Patent Publication Number: US-2004046638-A1

Title: Terminal lock system comprising key device carried by user and terminal-associated device incorporated in terminal device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a terminal lock system for verifying that the user of a terminal device is a person with the legitimate right to use the terminal device for thereby protecting the terminal device against unauthorized use by a third party.  
       [0003] 2. Description of the Related Art  
       [0004] In recent years, a variety of terminal devices including personal computers, PDAs, cellular phones, etc. are finding widespread use among many users. The terminal devices often have important personal information stored therein and need to be protected against unauthorized use by persons other than lawful users thereof.  
       [0005] There have heretofore been various schemes for making personal authentication to permit such terminal devices to be used only by lawful users for protection against unauthorized use of those terminal devices. According to one authentication process, a terminal device requires the user to enter a password to identify the lawful user. This process is, however, not highly convenient for the user, causes a problem as to the management of the password, and is complex to carry out.  
       [0006] According to other schemes, an ID card is used to authenticate the user of a terminal device, and a one-time password that is valid at one time only when the user uses a terminal device is automatically issued for the user to enter to use the terminal device. However, using the ID card is a rather tedious and time-consuming task to perform. When the user leaves the terminal device, the user needs to remove the ID card from the terminal device, and when the user uses the terminal device, the user needs to insert the ID card into the terminal device. If the user forgets to remove the ID from the terminal device and leaves the terminal device, then the terminal device becomes vulnerable to unauthorized use by a third party. If the terminal device is a cellular phone, then since it is usually necessary to keep the cellular phone in operation while waiting for incoming calls, the ID card is expected to be inserted in the cellular phone at all times during the waiting mode. Therefore, when the user loses the cellular phone with the ID card inserted therein, it is open to unauthorized use by a third party.  
       [0007] There are known personal authentication techniques that employ biological characteristics such as fingerprints, voiceprints, iris patterns, etc. for authentication. At present, however, these personal authentication techniques need highly costly devices, and are too expensive to be practically feasible solely for authentication purposes in various terminal devices.  
       [0008] Other conventional proposals for preventing unauthorized use of terminal devices include a system disclosed in Japanese laid-open patent publication No. 08-162994 entitled “Radio communication unit having a function to prevent unauthorized use”. The disclosed system gives a command to the radio communication unit to inhibit unauthorized use thereof from a remote location thereby disabling the radio communication unit in the event that the radio communication unit is lost or stolen. According to the disclosed prior art, since the radio communication unit is instructed against use by a radio signal, the system cannot transmit an inhibitory command to the radio communication unit unless the radio communication unit is turned on and positioned within a range that is reachable by the radio signal. Furthermore, the system requires the user to make an action to inhibit the radio communication unit from use. If the system is applied to a situation for making a personal computer not usable while the user is away, then the action made by the user tends to be more complex than if the user were asked to enter a password for authentication, and is not practical.  
       [0009] According to the conventional schemes described above, therefore, the user of the terminal device needs to make a complex action in order to prevent a third party from making unauthorized use of the terminal device. If the user has inadvertently made the password known or lost the terminal device together with the ID card, then it is impossible to reliably prevent unauthorized use of the terminal device by a third party.  
       SUMMARY OF THE INVENTION  
       [0010] It is therefore an object of the present invention to provide a terminal lock system and a terminal lock method which are able to authenticate the lawful user of a terminal device without the need for the user to make a complex action for thereby reliably preventing a third party from making unauthorized use of the terminal device.  
       [0011] To achieve the above object, there is provided a terminal lock system for verifying that the user of a terminal device is a person with the legitimate right to use the terminal device for thereby protecting the terminal device against unauthorized use by a third party, the terminal lock system comprising a key device and a terminal-associated device.  
       [0012] The key device is portable and has a radio communication means for performing short-range radio communications. The terminal-associated device requests a connection to the key device through the short-range radio communications, and inhibits the terminal device which is combined with the terminal-associated device from being used if information of the key device which is confirmed as being connected to the terminal-associated device does not agree with information registered in the terminal-associated device, or if the terminal-associated device is not confirmed as being connected to the key device through the short-range radio communications.  
       [0013] With the above arrangement, when the user who is carrying the key device moves away from the terminal device combined with the terminal-associated device until the terminal-associated device and the key device are no longer capable of connecting to each other based on a short-range radio communication technique, the terminal-associated device locks the terminal device against use. The terminal lock system thus authenticates the user without the need for asking the user to make any action, and reliably protects the terminal device against unauthorized use by a third party.  
       [0014] The key device may register information of the terminal-associated device in advance therein, and the key device may connect to the terminal-associated device through the short-range radio communications only when the information registered in the terminal-associated device which has requested a connection to the key device and the information registered in the key device agree with each other.  
       [0015] If a device in which the information of the key device is not registered requests a connection to the key device, then no short-range radio communications are carried out for thereby making the terminal lock system more reliable.  
       [0016] The key device may start the short-range radio communications with the terminal-associated device only when a predetermined action is made thereon.  
       [0017] Since the key device is brought from an inactivated state into a waiting mode for waiting for a radio connection when the user makes a predetermined action on the key device to use the key device, the consumption of electric energy by the key device is reduced, and the life of a battery of the key device is extended.  
       [0018] The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0019]FIG. 1 is a block diagram of a terminal lock system according to a first embodiment of the present invention;  
     [0020]FIG. 2 is a flowchart of an operation sequence of a terminal-associated device of the terminal lock system shown in FIG. 1;  
     [0021]FIG. 3 is a flowchart of an operation sequence of a key device of the terminal lock system shown in FIG. 1; and  
     [0022]FIG. 4 is a block diagram of a terminal lock system according to a second embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0023] 1st Embodiment:  
     [0024]FIG. 1 shows in block form a terminal lock system according to a first embodiment of the present invention. The terminal lock system according to the first embodiment of the present invention is a system for simply performing personal authentication and preventing a person other than the lawful owner from using a terminal device without permission, based on a short-range radio communication technique such as Bluetooth, radio LAN, or the like.  
     [0025] As shown in FIG. 1, the terminal lock system comprises terminal-associated device  100  and key device  200 . Terminal-associated device  100  is added to or incorporated in an information-related terminal device such as a personal computer, PDA, a cellular phone, or the like that needs to be protected. Key device  200  is carried at all times by the lawful owner of the terminal device, and is added to or incorporated in a cellular phone, a PDA, a wrist watch, a badge, a key holder, or the like. The cellular phone or the PDA may serve as a device on which terminal-associated device  100  is mounted or a device on which key device  200  is mounted.  
     [0026] A summary of operation of the terminal lock system according to the first embodiment of the present invention will be described below. Information of key device  200  is registered in advance in terminal-associated device  100 . Key-associated unit  200  is placed at all times in a mode for waiting for an attempt from terminal-associated device  100  to connect to key device  200 . After terminal-associated device  100  is turned on, it attempts to connect to key device  200  via a short-range radio communication link. If key device  200  is positioned in a range capable of radio communications with terminal-associated device  100 , then since key device  200  and terminal-associated device  100  are successfully connected, key device  200  acquires a right to use terminal-associated device  100 . Thus, once information of key device  200  is registered in terminal-associated device  100 , key device  200  can subsequently use terminal-associated device  100  insofar as key device  200  is in the range capable of radio communications with terminal-associated device  100  based on the short-range radio is communication technique such as Bluetooth, radio LAN, or the like. As a result, when the owner who is carrying key device  200  at all times is not located in the radio communication range, the terminal device cannot be used. For example, if the owner has lost a cellular phone as the terminal device, then the cellular phone cannot be used unless the key device is located in the radio communication range. If the owner is away from a notebook personal computer as the terminal device, then the notebook personal computer is not open to unauthorized use unless the key device is located in the radio communication range.  
     [0027] Details of the terminal lock system according to the first embodiment of the present invention will be described below. As shown in FIG. 1, the terminal lock system comprises terminal-associated device  100  that is combined with a terminal device and key device  200  that is carried by user  300 , most likely the owner thereof.  
     [0028] Actually, terminal-associated device  100  is added to or incorporated in a terminal device such as a personal computer, a PDA, a cellular phone, or the like, which should have limited access, i.e., cannot be used by persons other than the owner. Similarly, key device  200  is added to or incorporated in a device such as a cellular phone, a PDA, a wrist watch, a badge, a key holder, or the like that is carried by the owner at all times. The cellular phone or the PDA may serve as a device on which terminal-associated device  100  is mounted or a device on which key device  200  is mounted.  
     [0029] Terminal-associated device  100  comprises radio unit  110  for performing short-range radio communications based on a technique such as Bluetooth, radio LAN, or the like, computer (central processing unit)  120  which operates under programmed control, and user interface unit  130 . Key device  200  comprises radio unit  210  for performing short-range radio communications based on a technique such as Bluetooth, radio LAN, or the like, and computer (central processing unit)  220  which operates under programmed control.  
     [0030] Computer  120  includes communication controller  121 , terminal-associated device controller  122 , and memory  123 . Similarly, computer  220  includes communication controller  221  and key device controller  222 .  
     [0031] Communication controller  121  has a radio control function for controlling radio unit  110  and a function to perform communications using a communication protocol that is suitable for a radio technique that is employed. In order to connect to key device  200  as instructed by terminal-associated device controller  122 , communication controller  121  instructs radio unit  110  to connect to key device  200 , and returns a notification indicating that the connection has been successful or failed to terminal-associated device controller  122 .  
     [0032] At the time terminal-associated device  100  is activated, terminal-associated device controller  122  checks if information of key device  200  is registered in memory  123  or not. If information of key device  200  is not registered in memory  123 , then terminal-associated device controller  122  keeps terminal-associated device  100  usable, and waits until user  300  instructs terminal-associated device  100  via user interface unit  130 . Conversely, if information of key device  200  is registered in memory  123 , then terminal-associated device controller  122  locks the terminal device against use. Thereafter, according to the registered information, terminal-associated device controller  122  instructs communication controller  121  to connect to key device  200 . If notified of a connection success from communication controller  121 , then terminal-associated device controller  122  makes terminal-associated device  100  usable. If notified of a connection failure from communication controller  121 , then terminal-associated device controller  122  keeps terminal-associated device  100  unusable to inhibit the terminal device from use.  
     [0033] Terminal-associated device controller  122  is also instructed by user  300  via user interface unit  130  to register, delete, and edit information of key device  200 . If terminal-associated device controller  122  is instructed by user  300  to register information of key device  200 , then terminal-associated device controller  122  instructs communication controller  121  to connect to key device  200 . If notified of a connection success from communication controller  121 , then terminal-associated device controller  122  registers and stores information of key device  200  in memory  123 , and indicates to user  300  via user interface unit  130  that the registration of information of key device  200  has been successful. If notified of a connection failure from communication controller  121 , then terminal-associated device controller  122  indicates to user  300  via user interface unit  130  that the registration of information of key device  200  has failed.  
     [0034] Communication controller  221  has a has a radio control function for controlling radio unit  210  and a function to perform communications using a communication protocol that is suitable for a radio technique that is employed. When instructed by key device controller  222 , communication controller  221  instructs radio unit  210  to wait for a connection from terminal-associated device  100 . Key device controller  222  instructs communication controller  221  to wait for a connection from terminal-associated device  100 .  
     [0035] An overall operation sequence of the terminal lock system according to the first embodiment of the present invention will be described below with reference to FIGS. 1 through 3.  
     [0036] First, operation of terminal-associated device  100  will be described below with reference to FIG. 2.  
     [0037] When terminal-associated device  100  is activated, terminal-associated device controller  122  refers to memory  123  to check whether information of key device  200  is registered in memory  123  or not in step  1 . Since information of key device  200  is initially not registered in memory  123 , terminal-associated device  100  keeps the terminal device usable, and waits for an input from user  300  in step  2 . Memory  123  comprises a nonvolatile memory that is capable of storing information semipermanently. Alternatively, memory  123  may comprise a volatile memory if it can read information from an external memory when terminal-associated device  100  is activated.  
     [0038] In step  2 , user  300  instructs, via user interface unit  130 , terminal-associated device controller  122  to register information of key device  200  in memory  123 . In order to specify key device  200 , the terminal lock system may have a means for entering inherent information of key device  200  directly from user interface unit  130  or may have a means for generating a list of nearby devices based on a device search function according to the radio communication technique that is employed and selecting one of the devices in the list.  
     [0039] In step  3 , in response to the instruction from user  300  to register information of key device  200 , terminal-associated device controller  122  controls radio unit  110  to connect to key device  200  according to an appropriate radio communication protocol. Information for specifying key device  200  may be a production serial number inherent in key device  200 , an address inherent in key device  200 , or a software-based identification number inherent in key device  200  insofar as it is capable of uniquely identifying key device  200  through at least radio communications.  
     [0040] Operation of key device  200  will be described below with reference to FIG. 3.  
     [0041] In step  21  shown in FIG. 3, when key device  200  is turned on, key device controller  222  instructs communication controller  221  to wait for a connection from terminal-associated device  100 . As instructed, communication controller  221  waits until a connection comes from terminal-associated device  100 .  
     [0042] In step  3  shown in FIG. 2, a connection from radio unit  110  of terminal-associated device  100  is received by radio unit  210  of key device  200 , and communication controller  121  and communication controller  221  carry out a process to connect to each other according to the respective radio communication protocols thereof. Thereafter, key device  200  determines whether a connection is successful or not in step  22 .  
     [0043] If a connection is successful, then key device  200  keeps itself connected to terminal-associated device  100  in step  23 . At this time, key device  200  keeps itself connected to terminal-associated device  100  with a minimum consumption of electric energy that is achieved by a power saver scheme inherent in the employed ratio communication technique.  
     [0044] If the connection is broken in step  24 , then control goes back to step  21  immediately following the activation of key device  200 , and key device controller  222  instructs is communication controller  221  to wait for a connection from terminal-associated device  100 . If the connection is not broken in step  24 , then key device  200  keeps itself connected to terminal-associated device  100  in step  23 .  
     [0045] Operation of terminal-associated device  100  will be described again with reference to FIG. 2.  
     [0046] Communication controller  121  indicates a success or a failure in connecting to key device  200  in step  3  to terminal-associated device controller  122 . If a success in connecting to key device  200  is indicated to terminal-associated device controller  122  in step  4 , then terminal-associated device controller  122  registers information of key device  200  in memory  123  in step  6 . The information of key device  200  that is registered in memory  123  must be information for identifying key device  200 . If possible, a special calculation that cannot easily be forged should be carried out on such information for identifying key device  200  and the result should be registered as the information of key device  200  in memory  123 .  
     [0047] Thereafter, terminal-associated device controller  122  indicates that the registration of the information of key device  200  has been successful to user  300  via user interface unit  130  in step  7 .  
     [0048] If a failure in connecting to key device  200  is indicated to terminal-associated device controller  122  in step  4 , then terminal-associated device controller  122  indicates that the registration of the information of key device  200  has failed to user  300  via user interface unit  130  in step  5 . Thereafter, in step  2 , terminal-associated device  100  while being kept usable waits for an input from user  300  to attempt to register information of key device  200  again in memory  123 .  
     [0049] If information of key device  200  has already been registered in memory  123  in step  1  shown in FIG. 2, then terminal-associated device controller  122  makes terminal-associated device  100  unusable in step  8 .  
     [0050] While keeping terminal-associated device  100  unusable, terminal-associated device controller  122  attempts to connect to key device  200  via radio unit  110  according to an appropriate radio communication protocol in step  9 . The information for specifying key device  200  may be a production serial number inherent in key device  200 , an address inherent in key device  200 , or a software-based identification number inherent in key device  200 . If a special calculation has been carried out on such information for identifying key device  200 , then an inverse calculation is carried out to obtain the original information. At any rate, the information should be capable of uniquely identifying key device  200  through at least radio communications.  
     [0051] Communication controller  121  indicates a success or a failure in connecting to key device  200  in step  9  to terminal-associated device controller  122 . If a success in connecting to key device  200  is indicated to terminal-associated device controller  122  in step  10 , then terminal-associated device controller  122  makes terminal-associated device  100  usable in step  11 .  
     [0052] Thereafter, terminal-associated device controller  122  indicates to user  300  via user interface unit  130  that the connection to key device  200  has been successful and terminal-associated device  100  is usable in step  12 .  
     [0053] In step  13 , terminal-associated device  100  keeps itself connected to key device  200 . At this time, terminal-associated device  100  usually keeps itself connected to key device  200  with a minimum consumption of electric energy that is achieved by a power saver scheme inherent in the employed ratio communication technique. In this manner, user  300  can use the terminal device only when terminal-associated device  100  and key device  200  are connected to each other by a radio communication link.  
     [0054] If the connection to key device  200  is broken in step  14 , then terminal-associated device controller  122  makes terminal-associated device  100  unusable in step  15 . When step  15  is reached, the terminal lock system is considered to be in a situation where the use of terminal-associated device  100  is ended and the power supply thereof is readied to be turned off. However, if the radiation communications are turned off abnormally, then the connection between terminal-associated device  100  and key device  200  should automatically be recovered. Terminal-associated device  100  should be made unusable only when it is impossible to recover the connection between terminal-associated device  100  and key device  200 . Insofar as the connection to key device  200  is not broken in step  14 , terminal-associated device  100  usually keeps itself connected to key device  200  in step  13 .  
     [0055] If a failure in connecting to key device  200  is indicated from communication controller  121  to terminal-associated device controller  122  in step  10 , then terminal-associated device controller  122  indicates to user  300  via user interface unit  130  that the connection to key device  200  has failed and terminal-associated device  100  is not usable in step  16 . In this case, terminal-associated device  100  naturally remains unusable.  
     [0056] With the terminal lock system according to the first embodiment of the present invention, though key device  200  needs to be authenticated once when it is registered, after key device  200  is registered, the user of the terminal device is automatically authenticated as long as the user carries authenticated key device  200  at all times. Therefore, the user can be authenticated to use the terminal device without recognizing that the user is authenticated. Therefore, the user can unconsciously be personally authenticated without the need for making a complex action.  
     [0057] With the terminal lock system according to the first embodiment of the present invention, in addition, the terminal device can be used only if the authenticated key device is in the radio communication range. Therefore, even when the user has lost a cellular phone as the terminal device, other persons cannot make unauthorized use of the cellular phone unless the key device is in the radio communication range. Consequently any other persons than the user are prevented from making unauthorized use of the terminal device. Since the key device and the terminal device are connected to each other via short-range radio communications, it is almost impossible for the key device and the terminal device to be lost at the same time. As a result, even if the user has lost the terminal device, unauthorized use of the terminal device by a third party is reliably prevented.  
     [0058] With the terminal lock system according to the first embodiment of the present invention, furthermore, neither the key device nor the terminal-associated device depends upon the communication means used therebetween. Accordingly, any short-range radio communication techniques that are generally in widespread use can be used for the terminal lock system with compatibility maintained only by software modifications. The present invention is based on the mere concept that the key device and the terminal-associated device may be connected to each other. The present invention should allow systems in different companies to be connected with each other with high probability insofar as they employ the same radio communication technique. If such systems in different companies can be connected with each other, then the terminal lock system according to the present invention can be realized. Inasmuch as each of the terminal-associated device and the key device does not need to recognize how the other device has registered information of its own, there are few matters to be taken into account for mutual connectability between the terminal-associated device and the key device. Therefore, systems in different companies can be easily be interlinked.  
     [0059] Because neither the key device nor the terminal-associated device depends upon the communication means used therebetween as describe above, any short-range radio communication techniques that are generally in widespread use can be used for the terminal lock system. If devices of the terminal lock system have already employed a short-range radio communication technique for other purposes, then the terminal lock system can be realized by simply adding software for those devices. As the employed short-range radio communication technique can be used for other purposes, rather than authentication purposes only, the user finds an additional value in the terminal lock system. The terminal lock system is technically simple in system arrangement and low in cost.  
     [0060] 2nd Embodiment:  
     [0061] A terminal lock system according to a second embodiment of the present invention will be described below with reference to FIG. 4. Those parts of the terminal lock system shown in FIG. 4 which are identical to those of the terminal lock system shown in FIG. 1 are denoted by identical reference characters, and will not be described in detail below.  
     [0062] As shown in FIG. 4, the terminal lock system comprises terminal-associated device  100  and key device  400 .  
     [0063] Key device  4  comprises radio unit  210 , computer  420 , and user interface unit  230 . Computer  420  is different from computer  220  of key device  200  shown in FIG. 1 in that it additionally has memory  223 .  
     [0064] With the terminal lock system according to the first embodiment of the present invention, key device  200  stores no information whatsoever, and only waits for a connection from terminal-associated device  100 . Therefore, key device  200  may possibly be connected from an unintended device. According to the second embodiment, memory  223  of computer  420  allows key device  400  to register information of terminal-associated device  100 . Based on the information of terminal-associated device  100  registered in memory  223 , key device  400  can ignore a connection from an unintended device, or can notify user  300 . For example, even when a malicious third party attempts to connect to key device  400  for the purpose of obtaining information of key device  400 , the terminal lock system according to the second embodiment is effective to prevent such a malicious third party from knowing information of key device  400 .  
     [0065] In the first and second embodiments, no conditions are provided for connecting terminal-associated device  100  and key devices  200 ,  400 . However, a password or the like may be used in establishing a connection between terminal-associated device  100  and key devices  200 ,  400  at the time their information is registered, for thereby establishing a more reliable relationship therebetween. Though entering a password or the like is somewhat troublesome for the user, it should not be too burdensome as it needs to be entered only once when the information of the key devices  200 ,  400  is registered. Key device  400  shown in FIG. 4 includes user interface unit  130 . Since user interface unit  130  allows user  300  to enter information into key device  400 , a password can be exchanged between terminal-associated device  100  and key device  400  for thereby establishing a more reliable relationship therebetween. If information to be registered is generated according to a special calculation using information that only the user is aware of, e.g., a password, in addition to information inherent in the device, i.e., a production serial number, an address, and a software-based identification number, the possibility that the user is prevented from being impersonated by another person is increased. A much more reliable relationship can be achieved by regenerating the registered information periodically or at certain timings. Terminal-associated device  100  and key devices  200 ,  400  may agree to each other to exchange secret information that only they are aware of when they are connected to each other, thus establishing a more reliable relationship therebetween. Naturally, in view of the security as a weak point of radio communications, the information that needs to be exchanged may be encrypted to guard against other parties.  
     [0066] In the first and second embodiments, it has been described that only information of key device  200 ,  400  is registered in memory  123  of terminal-associated device  100 . However, such a description is illustrative only, and memory  123  of terminal-associated device  100  may register therein information of a plurality of key devices. In such a modification, the information of key devices registered in memory  123  may be checked in a sequence or at one time, and if terminal-associated device  100  can connect to one of the key devices whose information is registered, then the connected key device can be made usable. Similarly, in the terminal lock system where key device  400  has memory  223  according to the second embodiment, memory  223  may register therein information of a plurality of key devices.  
     [0067] Although not described in the above first and second embodiments, user interface unit  130  of terminal-associated device  100  or user interface unit  230  of key device  400  allows additional information representing a registration title, a date of registration, and an effective period to be added to the registered device information for the convenience of the user, and also allows information to be protected, added, deleted, and edited.  
     [0068] In the first and second embodiments, it has been described that the terminal device can be used only while terminal-associated device  100  and key devices  200 ,  400  are being connected to each other. However, the above description merely represents a rule introduced for simplifying the illustration. The principles of the present invention are based on whether both terminal-associated device  100  and key devices  200 ,  400  are in the radio communication range or not, and do not necessarily assume that terminal-associated device  100  and key devices  200 ,  400  have to be connected to each other at all times. One of these devices may be capable of confirming that the other device is in the radio communication range based on a device search function according to the short-range radio communication technique that is employed. Specifically, the devices may be connected only once at first for authentication purpose, and if the connection is successful, they may be disconnected, and thereafter one of these devices may confirm that the other device is in the radio communication range based on the device search function according to the employed short-range radio communication technique. According to a further modification, even the devices may not be connected once at first for authentication purpose, but one of these devices may confirm that the other device is in the radio communication range based on the device search function at periodic intervals. These processes described above fall within the scope of the present invention.  
     [0069] In the first and second embodiments, it has been described that the terminal lock system automatically starts operating immediately after terminal-associated device  100  and key devices  200 ,  400  are activated. However, the terminal lock system may start operating at other timings than the activation of terminal-associated device  100  and key devices  200 ,  400 . For example, the terminal lock system may be applied to the control of a screen saver of a personal computer. Specifically, when the user of a personal computer walks away from personal computer and out of the radio communication range, the screen saver of the personal computer is automatically activated and the personal computer is locked, thus preventing other persons from peeking into the personal computer or from making unauthorized actions on the personal computer. When the user walks back into the radio communication range, the screen saver is disabled, and the personal computer is unlocked for use again.  
     [0070] In the first and second embodiments, it has also been described that key device  200 ,  400  waits for a radio connection at all times. However, if such a waiting mode is not preferred from the standpoint of electric energy consumption, then key device  200 ,  400  may be usually inactivated, and may be brought into a waiting mode for waiting for a radio connection when it is activated by a simple action such as a touch on a key on key device  200 ,  400 . Though the above process is somewhat less convenient than the fully automatic terminal lock system because the user needs to be conscious of authentication, the life of the battery used in key device  200 ,  400  can be extended simply by touching a key on key device  200 ,  400 .  
     [0071] While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.