Abstract:
A control method executed by an information processing device having a function of wirelessly communicating with a wearable device and locking function of restricting operation of the information processing device, the control method includes acquiring acceleration information by an acceleration sensor; receiving information that is transmitted from the wearable device and relates to acceleration applied to the wearable device; and releasing the lock when the acceleration information acquired by the acceleration sensor matches the information relating to the acceleration.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-031893, filed on Feb. 20, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a control method, an information processing device, and a storage medium. 
       BACKGROUND 
       [0003]    In recent years, mobile terminal devices such as smartphones generally have a function that is able to provide a so-called locked state that restricts entry operation when there has been no operation for a predetermined period of time and to release the lock upon personal authentication when entry operation is started. This function allows for prevention of information leakage to a third party, because the mobile terminal device may not be used unless the personal authentication is successful. As a method of personal authentication, there are known methods involving entry of a personal identification number or a password and methods involving biological information such as a fingerprint, a face, an iris, a retina, a vein, a palm shape, DNA, a voice, a signature, an auricular, or the like, for example. 
         [0004]    Further, as a technique that can omit entry operation for personal authentication, Japanese Laid-open Patent Publication No. 2014-123204 discusses a method of performing personal authentication by using an equipped wearable device. This is a technique in which a wearable device and a mobile terminal device have been set in advance to be able to communicate with each other by Bluetooth (registered trademark), and the mobile terminal device can be unlocked when the wearable device is located near the mobile terminal device and the communication by Bluetooth is established. 
         [0005]    As another technique that can omit entry operation, Chuong H Nguyen, “Personal Unlocking makes security simple in Android L”, Internet website, URL: http://www.androidcentral.com/personal-unlocking-makes-security-simple, searched on Jan. 29, 2015, online, discusses a technique in which, after mutual authentication between a smartphone and a wrist-watch-type wrist terminal, a user performs an unlocking operation on the wrist terminal, and the wrist terminal then transmits an unlocking command to the smartphone. 
         [0006]    According to the technique disclosed in Japanese Laid-open Patent Publication No. 2014-123204, however, a third party is able to unlock a smartphone when the wearable device is located near the smartphone. For example, it is assumed that a user is wearing a wearable device and a third party places a user&#39;s smartphone in a location such as a neighboring room where mutual communication by Bluetooth is available but which is out of sight of the user. In this case, the third party is able to unlock the smartphone. 
         [0007]    According to Chuong H Nguyen, “Personal Unlocking makes security simple in Android L”, although entry operation at the smartphone side for releasing the lock is unnecessary, entry operation at the wearable device side is still involved. In view of the techniques discussed above, a simpler unlocking operation with high security is desirable in an information processing device such as a mobile terminal device. 
       SUMMARY 
       [0008]    According to an aspect of the invention, a control method executed by an information processing device having a function of wirelessly communicating with a wearable device and locking function of restricting operation of the information processing device, the control method includes: acquiring acceleration information by an acceleration sensor; receiving information that is transmitted from the wearable device and relates to acceleration applied to the wearable device; and releasing the lock when the acceleration information acquired by the acceleration sensor matches the information relating to the acceleration. 
         [0009]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a system configuration diagram according to a first embodiment; 
           [0012]      FIG. 2  is a diagram illustrating an example of a hardware configuration of a mobile terminal device, according to the first embodiment; 
           [0013]      FIG. 3  is a functional block diagram of a control unit illustrated in  FIG. 2 ; 
           [0014]      FIG. 4  is a diagram illustrating an example of a hardware configuration of a wearable device, according to the first embodiment; 
           [0015]      FIG. 5  is a functional block diagram of a control unit illustrated in  FIG. 4 ; 
           [0016]      FIG. 6  is a sequence diagram illustrating an example of a processing method by the system, according to the first embodiment; 
           [0017]      FIG. 7  is a flowchart illustrating an example of a process executed by the mobile terminal device, according to the first embodiment; 
           [0018]      FIG. 8  is a flowchart illustrating an example of a process executed by the wearable device, according to the first embodiment; 
           [0019]      FIG. 9A ,  FIG. 9B  and  FIG. 9C  are general diagrams of formats of various messages according to the first embodiment; 
           [0020]      FIG. 10  is a general diagram illustrating an example of acceleration information according to the first embodiment; 
           [0021]      FIG. 11  is a sequence diagram illustrating an example of a processing method by a system, according to a second embodiment; 
           [0022]      FIG. 12  is a flowchart illustrating an example of a process of a mobile terminal device, according to the second embodiment; 
           [0023]      FIG. 13  is a sequence diagram illustrating an example of a processing method by a system, according to a third embodiment; 
           [0024]      FIG. 14  is a flowchart illustrating an example of a process of a mobile terminal device, according to the third embodiment; and 
           [0025]      FIG. 15  is a flowchart illustrating an example of a process of a wearable device, according to the third embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    In view of the foregoing, it is an object of the disclosure is to conduct simpler unlocking operation with high security in an information processing device such as a mobile terminal device. 
         [0027]    Hereinafter, the embodiments will be described in detail with reference to  FIG. 1  to  FIG. 15 . 
       First Embodiment 
       [0028]      FIG. 1  is a system configuration diagram according to a first embodiment. As illustrated in  FIG. 1 , the system of the present embodiment includes a mobile terminal device  1  and a wearable device  2 . The mobile terminal device  1  is an information processing device involving personal authentication at a start of operation, and can be a smartphone, a mobile phone, a tablet terminal, or the like, for example. The wearable device  2  is a computer that can be carried by a user. The wearable device  2  is a wrist-watch-type device, for example. The wearable device  2  can be utilized in personal authentication executed by the mobile terminal device  1 . In the present embodiment, the mobile terminal device  1  and the wearable device  2  can communicate with each other by using a near-field wireless communication technique (such as Bluetooth, for example). 
         [0029]      FIG. 2  is a diagram illustrating an example of a hardware configuration of the mobile terminal device  1 , according to the first embodiment. As illustrated in  FIG. 2 , the mobile terminal device  1  includes a control unit  11 , a memory  12 , an input device  13 , a display device  14 , an authentication device  15 , a sensor  16 , a first wireless unit  17 , a second wireless unit  18 , and a third wireless unit  19 . 
         [0030]    The control unit  11  is a piece of hardware that manages the entire process of the mobile terminal device  1 . The control unit  11  is a CPU (Central Processing Unit), for example. Various functions of the control unit  11  will be described later. The memory  12  is hardware that stores therein data and programs used for the process executed by the control unit  11 . The memory  12  may be a RAM (Random Access Memory), a flash memory, or a ROM (Read Only Memory), for example, or may be any combination thereof. For example, a RAM and a NAND type flash memory can be used for storage of data. On the other hand, a NOR type flash memory and a ROM can be used for storage of programs. The memory  12  can be formed of a plurality of memory devices depending on the application or a desired storage capacity. 
         [0031]    The input device  13  is a device through which the user of the mobile terminal device  1  inputs information. The input device  13  is a touch screen, keys, or the like, for example. The display device  14  is a device that displays resulting information processed by the control unit  11 . The display device  14  is implemented by a liquid crystal display, for example. 
         [0032]    The authentication device  15  is an electronic component utilized for personal authentication. The authentication device employs an authentication method using direct entry of character information such as a password, for example, or an authentication method using biological information. When biological information is used, a face, an iris, a retina, a vein, a palm shape, DNA, a voice, a signature, an auricular, or the like can be used as the biological information. The sensor  16  is a sensor for detecting a position and/or an orientation of the mobile terminal device  1 . The sensor  16  is an acceleration sensor, for example. 
         [0033]    The first wireless unit  17  is a piece of hardware for communicating with the mobile terminal device  1  and with a remote base station or a remote server apparatus by using a cellular communication system such as GSM (Global System for Mobile communication (registered trademark)), 3G (3rd Generation), LTE (Long Term Evolution), or the like. The second wireless unit  18  is a piece of hardware for establishing a short or middle range LAN connection by using Wi-Fi (Wireless Fidelity). The third wireless unit  19  is a piece of hardware for performing near-field communication with the wearable device  2  by using Bluetooth, which is a low-power wireless technology. The first wireless unit  17 , the second wireless unit  18 , and the third wireless unit  19  each have interfaces corresponding to a transmission unit and a receiving unit, respectively. 
         [0034]      FIG. 3  is a functional block diagram of the control unit  11 . As illustrated in  FIG. 3 , the control unit  11  includes a detection unit  111 , a determination unit  112 , a transmission unit  113 , a measurement instruction unit  114 , a receiving unit  115 , and a lock control unit  116 . 
         [0035]    The detection unit  111  detects that an operation for starting use of the mobile terminal device  1 , such as turning on the power of the mobile terminal device  1 , is performed by a user. The determination unit  112  performs various determination processing to be executed in the control unit  11 . The transmission unit  113  transmits to the wearable device  2  a message indicating a start request for starting a process of measuring acceleration information and storing the measured result. The transmission unit  113  transmits to the wearable device  2  a message indicating a termination request for terminating measurement and storage of acceleration. 
         [0036]    The measurement instruction unit  114  executes an instruction for starting measurement of acceleration information of the wearable device  2  and storage of the measured result. The receiving unit  115  receives acceleration information transmitted from the wearable device  2 . The lock control unit  116  controls an unlocking of the mobile terminal device  1  based on the determination result from the determination unit  112 . 
         [0037]      FIG. 4  is a diagram illustrating an example of a hardware configuration of the wearable device  2 , according to the first embodiment. As illustrated in  FIG. 4 , the wearable device  2  includes a control unit  21 , a memory  22 , an input device  23 , a display device  24 , a sensor  25 , and a wireless unit  26 . 
         [0038]    The control unit  21  is a piece of hardware that manages the entire process of the wearable device  2 . The control unit  21  is a CPU, for example. The memory  22  is a piece of hardware that stores therein data and programs used for the process executed by the wearable device  2 . The memory  22  can be formed of a plurality of memory devices in a manner similar to the memory  12 . 
         [0039]    The input device  23  is a device through which the user of the wearable device  2  inputs information. The input device  23  is a touch screen, keys, or the like, for example. The display device  24  is a device that displays resulting information processed by the control unit  21 . The display device  24  is implemented by a liquid crystal display, for example. 
         [0040]    The sensor  25  is a sensor for detecting a position and/or an orientation of the wearable device  2 . The sensor  25  is an acceleration sensor, for example. The wireless unit  26  is a piece of hardware for performing near-field communications with the mobile terminal device  1 . The wireless unit  26  has interfaces corresponding to a transmission unit and a receiving unit, respectively. 
         [0041]      FIG. 5  is a functional block diagram of the control unit  21 . As illustrated in  FIG. 5 , the control unit  21  includes a receiving unit  211 , a measurement instruction unit  212 , a determination unit  213 , and a transmission unit  214 . 
         [0042]    The receiving unit  211  receives from the mobile terminal device  1  a message indicating a start request for starting a process of measuring acceleration information and storing the measured result. The receiving unit  211  receives from the mobile terminal device  1  a message indicating a transmission request for transmitting acceleration information. The receiving unit  211  receives from the mobile terminal device  1  a message indicating a termination request for terminating measurement and storage of acceleration. 
         [0043]    The measurement instruction unit  212  executes an instruction for starting measurement of acceleration information of the wearable device  2  and storage of the measured result. The determination unit  213  executes various determination processes executed in the control unit  21 . The transmission unit  214  transmits acceleration information to the mobile terminal device  1  upon receiving a transmission request. When it is determined that the measured acceleration information is not normal, the transmission unit  214  transmits an indication of failure in acquisition of acceleration information to the mobile terminal device  1 . 
         [0044]      FIG. 6  is a sequence diagram illustrating an example of a processing method performed by the system, according to the first embodiment. First, a user wearing the wearable device  2  approaches the mobile terminal device  1  (S 100 ). Then, when the user enters a range where Bluetooth communication can be established, for example, mutual communication is started (S 101 ). 
         [0045]    The user is not necessarily carrying the mobile terminal device  1  and may leave his/her seat with the mobile terminal device  1  left placed on the desk. In any case, however, when the user wearing the wearable device  2  intends to use the mobile terminal device  1 , the user moves to pick up the mobile terminal device  1  and thus the distance between the mobile terminal device  1  and the wearable device  2  becomes short enough for Bluetooth communication to be established. 
         [0046]    When the user performs an operation to start use of the mobile terminal device  1 , such as turning on the power of the mobile terminal device  1 , for example (S 102 ), the mobile terminal device  1  transmits to the wearable device  2  a message indicating a start request for starting a process of measuring acceleration information and storing the measured result (S 103 ). In response, the wearable device  2  that has received the message starts measurement of acceleration information of the wearable device  2  and storage of the measured result (S 104 ). On the other hand, the mobile terminal device  1  also starts measurement of acceleration information of the mobile terminal device  1  and storage of the measured result (S 105 ). Here, “motion” refers to a situation in which a position or an orientation of a device changes in a three-dimensional space. Specifically, it refers to a transition of temporal changes in acceleration. That is, the mobile terminal device  1  and the wearable device  2  are able to acquire acceleration information that is caused by a motion of the device itself. 
         [0047]    The detection and storage of a motion can be executed at all times. In a terminal such as the wearable device  2  in particular, which is compact and whose battery capacity is limited, however, it is preferable to execute the detection and storage only at desired time in view of power saving. According to the method described above, upon the wearable device  2  receiving a message from the mobile terminal device  1 , measurement and storage of acceleration information is started by the wearable device  2 . This allows for power saving of the wearable device  2 . In the mobile terminal device  1 , when its battery capacity is sufficient, the method of detecting and storing acceleration information at all times can be used. 
         [0048]    After performing the operation to start use of the mobile terminal device  1 , the user performs an unlocking operation (S 106 ). At S 106 , the user performs an unlocking operation by performing a motion such as shaking the mobile terminal device  1  one or more times, for example. The shaking may be in any direction and/or at any strength. However, a somewhat large motion is preferable for accurate detection. After the unlocking operation has been performed, the mobile terminal device  1  transmits to the wearable device  2  a transmission request for acceleration information (S 107 ). Then, the wearable device  2  that has received the transmission request transmits the acceleration information stored therein to the mobile terminal device  1  (S 108 ). 
         [0049]    Next, the mobile terminal device  1  compares the acceleration information measured and stored by the mobile terminal device  1  with the acceleration information received from the wearable device  2  (S 109 ). Specifically, it is determined whether or not the acceleration information measured by the mobile terminal device  1  matches the acceleration information measured by the wearable device  2 . 
         [0050]    Here, “match” means that both have a predetermined relationship. For example, not only when both pieces of acceleration information fully match, but also when both pieces of acceleration information partially match, or when a correlation of both is greater than or equal to a predetermined threshold, it can be determined that both pieces of acceleration information match. For example, a motion of shaking the mobile terminal device  1  by the hand on which the wrist watch-type wearable device  2  is worn results in the acceleration data measured and stored by both devices becoming substantially the same temporal data. When there is a motion of shaking the mobile terminal device  1  by the other hand on which the wrist watch-type wearable device  2  is not worn or when the wearable device  2  is equipped not on the wrist but on the upper arm or other part of the body, there will be some correlation between the temporal data of the sensor data detected by both devices. When both pieces of acceleration information match, the mobile terminal device  1  releases the lock (S 110 ). 
         [0051]    In a manner as described above, unlocking of the mobile terminal device  1  by using the wearable device  2  can be executed. 
         [0052]    In the following, a process flow at the mobile terminal device  1  will be described in detail by using  FIG. 7 .  FIG. 7  is a flowchart illustrating an example of a process executed by the mobile terminal device, according to the first embodiment. 
         [0053]    First, an operation for starting use of the mobile terminal device  1 , such as turning on the power of the mobile terminal device  1 , is performed by the user. In response, the detection unit  111  detects that the operation has been performed (S 201 ). 
         [0054]    Next, the determination unit  112  determines whether or not near-field communication with the wearable device  2  is established (S 202 ). If it is determined that near-field communication with the wearable device  2  is not established (S 202 : No), in order to unlock the mobile terminal device  1 , the process enters a conventional personal authentication procedure applying direct input to the mobile terminal device  1  by using the authentication device  15  (S 212 ). In the personal authentication procedure, personal authentication is performed by direct input of a password, for example. On the other hand, if it is determined that near-field communication with the wearable device  2  is established (S 202 : Yes), the transmission unit  113  transmits to the wearable device  2  a message requesting that a process of measuring acceleration information and storing the measured result be started (S 203 ). The measurement instruction unit  114  then causes the sensor  16  to start measurement of acceleration information of the mobile terminal device  1  and storage of the measured result (S 204 ). After the measurement of acceleration information is started, the user wearing the wearable device  2  performs an unlocking motion such as shaking the mobile terminal device  1 . The sensor  16  then measures changes in the acceleration of the mobile terminal device  1  caused by the unlocking motion. The sensor  16  then stores information of the acquired acceleration in the memory  12  as acceleration information. 
         [0055]    Next, the determination unit  112  determines whether or not the unlocking motion has finished (S 205 ). If it is determined that the unlocking motion has not finished (S 205 : No), the process of S 205  is executed again. The determination as to whether or not the unlocking motion has finished can be made by determining whether or not a predetermined time period such as one or several seconds, for example, has elapsed. Alternatively, the determination can be made by analyzing the acceleration information measured by the sensor  16  and determining whether or not the motion such as shaking the mobile terminal device  1  ceases. 
         [0056]    On the other hand, if it is determined that the unlocking motion has finished (S 205 : Yes), the determination unit  112  determines whether or not the acceleration information measured by the sensor  16  is normal (S 206 ). For example, when the user did not perform any motion such as shaking the mobile terminal device  1  after turning on the power of the mobile terminal device  1 , when the motion was insufficient, when, in contrast, the motion was so strong that the acceleration of the mobile terminal device  1  exceeds a detection limit, or when normal detection or storage was not carried out due to some other reason, it is determined that the measured acceleration information is not normal (S 206 : No) and S 212  is entered. The process then enters personal authentication that uses direct input to the mobile terminal device  1 . 
         [0057]    On the other hand, if it is determined that the measured acceleration information is normal (S 206 : Yes), the transmission unit  113  transmits to the wearable device  2  a message requesting transmission of acceleration information (S 207 ). 
         [0058]    Then, the determination unit  112  determines whether or not acceleration information has been received from the wearable device  2  (S 208 ). At S 208 , the determination unit  112  refers to a timer (not illustrated) set to a predetermined time period. Then, if it is determined that neither acceleration information has been received from the wearable device  2  nor the timer has expired, No is determined and the process of S 208  is executed again. On the other hand, if it is determined that no acceleration information has been received from the wearable device  2  but the timer has expired, the process transfers to S 212  and enters personal authentication applying direct input to the mobile terminal device  1 . 
         [0059]    At S 208 , if it is determined that acceleration information has been received from the wearable device  2 , Yes is determined and the determination unit  112  determines whether or not the received acceleration information is normal (S 209 ). At S 209 , when the message received from the wearable device  2  is an error message or when the information length of the acceleration information transmitted from the wearable device  2  is an improper length, for example, it is determined that the received acceleration information is not normal. When the near-field wireless communication system in use has a data error detection function and when an error is detected in the received data, it is also not determined that the received acceleration information is normal. 
         [0060]    At S 209 , if it is determined that the received acceleration information is not normal (S 209 : No), the process transfers to S 212  and enters personal authentication applying direct input to the mobile terminal device  1 . On the other hand, if it is determined that the received acceleration information is normal (S 209 : Yes), the determination unit  112  determines whether or not the acceleration information measured by the mobile terminal device  1  matches the acceleration information measured by the wearable device  2  (S 210 ). At S 210 , when it is determined that both pieces of acceleration information have a predetermined relationship, that is, both pieces of acceleration information match, or when both pieces of acceleration information have a correlation above a certain degree, Yes is determined. If Yes is determined, the lock control unit  116  releases the lock (S 211 ). On the other hand, if it is determined that both pieces of acceleration information do not match (S 210 : No), the process transfers to S 212  and enters personal authentication applying direct input to the mobile terminal device  1 . 
         [0061]    In a manner as described above, the process by the mobile terminal device  1  is executed. 
         [0062]    Next, a process flow at the wearable device  2  will be described by using  FIG. 8 .  FIG. 8  is a flowchart illustrating an example of a process executed by the wearable device  2 , according to the first embodiment. 
         [0063]    First, the receiving unit  211  of the wearable device  2  receives from the mobile terminal device  1  a message requesting starting of measurement of acceleration information and storage of the measured result (S 301 ). Upon receiving the message, the measurement instruction unit  212  causes the sensor  25  to start measurement of acceleration information of the wearable device  2  and storage of the measured result (S 302 ). After measurement of the acceleration information is started, the user wearing the wearable device  2  performs an unlocking motion such as shaking the mobile terminal device  1 . The sensor  25  then measures changes in acceleration of the wearable device  2  caused by the unlocking motion. The sensor  25  then stores information of the acquired acceleration in the memory  22  as acceleration information. 
         [0064]    Next, the determination unit  213  determines whether or not a transmission request for acceleration information has been received from the mobile terminal device  1  (S 303 ). If it is determined that a transmission request for acceleration information has not been received from the mobile terminal device  1  (S 303 : No), the process of S 303  is executed again. On the other hand, if it is determined that a transmission request for acceleration information has been received from the mobile terminal device  1  (S 303 : Yes), the determination unit  213  determines whether or not the acceleration information measured by the sensor  25  is normal (S 304 ). The same process as in S 206  can be used for the determination process at S 304 . 
         [0065]    If it is determined that the acceleration information measured by the sensor  25  is normal (S 304 : Yes), the transmission unit  214  transmits the acceleration information to the mobile terminal device  1  (S 305 ). On the other hand, if it is determined that the acceleration information measured by the sensor  25  is not normal (S 304 : No), the transmission unit  214  transmits an indication of failure in acquisition of acceleration information to the mobile terminal device  1  (S 306 ). 
         [0066]    In a manner as described above, the process by the wearable device  2  is executed. 
         [0067]    Now, examples of formats of the messages transmitted between the mobile terminal device  1  and the wearable device  2  will be described by using  FIG. 9A  to  FIG. 9C .  FIG. 9A  to  FIG. 9C  are general diagrams of formats of various messages according to the first embodiment. 
         [0068]    Codes indicating a type of message are included in message formats. For example, code 0x01 illustrated in  FIG. 9A  represents a message from the mobile terminal device  1  to the wearable device  2 . The code 0x01 is for a request for starting measurement of acceleration information and storage of the measured result. Code 0x02 illustrated in  FIG. 9B  also represents a message from the mobile terminal device  1  to the wearable device  2 . The code 0x02 is for a request for transmission of acceleration information. Code 0xNN means a number NN in hexadecimal representation. 
         [0069]    Code 0x03 represents a message from the wearable device  2  to the mobile terminal device  1 . The code 0x03 is for transmission of the acceleration information measured by the wearable device  2  to the mobile terminal device  1 . This message includes “information length” that indicates a length of motion information in addition to the type code. Further, there is subsequent acceleration information as illustrated in  FIG. 9C . 
         [0070]      FIG. 10  is a general diagram illustrating an example of acceleration information according to the first embodiment. As illustrated in  FIG. 10 , information of a sampling interval that is a reading period of the acceleration sensor output is stored in the head of the acceleration information. Further, following the information of the sampling interval, sampling data for acceleration of respective directions in the three-dimensional system (X axis, Y axis, and Z axis) are stored in a temporal manner. Finally, an identifier that indicates the end of data is added and stored. 
         [0071]    When the end of an unlocking motion is determined according to whether or not a predetermined time period has elapsed, the acceleration information has a fixed length, because the number of sampling data is fixed in advance. In this case, the “information length” of  FIG. 9C  may be omitted. The acceleration information stored by the mobile terminal device  1  and the acceleration information stored by the wearable device  2  may not necessarily be of the same format. 
         [0072]    Next, advantages of the present embodiment will be described for the case where, assuming that a valid user leaves his/her seat with the mobile terminal device  1  left placed on a desk, a malicious third party attempts an unauthorized use of the mobile terminal device  1 . When the distance between the valid user and the third party is so distant that a near-field communication such as Bluetooth is not established, no unlocking process utilizing the wearable device  2  can be executed. Without performing of unlocking operation of the mobile terminal device  1  through a personal authentication procedure using direct input, the third party is unable to use the mobile terminal device  1 . 
         [0073]    On the other hand, when the distance between the valid user and the third party is short, such as when, while the valid user is taking a nap, the third party attempts to operate the mobile terminal device  1  placed near the valid user, a near-field communication such as Bluetooth is possible. Therefore, the unlocking process utilizing the wearable device  2  as illustrated in  FIG. 4  appears to be executable. Even when the third party performs a motion of shaking the mobile terminal device  1 , however, the wearable device  2  carried by the valid user does not detect that motion. Therefore, since both pieces of acceleration information do not match and no effective correlation thereof is acquired, unlocking is not executed. 
         [0074]    According to the first embodiment, acceleration information of the mobile terminal device  1  and acceleration information of the wearable device  2  are compared and the relationship thereof is determined. Then, when both pieces of acceleration information are determined to have a predetermined relationship, the mobile terminal device  1  is unlocked. According to this method, comparison of both pieces of acceleration information allows for determining that the user wearing the wearable device  2  has held the mobile terminal device  1  by the hand, so that a risk of a use of the mobile terminal device  1  by a third party against the valid user&#39;s will can be reduced. Therefore, a simpler unlocking operation with high security can be performed. 
       Second Embodiment 
       [0075]    Next, a second embodiment will be described. In the first embodiment, measurement of acceleration information and storage of the measured result of the mobile terminal device  1  and the wearable device  2  are triggered by user&#39;s operation to start use of the mobile terminal device  1 . In contrast, the second embodiment is featured in that, prior to an operation to start use of the mobile terminal device  1 , acceleration information has been stored in the mobile terminal device  1  and the wearable device  2 . A system for implementing the second embodiment can use the system configuration exemplified in  FIG. 1  to  FIG. 5 , and thus description thereof will be omitted. 
         [0076]    In general, when a user intends to use the mobile terminal device  1 , the user will perform some motion for holding the mobile terminal device  1  by the hand, such as a motion of picking up the mobile terminal device  1  that has been placed on a desk, a motion of taking it out of a pocket, or the like. In the following second embodiment, such a motion itself is utilized as an unlocking motion. 
         [0077]    In the following, the second embodiment will be described with reference to  FIG. 11 .  FIG. 11  is a sequence diagram illustrating an example of a processing method by the system, according to the second embodiment. 
         [0078]    First, the user wearing the wearable device  2  approaches the mobile terminal device  1  (S 400 ). Then, when the user enters a range where Bluetooth communication can be established, for example, mutual communication is started (S 401 ). 
         [0079]    Then, the user wearing the wearable device  2  starts a motion of holding the mobile terminal device  1  by the hand (S 402 ). At S 402 , in order to use the mobile terminal device  1 , the user starts some “motion of holding it by the hand” such as picking up the mobile terminal device  1  placed on a desk, taking it out of a pocket, taking it out of a bag, or the like. At this time, the motion generally involves a motion with an upward or horizontal movement at a certain speed or faster. It is thus possible to assume a detection of such acceleration as a start of a “motion of holding it by the hand”. In this assumption, so a high accuracy is unnecessary. Because, even when the motion is not a motion for starting a use in fact, the process will be cancelled somewhere in the subsequent process, which neither causes any inconvenience to the user nor causes malfunction. 
         [0080]    Upon detecting the start of such a “motion of holding it by the hand”, the mobile terminal device  1  transmits to the wearable device  2  a message indicating a start request for starting a process of measuring acceleration information and storing the measured result (S 403 ). The wearable device  2  that has received the message then starts measurement of acceleration information of the wearable device  2  and storage of the measured result (S 404 ). On the other hand, the mobile terminal device  1  also starts measurement of acceleration information of the mobile terminal device  1  and storage of the measured result (S 405 ). 
         [0081]    Next, the user who has held the mobile terminal device  1  by the hand performs an operation to start use of the mobile terminal device  1 , such as turning on the power of the mobile terminal device  1 , for example (S 406 ). Upon detecting the operation to start a use, the mobile terminal device  1  transmits to the wearable device  2  a transmission request for transmission of acceleration information (S 407 ). The wearable device  2  that has received the transmission request then transmits acceleration information that has been stored by itself to the mobile terminal device  1  (S 408 ). 
         [0082]    Next, the mobile terminal device  1  compares the acceleration information measured and stored by the mobile terminal device  1  with the acceleration information received from the wearable device  2  (S 409 ). Specifically, it is determined whether or not the acceleration information measured by the mobile terminal device  1  matches the acceleration information measured by the wearable device  2 . When both pieces of acceleration information match, the mobile terminal device  1  releases the lock (S 410 ). 
         [0083]    In a manner as described above, unlocking of the mobile terminal device  1  by using the wearable device  2  can be executed. 
         [0084]    In the second embodiment, the time period from the time of the user&#39;s motion of holding the mobile terminal device  1  by the hand to the time of performing the operation to start a use such as pressing a power key varies, and the number of sampling data of measured acceleration also varies. Thus, the acceleration information illustrated in  FIG. 10  has a variable length, and thus the “information length” described with respect to  FIG. 9C  is prerequisite. 
         [0085]    In the following, a process flow at the mobile terminal device  1  will be described by using  FIG. 12 .  FIG. 12  is a flowchart illustrating an example of a process executed by the mobile terminal device, according to the second embodiment. 
         [0086]    First, the detection unit  111  detects that the user starts a motion of holding the mobile terminal device  1  by the hand (S 501 ). Next, the determination unit  112  determines whether or not a near-field communication with the wearable device  2  is established (S 502 ). If it is determined that a near-field communication with the wearable device  2  is not established (S 502 : No), in order to unlock the mobile terminal device  1 , the process enters personal authentication applying direct input to the mobile terminal device  1  (S 512 ). On the other hand, if it is determined that a near-field communication with the wearable device  2  is established (S 502 : Yes), S 503  is entered. Each process of S 503  and S 504  executed after S 503  is substantially the same as each process of S 203  and S 204  of  FIG. 7 , respectively, and thus description thereof will be omitted. 
         [0087]    After the process of S 504 , the determination unit  112  determines whether or not an operation to start use of the mobile terminal device  1 , such as turning on the power of the mobile terminal device  1 , is detected (S 505 ). At S 505 , the determination unit  112  refers to a timer (not illustrated) set to a predetermined time period, and if it is determined that neither operation to start use of the mobile terminal device  1  is detected nor the timer has expired, No is determined and the process of S 505  is executed again. On the other hand, if it is determined that an operation to start use of the mobile terminal device  1  is not detected but the timer has expired, the control unit  11  determines that the user has no intention of using the mobile terminal device  1 . The transmission unit  113  then transmits to the wearable device  2  a termination request for terminating measurement and storage of acceleration (S 513 ), and the process ends. 
         [0088]    On the other hand, if it is determined that an operation to start use of the mobile terminal device  1  is detected (S 505 : Yes), the control unit  11  determines whether or not the acceleration information measured by the sensor  16  is normal (S 506 ). If it is determined that the measured acceleration information is not normal (S 506 : No), the process transfers to S 512  and enters personal authentication applying direct input to the mobile terminal device  1 . 
         [0089]    On the other hand, if it is determined that the measured acceleration information is normal (S 506 : Yes), the control unit  11  transmits to the wearable device  2  a message requesting transmission of the acceleration information (S 507 ). Each process of S 508 , S 509 , S 510 , and S 511  executed after S 507  is substantially the same as each process of S 208 , S 209 , S 210 , and S 211  illustrated in  FIG. 7 , respectively, and thus description thereof will be omitted. 
         [0090]    In a manner as described above, the process by the mobile terminal device  1  is executed. 
         [0091]    The process by the wearable device  2  is substantially the same as the process illustrated in  FIG. 8 , and thus the description thereof will be omitted. 
         [0092]    In the second embodiment, prior to an operation to start use of the mobile terminal device  1 , acceleration information has been stored in the mobile terminal device  1  and the wearable device  2 . According to this method, the user does not have to consciously perform a motion such as shaking the mobile terminal device  1  for releasing the lock. The user is able to immediately release the lock only by holding the mobile terminal device  1  by the hand and pressing the power key. This method can reduce the time for releasing the lock and therefore improve convenience at the user. 
       Third Embodiment 
       [0093]    Next, a third embodiment will be described. When a battery capacity of the mobile terminal device  1  and/or the wearable device  2  is sufficient, measurement and storage of acceleration information can be triggered by establishment of a communication between the mobile terminal device  1  and the wearable device  2 , rather than triggered by a “motion of holding it by the hand” as in the second embodiment. Since a system for implementing the third embodiment can use the system configuration exemplified in  FIG. 1  to  FIG. 3 , description thereof will be omitted. 
         [0094]    In the following, the third embodiment will be described with reference to  FIG. 13 .  FIG. 13  is a sequence diagram illustrating an example of a processing method by the system, according to the third embodiment. 
         [0095]    First, a user wearing the wearable device  2  approaches the mobile terminal device  1  (S 601 ). Then, when the user enters a range where Bluetooth communication can be established, for example, mutual communication is started (S 602 ). 
         [0096]    Upon the start of the communication of both devices, the mobile terminal device  1  transmits to the wearable device  2  a message indicating a start request for starting a process of measuring acceleration information at all times and storing the measured result (S 603 ). Then, the wearable device  2  that has received the message starts measurement of acceleration information of the wearable device  2  and storage of the measured result (S 604 ). On the other hand, the mobile terminal device  1  also starts measurement of acceleration information of the mobile terminal device  1  and storage of the measured result (S 605 ). 
         [0097]    Here, the mobile terminal device  1  and the wearable device  2  may update information stored in the memories  12  and  22  at all times so as to store the measured acceleration information for a predetermined time period (for several seconds to several ten seconds), respectively. That is, acceleration information for a predetermined time period only is stored in the memories  12  and  22  by erasing the previous data obtained before the predetermined time period and overwriting newly obtained data. This method allows for saving the capacities of the memories  12  and  22 . 
         [0098]    Next, the user who has held the mobile terminal device  1  by the hand performs an operation to start use of the mobile terminal device  1  such as turning on the power of the mobile terminal device  1 , for example (S 606 ). Each process of S 607  to S 610  executed after S 606  is substantially the same as each process of S 407  to S 410  illustrated in  FIG. 11 , respectively, and thus description thereof will be omitted. 
         [0099]    In a manner as described above, unlocking of the mobile terminal device  1  by using the wearable device  2  can be executed. 
         [0100]    In the following, a process flow at the mobile terminal device  1  will be described in detail by using  FIG. 14 .  FIG. 14  is a flowchart illustrating an example of a process executed by the mobile terminal device, according to the third embodiment. 
         [0101]    First, the control unit  11  confirms whether or not a near-field communication with the wearable device  2  is established (S 702 ). If it is determined that a near-field communication with the wearable device  2  is not established (S 702 : No), the process ends, because pieces of acceleration information of both devices are not compared even if they are measured. On the other hand, if it is determined that a near-field communication with the wearable device  2  is established (S 702 : Yes), the control unit  11  transmits to the wearable device  2  a message indicating a request for starting a process of measuring acceleration information at all times and storing the measured result (S 703 ). The control unit  11  then causes the sensor  16  to start continuous measurement of acceleration information of the mobile terminal device  1  and storage of the measured result (S 704 ). 
         [0102]    After the process of S 704 , the control unit  11  determines whether or not an operation to start use of the mobile terminal device  1  such as turning on the power of the mobile terminal device  1 , for example, is detected (S 705 ). If it is determined that an operation to start use of the mobile terminal device  1  is not detected (S 705 : No), the process of S 705  is executed again. On the other hand, if it is determined that an operation to start use of the mobile terminal device  1  is detected (S 705 : Yes), S 706  is entered. Each process of S 706  to S 712  is substantially the same as each process of S 506  to  512  illustrated in  FIG. 12 , respectively, and thus description thereof will be omitted. 
         [0103]      FIG. 15  is a flowchart illustrating an example of a process executed by the wearable device, according to the third embodiment. 
         [0104]    In the process executed by the wearable device, first, at S 801 , the control unit  21  of the wearable device  2  receives from the mobile terminals device  1  a message indicating a start request for starting continuous measurement of acceleration information and storage of the measured result. Each process of S 802  to S 806  executed after S 801  is substantially the same as each process of S 302  to  306  illustrated in  FIG. 8 , respectively, and thus description thereof will be omitted. 
         [0105]    In the third embodiment, measurement and storage of acceleration information are triggered by establishment of a communication between the mobile terminal device  1  and the wearable device  2 . In this method, in a similar manner to the second embodiment, the user is able to immediately release the lock only by holding the mobile terminal device  1  by the hand and pressing the power key without consciously performing a motion for releasing the lock. According to the third embodiment, since the timing of starting measurement and storage of acceleration information is earlier than that in the second embodiment, a change in the acceleration caused by a motion of holding the mobile terminal device  1  by the hand is ensured to be acquired as the acceleration information. 
         [0106]    As set forth, while the preferable embodiments of the present disclosure have been described in detail, the present disclosure is not limited to a particular embodiment, but various modifications and alternations are possible. For example, in the second or third embodiment, it is considered that, when the time period from the time of holding the mobile terminal device  1  by the hand to the time of performing an operation to start a use is quite short, the information amount of the acceleration information is reduced and thus no comparison determination of the acceleration information may be executed or no matching may be determined. In such a case, at S 512  of  FIG. 12  or S 712  of  FIG. 14 , in place of entering a personal authentication procedure using direct input, a message such as “Please do an unlocking motion” may be displayed to the user by using the display device  14  to facilitate an unlocking motion so that the process of the first embodiment is executed, for example. 
         [0107]    In executing the comparison determination for acceleration information matching, in addition to the acceleration information, information of the time at which the acceleration information is stored may be added. According to this method, reference to the time information allows for improvement of accuracy in the determination as to whether or not acceleration information matches at any one of the mobile terminal device  1  and the wearable device  2 . 
         [0108]    A computer program that causes a computer to execute the functions of respective units of the mobile terminal device and the control method as described above, and a non-transitory computer-readable storage medium in which the program is stored are included in the scope of the present disclosure. The non-transitory computer-readable storage medium herein is a memory card such as an SD memory card, for example. The computer program described above is not limited to the program stored in the storage medium described above. For example, it may be a program transmitted via telecommunication lines, wireless or wired communication lines, networks such as the Internet, and the like. 
         [0109]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.