Abstract:
A communication apparatus having a public key authentication function and a communication method thereof are disclosed. The communication apparatus includes a calculating unit to calculate a first user authentication data for authenticating public information, and a transmitting and receiving unit to transmit the calculated first user authentication data and the public information to be authenticated, and to transmit a password in a form in which a user characteristic input for authenticating the public information is reflected. Accordingly, if the parties to a communication unexpectedly request mutual authentication under an IP-based communication environment, the apparatus can safely authenticate the public information with a use of a user characteristic sensing channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of a U.S. Provisional Application No. 60/795193, filed Apr. 27, 2006, in the U.S. Patent and Trademark Office, and 35 U.S.C. §119(a) of a Korean Patent Application No. 10-2006-050984, filed Jun. 7, 2006, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a communication apparatus, which can provide a public information authentication, and a communication method thereof. More particularly, the present invention relates to a communication apparatus, which can authenticate public information using a user characteristic sensing channel, and a communication method thereof. 
         [0004]    2. Background of the Invention 
         [0005]    With a diversification of communication environments, such as a moving network, a home network, and the like, a safety between the parties to a communication is one of important concerns. The IP-based communication environments are developing to improve the convenience of users, but have a problem in that it is possible for the third party to easily access. To prevent the problem, there is a need for a communication apparatus to authenticate whether an opposite communication apparatus, which is in the communication, is the very same communication apparatus, which is to be communicated at first. As methods of authenticating the communication apparatus, there are a public key infrastructure (PKI) on the basis of a Rivest Shamir Adlman (RSA), and a password-based public key agreement protocol. 
         [0006]    The public key infrastructure is a security system environment, which provides an encryption and an electronic signature through a public key algorithm. The public key infrastructure encrypts transmitted data and decrypts received data using a public key comprising an encrypted key and a decrypted key. 
         [0007]    Such a public key infrastructure includes a certificate authority to issue a certificate to the public key, a registration authority to confirm positions and identifies of users instead of the certificate authority in certificate requests of users, a directory to store and search the certificate/user&#39;s related information, a mutual certificate, and a certificate retraction list, and users to produce and verify an electronic signature using the public key in various applications and to perform encryption and decryption to data. 
         [0008]    In the password-based public key agreement protocol, a communication apparatus should get a password in advance in an off-line environment. 
         [0009]    However, in the state that communication apparatuses communicate in real time with each other, if the communication apparatuses unexpectedly request mutual authentication, it is difficult to authenticate the other parties to the communication using the password-based public key agreement protocol and the public key infrastructure. 
         [0010]    Also, in the authentication method of using the public key infrastructure, there is a problem in that a procedure to register the certificate to the public key to the certificate authority is complicated, and if a communication apparatus does not possess the certificate, it is not possible to authenticate the communication apparatus. 
       SUMMARY OF THE INVENTION 
       [0011]    An aspect of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a communication apparatus having a public information authentication function, which when the parties to a communication unexpectedly request mutual authentication under an IP-based communication environment, can safely authenticate public information using a user characteristic sensing channel, and a communication method thereof. 
         [0012]    According to an aspect of an exemplary embodiment of the present invention, a communication apparatus is provided. The communication apparatus comprises a calculating unit for calculating a first user authentication data for authenticating public information, and a transmitting and receiving unit for transmitting the calculated first user authentication data and the public information to be authenticated, and for transmitting a password in a form in which a user characteristic input for authenticating the public information is reflected. 
         [0013]    The transmitting and receiving unit may transmit the first user authentication data prior to transmitting the password. 
         [0014]    The transmitting and receiving unit may transmit the password after receiving an acknowledgement message to the first user authentication data. 
         [0015]    The transmitting and receiving unit may receive the acknowledgement message to the first user authentication data in the form of one of audio data and image data in which the user characteristic is reflected. 
         [0016]    The calculating unit may produce a random number, which is used to the calculation of the first user authentication data, and the transmitting and receiving unit may transmit the produced random number after receiving an acknowledgement message to the first user authentication data. 
         [0017]    The transmitting and receiving unit may transmit the random number after transmitting the password. 
         [0018]    The calculating unit may calculate the first user authentication data by applying the password, the random number and the public information to a Hash function. 
         [0019]    The transmitting and receiving unit may transmit the password in the form of one of audio data and image data in which the user characteristic is reflected. 
         [0020]    The password may be a one-time password, which is used when the public information is authenticated to allow a plurality of communication apparatuses to have the public information authenticated in intercommunication. 
         [0021]    The calculating unit may produce a response to a random challenge, which is received, and the transmitting and receiving unit may transmit the produced response to the random challenge. 
         [0022]    According to another aspect of an exemplary embodiment of the present invention, a communication method is provided. The method comprises calculating a first user authentication data for authenticating public information, and transmitting the calculated first user authentication data and the public information to be authenticated, and transmitting a password in a form in which a user characteristic input for authenticating the public information is reflected. 
         [0023]    The transmitting may include transmitting the first user authentication data prior to transmitting the password. 
         [0024]    The transmitting may include transmitting the password after receiving an acknowledgement message to the first user authentication data. 
         [0025]    The transmitting may include transmitting the acknowledgement message to the first user authentication data in the form of one of audio data and image data in which the user characteristic is reflected. 
         [0026]    The calculating may include producing a random number, which is used to the calculation of the first user authentication data, and the transmitting may include transmitting the produced random number after receiving an acknowledgement message to the first user authentication data. 
         [0027]    The transmitting may include transmitting the random number after transmitting the password. 
         [0028]    The calculating may include calculating the first user authentication data by applying the password, the random number and the public information to a Hash function. 
         [0029]    The transmitting may include transmitting the password in the form of one of audio data and image data in which the user characteristic is reflected. 
         [0030]    The password may be a one-time password, which is used when the public information is authenticated to allow a plurality of communication apparatuses to have the public information authenticated in intercommunication. 
         [0031]    The calculating may include producing a response to a random challenge which is received, and the transmitting may include transmitting the produced response to the random challenge. 
         [0032]    According to still another aspect of an exemplary embodiment of the present invention, a communication apparatus is provided. The apparatus comprises a transmitting and receiving unit for receiving a first user authentication data for authenticating public information and the public information, and for receiving a password in a form in which a user characteristic input for authenticating the public information is reflected, a calculating unit for calculating a second user authentication data on the basis of the password and the public information, which are received, and a displaying unit for displaying a comparison result between the received first user authentication data and the calculated second user authentication data. 
         [0033]    The transmitting and receiving unit may receive the first user authentication data prior to receiving the password and the displaying unit may output at least one out of a message, an alarm and an icon acknowledging a receipt of the first user authentication data. 
         [0034]    The transmitting and receiving unit may receive the password after transmitting an acknowledgement message to the first user authentication data. 
         [0035]    The transmitting and receiving unit may transmit an acknowledgement message to the first user authentication data and an acknowledgement message to the password in the form of one of audio data and image data in which the user characteristic is reflected. 
         [0036]    The transmitting and receiving unit may receive a random number, which is used to an authentication of the first user authentication data, after transmitting the acknowledgement message to the first user authentication data. 
         [0037]    The calculating unit may calculate the second user authentication data by applying the received password, the received random number and the received public information to a Hash function. 
         [0038]    The calculating unit may calculate a random challenge using the received public information, and the transmitting and receiving unit may transmit the calculated random challenge. 
         [0039]    The transmitting and receiving unit may receive the password in the form of one of audio data and image data in which the user characteristic is reflected. 
         [0040]    The communication apparatus may further include a comparing unit to compare whether the first user authentication data is substantially identical to the second user authentication data. In this case, the displaying unit may display the comparison result of the comparing unit to inform a user of the comparison result. 
         [0041]    The transmitting and receiving unit may receive the first user authentication data and the public information once at first, and refuse to receive the first user authentication data and the public information after that time. 
         [0042]    According to also another aspect of an exemplary embodiment of the present invention, there is provided a communication method including: receiving a first user authentication data for authenticating public information and the public information, and receiving a password in a form in which a user characteristic input for authenticating the public information is reflected, calculating a second user authentication data on the basis of the password and the public information, which are received, and displaying a comparison result between the received first user authentication data and the calculated second user authentication data. 
         [0043]    The receiving may include receiving the first user authentication data prior to receiving the password and the displaying may include outputting at least one out of a message, an alarm and an icon acknowledging a receipt of the first user authentication data. 
         [0044]    The receiving may include receiving the password after transmitting an acknowledgement message to the first user authentication data. 
         [0045]    The receiving may include transmitting an acknowledgement message to the first user authentication data and a acknowledgement message to the password in the form of one of audio data and image data in which the user characteristic is reflected. 
         [0046]    The receiving may include receiving a random number, which is used to an authentication of the first user authentication data, after transmitting a acknowledgement message to the first user authentication data. 
         [0047]    The calculating may include calculating the second user authentication data by applying the received password, the received random number and the received public information to a Hash function. 
         [0048]    The calculating may include calculating a random challenge using the received public information. In this case, the transmitting may include transmitting the calculated random challenge. 
         [0049]    The receiving may include receiving the password in the form of one of an audio date and an image date in which the user characteristic is reflected. 
         [0050]    The communication method may further include comparing whether the first user authentication data is substantially identical to the second user authentication data. In this case, the displaying may include displaying the comparison result of the comparing to inform a user of the comparison result. 
         [0051]    The receiving may include receiving the first user authentication data and the public information once at first, and refusing to receive the first user authentication data and the public information after that time. 
         [0052]    Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0053]    The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, wherein; 
           [0054]      FIG. 1  is a block diagram illustrating an authentication system to which communication apparatuses according to an exemplary embodiment of the present invention are applied; 
           [0055]      FIG. 2  is a flow chart illustrating a communication method according to an exemplary embodiment of the present invention, which is used in the authentication system; and 
           [0056]      FIG. 3  is a flow chart illustrating a process of confirming whether a first communication apparatus possesses a secret key for a public key in the authentication system. 
       
    
    
       [0057]    Throughout the drawings, it should be noted that the same drawing reference numerals will be understood to refer to the same elements, features, and structures. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0058]    The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention and are merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
         [0059]      FIG. 1  is a block diagram illustrating an authentication system to which communication apparatuses according to an exemplary embodiment of the present invention are applied. Referring to  FIG. 1 , the authentication system includes a first communication apparatus  100  and a second communication apparatus  200 , which can communicate with each other through a user characteristic sensing channel. Here, the user characteristic sensing channel refers to a channel, which transmits voice data or image data capable of recognizing users in intercommunication. 
         [0060]    In the authentication system, for clarity and conciseness, a mutual authentication between the communication apparatuses to a public key, which is an example of public information, will be explained as an example of authentication. Here, it should be noted that the public key is merely an example of the public information, and the public information is not always limited to that. 
         [0061]    First, referring to the first communication apparatus  100 , the first communication apparatus  100  includes a first key inputting unit  110 , a microphone  120 , a first audio codec  130 , a first photographing unit  140 , a first video codec  150 , a first storing unit  160 , a first calculating unit  170 , a first transmitting and receiving unit  180 , and a first displaying unit  190 . 
         [0062]    The first key inputting unit  110  comprises a key button, a touch panel or the like, and receives a one-time password and required information from a user. Here, the one-time password refers to a password, which is used for authenticating the public information, such as, the public key, while the plurality of communication apparatus communicate with each other. 
         [0063]    The microphone  120  converts an acoustic signal input from the outside into an electrical signal. 
         [0064]    The first audio codec  130  converts data, such as a music, a voice, or the like, input from the microphone  120  from an analogue signal into a digital signal, which is recognizable by the first communication apparatus  100 , and then compresses the converted data in a reference format. And, if necessary, the first audio codec  130  extracts the compressed data again, converts the extracted data from the digital signal into the analogue signal, and then outputs the converted data through a speaker (not illustrated). 
         [0065]    The first photographing unit  140  receives an optic or light signal from an external subject for photography through a lens (not illustrated), and converts the received light signal into an electric signal. 
         [0066]    And the first photographing unit  140  performs signal processing, such as a gain adjustment, a noise removal, a gamma adjustment, a luminance signal separation, and so on, on the electric signal. 
         [0067]    The first video codec  150  compresses input data in a reference format, and if necessary, extracts the compressed data again. 
         [0068]    In an exemplary implementation, the first video codec  150  compresses data input from the first photographing unit  140  in a reference format, and then transmits the compressed data to the first transmitting and receiving unit  180 . Also, the first video codec  150  extracts image data of the second communication apparatus  200  input from the first transmitting and receiving unit  180 , performs signal processing on the extracted image data, and then transmits the processed data to the first displaying unit  190 . 
         [0069]    The first storing unit  160  stores all sorts of programs required for operating the first communication apparatus  100 , a cryptographic algorithm, and a public key and a Hash function of the first communication apparatus  100 . 
         [0070]    The first calculating unit  170  produces a random number R using a random function, and a first user authentication data H using the Hash function. Here, the first calculating unit  170  can produce a null as the random number R. The principal of producing the first user authentication data H will be described with reference to the following mathematical formula 1 
         [0000]        H =Hash( K, R,PW )   [Mathematical formula 1] 
         [0071]    Here, H is the first user authentication data, Hash is the Hash function, K is the public key, R is the random number, and PW is the one-time password. 
         [0072]    That is, the first calculating unit  150  produces the first user authentication data H by applying the one-time password received from the first inputting unit  110 , the random number R, and the public key read from the first storing unit  160  to the Hash function. 
         [0073]    Here, the Hash function refers to a function to compress an input value with an optional length into an output value with a reference length, and has properties as follows. It is not possible to calculatively find an input value to a given output value and to calculatively find another input value of producing the same output value to a given input value, on the Hash function. Also, it is not possible to calculatively find two different optional values of producing the same output value on the Hash function. 
         [0074]    The Hash function of satisfying the properties as described as above is one of important functions, which are applied to an authentication, a denial prevention, an integrity, and the like of data. Accordingly, in an exemplary embodiment of the present invention, communication apparatuses, which communicate with the first communication apparatus  100 , will be configured to share for the Hash function. That is, in the authentication system of  FIG. 1 , the first and the second communication apparatuses  100  and  200  share for the Hash function. 
         [0075]    Also, since the Hash function is an example of one-way functions, an exemplary embodiment of the present invention may employ other one-way function as well as the Hash function. 
         [0076]    The first transmitting and receiving unit  180  transmits the first user authentication data H and the random number R calculated by the first calculating unit  170  and the public key K read from the first storing unit  160  to the second communication apparatus  200 . At this time, the first transmitting and receiving unit  180  transmits the first user authentication data H prior to transmitting the one-time password, and transmits the random number R after confirming a receipt of the one-time password from the second communication apparatus  200 . 
         [0077]    For example, the first user authentication data H, the public key K, and the random number R are transmitted through a network channel. Since the network channel is a channel to transmit and receive data, such as a text and the like, the first transmitting and receiving unit  180  transmits the first user authentication data H, the public key K, and the random number R in the form of text data. 
         [0078]    Also, the first transmitting and receiving unit  180  receives a acknowledgement message to the transmitted first user authentication data from the second communication apparatus  200 , and transmits and receives data, such as a voice, an image, a letter, and the like. 
         [0079]    That is, the first transmitting and receiving unit  180  transmits image data and audio data received from the first video codec  150  and the first audio codec  130 , respectively. For example, the acknowledgement message to the first user authentication data is received through the user characteristic sensing channel. Since the user characteristic sensing channel is a channel to transmit and receive an image and a voice through which a user can determine the other party&#39;s characteristics, the first transmitting and receiving unit  180  receives the acknowledgement message to the first user authentication data in the form of image data and voice data. For example, the user characteristic sensing channel and the network channel may be a physically identical channel, but an exemplary embodiment of the present invention is not limited to that. 
         [0080]    The first displaying unit  190  includes a liquid display panel (LCD), and the like, and displays information on operations of the first communication apparatus  100 , system information, operation conditions of the first communication apparatus  100 , user interfaces, and the like. That is, the first displaying unit  190  displays the acknowledgement message to the first user authentication data received from the second communication apparatus  200 , and an image signal of the second communication apparatus  200  received through the first transmitting and receiving unit  180 . 
         [0081]    Next, referring to the second communication apparatus  200 , the second communication apparatus  200  includes a second transmitting and receiving unit  210 , a second audio codec  220 , a second photographing unit  230 , a second video codec  240 , a second storing unit  250 , a second key inputting unit  260 , a second calculating unit  270 , a second comparing unit  280  and a second displaying unit  290 . 
         [0082]    The second transmitting and receiving unit  210  receive the first user authentication data H, the random number R and the public key K from the first communication apparatus  100 . At this time, the second transmitting and receiving unit  210  transmits the first user authentication data H and the public key K once at first, and refuse to receive the first user authentication data H and the public key after that time. For example, the first user authentication data H, the public key K, and the random number R can be received through the network channel, but an exemplary embodiment of the present invention is not limited to that. 
         [0083]    Also, the second transmitting and receiving unit  210  transmits a acknowledgement message to the first user authentication data H to the first communication apparatus  100  when receiving the first user authentication data H, and transmits and receives data, such as a voice, an image; a letter, and the like. When the first user authentication data H is received through the second transmitting and receiving unit  210 , the second displaying unit  290  outputs at least one out of a message, an alarm, and an icon acknowledging a receipt of the first user authentication data. For example, the second transmitting and receiving unit  210  receives image data and audio data of the first communication apparatus  100  from the first communication apparatus  100 , and transmits image data and audio data of the second communication apparatus  200  to the first communication apparatus  100 . At this time, one of the image data and the audio data includes a one-time password, and the acknowledgement message to the first user authentication data H is transmitted through the user characteristic sensing channel. 
         [0084]    Also, the second transmitting and receiving unit  210  transmits voice data or image data to acknowledge a receipt of the one-time password. That is, when receiving the one-time password, a user of the second communication apparatus  200  informs a user of the first communication apparatus  100  of the reception of the one-time password through a voice or an image. 
         [0085]    The second audio codec  220  converts data, such as a music, a voice, or the like, input from the second transmitting and receiving unit  210  from an analogue signal into a digital signal, which is recognizable by the second communication apparatus  200 , and then compresses the converted data in a reference format. And, if necessary, the second audio codec  220  extracts the compressed data again, converts the extracted data from the digital signal into the analogue signal, and then outputs the converted data through a speaker (not illustrated). According to this, the user can perceive the one-time password included in the audio data. 
         [0086]    The second photographing unit  230  receives an optic or light signal from an external subject for photography through a lens (not illustrated), and converts the received light signal into an electric signal. 
         [0087]    And the second photographing unit  230  performs signal processing, such as a gain adjustment, a noise removal, a gamma adjustment, a luminance signal separation, and the like, on the electric signal. 
         [0088]    The second video codec  240  compresses input data in a reference format, and if necessary, extracts the compressed data again. 
         [0089]    In an exemplary implementation, the second video codec  240  compresses data received from the second photographing unit  230  in the reference format, and then transmits the compressed data to the second transmitting and receiving unit  210 . Also, the second video codec  240  extracts image data of the first communication apparatus  100  input from the second transmitting and receiving unit  210 , performs signal processing on the extracted image data, and then transmits the processed data to the second displaying unit  290 . 
         [0090]    The second storing unit  250  stores the first user authentication data H and the public key K received from the second transmitting and receiving unit  210 , and stores all sorts of programs required for operating the second communication apparatus  200 , a cryptographic algorithm, a public key and a Hash function. The Hash function stored in the second storing unit  250  is shared with the first communication apparatus  100 . 
         [0091]    The second key inputting unit  260  comprises a key button, a touch panel or the like, and receives a one-time password and required information from a user. At this time, the one-time password input from the user is the very same one-time password, which is received from the first communication apparatus  100  and outputted through the speaker. 
         [0092]    That is, if the one-time password input through the microphone  120  from the user of the first communication apparatus  100  is processed by the first video codec  130  and then transmitted to the second communication apparatus  200 , the user of the second communication apparatus  200  perceives the one-time password received from the first communication apparatus  100 , and inputs the received one-time password through the second key inputting unit  260 . 
         [0093]    The second calculating unit  270  calculates a second user authentication data H′ using the Hash function and the public key K read from the second storing unit  250 , the one-time password PW received from the second key inputting unit  260 , and the random number R. The principal of producing the second user authentication data H′ will be described with reference to the following mathematical formula 2. 
         [0000]        H′= Hash( K, R,PW )   [Mathematical formula 2] 
         [0094]    Here, H′ is the second user authentication data, Hash is the Hash function, K is the public key, R is the random number, and PW is the one-time password. 
         [0095]    That is, the second calculating unit  270  produces the second user authentication data H′ by applying the public key K read from the second storing unit  250 , the one-time password received from the second key inputting unit  260 , the random number R received from the second transmitting and receiving unit  210  to the Hash function. 
         [0096]    The comparing unit  280  compares whether the first user authentication data H read from the second storing unit  250  is substantially identical to the second user authentication data H′ calculated by the second calculating unit  270 . And the comparing unit  280  informs the user of the comparison result through the second displaying unit  280   
         [0097]      FIG. 2  is a flow chart illustrating a communication method according to an exemplary embodiment of the present invention, which is used in the authentication system. 
         [0098]    Referring to  FIG. 2 , first, the first and the second communication apparatuses  100  and  200  communicate with each other through a user characteristic sensing channel at step S 310 . Here, the user characteristic sensing channel is a channel to transmit and receive an image and a voice through which users of the first and the second communication apparatuses  100  and  200  can determine the other party&#39;s characteristics. That is, the users of the first and the second communication apparatuses  100  and  200  are in an image or voice communication state, which they can determine the other party&#39;s characteristics. 
         [0099]    Subsequently, the first key inputting unit  110  receives a one-time password from the user of the first communication apparatus  100  at step S 320 . 
         [0100]    And then, the first calculating unit  170  produces a random number R using a random function, and calculates a first user authentication data H at step S 330 . 
         [0101]    To be more specific, the first calculating unit  170  produces the first user authentication data H by applying the produced random number R, the one-time password PW received from the first key inputting unit  110 , and the public key K read from the first storing unit  160  to the Hash function, as in the mathematical formula 1 described above. Here, the first and the second communication apparatuses  100  and  200  share for the Hash function. 
         [0102]    Subsequently, the first transmitting and receiving unit  180  transmits the first user authentication data H and the public key K to the second communication apparatus  200  at step S 340 . At this time, the first transmitting and receiving unit  180  transmits the first user authentication data H and the public key K through a network channel. Here, the network channel and the user characteristic sensing channel may be a physically identical channel, but an exemplary embodiment of the present invention is not limited to that. 
         [0103]    And then, the second transmitting and receiving unit  210  stores the first user authentication data H and the public key K received through the network channel in the second storing unit  250  at step S 350 . At this time, the second transmitting and receiving unit  210  receives the first user authentication data H and the public key K once at first, and refuses to receive the first user authentication data H and the public key K after that time. 
         [0104]    Subsequently, the second transmitting and receiving unit  210  transmits an acknowledgement message to the received first user authentication data H to the first communication apparatus  100  at step S 355 . Here, the acknowledgement message to the first user authentication data H is transmitted through the user characteristic sensing channel. 
         [0105]    That is, the second transmitting and receiving unit  210  transmits the acknowledgement message to the first user authentication data H in the form of image data and audio data. 
         [0106]    And the second transmitting and receiving unit  210  receives the one-time password transmitted from the first communication apparatus  100  after the first communication apparatus  100  receives the acknowledgement message to the first user authentication data H at step S 360 . 
         [0107]    That is, the second transmitting and receiving unit  210  receives a one-time password transmitted by a voice of the user of the first communication apparatus  100 . At this time, the second transmitting and receiving unit  210  receives the one-time password through the user characteristic sensing channel. 
         [0108]    To be more specific, when the user of the first communication apparatus  100  inputs the one-time password through the microphone  120 , the first transmitting and receiving unit  180  transmits image data and audio data processed by the first video codec  150  and the first audio codec  130 , respectively, through the user characteristic sensing channel to the second communication apparatus  200 . Then, the second transmitting and receiving unit  210  receives the one-time password included in either the image data or the audio data. Here, the one-time password input through the microphone  120  is substantially identical to the one-time password input by the user at and through first key inputting unit  110 . 
         [0109]    When the one-time password is received, the second displaying unit  290  displays the received one-time password, and the second transmitting and receiving unit  210  transmits voice or image data of acknowledging a receipt of the one-time password to the first communication apparatus  100 . That is, after receiving the one-time password, the user of the second communication apparatus  200  acknowledges the receipt of the one-time password to the user of the first communication apparatus  100  through a voice or an image. 
         [0110]    After the acknowledgment to the receipt of the one-time password from the second communication apparatus  200 , the first transmitting and receiving unit  180  transmits the random number R produced by the first calculating unit  170  at step S 365 . That is, the first transmitting and receiving unit  180  transmits the random number R used in the calculation of the first user authentication data H to the second communication apparatus  200 . Here, the random number R is transmitted through the user characteristic sensing channel to the second communication apparatus  200 . 
         [0111]    When the random number R is received from the first communication apparatus  100 , the second key inputting unit  260  receives the one-time password from the user of the second communication apparatus  200  at step S 370 . That is, the user of the second communication apparatus  200  inputs the one-time password received at the step  360  through the second key inputting unit  260 . 
         [0112]    Subsequently, the second calculating unit  270  calculates a second user authentication data H′ by applying the first user authentication data H, the public key K, the one-time password PW and the random number R to the Hash function at step S 375 . 
         [0113]    That is, the second calculating unit  270  calculates the second user authentication data H′ by applying the public key read from the second storing unit  250 , the random number R received from the second transmitting and receiving unit  210 , and the one-time password PW received from the second key inputting unit  260  to the Hash function, as in the mathematical formula 2 described above. 
         [0114]    And then, the comparing unit  280  compares whether the first user authentication data H read from the second storing unit  250  is substantially identical to the second user authentication data H′ calculated by the second calculating unit  270  (H=H′) at step S 380 . 
         [0115]    Subsequently, the displaying unit  290  displays the comparison result of the comparing unit  280  to inform the user at step S 385 . According to this, it is possible for the second communication apparatus  200  to confirm whether the other party, which is in the communication at present, is the first communication apparatus  100 . That is, the user of the second communication apparatus  200  can perceive whether the other party, which is in the communication at present, is the same other party, which she/he wants to communicate with her/him, or an intermediate invader, which she/he does not want to communicate with her/him. 
         [0116]    Although in the communication method according to an exemplary embodiment of the present invention, the public key K is explained as transmitted along with the first user authentication data H at the step  340 , an exemplary embodiment of the present invention is not limited to that. That is, the public key K can be transmitted at any one of the steps  320  through  385 . For example, the public key K is not transmitted along with the first user authentication data H at the step  340 , but along with the random number R at the step  365 . 
         [0117]      FIG. 3  is a flow chart illustrating a process of confirming whether a first communication apparatus possesses a secret key for a public key in the authentication system as described above. 
         [0118]    Referring to  FIG. 3 , since processes of authenticating the public key in the state at step S 310  which the first and the second communication apparatuses  100  and  200  communicates with each other are the same as those of the steps S 320  through S 385 , descriptions thereof will be omitted, and hereinafter, processes after displaying the comparison result between the first and the second user authentication data as the step  385  will be described. 
         [0119]    First, the second calculating unit  270  produces a random number and calculates a random challenge using the public key of the first communication apparatus  100  at step S 410 , and then transmits the produced random number and the calculated random challenge at step S 420 . 
         [0120]    Here, the random challenge refers to a question message to confirm whether the first communication apparatus  100  possesses a secret key for the public key. Since a method of calculating the random challenge is the same as a conventional method used in the art of key authentication, descriptions thereof will be omitted. 
         [0121]    Subsequently, the first calculating unit  170  produces a response to the random challenge received through the first transmitting and receiving unit  180 , using a private key of the first communication apparatus  100  at step S 430 , and transmits the produced response to the second communication apparatus  200  at step S 440 . 
         [0122]    And the second comparing unit  280  determines whether the response to the random challenge received through the second transmitting and receiving unit  210  is a right response, and then displays the determination result on the second displaying unit  290  at step S 450 . 
         [0123]    That is, the second comparing unit  280  determines whether the response to the random challenge is a response, which meets the question message transmitted to confirm whether the first communication apparatus  100  possesses the secret key for the public key at the step S 420 , and displays the determination result on the second displaying unit  290  to inform the user. According to this, the user of the second communication apparatus  200  can perceive whether the first communication apparatus  100  possesses the secret key for the public key. 
         [0124]    In the communication method according to an exemplary embodiment of the present invention and the authentication system employing the same, one communication apparatus is explained as authenticating the public information, but an exemplary embodiment of the present invention is not limited to that. An exemplary implementation of the present invention is applicable to public information authentication of a plurality of communication apparatuses, each of which a corresponding user want to authenticate a public information. That is, the first communication apparatus as well as the second communication apparatus can authenticate the public information by applying the communication method of an exemplary embodiment of the present invention to a Key agreement protocol of Diffie-Hellman. 
         [0125]    Also, the communication method according to an exemplary embodiment of the present invention and the authentication system employing the same can be used even when authenticating the public information on the basis of user characteristics, such as a facial recognition, a fingerprint recognition, and the like. 
         [0126]    Although the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various modifications and changes in forms and details can be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Therefore, it shall be considered that such modifications, changes and equivalents thereof are all included within the scope of the present invention.