Patent Publication Number: US-2023143028-A1

Title: Personal authentication device, personal authentication method, and recording medium

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. Pat. Application Ser. No. 16/608281 filed on Oct. 25, 2019, which is a National Stage of International Application No. PCT/JP2017/016914, filed Apr. 28, 2017. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a personal authentication device and the like for authenticating an individual. 
     BACKGROUND ART 
     Biometrics-based authentication has a lower risk of leakage or theft compared with a password and the like created by a user. For this reason, cases of introducing the biometrics-based authentication are increasing for the purpose of identifying an individual and confirming his/her rights, or protecting security. In biometrics-based authentication, techniques using, such as a living body, a fingerprint, a vein, a face, an iris, voice are generally known. Among them, personal authentication using voice can be performed by using a generally used inexpensive device such as a telephone or a microphone, instead of a special device. 
      Among biometrics authentication, personal authentication (otoacoustic authentication) using a change of an acoustical feature in an ear (an ear canal) has attracted attention in recent years. When personal authentication is performed by acquiring biometric information other than otoacoustic authentication, a user is requested to make some motions for the authentication. For example, in a case of personal authentication by using a fingerprint or a vein, a user required a motion such as putting a finger on a dedicated scanner. In a case of personal authentication by using a face or an iris, a use is required a motion such as pointing the face to a camera. In a case of personal authentication by using voice or bone conduction sound, a user is required a motion such as uttering a password. A user feels psychologically and physically loaded by forced to perform such a motion even in a short time. Further, continuing such a motion for a long time is not preferable because it prevents a user from making a next expected motion. In the case of the otoacoustic authentication, however, it is merely necessary to put an acoustic radio wave transceiver such as a handset or an earphone on an ear or insert it into an ear. Therefore, even in a long time, a psychological and physical burden of a user is less than other biometrics authentication methods. Techniques for the otoacoustic authentication are disclosed in PTLs 1 and 2. 
     Citation List 
     Patent Literature 
     
         
         PTL 1] International Publication No. WO2014/061578 
         PTL 2] Japanese Unexamined Patent Application Publication No. 2005-032056 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The otoacoustic authentication disclosed in PTLs 1 and 2 has a problem that an acoustical feature of an ear canal is changeable. It is due to a vibration and a micromotion of an earphone/microphone device that occur at the time of insertion and removal of the device into and from an ear for transmitting and receiving an acoustical signal for authentication. 
     As for the problem of change in an acoustical feature, for example, when a user feels uncomfortable at an ear with inserted an earphone/microphone device, the device is re-inserted by the user. However it is difficult for the ordinary user to re-insert the earphone/microphone device in exactly the same position as the previous position. In many cases, the earphone/microphone device may be inserted at a slightly shifted position from the previously inserted one. Due to the displacement of the inserted position, an acoustical signal to be bounced off the ear canal changes and therefore it makes accurate authentication difficult based on the acoustical signal. 
     Furthermore, PTL 2 has a problem that extra authentication means (e.g., an input of a user ID) is required in order to authenticate with high accuracy. For example, when a user ID is required, forgetting his/her user ID makes authentication impossible. In a case of quick accessing highly confidential information at an emergency site (e.g., at an accident site or inside an ambulance), environmental situation, for instance, rain, a gust of wind, vibration caused by such as an earthquake might interfere with the user ID entry on the site using a keyboard. Taking time to input a user ID may prevent a quick access to the information. Further, a mouse or a keyboard for inputting a user ID is separately required. 
     In view of the above-described problems, an object of the present invention is to provide a personal authentication device and the like that are able to quickly perform highly accurate authentication and prevent spoofing after authentication. 
     Solution to Problem 
     In view of the above problems, a first aspect of the present invention is a personal authentication device. The device includes:
     sensor means that detects a contact with a propagation path being a part of a head of a person to be authenticated;   acoustical signal generation means that generates, when the sensor means detects the contact, a first acoustical signal including an audible range, and generates a second acoustical signal in an inaudible range having a higher frequency than the audible range;   acoustical signal measurement means that measures an acoustical signal after the first acoustical signal propagates a part of the head and measures an acoustical signal after the second acoustical signal propagates a part of the head; and   identification means that performs first authentication of the person to be authenticated when the measured first acoustical signal satisfies a predetermined condition, and when the second acoustical signal satisfies a predetermined condition after the first authentication, performs second authentication for determining whether a person to be authenticated successful in the first authentication is a same person.   

     A second aspect of the present invention is a personal authentication method. The method includes:
     detecting a contact with a propagation path being a part of a head of a person to be authenticated;   generating, when detecting the contact, a first acoustical signal including an audible range;   measuring an acoustical signal after the first acoustical signal propagates the propagation path;   generating a second acoustical signal in an inaudible range having a higher frequency than the audible range;   measuring an acoustical signal after the second acoustical signal propagates the propagation path;   performing, when the measured first acoustical signal satisfies a predetermined condition, first authentication of the person to be authenticated; and   performing, when the second acoustical signal satisfies a predetermined condition after the first authentication, second authentication for determining whether a person to be authenticated successful in the first authentication is a same person.   

     A third aspect of the present invention is a personal authentication program to causes a computer to perform instructions. The program includes:
     detecting a contact with a propagation path being a part of a head of a person to be authenticated;   generating, when detecting the contact, a first acoustical signal including an audible range;   measuring an acoustical signal after the first acoustical signal propagates the propagation path;   generating a second acoustical signal in an inaudible range having a higher frequency than the audible range;   measuring an acoustical signal after the second acoustical signal propagates the propagation path;   performing, when the measured first acoustical signal satisfies a predetermined condition, first authentication of the person to be authenticated; and   performing, when the second acoustical signal satisfies a predetermined condition after the first authentication, second authentication for determining whether a person to be authenticated successful in the first authentication is a same person.   

     The personal authentication program can be stored in a nontransitory computer readable storage medium. 
     Advantageous Effects of Invention 
     The present invention is able to provide a personal authentication device and the like capable of quickly performing highly accurate authentication and preventing spoofing after authentication. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG.  1   ]  FIG.  1    is a block diagram illustrating a configuration example of a personal authentication device according to a first example embodiment of the present invention. 
       [ FIG.  2   ]  FIG.  2    is a configuration diagram illustrating a specific configuration example of the personal authentication device according to the first example embodiment. 
       [ FIG.  3   ]  FIG.  3    is a graph illustrating an ear canal transfer function (ECTF). 
       [ FIG.  4   ]  FIG.  4    is a flowchart illustrating an operation of a user registration in the personal authentication device according to the first example embodiment. 
       [ FIG.  5   ]  FIG.  5    is a chart illustrating a transmission timing of an acoustical signal to be transmitted. 
       [ FIG.  6   ]  FIG.  6    is a graph schematically illustrating a waveform of the acoustical signal to be transmitted. 
       [ FIG.  7   ]  FIG.  7    is a graph schematically illustrating a waveform of an acoustical signal to be measured. 
       [ FIG.  8   ]  FIG.  8    is a graph illustrating one example of a waveform of a signal after synchronous addition processing. 
       [ FIG.  9   ]  FIG.  9    is a graph illustrating one example of an impulse response as an acoustical characteristic. 
       [ FIG.  10   ]  FIG.  10    is a graph illustrating the acoustical characteristic by the ear canal transfer function (ECTF). 
       [ FIG.  11   ]  FIG.  11    is a graph illustrating a spectrum envelope. 
       [ FIG.  12 A ]  FIG.  12 A  is a graph illustrating spectrum envelopes of a person. 
       [ FIG.  12 B ]  FIG.  12 B  is a graph illustrating spectrum envelopes of a person. 
       [ FIG.  12 C ]  FIG.  12 C  is a graph illustrating spectrum envelopes of a person. 
       [ FIG.  13   ]  FIG.  13    is a flowchart illustrating an operation of a user identification in the personal authentication device according to the first example embodiment. 
       [ FIG.  14   ]  FIG.  14    is a chart illustrating the transmission timing of the acoustical signal to be transmitted. 
       [ FIG.  15   ]  FIG.  15    is a block diagram illustrating a configuration example of a personal authentication device according to a second example embodiment of the present invention. 
       [ FIG.  16   ]  FIG.  16    is a flowchart illustrating an operation of a user identification in the personal authentication device according to the second example embodiment. 
       [ FIG.  17   ]  FIG.  17    is a block diagram illustrating a configuration example of a personal authentication device according to a third example embodiment of the present invention. 
       [ FIG.  18   ]  FIG.  18    is a block diagram illustrating a configuration example of an information processing device applicable to each example embodiment. 
     
    
    
     EXAMPLE EMBODIMENT 
     In general, a range of frequency audible to human beings (an audible range) is around 20 Hz at low sound and around 20 kHz at high sound. These sounds audible to human beings are referred to as an “audible sound”, a high sound inaudible to human ears is referred to as an “ultrasound” (hereinafter, also referred to as “inaudible sound”), and a low sound inaudible to human ears is referred to as “infrasound”. The frequency of sound to be heard clearly by human beings is around 2 kHz to 4 kHz. 
     According to the present example embodiment, the audible sound and the inaudible sound are used for otoacoustic authentication. Generally, a user feels uncomfortable when the user must listen to an undesired audible sound for authentication for a long time or the user must listen to the audible sound at every certain time interval. For this reason, there is an opinion that an inaudible sound for the otoacoustic authentication may reduce a burden on a user (see PTL 2). 
     However, the inventors of the present invention have discovered that, even though an acoustical feature of an ear canal changes due to insertion and removal of an earphone/microphone device into and from an ear which transmits and receives an acoustical signal, an acoustical feature in the audible range is stable compared with the inaudible range (described in detail later). Each example embodiment of the present invention is devised based on this idea. 
     Hereinafter, each example embodiment of the present invention is described with reference to the drawings. In the following description of the drawings, a same or similar component is assigned with a same or similar reference sign. However, the drawings schematically illustrate configurations according to the example embodiments of the present invention. Further, the example embodiments of the present invention described below are examples, and can be modified as appropriate within the scope of which essence is identical to the present invention. 
     First Example Embodiment 
     Personal Authentication Device 
     As illustrated in  FIG.  1   , personal authentication device  100  according to a first example embodiment of the present invention includes first acoustical signal generation unit  101 , second acoustical signal generation unit  102 , acoustical signal measurement unit  103 , acoustical characteristic calculation unit  104 , feature extraction unit  105 , identification unit  106 , first feature quantity storage  107 , and second feature quantity storage  108 . 
     First acoustical signal generation unit  101  generates an acoustical signal (a first acoustical signal) in the audible range. Earphone  14  inputs this first acoustical signal and transmits the first acoustical signal to a propagation path being a part of a head of a user (a person to be authenticated). Herein, the part of a head to which the acoustical signal is transmitted is a cavity inside the head and a region formed in such a way as to have an opening toward an outside, for example, typically an ear canal of an auditory organ. In addition, it may be a nasal cavity. It may be a cavity inside a head without an opening toward an outside. Further, it may be at least a part of a region to which an apparatus for expressing an acoustical effect can be attached or approached. 
     Second acoustical signal generation unit  102  generates an acoustical signal (a second acoustical signal) in the inaudible range (range of ultrasound) of which frequency is higher than the frequency in the audible range. Earphone  14  inputs this second acoustical signal and transmits the second acoustical signal to the above-described propagation path being the part of the user’s head. It is desirable that the inaudible range is an inaudible range having a frequency higher than a frequency in the audible range. This is to prevent a user from being stressed by the occurrence of an audible sound in second authentication. 
     Acoustical signal measurement unit  103  inputs an output signal by microphone  15  provided on earphone  14 . Then, acoustical signal measurement unit  103  measures the first acoustical signal after the acoustical signal in the audible range transmitted from first acoustical signal generation unit  101  propagates the part of the user’s head. Further, acoustical signal measurement unit  103  also measures the second acoustical signal after the acoustical signal in the inaudible range transmitted from second acoustical signal generation unit  102  propagates the part of the user’s head. Note that it is preferable that second acoustical signal generation unit  102  generates the second acoustical signal after acoustical signal measurement unit  103  measures the first acoustical signal. 
     A part of a head referred to as the propagation path for the first and second acoustical signals may be, more specifically, at least a part of a skull, a brain, a sensory organ and a cavity therebetween constituting a head. Further, the acoustical signal after the propagation includes a signal reflected in the propagation path. 
     Further, first acoustical signal generation unit  101  and second acoustical signal generation unit  102  are illustrated as separate units in  FIG.  1   , however, these units may be an identical unit or device. 
     Acoustical characteristic calculation unit  104  calculates an acoustical characteristic (a first acoustical characteristic) of the first acoustical signal that propagates the part of the user’s head, based on the first acoustical signal measured by acoustical signal measurement unit  103 . Further, acoustical characteristic calculation unit  104  calculates an acoustical characteristic (a second acoustical characteristic) of the second acoustical signal that propagates the part of the user’s head, based on the second acoustical signal measured by acoustical signal measurement unit  103 . 
      Feature extraction unit  105  calculates, from the calculated first acoustical characteristic, a feature quantity (a first feature quantity) with regard to the user whose acoustical signal is propagated. Further, feature extraction unit  105  calculates, from the calculated second acoustical characteristic, a feature quantity (a second feature quantity) with regard to the user whose acoustical signal is propagated. 
     First feature quantity storage  107  stores at least one of the first acoustical characteristic and the first feature quantity associated with a predetermined user. The number of users may be single or plural. Second feature quantity storage  108  stores at least one of the second acoustical characteristic and the second feature quantity associated with the predetermined user. In other words, the two feature quantities (the first and second acoustical characteristics or the first and second feature quantities) associated with one user are stored in the two storages (first feature quantity storage  107  and second feature quantity storage  108 ). Hereinafter, the user whose acoustical characteristic and feature quantity are stored in first feature quantity storage  107  and second feature quantity storage  108  may be referred to as a registered user. Note that, in  FIG.  1   , first feature quantity storage  107  and second feature quantity storage  108  are illustrated as being stored in separate storage medium, however, these units may be stored in one storage medium. Further, these units may be set to be connectable to the storage medium via a wireless or wired line. In addition, user identification is possible by using any of an acoustical characteristic and a feature quantity. In the following, an example in which authentication is mainly performed by using a feature quantity is described. 
      Identification unit  106  determines, when the measured first acoustical signal satisfies a predetermined condition, that first authentication of the user (the person to be authenticated) is successful. Then, identification unit  106  performs, when the second acoustical signal satisfies a predetermined condition, second authentication for determining whether the user (the person to be authenticated) of whom the first authentication is successful is the same person. For example, identification unit  106  compares the first feature quantity extracted by feature extraction unit  105  with the first feature quantity of the registered user stored in first feature quantity storage  107 . Then, identification unit  106  determines, based on the comparison result (first authentication), whether the user to be authenticated is the registered user. Further, identification unit  106  compares the second feature quantity extracted by feature extraction unit  105  with the feature quantity of the registered user stored in second feature quantity storage  108 . Then, identification unit  106  determines, based on the comparison result (second authentication), whether swapping identities (spoofing) of the registered user has not occurred. In general, the first feature quantity has higher authentication accuracy, however, a user feels easily uncomfortable since the first feature quantity is in the audible range. Therefore, identification unit  106  performs the initial first authentication of the user immediately after the user inserts an earphone/microphone device (contacts with the propagation path), based on the first feature quantity. This is because, immediately after the insertion of the earphone/microphone device, an audible sound for a few seconds can be accepted without stress by the user as a signal that authentication processing has properly started. Further, a sound wave in the audible range has robustness to a vibration and a micromotion at the time of insertion, and authentication accuracy is high, and therefore, it is possible to determine with high reliability whether or not a user to be authenticated is a registered user. 
     Identification unit  106  performs the second authentication, based on the second feature quantity. This is because it is considered that a user may be doing some processing or listening to another sound while using an earphone/microphone device, and the authentication by the audible sound may interrupt the user’s concentration or the user may feel stress upon authentication. Further, for the user of whom the initial authentication processing is successful, even the authentication by an inaudible sound (ultrasound) can be an authentication with accuracy sufficient to determine spoofing and the like. 
     Note that identification unit  106  may permit, when a result of the first authentication is successful or when results of the first authentication and the second authentication immediately after the first authentication are successful, a predetermined access. Then, identification unit  106  may continue, when a result of the second authentication performed after the second authentication immediately after the first authentication is successful, permission of the predetermined access. This enables the security of the initial access permission to be more secure. 
     Configuration Example of a Personal Authentication Device 
       FIG.  2    is a diagram illustrating a specific configuration example of the personal authentication device according to the present example embodiment. The personal authentication device illustrated in  FIG.  2    includes personal computer (PC)  11 , sound processor  12 , microphone amplifier  13 , earphone  14 , microphone  15  (referred to as earphone  14  and microphone  15  together as earphone/microphone device  17 ), and sensor  18 . Note that reference sign  16  represents a user to be recognized. 
     Earphone  14  outputs the acoustical signal to be transmitted by above-described first acoustical signal generation unit  101  and second acoustical signal generation unit  102 . Further, microphone  15  receives the acoustical signal and outputs the acoustical signal to acoustical signal measurement unit  103 . Note that, as illustrated in  FIG.  2   , it is desirable that microphone  15  and earphone  14  are integrated in such a way that relative positional relation does not change. However, this may not apply when the relative positional relation between microphone  15  and earphone  14  do not change significantly. Earphone/microphone device  17  is held in a contact state, a press-contacting state, or a substantially fitting state on a piece of the propagation path of the acoustical signal. In the example illustrated in  FIG.  2   , as a configuration example of earphone  14 , microphone  15 , and sensor  18 , earphone/microphone device  17  in which these are integrated is cited. This earphone/microphone device  17  is inserted into the entrance of an ear canal. Sensor  18  detects a contact with a propagation path being a part of a head of a person to be authenticated. Sensor  18  is typically a sensor capable of determining whether a user wears such earphone/microphone device  17  on the body, such as a temperature detection sensor, an optical sensor, or a touch sensor. 
     In addition to the above-described example, earphone/microphone device  17  may be achieved by a device in which a microphone is provided on a headphone of a type covering auricles (over-ear type microphone-integrated earphone/microphone device). Further, earphone/microphone device  17  may be achieved by a telephone provided with a microphone on a receiver part. In such a case, functions may be divided into right and left sides in such a way that an acoustical signal transmitted from earphone  14  located at the ear canal entrance or the like on the left ear is measured with microphone  15  located at the ear canal entrance or the like on the right ear, or vice versa. 
     Acoustical characteristic calculation unit  104 , feature extraction unit  105 , and identification unit  106  are each achieved by a central processing unit (CPU) and a memory which operate according to a personal authentication program included in PC  11 . A specific configuration example of PC  11  is described later (see  FIG.  18   ). Further, first feature quantity storage  107  and second feature quantity storage  108  are achieved by a storage medium such as a hard disk included in PC  11 . 
     Next, a difference in robustness of authentication between the audible range and the inaudible range is described.  FIG.  3    is a graph illustrating an ear canal transfer function (ECTF) when a same person repeatedly inserts and removes earphone/microphone device  17  into and from the same ear ten times. The vertical axis of the graph indicates amplitude (dB: decibel) of a sound wave, and the horizontal axis indicates a frequency (Hz: hertz). Referring to  FIG.  3   , the graphs of the ECTF overlap at a high rate in a frequency range approximately between 0 kHz and 20 kHz, even though the insertion and removal are repeated. In other words, the ECTF has high robustness (reproducibility) with regard to a micromotion of the inserted position of earphone/microphone device  17 . Note that, as illustrated by the graph, the reproducibility of the ECTF gradually decreases in a frequency range greater than 20 kHz. Since a high sound range of the audible sound is around 20 kHz as described above, in the ECTF, an audible sound is not influenced by a motion for insertion and removal compared with an inaudible sound, and it can be said that an authentication rate is high. Note that, in general, the authentication success rate in the audible range is about 97%, and the authentication success rate in the inaudible range is about 90%. Therefore, combining authentication results of these audible range and inaudible range enables a user to bear less burden than authentication only in the audible range. Further, the combination of the authentication results enables acquiring an authentication result with higher accuracy than an authentication result only in the inaudible range. 
     Operation of Personal Authentication Device 
     Next, an operation of personal authentication device  100  according to the first example embodiment is described. The operation of the present example embodiment is divided into “1. user registration” and “2. user identification”. 
     Hereinafter, the operation of “1. user registration” is described with reference to the flowchart illustrated in  FIG.  4   . Note that identification unit  106  performs determination whether to be user registration or user identification. For example, when a coincident feature quantity is not stored in first feature quantity storage  107  or when earphone/microphone device  17  is powered on, identification unit  106  determines that it is processing of the user registration. The user registration processing is also determined when acoustical signal measurement unit  103  detects, by a change in the acoustical signal, insertion of earphone/microphone device  17  by a user, or the like. Note that the determination method is not limited to these examples. 
     First, in step S 101 , first acoustical signal generation unit  101  generates a first acoustical signal and outputs the generated first acoustical signal from earphone  14 . Next, second acoustical signal generation unit  102  generates a second acoustical signal and transmits the generated second acoustical signal from earphone  14 .  FIG.  5    is a chart schematically illustrating a timing for transmitting the first acoustical signal and the second acoustical signal. The vertical axis of the graph indicates a frequency (kHz), and the horizontal axis indicates time (t). First, first acoustical signal generation unit  101  transmits, toward a part of a user’s head to be authenticated, the first acoustical signal in the audible range multiple times at every predetermined interval (n). This is because it is preferable to transmit the signal multiple numbers of times from the viewpoint of accuracy. In  FIG.  5   , first acoustical signal generation unit  101  transmits the first acoustical signal of which frequency is from a minimum as an audible sound (illustrated as 0 kHz in  FIG.  5    for simplification of explanation) to 20 kHz five times at every 0.2 seconds. 
     Then, similarly to above-described first acoustical signal generation unit  101 , second acoustical signal generation unit  102  transmits, toward the part of the user’s head to be authenticated, the second acoustical signal in the inaudible range multiple times at every predetermined interval (n). In  FIG.  5   , for example, second acoustical signal generation unit  102  transmits the second acoustical signal from 20 kHz to 40 kHz five times at every 0.2 seconds. 
     Note that it is preferable that the first acoustical characteristic and the first feature quantity are extracted in the audible range, and the second acoustical characteristic and the second feature quantity are extracted in the inaudible range. However, it is not necessarily limited thereto. This is because, depending on a shape of a head or the like of a user to be authenticated or a type of an acoustical signal and feature quantity to be used, a frequency range in which a highly accurate acoustical signal and feature quantity can be extracted may differ. Therefore, a designer may set a band in which an acoustical characteristic or the like can be calculated with high accuracy in the audible range and the inaudible range. 
       FIG.  6    is a graph schematically illustrating a waveform of the acoustical signals (the first acoustical signal and the second acoustical signal) to be transmitted in a time area expression. The vertical axis represents amplitude of a signal value of an acoustical signal measured at time t, and the horizontal axis represents time t. The acoustical signals generated by first acoustical signal generation unit  101  and second acoustical signal generation unit  102  may be transmitted, for example, from an entrance of ear canal toward the ear canal. At this time, a maximal length sequence signal, a time stretched pulse (TSP) signal, or the like which are widely used for a purpose of measuring an impulse response may be used for these acoustical signals. 
     Note that set values of the transmission interval and the sound range (the frequency) are one example, and can be modified as appropriate according to a device to be used, application, and the like. 
     In step S 102 , acoustical signal measurement unit  103  measures the first acoustical signal after the part of the user’s head to be authenticated is propagated. Similarly, acoustical signal measurement unit  103  measures the second acoustical signal after the part of the user’s head to be authenticated is propagated. 
       FIG.  7    is a graph schematically illustrating a waveform of the acoustical signals (the first acoustical signal and the second acoustical signal) to be measured in a time area expression. In the graph, the vertical axis represents a signal value (amplitude) of an acoustical signal measured at time t, and the horizontal axis represents time (t). During the propagation in an ear canal, the first acoustical signal to be measured changes as the graph illustrated in  FIG.  6    into the graph illustrated in  FIG.  7   . This change occurs due to the influence of noises caused inside the body such as a heartbeat sound, a motion sound (an arthrosound and a muscle sound), a breath sound, and a vocalized sound. 
     Further, acoustical signal measurement unit  103  performs synchronous addition processing and removes noises in the measured acoustical signals (the first acoustical signal and the second acoustical signal).  FIG.  8    illustrates a waveform of the signal after the synchronous addition processing in 0.2 seconds described above. 
     In step S 103 , acoustical characteristic calculation unit  104  compares the transmitted first acoustical signal (see  FIG.  6   ) with the measured first acoustical signal (including the signal after the synchronous addition processing) (see  FIGS.  7  and  8   ). Then, acoustical characteristic calculation unit  104  calculates, from these changes, the acoustical characteristic (the first acoustical characteristic) when the first acoustical signal propagates the part of the user’s head. Similarly, acoustical characteristic calculation unit  104  compares the transmitted second acoustical signal (see  FIG.  6   ) with the measured second acoustical signal (including the signal after the synchronous addition processing) (see  FIGS.  7  and  8   ). Then, acoustical characteristic calculation unit  104  calculates, from these changes, the acoustical characteristic (the second acoustical characteristic) when the second acoustical signal propagates the part of the user’s head. 
     The acoustical characteristics (the first acoustical characteristic and the second acoustical characteristic) are a characteristic to represent, when transmitting the acoustical signal, how the transmitted acoustical signal propagates a target (which is a part of a user’s head in the present invention) and is measured. The acoustical signal to be measured varies depending on the transmitted signal. However, in principle, a measurement signal for any transmission signal can be calculated by acquiring a signal to be measured when transmitting a sudden and very short acoustical signal called an impulse signal. Therefore, a signal to be measured for an impulse signal, i.e., an impulse response is a typical acoustical characteristic. Further, a transfer function (TF) which is acquired by applying Fourier analysis to the impulse response is also a typical acoustical characteristic. It is preferable that the acoustical characteristic includes information on how the acoustical signal is reflected and/or attenuated in a living body. 
     In the following description, it is assumed that the propagation path is an ear canal.  FIG.  9    is a graph of an ear canal impulse response (ECIR) illustrating the acoustical characteristic calculated by acoustical characteristic calculation unit  104  in a time area expression. The graph illustrated in  FIG.  9    indicates that the horizontal axis represents time t and the vertical axis represents a value h (t) of the ear canal impulse response of the measured acoustical signal at time t. Note that there is relation indicated by the following equation (1) among a signal value x (t) of the acoustical signal to be transmitted, a signal value y (t) of the acoustical signal to be measured after propagation, and a value h (t) of the ear canal impulse response. Herein, τ is a shift coefficient. [Equation 1] 
     
       
         
           
             y 
             
               t 
             
             = 
             h 
             
               t 
             
             ∗ 
             x 
             
               t 
             
             = 
             
               
                 
                   ∫ 
                   
                     − 
                     ∞ 
                   
                   ∞ 
                 
                 
                   h 
                   
                     r 
                   
                   x 
                   
                     
                       t 
                       − 
                       r 
                     
                   
                 
               
             
               
             d 
             r 
           
         
       
     
     The acoustical characteristic may be the ear canal transfer function (ECTF).  FIG.  10    is a graph of the ECTF representing the acoustical characteristic illustrated in  FIG.  9    in a frequency region. In the graph, the vertical axis represents amplitude (dB) and the horizontal axis represents a frequency (kHz). In the graph, it can be seen that a plurality of maxima (peaks) and minima (valleys) are clearly measured in the audible range, compared with the inaudible range. 
     In step S 104 , feature extraction unit  105  calculates the feature quantity (first feature quantity) from the first acoustical characteristic calculated by acoustical characteristic calculation unit  104 . 
     Herein, the feature quantities (first feature quantity and second feature quantity described later) are a numerical value useful for required processing (personal authentication in the present invention) extracted by applying some processing to the acoustical signal. The feature quantity is also referred to as an acoustical feature quantity. For example, melfrequency cepstrum coefficients (MFCC) widely used for speech recognition are a typical acoustical feature quantity. The MFCC is acquired by applying processing such as Fourier analysis, logarithmic transformation, mel conversion, and discrete cosine transform with regard to the acoustical signal. The MFCC represents a vocal tract characteristic while considering speech perception of human beings. Note that the ECTF is acquired by performing processing of fast Fourier transform (FFT) with regard to the ECIR and the MFCC is a lower-order component of cepstrum which is acquired by applying the above-described processing to the ECTF. 
     For the first feature quantity, the impulse response or the transfer function calculated as the acoustical characteristic may be used as it is. In other words, feature extraction unit  105  may use a value of each time of the impulse responses as the first acoustical characteristic or a value of each frequency of the transfer functions as the feature quantity. 
       FIG.  11    is a graph illustrating a certain ECTF spectrum envelope. In the graph, the horizontal axis represents a frequency (Hz) and the vertical axis represents a sound pressure (both are logarithmic scales). The feature quantity of a user illustrated in the graph of  FIG.  11    forms a first maximum around 1.5 kHz to 1.8 kHz, a first minimum around 3 kHz to 4 kHz, and a maximum again around 5 kHz to 8 kHz. The distance from the external opening of ear canal to the eardrum at the maximum time around 5 kHz to 8 kHz is approximately 2 to 3 cm on average. This shape or a numerical value associated with this is the feature quantity of the user.  FIGS.  12 A,  12 B and  12 C  illustrate other graphs each representing the spectrum envelope.  FIGS.  12 A,  12 B, and  12 C  illustrate graphs of the MFCC at first and 30th measurements relating a male A, a male B, and a female C, respectively. In the graph, circled areas represent features unique to each person. Note that, since it is a low sound (an audible range), it can be measured from the graph that a matching rate is high whether it is the first measurement or the 30th measurement. 
     Feature extraction unit  105  calculates, by a similar method, the feature quantity (second feature quantity) also from the second acoustical characteristic calculated by acoustical characteristic calculation unit  104 . 
     In step S 105 , identification unit  106  stores the first feature quantity to be acquired from feature extraction unit  105  in first feature quantity storage  107 . Further, identification unit  106  stores the second feature quantity to be acquired from feature extraction unit  105  in second feature quantity storage  108 . Specifically, assuming that the feature quantity is the ECTF, for example, identification unit  106  stores the graph of 0 kHz to 20 kHz in the graph illustrated in  FIG.  10    or a numerical value representing thereof as the first feature quantity in first feature quantity storage  107 . Further, identification unit  106  stores the graph of 20 kHz to 40 kHz or a numerical value representing thereof as the second feature quantity in second feature quantity storage  108 . 
     With the above, the processing of user registration ends. 
     Next, the operation of “2. user identification” is described with reference to the flowchart illustrated in  FIG.  13   . Note that steps S 201  to S 207  are first authentication processing using the first feature quantity in the audible range, and steps S 208  to S 215  are second authentication processing using the second feature quantity in the inaudible range. 
     First, when a person to be authenticated inserts earphone/microphone device  17  into a propagation path (for example, an ear canal entrance) being a part of his/her own head, sensor  18  detects a contact to the propagation path. In step S 201 , first acoustical signal generation unit  101  generates a signal in the audible range (a first acoustical signal) and transmits the generated signal to the propagation path via earphone  14  at every predetermined interval. 
     In step S 202 , acoustical signal measurement unit  103  receives and measures, via microphone  15 , the acoustical signal after the first acoustical signal propagates a part of a user’s head to be authenticated. 
       FIG.  14    is a chart schematically illustrating a timing for transmitting the first acoustical signal and the second acoustical signal in steps S 201  and S 202 . The vertical axis of the graph represents a frequency (kHz) of a sound wave and the horizontal axis represents time (t). First, first acoustical signal generation unit  101  transmits, toward the part of the user’s head to be authenticated, the generated first acoustical signal in the audible range multiple times (5 times in  FIG.  14   ) at every predetermined interval (n). Then, similarly to above-described first acoustical signal generation unit  101 , second acoustical signal generation unit  102  generates the generated second acoustical signal in the inaudible range. Then, second acoustical signal generation unit  102  transmits, toward the propagation path being the part of the user’s head to be authenticated via earphone  14 , the generated second acoustical signal in the inaudible range multiple times (5 times in  FIG.  14   ) at every predetermined interval (n). 
     In step S 203 , acoustical characteristic calculation unit  104  compares the first acoustical signal with the first acoustical signal measured by acoustical signal measurement unit  103 . Then, acoustical characteristic calculation unit  104  calculates, from these changes, an acoustical characteristic (a first acoustical characteristic) of the acoustical signal when the first acoustical signal propagates the part of the user’s head. 
     In step S 204 , feature extraction unit  105  calculates a feature quantity (first feature quantity) from the first acoustical characteristic calculated by acoustical characteristic calculation unit  104 . 
     In step S 205 , identification unit  106  determines whether the first feature quantity acquired from feature extraction unit  105  coincides with any of the feature quantity stored in first feature quantity storage  107 . In other words, identification unit  106  determines whether the user to be authenticated is a registered user. 
     In step S 206 , when identification unit  106  determines that the user to be authenticated is a registered user, the processing proceeds to step S 207 . When not coincident, the processing proceeds to step S 215 . 
     In step S 207 , identification unit  106  determines that the first authentication processing is successful and permits the registered user to access a predetermined device. Access to the predetermined device is, for example, login to a certain system and use of an application and database in the system after login. Usable applications and databases may be set differently for each registered user. 
     In step S 208 , when a predetermined time, for example, 10 seconds elapses, the processing proceeds to step S 209 , and the second authentication processing for continuing access permission is performed. 
     First, in step S 209 , second acoustical signal generation unit  102  transmits, toward the part of the user’s head to be authenticated via earphone  14 , the generated signal in the inaudible range (the second acoustical signal) at every predetermined interval. 
     In step S 210 , acoustical signal measurement unit  103  receives and measures, via microphone  15 , the acoustical signal after the second acoustical signal propagates the part of the user’s head to be authenticated. 
     In step S 211 , acoustical characteristic calculation unit  104  compares the second acoustical signal with the second acoustical signal measured by acoustical signal measurement unit  103 . Then, acoustical characteristic calculation unit  104  calculates, from these changes, an acoustical characteristic (a second acoustical characteristic) of the acoustical signal when the second acoustical signal propagates the part of the user’s head. 
     In step S 212 , feature extraction unit  105  calculates a feature quantity (second feature quantity) from the second acoustical characteristic calculated by acoustical characteristic calculation unit  104 . 
     In step S 213 , identification unit  106  determines whether the second feature quantity acquired from feature extraction unit  105  coincides with any of the feature quantity stored in second feature quantity storage  108 . In other words, identification unit  106  determines whether the user to be authenticated is a registered user. 
     In step S 214 , when identification unit  106  determines that the user to be authenticated is a registered user, the processing proceeds to step S 215 . When not coincident, the processing proceeds to step S 216 . 
     In step S 215 , identification unit  106  determines that the first authentication processing or the second processing fails, does not permit the user to be authenticated to access a predetermined device, and disconnects the access. 
     In step S 216 , identification unit  106  determines that the second authentication processing is successful and permits the registered user to continue the access to the predetermined device. Then, the processing proceeds to step S 208 , and the second authentication processing is performed again after a predetermined time has elapsed. Specifically, the second acoustical signal is transmitted again, when a waiting time (m) illustrated in  FIG.  14    has elapsed after the first transmission of the second acoustical signal. 
     Note that the second authentication processing is repeated until sensor  18  detects the removal of earphone/microphone device  17  by the user. 
     On the contrary, when sensor  18  detects the insertion of earphone/microphone device  17 , the processing of “1. user registration” is started again in a next processing step. The detection of insertion of earphone/microphone device  17  may be performed by using a sensor other than sensor  18 . For example, power-on of the earphone/microphone device may be asked to a user, each time earphone/microphone device  17  is inserted and removed. Alternatively, the insertion of earphone/microphone device  17  by a user may be detected by a change in acoustical signal to be measured by acoustical signal measurement unit  103 . 
     In addition, identification unit  106  may use one-to-one authentication or one-to-N authentication. Herein, N is an integer equal to or more than 1. 
     Identification unit  106  compares, when using the one-to-one authentication, a feature quantity of a user to be authenticated (a feature quantity acquired by feature extraction unit  105 ) with a feature quantity of a registered user by one-to-one. At this time, an administrator of a personal authentication device may give a designation of which registered user to perform comparison to identification unit  106  in advance by using a user ID or the like. For example, identification unit  106  calculates, when using the one-to-one authentication, a distance between a feature quantity of a user to be authenticated and a feature quantity of a designated registered user. Then, identification unit  106  may determine that, when the distance is smaller than a threshold value, both are the same person. On the other hand, user identification unit  106  may determine that, when the calculated distance is greater than the threshold value, both are different persons. 
     Identification unit  106  compares, when using the one-to-N authentication, a user to be authenticated with N registered users. Identification unit  106  calculates distances between a feature quantity of the user to be authenticated and each of feature quantities of the N registered users. Then, identification unit  106  sets an appropriate threshold value and determines that the registered user of whom distance is the smallest within the threshold value is the user to be authenticated. Further, identification unit  106  can use a combination of the one-to-one authentication and the one-to-N authentication. In this case, user identification unit  106  may perform the one-to-N authentication, extract a registered user having the smallest distance, and then perform the one-to-one authentication by using the extracted registered user as a target to be compared. Further, as a distance scale to be calculated, a Euclid distance, a cosine distance, and the like can be considered, however, the distance scale is not limited to these. 
     Further, in the above description, an example is described in which first feature quantity storage  107  and second feature quantity storage  108  store feature quantities acquired from a plurality of persons in advance. However, a statistical model may be stored instead of the feature quantities. The statistical model may be, for example, by acquiring feature quantities for each user multiple times, the average value and variance value of the feature quantities or a relational expression calculated by using the average value and variance value. Further, the statistical model may be a gaussian mixture model (GMM), a support vector machine (SVM), a model using a neural network, or the like. 
     Modification Example of First Example Embodiment 
     In step S 207  of  FIG.  13   , identification unit  106  permits, when the first authentication processing is successful, a registered user to access a predetermined device. However, identification unit  106  may permit, when the first authentication processing and the initial second authentication processing are successful, the registered user to access the predetermined device. Specifically, identification unit  106  may permit, when being YES in step S 214 , the registered user to access the predetermined device (step S 207 ). Modifying the design in this way enables the access permission to be performed more strictly, leading to enhancing authentication security. 
     Advantageous Effects of First Example Embodiment 
     As described above, with an earphone/microphone device as a single unit, the first example embodiment of the present invention is able to provide a personal authentication device and the like capable of quickly performing highly accurate authentication even at the time of insertion and preventing spoofing after authentication. The reason for this is as follows: Identification unit  106  performs, when a measured first acoustical signal satisfies a predetermined condition, first authentication of a person to be authenticated. Then, identification unit  106  performs, when a second acoustical signal satisfies a predetermined condition after the first authentication, second authentication for determining whether the person to be authenticated whose first authentication is successful is the same person. According to the present example embodiment, sensor unit  301  detects the insertion. Then, using this detection as a trigger, a propagation result of the first acoustical signal including the audible range is acquired and then a propagation result of the second acoustical signal including the inaudible range having a higher frequency than the audible range is acquired. Based on the results, identification unit  106  performs a determination (first authentication) on whether the user is a registered user. Then, identification unit  106  performs a determination (second authentication) on whether swapping identities (spoofing) of the user determined as the registered user in the first authentication has not occurred. 
     Second Example Embodiment 
     In authentication device  100  according to the first example embodiment, the second authentication processing is performed at a predetermined time interval. However, the second authentication processing over a long period of time requires electric power to continue outputting ultrasounds at every short time interval. The second authentication processing over a long period of time may also be a burden on a user depending on the constitution of the user who continues authentication for a long time. Therefore, according to a second example embodiment, personal authentication device  200  is described in which the number of times of second authentication processing is gradually reduced. This processing is performed for a user who have succeeded in second authentication processing a certain number of times or more, i.e., a user who have a history of not performing spoofing. 
     Personal Authentication Device 
     As illustrated in  FIG.  15   , personal authentication device  200  according to the second example embodiment of the present invention includes first acoustical signal generation unit  101 , second acoustical signal generation unit  102 , acoustical signal measurement unit  103 , acoustical characteristic calculation unit  104 , feature extraction unit  105 , identification unit  106 , first feature quantity storage  107  and second feature quantity storage  108 , detection unit  109 , counter unit  110  and adjustment unit  111 . 
     Detection unit  109  detects insertion and removal of earphone/microphone device  17  (see  FIG.  2   ) into and from the ear canal of a user. Detection unit  109  is, for example, a temperature detection sensor, an optical sensor, or a touch sensor. Detection unit  109  may detect insertion and removal by a change in an acoustical signal measured by acoustical signal measurement unit  103 . The determination method is not limited to these. 
     Detection unit  109  outputs, when detecting the insertion of earphone/microphone device  17  (contact to a propagation path), the detection result to first acoustical signal generation unit  101 . This is to notify a timing for transmitting a first acoustical signal being the start of first authentication. On the contrary, detection unit  109  restores, when detecting the removal of earphone/microphone device  17  (non-contact with the propagation path), a counter value of counter unit  110  to an initial value (e.g., 0). Then, detection unit  109  outputs the detection result to first acoustical signal generation unit  101  and second acoustical signal generation unit  102 . This is to stop transmitting the acoustic signal and stop the first and second authentication. 
     Counter unit  110  counts the number of times when a user to be authenticated is identified as successful in the first authentication, the number of times when a second acoustical signal is transmitted, and the like. Counter unit  110  may count the number of times when the first acoustical signal is transmitted. Counter unit  110  may count the number of times of the first authentication processing and the second authentication processing. 
     As an example, when counting authentication processing, the count may be individually performed in such a way that the number of times of the first authentication processing is “once” and the number of times of the second authentication processing is “45 times”. Alternatively, a first time of the authentication processing may be counted as the number of times of the first authentication processing and n-th time of second authentication processing may be calculated as (n-1)th time. 
     Adjustment unit  111  adjusts a waiting time interval for the second authentication processing, depending on the number of times of successful second authentication processing. For example, when the number of times of successful authentication is p times or more, the waiting time is delayed by (an initial value + q) seconds. Thus, the waiting time is lengthened depending on the magnitude of an absolute value relating to the number of times of successful authentication. As a specific example, when the number of times of successful authentication is 10 times or more, the waiting time is set to (the initial value + 5) seconds. Further, when the number of times of successful authentication is 20 times or more, the waiting time is set to (the initial value + 10) seconds. Adjustment unit  111  controls second acoustical signal generation unit  102  in such a way as to transmit the second acoustical signal at the adjusted waiting time interval. 
     Other devices are similar to the devices according to the first example embodiment. 
     Operation of Personal Authentication Device 
     Next, an operation of the personal authentication device  200  according to the second example embodiment is described. The operation of the personal authentication device  200  is divided into “1. user registration” and “2. user identification”. The operation of “1. user registration” is similar to the first example embodiment ( FIG.  4   ). In the following, the operation of “2. user identification” is described with reference to the flowchart illustrated in  FIG.  16   . 
     First, when a person to be authenticated inserts earphone/microphone device  17  into the propagation path (e.g., the ear canal entrance) being a part of his/her own head, detection unit  109  constituting the sensor detects a contact to the propagation path. Hereinafter, operations in steps S 301  to S 316  are similar to the operations according to the first example embodiment (see steps S 201  to S 216  in the flowchart of  FIG.  13   ). 
     In step S 317 , counter unit  110  counts, for example, the number of times of successful first authentication processing and successful second authentication processing in identification unit  106 . The number of times of the first authentication processing and the number of times of the second authentication processing may be counted individually or may be counted together. Note that counter unit  110  may count the number of times of transmission of the acoustic signals from first acoustical signal generation unit  101  and second acoustical signal generation unit  102 . Note that, when detection of the removal of earphone/microphone device  17  by detection unit  109  is notified, counter unit  110  restores the counter value to an initial value (for example, 0). 
     In step S 318 , adjustment unit  111  determines whether the number of times of successful authentication counted by counter unit  110  has reached a predetermined number of times or more. When the number of times is equal to or more than the predetermined number of times, the processing proceeds to step S 319 . When the number of times is not equal to or more than the predetermined number of times, the processing proceeds to step S 308 . 
     In step S 319 , adjustment unit  111  determines a waiting time interval for the second authentication processing, depending on the number of times of the successful authentication. Adjustment unit  111  may include a mathematical formula and a determination table for determining the waiting time interval. Adjustment unit  111  controls second acoustical signal generation unit  102  in such a way as to transmit the second acoustical signal at the determined waiting time interval. Thereby, second acoustical signal generation unit  102  transmits the generated second acoustical signal at the determined waiting time interval. 
     Modification Example of Second Example Embodiment 
     According to the second example embodiment, when removal of earphone/microphone device  17  is detected, the counter value of counter unit  110  is restored to an initial value. Then, the processing of “1. user registration” is restarted (i.e., the first acoustical signal is transmitted again). However, other than this, first acoustical signal generation unit  101  may perform transmission of the first acoustical signal as long as it is not a burden on a user. An example is when the number of times of the successful second authentication processing in counter unit  110  exceeds a predetermined number of times A, or when the number of times of success becomes a multiple of this A. By using this case as a trigger, first acoustical signal generation unit  101  may transmit the first acoustical signal. 
     Advantageous Effects of Second Example Embodiment 
     As described above, the second example embodiment of the present invention has similar advantageous effect to the first example embodiment. In other words, with an earphone/microphone device as a single unit, the second example embodiment is able to provide a personal authentication device and the like capable of quickly performing highly accurate authentication even at the time of insertion and preventing spoofing after authentication. Further, the waiting time interval for authentication processing is adjusted depending on the number of times of successful authentication. Then, adjustment unit  111  determines, depending on the number of times of successful authentication counted by counter unit  110 , an interval for transmission of the second acoustical signal. Therefore, the number of times of the second authentication processing can be gradually reduced for a user who has a history of not performing spoofing. As a result, the electric power for outputting ultrasound can be eliminated, and the possibility of imposing a burden on a part for authentication in a user’s body can be reduced. 
     Third Example Embodiment 
     As illustrated in  FIG.  17   , personal authentication device  300  according to a third example embodiment of the present invention includes sensor unit  301 , acoustical signal generation unit  302 , acoustical signal measurement unit  303 , and identification unit  304 . 
     Sensor unit  301  detects a contact to a propagation path being a part of the head of a person to be authenticated. 
     Acoustical signal generation unit  302  generates, when sensor unit  301  detects the contact, a first acoustical signal including an audible range. Further, acoustical signal generation unit  302  generates a second acoustical signal in an inaudible range that has a higher frequency than the audible range and that does not include the audible range. Then, acoustical signal generation unit  302  transmits the generated first acoustical signal and second acoustical signal toward the propagation path. 
     Acoustical signal measurement unit  303  measures an acoustical signal after the first acoustical signal propagates the part of the head and measures an acoustical signal after the second acoustical signal propagates the part of the head. 
     Identification unit  304  performs, when the measured first acoustical signal satisfies a predetermined condition, first authentication of a person to be authenticated. Then, identification unit  304  performs, when the second acoustical signal satisfies a predetermined condition after the first authentication, second authentication for determining whether the person to be authenticated whose first authentication is successful is the same person. 
     With an earphone/microphone device as a single unit, the third example embodiment of the present invention is able to provide a personal authentication device and the like capable of quickly performing highly accurate authentication even at the time of insertion and preventing spoofing after authentication. The reason for this is as follows: Identification unit  304  performs, when the measured first acoustical signal satisfies a predetermined condition, the first authentication of a person to be authenticated. Then, identification unit  304  performs, when the second acoustical signal satisfies a predetermined condition after the first authentication, the second authentication for determining whether the person to be authenticated whose first authentication is successful is the same person. According to the present example embodiment, sensor unit  301  detects the insertion. Then, using this detection as a trigger, a propagation result of the first acoustical signal including the audible range is acquired and then, a propagation result of the second acoustical signal including the inaudible range having a higher frequency than the audible range is acquired. Based on the results, identification unit  106  performs a determination (first authentication) on whether the user is a registered user. Then, identification unit  106  performs a determination (second authentication) on whether swapping identities (spoofing) of the user determined as a registered user in the first authentication has not occurred. 
     According to the above-described example embodiments of the present invention, personal authentication devices  100 ,  200 , and  300  may incorporate a personal authentication program inside earphone/microphone device  17  and perform authentication as a single device. As illustrated in  FIG.  2   , earphone/microphone device  17  and PC  11  are connected with each other and the entire operation may be controlled on PC  11  side. In other words, an application program for personal authentication on PC  11  side may be used under the following configuration. 
     Information Processing Device 
     According to the above-described example embodiments of the present invention, a part or all of the components in the personal authentication device illustrated in  FIGS.  1 ,  2    and the like can be also achieved by using, for example, any combination of information processing device  500  (PC  11 ) illustrated in  FIG.  18    and a program. Information processing device  500  includes, as one example, the following configuration. 
     Central processing unit (CPU)  501     Read only memory (ROM)  502     Random access memory (RAM)  503     Program  504   a  to be loaded into RAM  503     Storage device  505  storing program  504   b  and other data   Drive device  507  for reading and writing recording medium  506     Communication interface  508  to be connected with communication network  509     Input/output interface  510  for inputting/outputting data   Bus  511  for connecting each component   

     Each component of the personal authentication device according to each of the example embodiments of the present application is achieved by CPU  501  acquiring and executing program  504   b  that implements these functions. Program  504   b  which achieves the functions of each of components (e.g., an acoustical signal generation unit, an acoustical signal measurement unit, and an identification unit) of the personal authentication device is stored, for example, in storage device  505  or RAM  503  in advance. CPU  501  reads out program  504   b  as necessary. Note that program  504   b  may be provided to CPU  501  via communication network  509 . Program  504   b  is stored in recording medium  506  in advance and may be provided to CPU  501  by drive device  507  reading the program. 
     Note that input/output interface  510  is connected to sensor  18 , sound processor  12 , and the like illustrated in  FIG.  2   . Storage device  505  includes feature quantity storage  504   a  (the first feature quantity storage and the second feature quantity storage) illustrated in  FIGS.  1  and  15   . 
     A method of achieving each device includes various modification examples. For example, the personal authentication device may be achieved by any combination of each separate information processing device for each component and a program. Alternatively, a plurality of components provided in the personal authentication device may be achieved by any combination of one information processing device  500  and a program. 
     Further, a part or the whole of each of the components of the personal authentication device may be achieved by another general-purpose or dedicated circuit, a processor, and the like, or a combination thereof. These components may be configured by a single chip, or may be configured by a plurality of chips to be connected via a bus. 
     A part or the whole of each of the components of the personal authentication device may be achieved by a combination of the above-described circuit and the like and a program. 
     When a part or the whole of each of the components of the personal authentication device is achieved by a plurality of information processing devices, circuits, or the like, the plurality of information processing devices, circuits, or the like may be arranged in a concentrated manner or a distributed manner. For example, an information processing device, a circuit, or the like may be achieved as a form in which each of a client-and-server system, a cloud computing system, and the like is connected via a communication network. 
     In the foregoing, the present invention has been described by referring to the present example embodiments. The present invention, however, is not limited to the aforementioned example embodiments. The configuration and details of the present invention can be subjected to various modifications which can be understood by those skilled in the art, within the scope of the present invention. 
     Industrial Applicability 
      The present invention is applicable, for example, to a site that requires urgent and access to confidential information, for example, a system that requires quick and highly accurate authentication by ambulance team members, police officers, self-defense forces, and the like. Further, the present invention is also applicable to a personal authentication device and the like that authenticate a person by using an audio device. Further, the present invention is also applicable to a personalization system, a content right management system, a communication control system, and the like using such a personal authentication device or the like. 
     
       
         
           
               
             
               
                 Reference Signs List 
               
             
            
               
                   11  PC 
               
               
                   12  Sound processor 
               
               
                   13  Microphone amplifier 
               
               
                   14  Earphone 
               
               
                   15  Microphone 
               
               
                   16  User 
               
               
                   17  Earphone/microphone device 
               
               
                   18  Sensor 
               
               
                   101  First acoustical signal generation unit 
               
               
                   102  Second acoustical signal generation unit 
               
               
                   103  Acoustical signal measurement unit 
               
               
                   104  Acoustical characteristic calculation unit 
               
               
                   105  Feature extraction unit 
               
               
                   106  Identification unit 
               
               
                   107  First feature quantity storage 
               
               
                   108  Second feature quantity storage 
               
               
                   109  Detection unit 
               
               
                   110  Counter unit 
               
               
                   111  Adjustment unit 
               
               
                   100  Personal authentication device 
               
               
                   200  Personal authentication device 
               
               
                   300  Personal authentication device 
               
               
                   301  Sensor unit 
               
               
                   302  Acoustical signal generation unit 
               
               
                   303  Acoustical signal measurement unit 
               
               
                   304  Identification unit 
               
               
                   500  Information processing device 
               
               
                   501  CPU 
               
               
                   503  RAM 
               
               
                   504   b  Program 
               
               
                   505  Storage device 
               
               
                   506  Recording medium 
               
               
                   507  Drive device 
               
               
                   508  Communication interface 
               
               
                   509  Communication network 
               
               
                   510  Input/output interface 
               
               
                   511  Bus