Patent Publication Number: US-2009240941-A1

Title: Method and apparatus for authenticating device in multi domain home network environment

Description:
TECHNICAL FIELD 
     The present invention relates to a method and apparatus for authenticating a device in a multi domain home network environment, and more particularly, to a method and apparatus for authenticating a device in a multi domain home network environment thereby minimizing a user&#39;s intervention and device operation. 
     BACKGROUND ART 
     Devices are conventionally authenticated using a symmetric key and a public key infrastructure (PKI). 
     By using the symmetric key, two devices share the same key, confirm that either has a common key, and authenticate each other. In this case, it is very difficult to manage communicating two devices to share the same key, and since the more the number of devices increases, the more the number of keys shared by devices increases, it is difficult to increase the number of devices. 
     The PKI makes it easier to manage a key and has a global structure requiring no identification of local domains, whereas a user must authorize a third party to issue a certificate of a user&#39;s device, and a root certification authority (hereinafter referred to as a “root CA”) is authorized to issue all certificates, so that the more the number of devices increases, the more the number of lower CAs and the size of a certificate revocation list (CRL) increase, which increases costs incurred in the management of the lower CAs and CRL. Further, when authentication between devices having limited computing power is performed, it is unlikely to build and verify the path of certificates. Although a private authentication method or a local authentication method such as a simple PKI (SPKI) has been proposed in order to overcome the above defects of the PKI, each device needs a certificate of each local domain, which causes inconvenience with users who manage devices. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention provides a method and apparatus for authenticating a device in a multi domain home network environment where a user&#39;s intervention is minimized for easier use of a non-expert. 
     The present invention also provides a method and apparatus for authenticating a device in a multi domain home network environment where an authentication operation of a device having limited performance is minimized. 
     The present invention also provides a method and apparatus for authenticating a device in a multi domain home network environment that can be easily extended although the number of devices increases. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a device authentication method performed by a home gateway in a multi domain home network environment including a plurality of local domains, the method comprising; receiving a cross-domain certificate used to authenticate the home gateway from a device registered to another local domain by making a mutual link agreement between the local domain and the another local domain through a public key infrastructure (PKI) to authenticate a device registered to the another local domain; issuing a local domain certificate used in a local domain to a device requesting registration; and verifying whether a service request is valid through the local domain certificate or the cross-domain certificate with regard to a device requesting the service. 
     The receiving a cross-domain certificate may comprise: requesting the mutual link agreement between local domains to a home gateway of the another local domain; receiving the cross-domain certificate authenticating the mutual link agreement between local domains from the home gateway receiving a request of the mutual link agreement; and receiving identity of a local domain that made the mutual link agreement and a public key of the home gateway of the local domain and storing the identity and the public key. 
     The issuing a local domain certificate may comprise: generating and sending a first random value to the device; receiving a value obtained by hashing at least one of the first random value, identity of the device, a second random value generated in the device, and a public key of the device using a secret key of the device; sending the hash value received from the device to a server sharing the secret key with the device to allow the hash value authenticated in the server; and if the hash value is verified to be valid, accepting the registration request of the device. 
     The verifying whether a service request is valid may further comprise: sending the first random value to the device requesting the service; receiving from the device the second random value generated in the device, the local domain certificate included in the device, and the value obtained by signing the first random value using the public key of the device; verifying the signature and the local domain certificate; and if the signature and the local domain certificate are verified to be valid, generating a session key to be shared with the device, and sending to the device a message obtained by encrypting the session key using the public key of the device and a message obtained by signing the session key and the second random value using the public key of the home gateway. 
     The verifying of whether the service request is valid may further comprise: if it is impossible to authenticate the local domain certificate, confirming information of a home local domain from the local domain certificate; requesting the home local domain to make the mutual link agreement, verifying the local domain certificate of the device using a public key of the home local domain acquired by making of the mutual link agreement, and verifying the signature received from the device; and if the verification result is valid, generating a session key to be shared with the device, and sending to the device a message obtained by encrypting the session key using the public key of the device, a message obtained by signing the session key and the second random value using the public key of the home gateway, and the cross-domain certificate issued from the home local domain. 
     According to another aspect of the present invention, there is provided a device authentication apparatus in a multi domain home network environment including a plurality of local domains, the apparatus comprising; a cross-domain authentication means making a mutual link agreement between a local domain and another local domain to authenticate a device registered to the another local domain through a PKI, and exchanging cross-domain certificates used to establish a public key and the agreement fact; a device registration means verifying the device and issuing a local domain certificate used in a local domain to a device requesting registration; and a device verification means receiving the local domain certificate from a device requesting a service, verifying the local domain certificate using a public key thereof or a public key acquired from the cross-domain authentication means, if the local domain certificate is valid, generating a session key to be shared with the device requesting the service, and sending the session key to the device. 
     According to another aspect of the present invention, there is provided a device authentication method performed by a server in a multi domain home network environment including a plurality of local domains, the method comprising; sharing and storing a secret key and secret ID provided to each device; receiving a request of a home gateway to verify a device that is to be registered; verifying the home gateway using a global certificate issued through a PKI; and the server, if the global certificate of the home gateway is valid, verifying the device using the secret key and secret ID provided to each device; and sending a verification result message of the device to the home gateway. 
     According to another aspect of the present invention, there is provided a device authentication method performed by a device in a multi domain home network environment including a plurality of local domains, the method comprising; storing a secret key provided for each device when the device is manufactured; requesting registration of a home local domain to a home gateway; as information used to verify the device, providing the home gateway with a value obtained by hashing at least one of a first random value provided from the home gateway according to the request, identity of the device, a second random value generated by the device, and a public key of the device using the secret key of the device; receiving from the home gateway a verification result including a message obtained by encrypting a public key of the home gateway and the second random value using the secret key of the device and a local domain certificate available in the home local domain issued by the home gateway; 
     and verifying the encrypted messages using the secret key of the device, if both messages are valid, establishing the public key of the home gateway as a public key of a root certification authority of the device, and storing the local domain certificate. 
     The method may further comprise: sending a service request message to the home gateway of the home local domain to which the device is registered; as information used to authenticate a device requesting a service, providing the home gateway with a message obtained by encrypting a third random value generated by the home gateway using a public key of the device, a local domain certificate of the device, and a fourth random value generated by the device; receiving a message obtained by encrypting a session key, between the device and the home gateway, generated from the home gateway that verifies the message using the public key of the device, and a message obtained by signing the session key and the fourth random value using the public key of the home gateway; and if the signed message is verified to be valid, decrypting the encrypted message using the public key of the device and acquiring the session key. 
     The method may further comprise: sending the service request message to a home gateway of a local domain other than the home local domain to which the device is registered; as information used to authenticate a device requesting a service, providing the home gateway with a message obtained by encrypting a third random value generated by the home gateway using a public key of the device, a local domain certificate of the device, and a fourth random value generated by the device; receiving a message obtained by encrypting a session key, between the device and the home gateway, generated from the home gateway that verifies the message using the public key of the device, a message obtained by signing the session key and the fourth random value using the public key of the home gateway, and a cross-domain certificate used to establish an agreement between the home gateway and the home gateway of the home local domain; and verifying the signed message and the cross-domain certificate, if the cross-domain certificate and the signature are valid, decrypting the encrypted message using the public key of the device and acquiring the session key. 
     Advantageous Effects 
     As described above, the present invention divides an authentication layer into two authentication layers, and authenticates a device through an agreement between local domains, so that root CAs are distributed to home gateways, thereby securing extension, the registration of the device makes it possible to authenticate the device requesting a service in a different local domain, thereby minimizing a user&#39;s intervention, a certificate authentication path includes a single certificate, thereby reducing costs incurred in the building and verification of the path, after an agreement between local domains is finished, and all authentication process is carried out via communication inside local domains, thereby performing efficient authentication without access to outside local domains. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates the structure of a device authentication system in a multi domain home network environment according to an embodiment of the present invention; 
         FIG. 2  is a flowchart illustrating a device registration operation of purchasing a device by a user and registering the device to a home gateway according to a device authentication method of the present invention; 
         FIG. 3  is a flowchart illustrating a device authentication operation when a device registered to a home local domain requests a service in a home local domain thereof according to a device authentication method of the present invention; 
         FIG. 4  is a flowchart illustrating an operation of making an agreement between local domains to authenticate a device without an additional registration process when the device registered to a home local domain requests a service in another local domain according to a device authentication method of the present invention; 
         FIG. 5  is a flowchart illustrating an operation of authenticating devices belonging to different local domains that make an agreement there between according to a device authentication method of the present invention; and 
         FIG. 6  is a block diagram of a device authentication apparatus according to an embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Like reference numerals in the drawings denote like elements. 
       FIG. 1  illustrates the structure of a device authentication system in a multi domain home network environment according to an embodiment of the present invention. Referring to  FIG. 1 , the device authentication system comprises a third authentication server  102 , a manufacturing company server  103  that authenticates a device  108  accessing to a home network, home gateways  104  and  105  that are installed at home and relay connections of devices at home and outside, local domains  106  and  107  that are independent home network areas and formed by the home gateways  104  and  105 , and the device  108  connected to the home network. 
     The device authentication system is divided into a first public key-based authentication layer  100  according to a conventional authorized authentication system and a second public key-based authentication layer  101  according to each of the local domains  106  and  107  of the home network. 
     The first public key-based authentication layer  100 , like the conventional authorized authentication system, performs authentication using the third authentication server  102  that serves as a root certification authority (CA). When the device  108  is registered in the home gateways  104  and  105 , the first public key-based authentication layer  100  performs authentication between the manufacturing company server  103  and the home gateways  104  and  105 . When the device  108  registered in the local domain  106  moves to the local domain  107  and requests a service, the first public key-based authentication layer  100  mutually authenticates the home gateways  104  and  105  of the local domains  106  and  107  to make an agreement of device authentication between the two local domains  106  and  107 . Certificates that are issued between the home gateways  104  and  105  to perform the mutual device authentication between the two local domains  106  and  107  are referred to as cross-domain certificates. 
     The second public key-based authentication layer  101  issues certificates to devices registered at home using the home gateways  104  and  105  that serve as root CAs of the local domains  106  and  107 , respectively. The certificates that are issued to the devices registered at home in the home gateways  104  and  105  are referred to as local domain certificates. The local domain certificates are used to authenticate the devices at home. 
     A device authentication method of the present invention based on the device authentication system illustrated in  FIG. 1  may comprise a device registration operation of registering the device  108  in the local domain  106  of the home network, when the device  108  registered in the local domain  106  of the home network moves to the local domain  107 ; an operation of making an agreement between the local domains  106  and  107  to authenticate the device  108  without an additional registration process; and a device authentication operation of authenticating the device  108  when a service is requested in the local domain  107 . 
     The aforementioned device registration operation, operation of making the agreement between the local domains  106  and  107 , and device authentication operation are realized in the home gateways  104  and  105 . 
     Each of the operations will now be described with reference to  FIGS. 2 through 5 . 
     In addition, referring to  FIGS. 2 through 5 , random values used to avoid a replay attack are divided into a first random value that is generated in a home gateway, and a second random value that is generated in the device  108  for the sake of understanding. 
       FIG. 2  is a flowchart illustrating the device registration operation by purchasing a device  200  by a user and registering the device  200  to a home gateway  201  at home according to a device authentication method of the present invention. 
     Referring to  FIG. 2 , the device  200  may be registered to the home gateway  201  of a home network, and a server  202  may verify the device  200  and be managed by a manufacturing company. 
     According to the device authentication method of the present invention, a device manufacturing company safely inserts a secret key K MD  provided to each device into the device  200 , stores identification information ID identifying the device  200  and the secret key K MD  inserted into the device  200  in the server  202 , and shares the ID and the secret key K MD . When the user purchases the device  200 , the device manufacturing company informs the user of a secret ID that is to be shared by the user and the server  202 , and stores the secret ID in the server  202 . The secret key K MD  and secret ID are used to authenticate the device  200  when the device  200  is registered to the home gateway  201 . 
     The home gateway  201  receives its certificate (hereinafter referred to as a “global certificate Gcert H ” from a third authority through a first public key-based authentication layer. 
     In such an environment, the device  200  is authenticated and first registered in accordance with the following processes between the device  200 , the home gateway  201 , and the server  202 . 
     The device  200  sends a registration request message to the home gateway  201  in order for the registration in a home local domain (Operation  203 ). 
     The home gateway  201  that receives the registration request message sends the optionally selected first random value N H  in order to avoid the replay attack (Operation  204 ). 
     The device  200  that sends the registration request message provides the home gateway  201  with information necessary for the authentication of itself. In more detail, the device  200  receives the first random value N H  from the home gateway  201  in response to the registration request message, generates a pair of public key K D  and secret key that is to be used by itself, and provides the home gateway  201  with a value, which is the information necessary for the authentication of itself, obtained by hashing at least one of the device ID D ID  for identifying itself, the public key K D , the second random value N D  generated by itself, and the first random value N H  received from the home gateway  201  by using the secret key K MD  inserted into the device  200  when manufactured (Operation  205 ). 
     The home gateway  201  acquires the secret ID that is provided from the device manufacturing company when the device  200  is purchased (Operation  206 ). 
     The home gateway  201  verifies whether the hash value 
       (D ID ,K D ,N D ,H H )HMAC(K MD ) 
     received from the device  200  and the secret ID are valid by requesting the verification to the server  202  having the secret key K MD  and secret ID. To this end, the home gateway  201  sends a message in which the secret ID and first and second random values N H  and N D  are signed with its secret key K D   −1 , the global certificate Gcert H  issued through the first public key-based authentication layer  100 , and the hash value received from the device  200  to the server  202  (Operation  207 ). 
     The server  202  sequentially verifies the hash value generated by the device  200  among the messages received from the home gateway  201  using the secret key K MD  of the device  200 , the global certificate Gcert H  of the home gateway  201 , and a message signed by the home gateway  201  using a public key K H  of the home gateway  201  included in the global certificate Gcert H . If both messages generated by the device  200  and signed by the home gateway  201  are valid, the server  202  provides the home gateway  201  with the verification result, together with a message generated by hashing the public key K H  of the home gateway  201  and the second random value N D  of the device  200  by using the secret key K MD  of the device  200 , information DevInfo on the device  200 , a message generated by signing the first random value N H  and the device information DevInfo using a public key of the server  202 , and a global certificate Gcert M  of the server  202  (Operation  208 ). 
     The home gateway  201  that receives the response from the server  202  verifies the received signature and global certificate Gcert M , if the message is valid, issues a local domain certificate Lcert D  that is to be used in the second public key-based authentication layer to the device  200 , and sends the message 
       (K H N D )K MD    
     including the hash value obtained by using the secret key K MD  of the device  200 , the local domain certificate Lcert HD , and the device information DevInfo to the device  200  (Operation  209 ). 
     The device  200  verifies the hash value received from the home gateway  201  using the secret key K MD  thereof, if the hash value is valid, establishes the public key K H  of the home gateway  201  acquired from the hash value as a public key of the root CA for the authentication of itself, and uses the issued local domain certificate Lcert D  as a certificate for authenticating itself in the local domain. 
       FIG. 3  is a flowchart illustrating the device authentication operation when a device  300  registered to the home local domain requests a service in a home local domain thereof. 
     Referring to  FIG. 3 , the device  300  is registered to a home gateway  301  of the home local domain to which the device  300  is registered according to the device registration operation illustrated in  FIG. 2 . 
     The device authentication operation is performed in the device  300  and the home gateway  301  according to the following processes. 
     The device  300  sends a service request message to the home gateway  301  (Operation  302 ). The home gateway  301  sends the first random value N H  to the device  300  in order to avoid the replay attack (Operation  303 ). 
     The device  300  provides the home gateway  301  with a value obtained by signing the first random value N H  of the home gateway  301  using the public key K D  thereof, the local domain certificate Lcert D  thereof issued in the registration operation, and the second random value N D  (Operation  304 ). 
     The home gateway  301  verifies the signature of the device  300  and the local domain certificate Lcert D , if the verification result is valid, generates a session key K HD  of the device  300  so that the device  300  can receive the service, encrypts the session key K HD  using the public key K D  of the device  300 , and provides the device  300  with the signature and the encryption key (Operation  305 ). In more detail, in Operation  305 , the home gateway  301  sends a message generated by encrypting the session key K HD  using the public key K D  of the device  300  and the signature thereof with regard to the session key K HD  and second random value N D  to the device  300 . 
     The device  300  verifies the signature received from the home gateway  301  and, if the signature is valid, acquires the session key K HD . 
       FIG. 4  is a flowchart illustrating an operation of making an agreement between local domains for authenticating a device  400  without an additional registration process when the device  400  registered to the home local domain wishes to receive a service in another local domain. 
     When the device registered to a home gateway of the home local domain moves to another local domain (hereinafter, the another local domain is referred to as a “visit local domain”, a device registered to a different local domain needs to be authenticated in a home gateway of the visit local domain so that the device can receive the service in the visit local domain. 
     However, as described above, when the home gateway of the home local domain is used as a root CA, since devices registered to different local domains have no root CA, it is impossible to verify a certificate issued in a different local domain. 
     To address this problem, the device authentication method of the present invention comprises the operation of making the agreement between local domains for mutually authenticating local domains registered between home gateways that serve as root CAs in each of the local domains. 
     Referring to  FIG. 4 , the device  400  visit the local domain other than the home local domain to which the device  400  is registered, a home gateway  401  serves as a root CA of the visit local domain, and a home gateway  402  serves as a root CA of the home local domain. 
     If the device  400  requests the service to the home gateway  401  of the visit local domain (Operation  403 ), the home gateway  401  of the visit local domain sends a first random value N V  to the device  400  that requested the service in order to perform authentication according to the device authentication process described above (Operation  404 ). 
     The device  400 , like the device authentication operation described with reference to  FIG. 3 , sends a value obtained by signing the first random value N V  using a secret key K D   −1  thereof, a local domain certificate Lcert D  thereof received from the home gateway  402  of the home local domain, and a newly generated second random value N D  to the home gateway  401  of the visit local domain  401  (Operation  405 ). 
     The home gateway  401  of the visit local domain verifies the local domain certificate Lcert D  of the device  400 . However, since the home gateway  401  does not issue the local domain certificate Lcert D  of the device  400 , it is impossible to verify the received local domain certificate Lcert D  of the device  400 . Therefore, the home gateway  401  of the visit local domain acquires information on the home local domain included in the received local domain certificate Lcert D  of the device  400 , provides the home gateway  402  of the home local domain to which the device  400  is registered with a global certificate Gcert V  thereof, and requests a link agreement used to authenticate a device registered to another local domain without carrying out a process of registering the device registered to another local domain (Operation  406 ). The global certificate Gcert V  of the home gateway  401  is issued to the home gateway  402  from the third authentication server  102  through the first public key-based authentication layer  100 . 
     The home gateway  402  of the home local domain that receives the agreement request verifies the global certificate Gcert V  of the home gateway  401 , if the global certificate Gcert V  is valid, issues a cross-domain certificate Ccert HV  to the home gateway  401  of the visit local domain, and sends a global certificate Gcert H  that is issued thereto through the first public key-based authentication layer  100  to the home gateway  401  (Operation  407 ). 
     The home gateway  401  of the visit local domain verifies the global certificate Gcert H  of the home gateway  402  of the home local domain, and, if the global certificate Gcert H  is valid, stores a local domain name of the home gateway  402  of the home local domain and a public key of the home gateway  402 . As such, the home gateway  401  of the visit local domain can verify the local domain certificate Lcert D  of the device  400  after verifying the global certificate Gcert H  of the home gateway  402  of the home local domain, thereby verifying the signature of the message received from the device  400  in Operation  405 . If the signature of the message is valid, the home gateway  401  of the visit local domain generates a session key K VD  that is to be shared with the device  400 , and sends a message encrypted using the public key of the device  400 , a message generated by signing the session key K VD  and second random value N D  using the public key thereof, and the cross-domain certificate Ccert HV  issued from the home gateway  402  of the home local domain to the device  400  (Operation  408 ). 
     The device  400  verifies the signature of the home gateway  401  and the cross-domain certificate Ccert HV  to confirm whether the session key K VD  is acquired from the valid home gateway  401 . 
       FIG. 5  is a flowchart illustrating an operation of authenticating a device  500  belonging to different local domains that make an agreement there between. 
     Referring to  FIG. 5 , the device  500  requests a service in a visit local domain that made the agreement with a home local domain to which the device  500  is registered, and a home gateway  501  is included in the visit local domain. 
     For mutual authentication between devices, a client device requests a service, and informs a service device of identity of a home gateway of a local domain to which the client device belongs. The service device requests a public key of the home gateway corresponding to the identity to a home gateway to which the service device belongs, and verifies a certificate of the client device using the public key of the home gateway. When the mutual authentication is necessary, the home gateway of a service local domain sends to the client device a certificate that is issued to the home gateway of the service local domain by the home gateway of the client device. The operation of authenticating the device  500  registered to another local domain using the home gateway of the visit local domain will now be described. 
     If the device  500  requests the service to the home gateway  501  of the visit local domain, the home gateway  501  of the visit local domain sends a first random value N H  to the device  500  (Operation  503 ). 
     The device  500  sends a value obtained by signing the first random value N H  using a secret key thereof, a local domain certificate Lcert thereof, and a newly generated second random value N D  to the home gateway  501  (Operation  504 ). 
     The home gateway  501  verifies the local domain certificate Lcert of the device  500  using the public key of the home gateway of the home local domain obtained through the aforementioned agreement operation, and verifies a signature of the message. If the signature is valid, the home gateway  501  generates a session key K VD  that is to be shared with the device  500 , and sends a message encrypted using a public key of the device  500 , a message obtained by signing the session key K VD  and second random value N D  using the public key of the home gateway  501 , and the cross-domain certificate Ccert HV  issued from the home gateway of the home local domain of the device  500  through the agreement operation to the device  500  in response to the service request (Operation  505 ). 
     The device  500  verifies the cross-domain certificate Ccert HV  to confirm if it is the home gateway that made the agreement, verifies the signature of the received message, and, if the signature is valid, uses the received session key K VD . 
       FIG. 6  is a block diagram of a device authentication apparatus  630  according to an embodiment of the present invention. 
     The device authentication apparatus  630  of the present invention can be realized in a home gateway of each local domain in a multi domain home network environment. 
     Referring to  FIG. 6 , a home gateway  600  includes the device authentication apparatus  630 , a home network interface  610  connects the home gateway  600  and a plurality of devices, and an external network interface  620  connects the home gateway  600  to an external network. Devices, other home gateways, and servers make a communication through the home network interface  610  and the external network interface  620 . 
     The device authentication apparatus  630  includes a cross-domain authentication means  631  that makes a mutual link agreement between a local domain and another local domain to authenticate a device registered to the another local domain through a public key infrastructure (PKI), and exchanges a cross-domain certificate to establish a public key and the agreement fact, a device registration means  632  that verifies the device with respect to a device requesting registration thereof and issues a local domain certificate used in the local domain, and a device verification means  633  that receives the local domain certificate from the device requesting the service, verifies the local domain certificate using a public key thereof or a public key obtained by the cross-domain authentication means  631 , if the local domain certificate is valid, generates a session key that is to be shared with the device requesting the service, and provides the session key with the device. 
     The cross-domain authentication means  631  authenticates an authentication apparatus, i.e., between home gateways, through the PKI. 
     The cross-domain authentication means  631  operates when the device verification means  633  receives the local domain certificate of the device requesting the service but cannot verify the local domain certificate, and makes a link agreement with an authentication apparatus of a home local domain recorded in the received local domain certificate. 
     The device registration means  632  receives verification information from the device requesting the registration thereof, and verifies the received information through a server sharing the verification information with the device. In more detail, the verification information includes a secret key inserted into the device when the device is manufactured and secret ID of the device provided when the device is purchased. 
     The device registration means  632  generates a first random value in order to avoid a replay attack and sends the first random value to the device requesting registration thereof, receives from the device, as the verification information, a value obtained by hashing at least one of the first random value, identity of the device, a second random value generated in the device, and a public key of the device using a secret key of the device, and sends the received hash value to a server sharing the secret key with the device to verify the hash value. Mutual authentication between the server and home gateway is made through the PKI. 
     The device verification means  633  receives from the device requesting the service, as the verification information, a local domain certificate issued to the device, verifies the local domain certificate, if the local domain certificate is valid, generates a session key of the device, encrypts the session key, and provides the device with the encrypted session key and signature. 
     In this regard, when it is impossible to verify the local domain certificate that is issued in a different local domain, the device verification means  633  provides the cross-domain authentication means  631  with information on a home local domain recorded in the received local domain certificate and requests the agreement. 
     If a public key and cross-domain certificate of the home local domain are acquired as a result of the agreement, the device verification means  633  verifies the local domain certificate received via the public key, if the verification result is valid, generates a session key to the device, encrypts the session key, sends the encrypted session key together with signature thereof and the cross-domain certificate to the device, and informs that it is the authentication apparatus that made the agreement. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 
     INDUSTRIAL APPLICABILITY 
     As described above, the present invention divides an authentication layer into two authentication layers, and authenticates a device through an agreement between local domains, so that root CAs are distributed to home gateways, thereby securing extension, the registration of the device makes it possible to authenticate the device requesting a service in a different local domain, thereby minimizing a user&#39;s intervention, a certificate authentication path includes a single certificate, thereby reducing costs incurred in the building and verification of the path, after an agreement between local domains is finished, and all authentication process is carried out via communication inside local domains, thereby performing efficient authentication without access to outside local domains.