard disk and an image forming processing is performed to a medium to form an image on the basis of the image data stored in the hard disk. In such an image forming apparatus, in order to prevent the data stored in the storage device such as a hard disk from being stolen, the data is encrypted and stored in the storage device. Moreover, in the above-described image forming apparatus, in the case of encrypting the data to be stored in the storage device, an encryption scheme using a key code is used in many cases.  
      However, in the encryption scheme using a key code, the key code needs to be stored in the image forming apparatus. For this reason, if the key code used for encryption is stored in an easy position in the image forming apparatus, the key code itself is easily analyzed (stolen), so that there is presented a problem that the data stored in the storage device will probably be easily decrypted with ease.  
     BRIEF SUMMARY OF THE INVENTION  
      An object of the present invention is to provide an image forming apparatus and an image forming method capable of preventing data stored in a storage device from being stolen.  
      According to an aspect of the present invention, there is provided an image forming apparatus for forming an image on a medium to have an image formed thereon on the basis of data for image formation, the image forming apparatus comprising: a plurality of memories which store key information to be used for encrypting the data for image formation in a state where the key information is divided into a plurality of portions; a control section which collects the key information stored in the plurality of memories in the divided state and creates the key information in the complete state; an encryption section which encrypts the data for image formation on the basis of the key information in the complete state created by the control section; a storage device which stores the data for image formation encrypted by the encryption section; and a printer which subjects the encrypted data for image formation stored in the storage device, to a processing of forming an image on the basis of the data decoded by the encryption section.  
      According to an aspect of the present invention, there is provided an image forming method for use in an image forming apparatus comprising a plurality of memories in which various kinds of control data are stored, a storage device which stores data for image formation, and a printer which performs an image forming processing on the basis of the data for image formation stored in the storage device, the image forming method comprising: determining all of the memories having stored therein key information to be used for encrypting the data in the divided state; collecting the key information in the divided state from all of the memories determined to have stored therein the key information in the divided state; creating key information in the complete state from the key information in the divided state, collected from the plurality of memories; encrypting the data for image formation on the basis of the key information in the complete state which has been created from the key information in the divided state, collected from the plurality of memories, and storing the data for image formation in the storage device; reading and decoding the encrypted data for image formation stored in the storage device, on the basis of the key information in the complete state; and performing an image forming processing on the basis of the date for image formation read from the storage device and decoded.  
      Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
       FIG. 1  is a diagram showing a general configuration of a digital copying machine as an image forming apparatus.  
       FIG. 2  is a flow chart for explaining a first setting procedure for a key code at the time of setting up the digital copying machine.  
       FIG. 3  is a flow chart for explaining a second setting procedure for a key code at the time of setting up the digital copying machine.  
       FIG. 4  is a flow chart for explaining a procedure of encrypting data in the digital copying machine.  
       FIG. 5  is a flow chart for explaining a procedure of decoding data in the digital copying machine.  
       FIG. 6  is a flow chart for explaining a procedure of disposing the digital copying machine. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Embodiments of the present invention will be described with reference to the drawings.  
       FIG. 1  is a block diagram showing a configuration example of a control section of a digital copying machine  1  in accordance with an image forming apparatus of this invention.  
      The digital copying machine  1  has a control section  10 , a scanner  11 , a printer  12 , a control panel  13 , a network interface  14  and the like. With this configuration, the digital copying machine  1  has various kinds of functions such as image reading processing (scanner function), image forming processing (printer function), communications processing with external devices (network communication function), and copy function. Furthermore, in addition to the configuration described above, the digital copying machine  1  can be mounted with an optional device  15  for realizing various optional functions. The optional devices  15  include, for example, finisher, ADF, facsimile unit, paper feeder of large capacity, multistage paper feeder, hole punching unit, and network expanding unit.  
      As shown in  FIG. 1 , the control section  10  of the digital copying machine  1  has a system control board  20 , a scanner control board  21 , a printer control board  22 , a laser control board  23 , a printer controller  24 , an encryption board  25 , a hard disk drive  26  and the like. Moreover, in a case where the digital copying machine  1  is mounted with the above-described optional device  15 , it is mounted with an optional control board  27  for controlling the optional device  15 .  
      Each of the system control board  20 , the scanner control board  21 , the printer control board  22 , the laser control board  23 , the control panel  13 , and the optional control board  27  has at least one of NVRAMs  20   a  to  24   a ,  13   a , and  27   a  as a rewritable ROM. Each of the NVRAMs  20   a  to  24   a ,  13   a , and  27   a  is configured of, for example, an EEPROM. In each of the NVRAMs  20   a  to  24   a ,  13   a , and  27   a  is stored data (software) such as control program necessary for operating each part.  
      The above-described system control board  20  functions as a system control section that controls the whole copying machine (system) and performs an image processing and stores images.  
      The system control board  20  is mounted with a system CPU (control section)  31 , a ROM  32 , a RAM  33 , an NVRAM  20   a , an image processing part  34 , and various kinds of interfaces (not shown). The system CPU  31  controls the whole copying machine on the basis of control programs and control data stored in the ROM  32  or the NVRAM  34 .  
      The scanner control board  21  functions as a scanner control section for controlling the whole scanner  11 . The scanner control board  21  as the scanner control section controls an operation of reading an original image, performed by the scanner  11 .  
      The scanner control board  21  is mounted with a scanner CPU (not shown), a ROM (not shown), a RAM (not shown), the NVRAM  21   a , a scanner driving and control section (not shown), and an interface (not shown). The above-described scanner CPU controls the scanner  11  on the basis of the control program and control data that are stored in the ROM or the NVRAM  21   a  and used for controlling the scanner.  
      The printer control board  22  functions as an engine control section for controlling the whole printer  12 . The printer control board  22  as the engine control section drives and controls a main motor and transfer rollers in the printer  12  and prints an image on a medium to form an image.  
      The printer control board  22  is mounted with a printer CPU (not shown), a ROM (not shown), a RAM (not shown), the NVRAM  22   a , an engine driving and control section (not shown), and an interface (not shown). The printer CPU controls the printer  12  on the basis of the control program and control data that are stored in the ROM or the NVRAM  22   a  and used for controlling the printer.  
      The laser control board  23  functions as an exposure control section for forming an electrostatic latent image on a photoconductive drum in the printer  12 . The laser control board  23  as the exposure control section controls a laser light emitting device  31  and a polygon motor (not shown) in the printer  12 .  
      The laser control board  23  is mounted with a laser control CPU (not shown), a ROM (not shown), a RAM (not shown), the NVRAM  23   a , a light emission control section (not shown), and an interface (not shown). The laser control CPU controls the laser light emitting device  31  and the polygon motor on the basis of the control program and control data that are stored in the ROM or the NVRAM  23   a  and used for controlling exposure.  
      Here, the laser emitting device  31  emits laser light for forming an electrostatic latent image based on the image data on the photoconductive drum (not shown) as an image carrying body in the printer  12 . Moreover, the polygon motor rotates a polygon mirror for guiding the laser light emitted from the laser light emitting device  31  to the photoconductive drum.  
      The control panel  13  functions as a user interface used when the user operates the copying machine  1 .  
      The control panel  13  is mounted with a panel CPU (not shown), a ROM (not shown), a RAM (not shown), the NVRAM  13   a , a display (not shown), an operation key (not shown) and an interface (not shown). The panel control CPU controls a control panel on the basis of the control program, control data and display data that are stored in the ROM or the NVRAM  13   a  and used for controlling the control panel.  
      In a case where the digital copying machine  1  is mounted with the optional device  15 , it is mounted with an optional control board  27  for controlling the optional device  15 . The optional control board  27  functions as an option control section for controlling the optional device  13 .  
      The optional control board  27  is mounted with an option CPU (not shown), a ROM (not shown), a RAM (not shown), the NVRAM  27   a , an option driving and control section (not shown), and an interface (not shown). The option CPU controls the optional device  15  on the basis of the control program and control data that are stored in the ROM or the NVRAM  27   a  and used for controlling the optional device.  
      Moreover, the encryption board  25  functions as an encryption section for encrypting and decoding data. The encryption board  25  employs an encryption scheme of encrypting and decoding the data by a key code (key information). The key code to be used in the encryption board  25  is given from the system control board  20 .  
      For example, in a case where the image data read by the scanner  11  is stored in the hard disk  26 , the encryption board  25  encrypts the image data read by the scanner  11  on the basis of the key code set by the system control board  20  and stores the image data in the hard disk  26 . Further, also in a case where the data received from the external device is stored in the hard disk  26 , the encryption board  25  encrypts the data received from the external device on the basis of the key code set by the system control board  20  and stores the data in the hard disk  26 . Hence, in the hard disk  26  is stored the data encrypted by the encryption board  25 .  
      Further, in a case where the encrypted data stored in the hard disk  26  is read, the encryption board  25  decodes the data stored in the hard disk  26  on the basis of the key code set by the system control board  20  and outputs the data to the system control board  20 .  
      Next, a procedure of setting up the copying machine  1  configured in the manner described above will be described.  
       FIG. 2  is a flow chart for explaining a first setting procedure as a procedure of setting the above-described key code at the time of setup (setup mode). Here, in the following description, it is assumed that the setting of the key code is performed at the time of setting up the copying machine by the operation of a serviceman having expertise on the copying machine.  
      First, a serviceman turns on a power supply switch (not shown) and performs an operation to start a mode (setup mode) for setting a key code by the control panel  13 . Then, the system CPU  31  of the system control board  20  turns on the power supply of the copying machine  1  (step S 11 ) and starts a mode of setting a key code (step S 12 ). When the mode of setting a key code, the serviceman inputs a key code by the control panel  13  (step S 13 ). Here, it is assumed that the serviceman inputs a key code of a predeter-mined number of digits (for example, 32 digits).  
      When the serviceman inputs the key code in the mode of setting a key code, the system CPU  31  of the system control board  20  divides the key code on the basis of a predetermined program stored in the ROM  32  (step S 14 ). For example, the system CPU  31  of the system control board  20  divides the key code of 32 digits into two parts of 16 digits. Here, it is assumed that the key code is divided into two parts by the program previously stored in the ROM  32  and one of the two-divided parts is stored in the NVRAM  20   a  of the system control board  20  and the other is stored in the NVRAM  22   a  of the printer control board  22 .  
      That is, when the key code is divided into two parts, the system CPU  31  of the system control board  20  stores one of the key code divided on the basis of the predetermined program stored in the ROM  32  in the NVRAM  20   a  of the system control board  20  (step S 15 ).  
      Further, the system CPU  31  of the system control board  20  transfers the remaining key code of the divided key codes on the basis of the predetermined program stored in the ROM  32  to the printer control board  22  as a board to store the key code (step S 16 ).  
      The printer control board  22  to which the divided key code has been transferred from the system control board  20  receives the key code transferred from the system control board  20  and stores it in the NVRAM  22   a  on the printer control board  22  (step S 17 ).  
      Here, it is also recommended that the key code be divided into three or more parts and that the divided key codes be stored in three or more boards. For example, in this first setting procedure, the key code is divided on the basis of the program previously stored in the ROM (program for setting a key code). For this reason, by changing the program previously stored in the ROM, the number of divisions of the key code and boards to store the divided key codes can be arbitrarily set.  
      In this first setting procedure described above, the key code is divided on the basis of the key code setting program previously stored in the ROM and the divided key codes are stored in NVRAMs of a plurality of boards. With this, according to the first setting procedure, by dividing the key code and storing the divided key codes in the plurality of boards, it is possible to prevent the key code for encrypting the data from being analyzed with ease and hence to provide a copying machine having a high level of security of the data.  
      Next, a second setting procedure for a key code will be described.  
       FIG. 3  is a flow chart for explaining the second setting procedure as a procedure of setting the above-described key code at the time of setup (setup mode). Here, in this second setting procedure, it is assumed that a serviceman or a user can select the number of divisions of the key code and boards to store the divided key codes at the time of setting up the copying machine.  
      First, the serviceman turns on the power supply switch (not shown) and performs an operation to start the mode (setup mode) for setting a key code by the control panel  13 . Then, the system CPU  31  of the system board  20  turns on the power supply of the copying machine  1  (step S 21 ) and starts the mode for setting a key code (step S 22 ).  
      That is, when the mode for setting a key code is started, the serviceman inputs a key code by the control panel  13  (step S 23 ). Here, it is assumed that the serviceman inputs a key code of a predetermined number of digits (for example, 32 digits).  
      When the serviceman inputs the key code in the mode for setting a key code, the system CPU  31  of the system board  20  determines the number of memories (NVRAMs) capable of storing the key code (step S 24 ). Here, the number of memories capable of storing the key code is determined on the basis of the number of boards having the NVRAMs.  
      For example, the network controller  24  and the optional control board  27  are selectively provided according to the specifications of the copying machine 1. Hence, in the example of the second setting procedure, the system CPU  31  of the system control board  20  determines the boards having the NVRAMs as memories capable of storing the key code on the basis of the state of connection of the optional device. Here, there is also a possibility that the optional device  13  will be dismounted from the copying machine  1  after the setup. For this reason, it is also recommended that the NVRAM  27   a  of the optional control board  27  be not accounted as a memory capable of storing the key code.  
      When the system CPU  31  of the system control board  20  determines the number of memories capable of storing the key code in step S 24 , the system CPU  31  of the system control board  20  determines the number of divisions of the key code on the basis of the number of memories capable of storing the key code (step S 25 ). Here, the number of divisions of the key code may be any number, if it is within the number of memories capable of storing the key code. For example, the number of divisions of the key code may be the number of memories capable of storing the key code or may be smaller than the number of memories capable of storing the key code.  
      When the system CPU  31  of the system control board  20  determines the number of divisions of the key code, the system CPU  31  of the system control board  20  determines the boards (NVRAMs) for storing the plurality of divided key codes (step S 26 ). When the system CPU  31  of the system control board  20  determines the boards to store the divided key codes in this manner, the system CPU  31  of the system control board  20  makes a table to show the boards to store the divided key codes (step S 27 ). Here, the above-described table may be stored in the NVRAM  20   a  on the system control board  20  or a rewritable ROM (not shown).  
      When the system CPU  31  of the system control board  20  makes the table to show the boards to store the divided key codes, the system CPU  31  of the system control board  20  divides the key code inputted in step S 23  into the above-described number of divisions of the key codes (step S 28 ). When the system CPU  31  of the system control board  20  divides the key code, the system CPU  31  of the system control board  20  stores one of the divided key codes in the NVRAM  20   a  of the system control board  20  (step S 29 ). Here, it is assumed that one of the divided key codes is stored in the NVRAM  20   a  of the system control board  20 .  
      Further, the system CPU  31  of the system control board  20  transfers the remaining key codes of the divided key codes on the basis of the above-described table to the respective boards to store them (step S 30 ). The respective boards to which the divided key codes have been transferred from the system control board  20  receive the key codes transferred from the system control board  20  and store them in the NVRAMs of the respective boards (step S 31 ).  
      In the second setting procedure, it is also recommended that the number of divisions of the key code be selected by the serviceman or by the user. For example, the system CPU  31  of the system control board  20  makes the serviceman or the user designate the number of divisions of the key code from the control panel  13  on the condition that the number of memories capable of storing the key codes, determined in step S 24 , is the upper limit of the number of divisions of the key code. In this case, in step S 25 , it is assumed that the number of divisions of the key code designated by the user is the number of divisions of the key code.  
      In the second setting procedure described above, the number of divisions of the key code is determined on the basis of the number of control boards or the like in the copying machine and the divided key codes are stored in the plurality of control boards. Moreover, the table is made that shows the control board to store the divided key codes. With this, according to the second setting procedure described above, the key code can be divided and stored on the basis of the specifications of the copying machine to prevent the key code for encrypting the data from being analyzed with ease. Therefore, a copying machine can be provided that has a high level of security of the data.  
      Next, an encryption procedure by the above-described key code will be described.  
       FIG. 4  is a flow chart for explaining a procedure of encrypting and storing data in the hard disk drive  26  of this copying machine  1 .  
      The hard disk  26  of this copying machine  1  is adapted to store the encrypted data. For example, the image data read by the scanner  11  or the data for image formation, which is received from the external device via the network interface  14 , is encrypted by the encryption board  25  and is stored in the hard disk drive  26 .  
      That is, when the system control board  20  captures data to be stored in the hard disk drive  26  (step S 41 ), the system CPU  31  of the system control board  20  determines the boards to store the divided key codes (step S 42 ). For example, in a case where the boards to store the key codes are previously determined by the program stored in the ROM, the system CPU  31  of the system control board  20  determines the boards to store the divided key codes on the basis of the predetermined boards to store the key codes. Further, in a case where there is provided a table showing the boards to store the key codes, the system CPU  31  of the system control board  20  determines the boards to store the divided key codes on the basis of the table.  
      When the system CPU  31  of the system control board  20  determines the boards to store the key codes, the system CPU  31  of the system control board  20  collects the divided key codes stored in the NVRAMs of the respective boards from the respective boards as the boards to store the key codes (step S 43 ). Here, the key codes in the divided state, stored in the NVRAM  20   a  of the system control board  20 , are read from the NVRAM  20   a.    
      When the system CPU  31  of the system control board  20  collects the key codes in the divided state from the respective boards, the system CPU  31  of the system control board  20  develops the key code in the divided state, collected from the respective boards, on the RAM  33  to create a key code in the complete state (step S 44 ).  
      When the system CPU  31  of the system control board  20  creates the key code in the complete state, the system CPU  31  of the system control board  20  sets the key code in the complete state in the encryption board  25  (step S 45 ). With this, there is brought about a state where the data can be encrypted by the encryption board  25 . When the system CPU  31  of the system control board  20  sets the key code in the encryption board  25 , the system CPU  31  of the system control board  20  encrypts the data captured in step S 41  by the encryption board  25  and stores the encrypted data in the hard disk drive  26  (step S 46 ).  
      Next, a decoding procedure by the key code will be described.  
       FIG. 5  is a flow chart for explaining a procedure of reading and decoding the data stored in the hard disk drive  26  of this copying machine  1  and subjecting the decoded data to an image forming processing.  
      The encrypted data stored in the hard disk drive  26  of this copying machine  1  needs to be read and decoded by the use of the key code. Hence, the system CPU  31  of the system control board  20  needs to set the key code in the encryption board even when the data is read from the hard disk drive  26 .  
      First, when the data is read from the hard disk drive  26 , the system CPU  31  of the system control board  20  designates data to be read from the hard disk drive  26  and decoded (step S 51 )  
      When the data to be read from the hard disk drive  26  is designated, the system CPU  31  of the system control board  20  determines the boards to store the key codes in the divided state by the same operation as in the steps S 42  to S 45  (step S 52 ), collects the key codes in the divided state from the respective boards (step S 53 ), creates the key code in the complete state (step S 54 ) and sets the key code in the complete state in the encryption board  25  (step S 55 ).  
      Here, when the key code in the complete state is already set in the encryption board  25 , the processings in steps S 52  to S 55  are omitted.  
      The operation like this brings about a state in which the data can be decoded by the encryption board  25 . The CPU  31  that sets the key code in the encryption board  25  reads the data designated in the step S 51  and decodes the data by the encryption board  25  (step S 56 ).  
      Further, the system CPU  31  of the system control board  20  sends a print request to the printer control board  22 , decodes the data by the encryption board  25 , and outputs the data read from the hard disk drive  26  to the printer control board  22 . With this, the printer  12  performs an image forming processing on the basis of control performed by the printer control board  22  and the laser control board  23  (step S 57 ).  
      In the encrypting procedure and the decoding procedure described above, the key codes stored in the divided state in the plurality of boards in the copying machine are collected from the respective boards, the key code in the complete state is created from the key codes in the divided state that are collected from the respective boards, and this key code in the complete state is made a key code for encrypting the data to be stored in the hard disk drive or a key code for decoding the data stored in the hard disk drive. By storing the key code for encrypting and decoding the data in the divided state in this manner, the security of the data can be improved.  
      In this respect, the image forming processing by the copying machine  1  is realized in the following manner: the image data read by the scanner  11  or the image forming data received from the external device is encrypted and temporarily stored in the hard disk drive  26  (steps S 41  to S 46  described above) and the data stored in the hard disk drive  26  is read and decoded and printed on copy paper by the printer  12  (steps S 51 , S 56  and S 57 ).  
      Next, a procedure of disposing the copying machine  1  will be described.  
       FIG. 6  is a flow chart for explaining the procedure of disposing the copying machine  1 . Here, in the following description, it is assumed that an operation of disposing the copying machine  1  is performed by a serviceman having the expertise of copying machine.  
      First, the serviceman turns on the power supply switch (not shown) and performs an operation of starting a copying machine disposing processing mode for disposing the copying machine by the control panel  13 . Then, the system CPU  31  of the system control board  20  turns on the power supply of the copying machine  1  (step S 61 ) and starts the copying machine disposing processing mode (step S 62 ).  
      When the copying machine disposing mode is started, the serviceman selects and instructs the copying machine disposing mode by the use of the control panel  13  (step S 63 ). Here, the serviceman selects, as a method of disposing the copying machine, for example, whether or not the contents recorded in the hard disk drive  26  are erased, and whether or not the key code are erased.  
      When the method of disposing the copying machine is selected by the use of the control panel  13 , the system CPU  31  of the system control board  20  determines, on the basis of the selected method of disposing the copying machine, whether or not the contents recorded in the hard disk drive  26  are erased (step S 64 ). In a case where the system CPU  31  determines that the contents recorded in the hard disk drive  26  are to be erased (YES in step S 64 ), the system CPU  31  writes a predetermined value over all of the storage area of the hard disk drive  26  (step S 65 ). In general, there is a possibility that the data recorded in the hard disk drive  26  cannot be completely erased by one overwriting operation. For this reason, it is also recommended that the predetermined value be written over the storage area of the hard disk drive  26  for several times.  
      Further, in a case where the erasing of the key code is selected as the method of disposing the copying machine (YES in step S 66 ), the system CPU  31  of the system control board  20  erases the key codes stored in the divided state in the NVRAMs of the plurality of boards (step S 67  to S 69 ).  
      That is, in the case of erasing the key code, the system CPU  31  of the system control board  20  makes sure of the boards to store the divided key codes (step S 67 ). Here, in a case where the key codes are stored in the boards based on a predetermined program, the system CPU  31  makes sure of the boards based on the predetermined program. Moreover, in a case where a table showing the boards to store the divided key codes, the system CPU  31  makes sure of the boards to store the divided key codes on the basis of the table.  
      When the system CPU  31  of the system control board  20  makes sure of the boards to store the divided key codes, the system CPU  31  first erases the key code stored in the NVRAM  20   a  on the system control board  20  (step S 68 ). When the system CPU  31  of the system control board  20  erases the key code stored in the NVRAM  20   a  on the system control board  20 , the system CPU  31  further erases all of the key codes in the divided state that are stored in the NVRAMs on the other boards (step S 69 ). For example, in a case where the divided key code is stored in the NVRAM  22   a  on the printer control board  22 , the system CPU  31  outputs an instruction to erase the key code stored in the NVRAM  22   a  to the printer control board  22 . With this, the printer CPU (not shown) of the printer control board  22  erases the key code stored in the NVRAM  22   a.    
      All of the key codes stored in the plurality of boards are erased in the above steps S 67  to S 69 . Moreover, in general, when data is once erased in the NVRAM, the data is completely erased. In other words, the key codes stored in the NVRAMs in the divided state can be completely erased. For this reason, even if the data stored in the hard disk drive  26  is analyzed after the copying machine is disposed, the key codes are not analyzed and hence the security of the data stored in the hard disk drive  26  in the copying machine can be improved.  
      As described above, in this copying machine, at the time of setting up the copying machine, the key code for encrypting the data for image formation that is stored in the hard disk drive is divided in the plurality of key codes, and the divided key codes are stored in the plurality of memories mounted on the plurality of boards in the copying machine. Further, in this copying machine, in a case where the data is written to or read from the hard disk drive, the key codes stored in the plurality of memories in the divided state are collected to create the key code in the complete state and the data for image formation is encrypted or decoded by the created key code in the complete state.  
      With this, even if the whole copying machine or the control board and the hard disk drive are stolen, the key code is hard to analyze. Hence, even if the copying machine is stolen, it is impossible to read the data stored in the hard disk drive.  
      Furthermore, in the case of disposing the copying machine, not only the data stored in the hard disk drive is erased but also all of the key codes stored in the divided state are erased. With this, even if the disposed copying machine is analyzed, it is impossible to analyze the key code and hence to read the data stored in the hard disk.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.