Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. application Ser. No. 10/720,158, filed Nov. 25, 2003 now U.S. Pat. No. 6,811,083, and is based upon and claims the benefit of priority from the Japanese Patent Application No. 2002-373565, filed on Dec. 25, 2002; the entire contents of each are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a contact-type IC card without built-in batteries, and more particularly to an IC card to counter erroneous input by a legitimate user and illegal use by a third party, and also relates to a method and program for preventing illegal use of an IC card. 
   2. Description of the Related Art 
   In general, an IC card is used to record important data such as personal information. Therefore, it is necessary to prevent illegal use of the card by a third party if it is lost. To this end, before a general IC card can be used, identification is performed using a personal identification number (PIN) (hereinafter referred to as “PIN identification”), to identify the legitimate owner (hereinafter referred to simply as the “owner”) of the card. PIN information is generally stored in the IC card, and the owner of the card inputs their PIN through a terminal into which the IC card has been inserted. After the inserted PIN has been compared with the PIN stored in the IC card, the comparison result is sent to the terminal (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-76402). 
   In the PIN scheme, a card cracker who has acquired another person&#39;s IC card may guess and input the PIN of the owner of the card in order to impersonate the legitimate owner of the card. To thwart such PIN guessing, the process of locking an IC card when an incorrect PIN is input a predetermined number of times is now employed (this is called “PIN locking”). In a PIN-locked IC card, no further PIN input is possible, so the card cannot be used any more. PIN locking can be done on the system side (including the above-mentioned terminal, a server connected to the terminal, etc.) or on the IC card side. 
   PIN locking is performed to thwart card crackers. However, the owner of an IC card may well input their PIN incorrectly, resulting in PIN locking. If this happens, it is necessary to access, for example, the system manager to release the locked state. However, this is troublesome and so reduces the convenience of the IC card. 
   If the PIN locking of an IC card is limited to a certain length of time, a legitimate user can reuse the card sooner or later without the trouble of accessing, for example, the system manager. However, an illegitimate user is still prevented from continuously attempting to guess the PIN. So, there is a demand for setting a locking period. 
   However, if PIN locking is performed on the system side, it is necessary to centrally manage locking management information used for managing PIN locking, utilizing a server that handles a great many system-side terminals, and to access the locking management information each time PIN identification is performed. This increases the load on the system. 
   In light of the above, there is a need for a scheme in which PIN locking is performed on the IC card side. However, IC cards alone cannot provide their own power and so cannot time a PIN locking period. And if IC cards with built-in batteries are made, they lose the advantage of being usable without batteries. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention has been developed in light of the above, and aims to provide an IC card capable of realizing PIN locking for a predetermined period without external power and without increasing the load on the system side including a terminal, server, etc., and also to provide a method and program for preventing illegal use of an IC card. 
   According to a first aspect of the invention, there is provided an IC card receiving a power from an external terminal and performing a process, the IC card comprising: a storage which stores first identification information uniquely assigned to the IC card; an acquisition unit configured to acquire second identification information from the external terminal; a first timer including a first change unit whose state changes with lapse of time without the power, the state of the first change unit changing from a first initial state to a final state via an intermediate state, the first timer outputting a first signal indicative of a changed state of the first change unit in response to an instruction issued when the IC card receives the power; a comparison unit configured to compare the second identification information with the first identification information, determine whether or not the second identification information and the first identification information are identical to each other, and provide a first initializing signal according to at least one of determined results; and a controller which initializes the first change unit to the first initial state when receiving the first initializing signal from the comparison unit, the controller further controlling the IC card to make it inhibit the process until the state of the first change unit changes to the intermediate state. 
   According to a second aspect of the invention, there is provided a method of preventing illegal use of an IC card, the IC card receiving a power from an external terminal and performing a process, the method comprising: preparing an IC card including a storage which stores first identification information uniquely assigned to the IC card, an acquisition unit configured to acquire second identification information from the external terminal, a first timer including a first change unit whose state changes with lapse of time without the power, the state of the first change unit changing from a first initial state to a final state via an intermediate state, the first timer outputting a first signal indicative of a changed state of the first change unit in response to an instruction issued when the IC card receives the power; comparing the second identification information with the first identification information, determining whether or not the second identification information and the first identification information are identical to each other, and providing a first initializing signal according to at least one of determined results; and initializing the first change unit to the first initial state when the first initializing signal is received, and inhibiting the process until the state of the first change unit changes to the intermediate state. 
   According to a third aspect of the invention, there is provided a program stored in a storage medium and executed by a processor included in an IC card, the program comprising: means for instructing a processor to compare second identification information with first identification information, determine whether or not the second identification information and the first identification information are identical to each other, and providing a first initializing signal according to at least one of determined results the IC card receiving a power from an external terminal and performing a process using the program, the IC card including: a storage which stores the first identification information uniquely assigned to the IC card; an acquisition unit configured to acquire the second identification information from the external terminal; and a first timer including a first change unit whose state changes with lapse of time without the power, the state of the first change unit changing from a first initial state to a final state via an intermediate state, the first timer outputting a first signal indicative of a changed state of the first change unit in response to an instruction issued when the IC card receives the power; and means for instructing the processor to initialize the first change unit to the first initial state when the first initializing signal is received, and instructing the processor to inhibit the process until the state of the first change unit changes to the intermediate state. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  illustrates the whole system according to an embodiment of the invention; 
       FIG. 2  is a block diagram illustrating the internal configuration of an IC chip  22  incorporated in an IC card  20 ; 
       FIG. 3  is a block diagram illustrating the basic concept of a timer  36 / 37 ; 
       FIG. 4  illustrates a first example for realizing the timer  36 / 37 ; 
       FIG. 5  illustrates changes in the state of the timer  36 / 37  with lapse of time; 
       FIG. 6  is a graph showing the relationship between the time and the output signal of the timer  36 / 37 ; 
       FIG. 7  illustrates a second example for realizing the timer  36 / 37 ; 
       FIG. 8  illustrates a third example for realizing the timer  36 / 37 ; 
       FIGS. 9A and 9B  show examples of connection between the timer  36 / 37  and CPU  32 ; 
       FIGS. 10A and 10B  are schematic flowcharts illustrating the operation of the CPU  32  of the chip  22 ; 
       FIG. 11  is a flowchart useful in explaining the operations related to PIN identification; 
       FIGS. 12A and 12B  are time charts according to the flowchart of  FIG. 11  that illustrates the operation related to PIN identification; 
       FIG. 13  is a flowchart useful in explaining a modification of the operations related to PIN identification; and 
       FIGS. 14A and 14B  are time charts according to the flowchart of  FIG. 13  that illustrates the modification of the operation related to PIN identification. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1  illustrates the whole system according to an embodiment of the invention. As shown, the system comprises an IC card terminal and contact-type IC card  20 . It is a matter of course that the IC card terminal  10  may be connected via a network to, for example, a server that centrally manages a large number of IC card terminals  10 . 
   The contact-type IC card  20  comprises a plastic card member  25  of a rated size and an IC module  24 . The IC module  24  includes an IC chip  22  sealed with a sealing member  23  and configured to perform a predetermined logical operation, and an IC card interface  21  exposed to the outside and connected to the IC chip  22 . When the IC cared  20  is inserted in the IC card terminal  10 , it receives power from the terminal, and the IC chip  22  performs the predetermined logical operation. On the other hand, when the IC cared  20  is not inserted in the IC card terminal  10 , the IC chip  22  does not perform the logical operation. 
   The IC card terminal  10  comprises an insertion unit  11  for inserting therein the IC card  20 , and an IC card interface  13  to be electrically connected to the IC card  20  when the IC card  20  is inserted in the insertion unit  11 . When the IC card  20  is inserted, the IC card interface  13  opposes the IC card interface  21  of the IC card  20 . The IC card terminal  10  further comprises an input unit  12  for permitting a user to input a PIN (Personal ID Number) after the IC card  20  is inserted, and a controller  14  for controlling the whole IC card terminal  10 . The input unit  12 , controller  14  and power supply V for supplying power to the IC card  20  are connected to the IC card interface  13 . 
   In the system constructed as above, to use the IC card  20 , firstly, the IC card  20  is inserted into the IC card terminal  10 , then a user PIN is input through the input unit  12  and supplied to the IC chip  22  of the IC card  20  via the IC card interfaces  13  and  21 . The IC chip  22 , in turn, compares the supplied PIN with the legitimate PIN stored therein. If it is determined that these PINs are identical to each other, a command is supplied from the IC card terminal  10  to the IC card  20  via the IC card interfaces  13  and  21 . The IC card  20 , for example, interprets the command, operates in accordance with the command, and responds to the IC card terminal  10 . 
     FIG. 2  is a block diagram illustrating the internal configuration of the IC chip  22  incorporated in the IC card  20 . 
   As seen from  FIG. 2 , an input/output unit  31  is connected to the IC card interface  21  and internal bus  39 . When the IC card  20  is inserted in the IC card terminal  10 , the input/output unit  31  supplies a power supply unit  38  with the power acquired from the terminal  10  via the IC card interface  21 , transmits, to the internal bus  39 , the command or data received from the IC card interface  21 , and transmits, to the IC card interface  21 , the command or data received from the internal bus  39 . 
   A CPU  32  controls the whole IC chip  22 , and operates in accordance with the program stored in a ROM  33 . The ROM  33  stores, as well as the program, the PIN assigned to the IC card  20 . The PIN stored in the ROM  23  will hereinafter be referred to as a “legitimate PIN”, and any other PIN will be referred to as an “illegitimate PIN”. In the case of an IC card  20  that permits the PIN to be changed, the PIN may be stored in an EEPROM  35  described later. The ROM  33  also stores a threshold value for limiting the number of occasions an illegitimate PIN is input during a predetermined period of time. 
   A RAM  34  is a work memory used by the CPU  32 . The EEPROM  35  is a nonvolatile semiconductor memory that can be rewritten by the CPU  32 , and has a count value storing area for storing the number of occasions an illegitimate PIN is input during a predetermined period of time. 
   The power supply unit  38  is connected to the input/output unit  31  so that it receives the power supplied from the IC card terminal  10  and supplies it to each element of the IC chip  22 . 
   A timer  36  for locking and timer  37  for counting have the same structure, and are disposed to change in state with lapse of time without external power, thereby measuring whether or not a predetermined time period has elapsed. Each state of the timer  36  and timer  37  changes from an initial state to a final state via an intermediate state. The timers  36  and  37  measure different predetermined time periods. The timer  36  can measure a longer time period than the timer  37 . The lock timer  36  sets a locking period in which the IC card  20  cannot perform any process other than the time measurement. On the other hand, the count timer  37  sets a period in which the number of occasions an illegitimate PIN is input is counted. 
   The timers  36  and  37  (hereinafter generically referred to as a “timer  36 / 37 ”) will be described in more detail. 
     FIG. 3  is a block diagram illustrating the basic concept of the timer  36 / 37 . The timer  36 / 37  comprises: a change unit  41 , the state of which changes with lapse of time without a power supply, such as battery; an input unit  42  for inputting an input signal to the change unit  41 ; and an output unit  43  for outputting an output signal changed relative to the input signal based on the state of the change unit  41 . The change in the state of the change unit  41  is utilized to measure time. The input unit  42  and output unit  43  are used to confirm the state of the change unit  41 . 
     FIG. 4  illustrates a first example that realizes the basic concept of the timer  36 / 37  of FIG.  3 . 
   The first example of the timer  36 / 37  comprises: a first layer having a source region  51 , drain region  52  and channel region  53  therebetween; a second layer provided on the first layer and formed of a tunnel insulation film  54 ; a third layer provided on the second layer and formed of a floating gate  55 ; a fourth layer provided on the third layer and formed of an insulation film  56 ; and a fifth layer provided on the fourth layer and formed of a control gate  57 . A source electrode  58  and drain electrode  59  are provided on the source and drain regions  51  and  52 , respectively. 
     FIG. 5  illustrates changes with lapse of time in the state of the timer  36 / 37  of FIG.  4 . In the figure, hatched circles indicate electrons, and white circles indicate positive holes. 
   In  FIG. 5 , state  1  is the initial state. In the timer  36 / 37  that assumes the state  1 , a pre-process is performed, in which the control gate  57  applies a high electric field between the substrate boundary of the channel region  53  and the floating gate  55 , thereby injecting electrons from the channel into the floating gate  55  utilizing FN tunneling. At this time, positive holes gather at the substrate boundary of the channel region  53 , whereby a channel is formed on the substrate boundary between the source and drain regions  51  and  52 . 
   In the state  1 , the electrons in the floating gate  55  gradually shift, by direct tunneling, to the substrate boundary, thereby reducing the level of the electric field at the substrate boundary in the channel region  53 . State  2  of  FIG. 5  is assumed at a time point T 1  a certain time period after the state  1 . State  3  of  FIG. 5  is assumed at a time point T 2  a certain time period after the state  2 . Similarly, state  4  is the state assumed at a time point T 3  a certain time period after the state  3 . The circles indicated by the broken lines represent the shift of electrons made due to direct tunneling by the respective time points. In the state  4  (i.e. a final state) at the time point T 3 , most electrons escape from the floating gate  55 , therefore the channel at the substrate boundary of the channel region  53  disappears. As a result, no signals are output. 
     FIG. 6  is a graph illustrating the relationship between the time and the output signal of the timer  36 / 37 . Direct tunneling occurs between time points T a (=0) and T b  (i.e. between the states an initial state and an intermediate state), and lastly, the channel disappears, whereby the level of the output signal is reduced to the noise level. Since the timer  36 / 37  supplies an output signal corresponding to a change in level between T a  (=0) and T b  (=e.g. the time when the output signal level reaches the noise level), the side for receiving the output signal can determine whether or not a predetermined time period has elapsed, or can determine a specific time point (e.g. T 1 , T 2  or T 3  shown in  FIG. 6 ) a predetermined time period after the initial state if the relationship between the state of the timer  36 / 37  and the level of the output signal is always clear. The time points T 1 , T 2  and T 3  correspond to the states  2 ,  3  and  4  in FIG.  5 . 
     FIG. 7  is a second example that realizes the basic concept of the timer  36 / 37  of FIG.  3 . The second example of the timer  36 / 37  comprises: a first layer having a source region  61 , drain region  62  and channel region  63  therebetween; a second layer provided on the first layer and formed of a tunnel insulation film  64 ; a third layer provided on the second layer and formed of a gate  65 ; and a PN junction  66  provided on the third layer for controlling a leak current. A source electrode  68  and drain electrode  69  are provided on the source and drain regions  61  and  62 , respectively. 
   The change in the state of the second example of the timer  36 / 37  with lapse of time is similar to that of the first example of the timer  36 / 37 , although in the former, current leakage occurs in a PN junction, and in the latter, direct tunneling occurs. Therefore, no description is given of the change in the state of the second example of the timer  36 / 37  with lapse of time. 
     FIG. 8  is a third example that realizes the basic concept of the timer  36 / 37  of FIG.  3 . The third example of the timer  36 / 37  comprises: a first layer having a source region  71 , drain region  72  and channel region  73  therebetween; a second layer provided on the first layer and formed of a tunnel insulation film  74 ; a third layer provided on the second layer and formed of a gate  75 ; and a Schottky junction  76  provided on the third layer for controlling a leak current. A source electrode  78  and drain electrode  79  are provided on the source and drain regions  71  and  72 , respectively. 
   The change in the state of the third example of the timer  36 / 37  with lapse of time is similar to that of the first example of the timer  36 / 37 , although in the former, current leakage occurs in a Schottky junction, and in the latter, direct tunneling occurs. Therefore, no description is given of the change in the state of the third example of the timer  36 / 37  with lapse of time. 
   When the above-described timer  36 / 37  is used, it is constructed as shown in the examples of connection of  FIGS. 9A and 9B . 
   In the example of  FIG. 9A , a voltage can be applied between the opposite ends of the timer  36 / 37 . A power supply terminal  81  is connected to the source electrode  58 ,  68 ,  78  of the timer  36 / 37  via a switch element  83 , while a GND terminal  82  is connected to the drain electrode  59 ,  69 ,  79  via an ampere meter  84 . The switch element  83  is connected to an ON/OFF (enable) signal line, and is turned on when an ON signal is supplied thereto from the ON/OFF signal line. The ampere meter  84  is connected to output a current value to the CPU  32 . 
   To detect the state of the timer  36 / 37  during the operation of the IC chip  22 , the CPU  32  turns on the switch element  83 , thereby applying a predetermined voltage between the power supply terminal  81  and GND terminal  82 . As a result, a current flows through the timer  36 / 37 , which is measured by the ampere meter  84 . The measured current value is output to the CPU  32 . Thus, the CPU  32  detects the state of the timer  36 / 37 . 
   As described above referring to  FIG. 5 , a pre-process must be performed in the timer  36 / 37  before time measurement. Therefore, the timer  36 / 37  is equipped with a means for performing the pre-process (not shown). Upon receiving an instruction to start time measurement from the outside, the timer  36 / 37  performs the pre-process and then starts time measurement. 
   In the example of connection shown in  FIG. 9A , a single timer  36 / 37  is employed. However, a plurality of timers  36 / 37  may be employed. The states of the change units  41  of the timers  36 / 37  may change at the same rate or different rates, according to purpose.  FIG. 9B  illustrates timers  36 / 37  in which the states of the change units  41  change at different rates. As shown in  FIG. 9B , the timers  36 / 37  identical to that shown in  FIG. 9A  are arrange in parallel, and the current values output therefrom are input to an averaging circuit  85 . The average current value from the averaging circuit  85  is output to the CPU  32 . The ON/OFF (enable) signal line led from the CPU  32  is connected to the switch elements  83  so that the CPU  32  can commonly control the switch elements  83 . In this example, even if the change units  41  exhibit some different changes in state with lapse of time, the average current value output from the averaging circuit  85  enables a stable timer to be realized. Further, if change units  41  that exhibit different changes in state with lapse of time are intentionally employed (this example is not shown), various types of time information can be acquired. 
   Referring to  FIGS. 10A and 10B , the operation of the CPU  32  of the chip  22  will be schematically described. 
   After the IC card  20  is inserted into the IC card terminal  10  and before it is ejected therefrom, PIN identification is always performed, and a subsequent process can be performed if the PIN identification result indicates that the input PIN is legitimate. If the PIN identification result indicates that the input PIN is illegitimate, the card  20  is ejected (FIG.  10 A), or PIN identification is performed again instead of ejecting the card  20  (FIG.  10 B). 
   Referring to the flowchart of  FIG. 11 , the PIN identification process will be described in detail. 
   Firstly, a user inserts the IC card  20  into the IC card terminal  10 , then inputs a PIN. The input PIN is supplied to the input/output unit  31  of the IC card  20  via the IC card interfaces  13  and  21 . The PIN is then supplied therefrom to the CPU  32  (S 101 ). 
   Upon receiving the PIN, the CPU  32  firstly determines whether or not the lock timer  36  is now measuring time (S 102 ). Specifically, as described referring to  FIGS. 9A and 9B , the CPU  32  reads a current value from the lock timer  36  and determines whether or not the current value reaches a noise level. 
   If it is determined that the timer  36  is now measuring time, PIN identification is determined to have failed since the IC card  20  is locked, which is reported to the terminal  10  (S 103 ). 
   On the other hand, if it is determined that the timer  36  is not measuring time, it is then determined whether or not the count timer  37  is now measuring time (S 104 ). This determination is performed in the same manner as at the step S 102 . 
   Unless the count timer  37  is measuring time, an illegitimate data counter stored in an illegitimate data count value storing area in the EEPROM  35  is reset (S 105 ), thereby causing the count timer  37  to start time measurement (S 106 ). If, for example, the count timer  37  is the above-described first example, a high voltage is instantly applied to the timer upon reception of the instruction to start measurement, whereby electrons are accumulated in the floating gate. After that, time measurement is started automatically. 
   Subsequently, the CPU  32  compares the PIN received at the step S 101 , with the legitimate PIN stored in the ROM  33  (S 107 ). 
   If the received PIN is determined to be a legitimate one as a result of the comparison, the measurement by the count timer  37  is stopped (S 108 ), thereby determining that the PIN identification process has succeeded, and informing the terminal  10  of this (S 109 ). More specifically, at the step S 108 , the change in the state of the count timer  37  with lapse of time may be stopped. Alternatively, the timer  37  may be managed using a valid/invalid flag that is stored in, for example, the EEPROM  35  and indicates the validity/invalidity of the time measurement by the count timer  37 . 
   If, on the other hand, the received PIN is determined to be illegitimate as a result of the PIN comparison, the value of the illegitimate data counter stored in the illegitimate data counter storing area of the EEPROM  35  is incremented (S 110 ). After that, it is determined whether or not the incremented counter value reaches a threshold value stored in the ROM  33  (S 111 ). 
   If the value of the illegitimate data counter reaches the threshold value, it is determined to be very possible that an illegitimate user is trying to illegally use the IC card  20 , thereby causing the lock timer  36  to start measurement of time (S 112 ). As a result, the IC card  20  is locked. The start of the time measurement may be performed in the same manner as that employed at the step S 106 . When the lock timer  36  starts time measurement, it is determined that PIN identification has failed, which is reported to the terminal  10  (S 113 ). 
     FIGS. 12A and 12B  are time charts according to the flowchart of  FIG. 11  that illustrates the operation of the first example related to PIN identification. In the figures, it is assumed that the threshold value for input of an illegitimate PIN is 3, and the time periods of the time measurement by the count timer  37  and lock timer  36  are T 1  and T 2  (T 1 &lt;T 2 ), respectively. Further, “Illegitimate PIN” indicates that an illegitimate PIN has been input through the input unit  12 , and “Legitimate PIN” indicates that a legitimate PIN has been input through the input unit  12 . 
   In  FIG. 12A , the initial value of the illegitimate data counter is indefinite (any value is OK), and the timers  36  and  37  do not yet start time measurement. In this state, if the first illegitimate PIN is input, the illegitimate data counter is reset to 0 at the step S 105 , whereby the count timer  37  starts time measurement, and the illegitimate data counter is incremented and set to “1” at the step S 110 . In this state, since the illegitimate data counter value is lower than the threshold value, the step S 112  is not yet started. 
   Assume that before the time period T 1  elapses from the input of the initial illegitimate PIN, the second illegitimate PIN is input. At this time, since the count timer  37  is measuring time, the steps S 105  and S 106  are not executed, and the illegitimate data counter is incremented to 2 at the step S 110 . Even in this state, the value of the illegitimate data counter is lower than the threshold value, therefore the step S 112  is not yet started. 
   After that, assume that before the period T 1  elapses from the input of the initial illegitimate PIN, the third illegitimate PIN is input. At this time, since the count timer  37  is measuring time, the steps S 105  and S 106  are not executed, and the illegitimate data counter is incremented to 3 at the step S 110 . At this time, the value of the illegitimate data counter reaches the threshold value, therefore the step S 112  is executed. Specifically, the lock timer  36  starts time measurement, thereby locking the IC card  20  until the period T 2  elapses. Within the period T 2 , even if a legitimate PIN is input, the locked state is maintained, and the identification process is finished at the step S 103 . 
   After the period T 2  elapses, the lock timer  36  stops its time measurement. At this time, the count timer  37  has already finished its time measurement (since T 1 &lt;T 2 ). Thus, the timers  36  and  37  assume states similar to the initial states. Also at this time, the illegitimate data counter may have any value as in the initial state, since it is always reset at the step S 105  when the next PIN is input. 
     FIG. 12B  illustrates the case where a legitimate PIN is input when the count timer  37  is measuring time. In  FIG. 12B , the initial state, initial illegitimate PIN and second illegitimate PIN are assumed to be identical to those of FIG.  12 A. If the third PIN is a legitimate one, the steps S 101 , S 102 , S 104  and S 107  are executed in this order, and it is determined at the step S 107  that the third PIN is a legitimate one, followed by the step S 108  where the count timer  37  finishes time measurement and the PIN identification process is returned to the initial stage. 
   As described above, the IC card of the embodiment incorporates a lock timer that operates for a predetermined time period without external power, therefore can assume a PIN receivable state again a predetermined period after it is locked. 
   Further, since a timer that operates for a predetermined time period without external power is used as a timer for counting, if the card  20  is not locked within a predetermined period after the initial illegitimate PIN is input, the illegitimate data counter can be reset. 
   By virtue of this structure, even if a legitimate user has unintentionally input an illegitimate PIN a number of times higher than the threshold value, they can reuse the IC card after a predetermined period, without, for example, accessing the system managing side. Furthermore, since a PIN cannot be input for a predetermined period of time, a lot of time is required until an illegitimate user reaches the legitimate PIN by guessing and inputting a PIN a large number of times. 
   It is also advantageous that IC cards according to the invention enable their users to utilize conventional IC card terminals without modifying them. 
   Referring to the flowchart of  FIG. 13 , another modification of the above-described PIN identification process will be described in detail. 
   This modification differs from the flowchart of  FIG. 11  only in that in the latter, the count timer starts time measurement at the step S 106 , while in the former, the count timer does it after the step S 107 . In the modification, when an illegitimate PIN is detected by PIN identification, the count timer  37  restarts time measurement. 
     FIGS. 14A and 14B  are time charts according to the last-mentioned modification. The conditions employed in these time charts are the same as those in  FIGS. 12A and 12B . 
   As is understood from  FIGS. 14A and 14B , when the lock timer  36  does not perform time measurement (when the value of the illegitimate data counter does not exceed the threshold value), the count timer  37  restarts time measurement each time an illegitimate PIN is input during time measurement, resulting in an extension of time measurement. Further, as shown in the left portion of  FIG. 14B , if an illegitimate PIN is input, when the lock timer  36  does not perform time measurement (when the value of the illegitimate data counter does not exceed the threshold value), and when the count timer  37  is measuring time, the time measurement of the timer  37  is stopped. On the other hand, as shown in the right portion of  FIG. 14B , when the lock timer  36  is measuring time (when the value of the illegitimate data counter exceeds the threshold value), the operation of the count timer  37  does not change (the period of the time measurement of the timer  37  is not extended), even if either a legitimate PIN or an illegitimate PIN is input. 
   The above-described modification provides a further advantage (compared to the flowchart of  FIG. 11 ) of being assured that if the IC card is not locked, PIN input can be resumed a predetermined period after the last PIN input, unless no further PIN is input during the predetermined period. 
   As described above, the IC card according to the modification of the embodiment uses, for locking, a timer operable without external power, therefore can receive a further PIN a predetermined period after the IC card is locked. 
   Furthermore, the IC card according to the modification uses, for counting, a timer operable without external power, therefore can reset the illegitimate data counter if a predetermined period elapses from the last PIN input. 
   By virtue of the above structure, even if a legitimate user has unintentionally input an illegitimate PIN a number of times that is larger than the threshold value, they can reuse the IC card after a predetermined period, without, for example, accessing the management side. Moreover, even if a third party attempts to crack the card by repeatedly guessing the legitimate PIN of the card, this attempt may well be thwarted, since PIN input is prevented until a predetermined period elapses and therefore an enormous amount of time is required to detect the legitimate PIN. 
   It is also advantageous that IC cards according to the embodiment enable their users to utilize conventional IC card terminals without modifying them. 
   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.

Technology Category: 3