IC memory card and method of protecting data therein

Claims

What is claimed is:

1. A method of protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first area and a second area, wherein first key data is stored in the first area, the method comprising:

a step of writing a file in the second area;

a step, executed when the file is written in the second area of the IC memory card, of deciding second key data, which is inserted into a header of the file, such that a fixed correlation is provided with respect to the first key data stored in the first area of the IC memory card, and writing a file in which the second key data is inserted in the second area;

a step of reading out a file from the IC memory card;

a step, executed when the file is read out of the IC memory card, of checking to determine whether the fixed correlation holds between the first key data that has been stored in the first area of the IC memory card and the second key data that has been inserted in the header of said file; and

a step of reading out said file if the fixed correlation holds between the first and second key data, and not reading out said file if the fixed correlation does not hold.

2. A method of protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first area and a second area, the method comprising:

a step of writing a file in said first area of the IC memory card;

a step, executed at said writing step, of deciding first and second key data in such a manner that a fixed correlation is provided between the first and second key data;

a step of writing the first key data in the first area, inserting the second key data in a header of a file and writing the file in the second area;

a step of reading a file out of the IC memory card;

a step executed at said reading step, of checking to determine whether the fixed correlation holds between the first key data that has been written in the first area of the IC memory card and the second key data that has been inserted in the header of said file; and

a step of reading out said file if the fixed correlation holds, and not reading out said file if the fixed correlation does not hold.

3. A method of protecting data in an IC memory card according to claim 2, wherein a device for writing files in the IC memory card and a device for reading files out of the IC memory card are separately provided.

4. A method of protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first area and a second area, the method comprising:

a step of writing first key data for preventing copying in the first area of the IC memory card in advance, and making the first key data differ from one IC memory card to another IC memory card in advance;

a step of writing a file in the second area;

a step, executed when the file is written in the second area of the IC memory card, of reading out the first key data for preventing copying that has been stored in the first area;

a step of deciding second key data in such a manner that a fixed correlation will hold with respect to said first key data;

a step of inserting said second key data in a header of the file and writing the file in the second area;

a step of reading out a file from the IC memory card;

a step, executed when the file is read out of the IC memory card, of checking to determine whether said fixed correlation holds between the first key data that has been written in the first area and the second key data that has been inserted in the header of said file;

a step of allowing read-out of said file if the fixed correlation holds, and inhibiting read-out of said file if the fixed correlation does not hold.

5. A method of protecting data in an IC memory card according to claim 4, wherein a device for writing files in the IC memory card and a device for reading files out of the IC memory card are separately provided.

6. A method of protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first area and a second area, the method comprising:

a step of writing first key data K1 in the first area of the IC memory card in advance, and making the first key data differ from one IC memory card to another IC memory card in advance;

a step of writing data in the IC memory card;

a step, executed when data is written in the IC memory card, of encrypting the data, which is to be written in the IC memory card, using the first key data K1;

a step of reading out data from the IC memory card; and

a step, executed when data is read out of the IC memory card, or deciphering the read data into original data using the first key data.

7. A method of protecting data in an IC memory card according to claim 6, further comprising:

a step of writing second key data K2 in the first area of the IC memory card in advance, and making said second key data K2 differ from one IC memory card to another IC memory card in advance;

a step, executed when data is written in the IC memory card, of converting a data-storage destination address of the IC memory card into another address using the second key data K2, and writing said encrypted data in the IC memory card at a location thereof indicated by the address obtained by the address conversion; and

a step, executed when data is read out of the IC memory card, of converting a data-read-out address into another address using the second key data K2, reading data out of the IC memory card from a location thereof indicated by the address obtained by said address conversion, and subjecting said read data to said deciphering step.

8. A method of protecting data according to claim 6, comprising:

providing a pattern generator;

a step, executed when data is written in the IC memory card, of loading said first key data K1 in the pattern generator as initial pattern data, generating successively different pattern data in said pattern generator, and changing pattern data, which is used in order to perform encryption, whenever data is written in the IC memory card; and

a step, executed when data is read out of the IC memory card, of loading said first key data K1 in the pattern generator as initial pattern data, generating successively different pattern data in said pattern generator, and changing pattern data, which is used in order to perform deciphering, whenever data is read out of the IC memory card.

9. A method of protecting data in an IC memory card according to claim 8, wherein said encryption and deciphering steps are performed by exclusive-OR operations.

10. A method of protecting data in an IC memory card according to claim 8, wherein said encryption step is performed by one of addition and subtraction operation in which carries and borrows are ignored, and the deciphering step is performed by one of subtraction and addition operation in which carries and borrows are ignored.

11. A method of protecting data in an IC memory card according to claim 8, wherein said pattern data is initialized whenever the IC memory card is accessed a predetermined number of times.

12. A method of protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first area and a second area, the method comprising:

a step of writing key data K2 in the first area of an IC memory card in advance, and making said key data differ from one IC memory card to another IC memory card in advance;

a step, executed when data is written in the IC memory card, of converting a data-storage destination address of the IC memory card into another address using the key data K2, and writing said data in the IC memory card at a location thereof indicated by the address obtained by the address conversion; and

a step, executed when data is read out of the IC memory card, of converting a data-read-out address into another address using the key data K2, and reading data out of the IC memory card from a location thereof indicated by the address obtained by said address conversion.

13. An IC memory card used as an external storage medium of a computer system, comprising:

a first storage area and a second storage area; and wherein

key data for preventing copying is written in the first area in advance and said key data is made to differ from one IC memory card to another.

14. An IC memory card used as an external storage medium of a computer system, comprising:

a first storage area and a second storage area; and wherein

first key data K1 used to encrypt and decipher data stored in the second area and second key data K2 used in order to make an address conversion is written in the first area in advance, the first key data and the second key data being made to differ from one IC card to another.

15. IC memory card writing apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

deciding means for deciding, when a file is written in the second storage area of the IC memory card, second key data, which is inserted into a header of the file, in such a manner that a fixed correlation is provided with respect to first key data stored in the first storage area of the IC memory card; and

write control means for writing the file in the second storage area after inserting the second key data into the header of the file.

16. IC memory card reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

checking means for checking, when a file is read out of the IC memory card, to determine whether a fixed correlation holds between first key data that has been written is the first storage area of the IC memory card and second key data that has been inserted in a header of the file; and

read control means for reading out said file if the fixed correlation holds between the first and second key data, and not reading out said file if the fixed correlation does not hold.

17. IC memory card writing/reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area storing first key data and a second storage area, the apparatus comprising:

deciding means, for deciding when a file is written in the second storage area of the IC memory card, second key data, which is inserted into a header of the file, in such a manner that a fixed correlation is provided with respect to the first key data stored in the first storage area of the IC memory card;

write control means for writing the file in the second storage area after inserting the second key data into the header of the file;

checking means for checking, when a file is read out of the IC memory card, to determine whether the fixed correlation holds between the first key data that has been stored in the first storage area of the IC memory card and the second key data that has been inserted in the header of said file; and

read control means for reading out said file if the fixed correlation holds between the first and second key data, and not reading out said file if the fixed correlation does not hold.

18. IC memory card writing apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

deciding means for deciding, when writing a file in the second storage area of the IC memory card, first and second key data in such a manner that a fixed correlation is provided therebetween; and

write control means for writing the first key data in the first storage area, inserting the second key data in a header of a file and writing the file in the second storage area.

19. IC memory card writing/reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having first storage area and a second storage area, the apparatus comprising:

deciding means for deciding, when writing a file in the second storage area of the IC memory card, first and second key data in such a manner that a fixed correlation is provided therebetween;

write control means for writing the first key data in the first storage area, inserting the second key data in a header of a file and writing the file in the second storage area;

checking means for checking, when reading a file out of the IC memory card, to determine whether the fixed correlation holds between the first key data that has been written in the first storage area of the IC memory card and the second key data that has been inserted in the header of said file; and

read control means for reading out said file if the fixed correlation holds, and not reading out said file if the fixed correlation does not hold.

20. IC memory card writing apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

writing means for writing first key data for preventing copying in the first storage area of the IC memory card in advance, and making the first key data differ from one IC memory card to another;

reading means for reading out, when a file is written in a second area of the IC memory card, the first key data for preventing copying that has been stored in the first storage area;

deciding means for deciding second key data in such a manner that a fixed correlation will hold with respect to said first key data; and

means for inserting said second key data in a header of the file and writing the file in the second storage area.

21. IC memory card reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, comprising:

writing means for writing first key data for preventing copying in the first storage area of the IC memory card in advance, and making the first key data differ from one IC memory card to another;

checking means for checking, when a file is read out of the IC memory card, to determine whether a fixed correlation holds between the first key data that has been written in the first storage area and second key data that has been inserted in a header of the file; and

means for allowing read-out of said file if the fixed correlation holds, and inhibiting read-out of said file if the fixed correlation does not hold.

22. IC memory card reading/writing apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

means for writing first key data for preventing copying in the first storage area of the IC memory card in advance, and making the first key data differ from one IC memory card to another;

means for reading out, when a file is written in the second storage area of the IC memory card, the first key data for preventing copying that has been stored in the first storage area;

means for deciding second key data in such a manner that a fixed correlation will hold with respect to said first key data;

means for inserting said second key data in a header of the file and writing the file in the second storage area;

checking means for checking, when a file is read out of the IC memory card, to determine whether said fixed correlation holds between the first key data that has been written in the first storage area and the second key data that has been inserted in a header of the file; and

means for allowing read-out of said file if the fixed correlation holds, and inhibiting read-out of said file if the fixed correlation does not hold.

23. IC memory card writing apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

first means for writing first key data K1 in the first storage area of the IC memory card in advance, and making the first key data K1 differ from one IC memory card to another;

second means for encrypting, when data is written in the IC memory card, the data, which is to be written in the IC memory card, using the first key data K1; and

third means for writing the encrypted data in the IC memory card.

24. IC memory card writing apparatus according to claim 23, wherein second key data K2 is written in the first storage area of the IC memory card in advance so that said second key data K2 differs from one IC memory card to another and when data is written in the IC memory card, said third means converts a data-storage destination address of the IC memory card into another address using the second key data K2 and writes said encrypted data in the IC memory card at a location thereof indicated by the address obtained by the address conversion.

25. IC memory card writing apparatus according to claim 23, wherein a pattern generator is provided and when data is written in the IC memory card, said first key data K1 is loaded in the pattern generator as initial pattern data, then the pattern generator generates successively different pattern data so that pattern data, which is used in order to perform encryption, changes whenever data is written in the IC memory card.

26. IC memory card reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

first means for writing first key data K1 in the first storage area of the IC memory card in advance, and making the first key data K1 differ from one IC memory card to another;

second means for reading data out of the IC memory card; and

third means for deciphering the read data into original data using the first key data K1.

27. IC memory card reading apparatus according to claim 26, wherein second key data K2 is written in the first storage area of an IC memory card in advance so that said second key data K2 differ from one IC memory card to another, and when data is read out of the IC memory card, said second means converts a data-read-out address into another address using the second key data K2 and reads data out of the IC memory card from a location thereof indicated by the address obtained by said address conversion, and said third means subjects said read data to said deciphering.

28. IC memory card reading apparatus according to claim 26, wherein a pattern generator is provided and when data is read out of the IC memory card, said first key data K1 is loaded in the pattern generator as initial pattern data and the pattern generator generates successively different pattern data so that pattern data, which is used in order to perform deciphering, changes whenever data is read out of the IC memory card.

29. IC memory card writing/reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

first means for writing first key data K1 in the first area of the IC memory card in advance, and making the first key data K1 differ from one IC memory card to another;

second means for encrypting, when data is written in the IC memory card, the data, which is to be written in the IC memory card, using the first key data K1;

third means for writing the encrypted data in the IC memory card;

fourth means for reading data out of the IC memory card; and

fifth means for deciphering the read data into original data using the first key data K1.

30. IC memory card writing/reading apparatus according to claim 29, wherein second key data K2 is written in the first storage area of the IC memory card in advance so that said second key data K2 differs from one IC memory card to another;

and wherein:

when data is written in the IC memory card, said third means converts a data-storage destination address of the IC memory card into another address using the second key data K2 and writes said encrypted data in the address obtained by the address conversion; and

when data is read out of the IC memory card, said fourth means converts a data-read-out address into another address using the second key data K2 and reads data out of the IC memory card from a location thereof indicated by the address obtained by said address conversion, and said fifth means subjects said read data to said deciphering.

31. IC memory card writing/reading apparatus according to claim 29, wherein a pattern generator is provided and wherein;

when data is written in the IC memory card, said first key data K1 is loaded in the pattern generator as initial pattern data, and the pattern generator generates successively different pattern data so that pattern data, which is used in order to perform encryption, changes whenever data is written in the IC memory card; and when data is read out of the IC memory card, said first key data K1 is loaded in the pattern generator as initial pattern data and the pattern generator generates successively different pattern data so that pattern data, which is used in order to perform deciphering, changes whenever data is read out of the IC memory card.

32. IC memory card writing/reading apparatus according to claim 31, wherein said encryption and deciphering are performed by exclusive-OR operations.

33. IC memory card writing/reading apparatus according to claim 31, wherein said encryption is performed by one of addition and subtraction in which carries and borrows are ignored, and the deciphering is performed by one of subtraction and addition in which carries and borrows are ignored.

34. IC memory card writing/reading apparatus according to claim 31, wherein said pattern data is initialized whenever the IC memory card is accessed a predetermined number of times.

35. IC memory card writing apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

first writing means for writing key data K2 in the first storage area of the IC memory card in advance so that said key data differs from one IC memory card to another;

converting means for converting, when data is written in the IC memory card, a data-storage destination address of the IC memory card into another address using the key data K2; and

second writing means for writing said data in the IC memory card at a location thereof indicated by the address obtained by the address conversion.

36. IC memory card reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

means for writing key data K2 in the first storage area;

means for converting, when data is read out of the IC memory card, a data-read-out address into another address using the key data K2; and

means for reading data out of the IC memory card from a location thereof indicated by the address obtained by said address conversion.

37. IC memory card writing/reading apparatus for protecting data recorded on an IC memory card used as an external storage medium of a computer system and having a first storage area and a second storage area, the apparatus comprising:

first writing means for writing key data K2 in the first storage area of the IC memory card in advance so that said key data differs from one IC memory card to another;

first address converting means for converting, when data is written in the IC memory card, a data-storage destination address of the IC memory card into another address using the key data K2;

second writing means for writing said data in the IC memory card at a location thereof indicated by the address obtained by the address conversion;

second address converting means for converting, when data is read out of the IC memory card, a data-read out address into another address using the key data K2; and

means for reading data out of the IC memory card from a location thereof indicated by the address obtained by said address conversion.

DESCRIPTION

1. Technical Field

This invention relates to an IC memory card used as an external storage medium of a computer system, as well as to a method of protecting data in the IC memory card.

2. Background Art

An IC memory card is a thin card, of a size equivalent to that of a business card, and is equipped with a memory. These cards, examples of which are ROM cards, RAM cards for managing data, etc., are advantageous in that they are compact, have a high access speed and are highly reliable. Such IC memory cards have been standardized by the PCMCIA (Personal Computer Memory Card International Association), whereby their mechanical shape, pin arrangement, data read and writing timings, etc., have been stipulated. In Japan also the standardization proposals of the PCMCIA have been adopted the JEIDA (Japan Electric Industry Development Association).

An information sales system is one example of a system in which an IC memory card is adopted at an external storage medium. In an information sales system, information for sale, such as newspapers, magazines and other publications in electronic form, is transferred, via a communication line, from an information center to automatic information vending machines disposed in various areas. The information is sold by being copied onto the IC memory card.

Computer systems in which an IC memory card serves as an external storage medium have been designed in accordance with the specifications of the PCMCIA. If all of these computer systems have the same operating system (OS), data can be written/read and copied at will from any IC memory card. More specifically, the data recorded on an IC memory card can readily be read/written by any personal computer or the like having a slot for the IC memory card, and information can readily be copied to another IC card by execution of a copy command. However, the fact that data created by oneself can be freely read/written by another individual and the content of the IC card can be copied at will is extremely inconvenient insofar as maintaining the confidentiality of stored information and protecting copyrights is concerned.

Accordingly, the practice in the prior art is to convert the address data of the memory card into a different address by encryption data possessed by the computer system and store data in a storage area designated by the converted address. If this expedient is adopted, the arrangement of data in the memory card is made random so that the data cannot be read out in the correct order by another computer system, thereby making it possible to enhance the confidentiality of data and to prevent copying.

There is available a system in which an IC memory card (master card) on which prescribed data has been recorded is rented, as in the manner of video software and CD software, as well as a system in which information is sold by being recorded on an IC memory card (which becomes the master card) brought in by the purchaser, as in the manner of an automatic information vending machine. In systems of this kind it is necessary to render data meaningless if it is copied from the master card and, if the card is the master card, to allow the data recorded on the card to be viewed using any computer system (terminal device). However, a problem encountered in the conventional systems is that these requirements cannot be satisfied.

Accordingly, an object of the present invention is to provide an IC memory card that is effective in preventing copying and protecting copyrights, as well as a method of protecting data in the card.

Another object of the present invention is to provide an IC memory card, as well as a method of protecting data in the card, in which even if data is copied from a master card, the data cannot be reproduced from the card copy.

A further object of the present invention is to provide an IC memory card which, if the card is a master card, is capable of having its recorded data reproduced by any computer system, as well as a method of protecting data in the card.

Still another object of the present invention is to provide an IC memory card in which confidentiality can be maintained to the maximum degree, as well as a method of protecting data in the card.

DISCLOSURE OF THE INVENTION

In a method of protecting data on an IC memory card having a ROM area and a RAM area and used as an external storage medium of a computer system, key data for preventing copying is stored in the ROM area of the IC memory card and the copying of data that has been stored in the RAM area of the IC memory card is prevented using the key data.

More specifically, when a file is written in a RAM area of an IC memory card, second key data, which is inserted into a header of the file, is decided and written in the RAM area in such a manner that a fixed correlation will exist with regard to first key data stored in a ROM area of the IC memory card. When a file is read out of the IC memory card, the first key data that has been written in the ROM area of the IC memory card is read out, the second key data that has been inserted in the header of the file is read out, and a check is performed to determine whether the fixed correlation holds between the first and second key data. Read-out of the file is allowed in a case where the fixed correlation holds and is inhibited in a case where the fixed correlation does not hold.

Further, first key data K1 is written in the ROM area of the IC memory card in advance and the first key data K1 is made to differ from one IC memory card to another. When data is written in the IC memory card, the data to be written in the IC memory card is written upon being encrypted using the first key data K1. When data is read out of the IC memory card, the read data is deciphered into the original data using the first key data.

Furthermore, the key data K2 is written in the ROM area of the IC memory card in advance and this key data is made to differ from one IC memory card to another. When data is written in the IC memory card, a data-storage destination address of the IC memory card is converted into another address using the key data K2 and data is written in the IC memory card at a location thereof indicated by the address obtained from this address conversion. When data is read out of the IC memory card, a data-read-out address is converted into another address using the key data K2 and data is read out of the IC memory card from a location thereof indicated by the address obtained from this address conversion.

Thus, as set forth above, it is so arranged that key data for preventing copying is stored in the ROM area of the IC memory card, and predetermined data is appended to a file stored in the RAM based upon this key data. Alternatively, data to be written in the RAM is encrypted or a data-storage address is converted. When data is read out, the original data is restored using the key data. If key data has not been stored in the ROM area, therefore, restoration of the original data cannot be carried out. As a result, even if a master card is copied, the key data that has been stored in the ROM area of the master card cannot be copied. This means that the original data cannot be recovered from the card copy, thereby rendering the copy meaningless.

Further, the first key data K1 is written in the ROM area of the IC memory card in advance. When data is written in the IC memory card, data to be written in the IC memory card is encrypted using the first key data K1, a data-storage destination address of the IC memory card is converted into another address using the key data K2 and the encrypted data is written in the IC memory card at a location thereof indicated by the address obtained from this address conversion. When data is read out of the IC memory card, a data-read-out address is converted into another address using the second key data K2 and data read out of the IC memory card from a location thereof indicated by the address obtained from this address conversion is deciphered into the original data using the first key data. Thus, data to be written in an IC memory card is encrypted and the address is converted into another address, thereby enhancing confidentiality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a first embodiment of the present invention;

FIG. 2 is a flowchart for writing a file;

FIG. 3 is a flowchart of reading out a file;

FIG. 4 is an explanatory view for a case in which the present invention is applied to an information sales system;

FIG. 5 is an explanatory view of a second embodiment of the present invention;

FIG. 6 is a block diagram of the second embodiment of the present invention;

FIG. 7 is an explanatory view of memory space of an IC memory card;

FIG. 8 is a diagram of the construction of a pattern generator;

FIG. 9 is a flowchart of encryption;

FIG. 10 is a flowchart of deciphering;

FIG. 11 is an explanatory view of repetition of pattern data;

FIG. 12 is a flowchart of encryption in a modification;

FIG. 13 is a flowchart of deciphering in a modification;

FIG. 14 is a block view of the third embodiment of the present invention;

FIG. 15 is a diagram of the construction of an encryption unit; and

FIG. 16 is a diagram of the construction of a deciphering unit,

BEST MODE FOR CARRYING OUT THE INVENTION

(a) First Embodiment of the Invention

FIG. 1 is an explanatory view of a first embodiment of the present invention. Numeral 1 denotes a writing terminal; 2 and 3 read-out terminals; 4 a copying machine; 11 an IC memory card (master card); and 11' a card copy that has been copied from the master card. The IC memory card 11 is provided with an attribute memory area 11a serving as a ROM area, and a common memory area 11b serving as a RAM area. The attribute memory area 11a is an area which the PCMCIA stipulates may be provided. This memory area stores the type of IC memory card (whether it is a ROM card or RAM card), its capacity and other data, and it is stipulated that the maker can use this memory area freely. In this invention, first key data K1, K2, . . . for preventing copying is written in the attribute memory area 11a. A number of files (newspapers, magazines, etc.) 11c-1, 11c-2, . . . 11c-n are stored in the common memory area 11b, and the files are assigned respective headers H1, H2, . . . Hn for specifying the file name, creation date, creator, etc. In this invention, second key data k1, k2, . . . for preventing copying is written in respective headers.

FIG. 2 is a flowchart for writing a file, and FIG. 3 is a flowchart for reading out a file.

When the writing terminal 1 writes a file 11c-i (i=1, 2, . . . n) in the common memory 11b of the IC memory card 11, the writing terminal 1 decides the first key data Ki for preventing copying and writes the first key data Ki in the attribute memory area 11a so as to correspond to the above-mentioned file (step 001). Next, the writing terminal 1 decides the second key data ki in such a manner that a fixed correlation is established with respect to the first key data Ki (step 002), inserts the second key data ki in the header Hi of the file 11c-i (step 003) and writes the header in the common memory area 11b in a form combined with the file (step 004). In a simple case, the fixed correlation may be a relation such as Ki=ki, by way of example.

When the read-out terminal 2 reads a prescribed file out of the IC memory card (master card) 11, the second key data that has been written in the header of this file is read out (step 005) and the first key data corresponding to this file, and which has been written in the attribute memory 11a, is read out (006). Next, the read-out terminal 2 checks to determine whether the aforesaid correlation holds between the first and second key data (step 007). If the fixed correlation holds, then the read-out terminal reads out the file and displays it (step 008). If the fixed correlation does not hold, the read-out terminal does not perform read-out and presents a display to this effect (step 009).

If the IC memory card is a master card, the aforementioned fixed correlation will hold between the first key data K1.about.Kn and the second key data k1.about.kn, and therefore read-out of the designated file is performed and the file is displayed on a display unit.

If the IC memory card is the card copy 11', however, the fixed correlation will not hold and read-out is refused as a result. More specifically, in a case where the card copy 11' is created from the master card 11 using the copy machine 4, only the content of the common memory area 11b can be copied and not the content of the attribute memory area 11a. As a consequence, the fixed correlation is not established between the first key data X1.about.Xn originally written in the attribute memory area 11a of the card copy 11' and the second key data k1.about.kn inserted in the headers H1.about.Hn of the files 11c-1.about.11c-n, and the read-out terminal 3 does not perform read-out from the card copy 11'.

Accordingly, read-out of a file from the IC memory card 11' obtained by copying the master card 11 cannot be performed. In essence this means that copying has not been achieved, thus making it possible to attain the object of preventing copying.

The above-mentioned copy-preventing function is implemented paying attention to one fact. This fact is that the common memory area 11b in the ID memory card be established as an area which the user can access freely while the attribute memory area 11a be established as an area which a general user cannot access freely. This means that an operation such as rewriting of the attribute memory area 11a can be performed only by a specific individual.

As a result, even if the master card 11 is copied and the card copy 11' created using the card copying machine 4 shown in FIG. 1, what can be copied is solely the files 11c-1.about.11c-n of the common memory area 11b; the first key data that has been written in the attribute memory area 11a is excluded from copying. Accordingly, the content (X1, X2 . . . ) of the attribute memory 11a originally possessed by the card copy 11' remains without be altered. Thus, the predetermined fixed correlation cannot be obtained between the second key data (k1, k2, . . . ) in the headers and the first key data (X1, X2 . . . ) in the attribute memory area 11a, and the read-out terminals 2, 3 are incapable of reading files from the card copy 11'.

There are cases in which the predetermined fixed correlation between the first and second key data in its simplest form is such that the first key data K1, K2, . . . and second key data k1, k2, . . . are made e