Abstract:
A method of constructing a unique domain for preventing content from being illegally used by an unauthorized third person in a public key-based architecture and applying the constructed domain to a home network using universal plug and play (UPnP). The method of the present invention includes selecting one of controlled devices that are operable as a master device and determining the selected device as the master device; performing device authentication in such a manner that other controlled devices receive a secret information block from the determined master device and create certificates; and determining slave devices by selecting one or more devices among the authenticated controlled devices.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims priority of Korean Patent Application No. 10-2003-0068837 filed on Oct. 2, 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
         [0002]     1. Field of Invention  
         [0003]     The present invention relates to the authentication of devices present in a domain, and more particularly, to a method of constructing a unique domain for preventing content from being illegally used by an unauthorized third person in a public key-based architecture and applying the constructed domain to a home network using universal plug and play (UPnP).  
         [0004]     2. Description of the Prior Art  
         [0005]     As digital and communication technologies have increasingly advanced, a variety of content such as audio or video materials have become popular. There have been proposed a variety of techniques for protecting content against illegal copying and unauthorized distribution. In particular, there have been developed techniques by which content is encrypted and only particular devices can decrypt the encrypted content using predetermined rules. For example, the techniques include a DVD content scrambling system, content protection for recordable media (CPRM), digital transmission content protection (DTCP), high definition content protection (HDCP), content protection system architecture (CPSA), digital rights management (DRM) and the like.  
         [0006]     Specifically, with the development of the home network field, there have been proposed techniques for protecting content on a home network. Typical examples of the techniques include “SmartRight” proposed by Thomson Corporation, “OCCAM (Open Conditional Content Access Management”) proposed by Sysco Corporation, or “xCP (extensible Content Protection) Cluster Protocol” proposed by IBM.  
         [0007]     “SmartRight” is a technique by which each device constituting a home network has a smart card including a public key certificate and a key for the home network is created by the exchange of certificates among devices using the smart cards.  
         [0008]     “OCCAM” is a technique by which respective devices in a home can use content by using a unique “ticket” for each piece of content.  
         [0009]     “xCP Cluster Protocol” is a technique based on broadcast encryption, by which the concept of a domain called “cluster” is employed and devices belonging to the same cluster can freely use content among the devices.  
         [0010]     As shown in  FIG. 1 , conventional domain management comprises a master device  110  and slave devices  120 ,  130  and  140  within an authenticated home domain  100 . Domain management is performed between the master device and the slave devices. The process of reproducing content based on the ‘xCP Cluster Protocol’ in accordance with such a configuration of the master device and the slave devices will be described with reference to  FIG. 2 . The process can be roughly divided into the following processes: a cluster-forming process (S 201 ), a device-authenticating process (S 202 ), a content-encrypting process (S 203 ), and a content-decrypting process (S 204 ). The detailed description thereof will be made below. A server that initially connects with a given home network creates a binding ID (hereinafter, referred to as “ID b ”) for the home network (S 200 ). An ID b  may be, a unique identifier for a server established upon manufacture of the server or arbitrarily established by a user. When an ID b  is thus established, a cluster identified with ID b  is formed.  
         [0011]     When a device intends to use content present in the server, the device extracts a media key (hereinafter, referred to as “K m ”) from a media key block (MKB) by using its own device key set (S 210 ). Thereafter, the device creates its own unique key K p  by using “K m ” extracted in step S 210  and its own identifier ID p  (S 212 ).  
         [0012]     When the device intends to go through device authentication, it requests the server to authenticate the device itself (S 214 ).  
         [0013]     Specifically, the device sends its own unique “ID p ,” a “type” indicating the kind of device, and a hash value of the “type” and “ID p ” derived using “K p ,” i.e. h=MAC(ID p ∥type)K p , to the server present in the cluster or an authentication server present outside the home network.  
         [0014]     The server obtains K p ′ from K m  and ID p , and checks whether a hash value, h′=MAC(ID p ∥type)K p ′, which is obtained using K p ′, is identical to the value h already received from the device.  
         [0015]     If it is determined that the value h is equal to the value h′, the server sends the device E(ID b ) K p , which is obtained by encrypting ID b  using K p , and the unique identifier ID p  of the device, and then adds ID p  to an authentication table of the server, “auth.tab.” The authentication for the device can be accomplished by extracting ID b  from E(ID b ) K p  received from the server (S 216 ).  
         [0016]     After the device authentication has been completed, the server encrypts content to be transmitted to the device (S 203 ). A binding key (hereinafter, referred to as “K b ”) is first created using ID b , auth.tab and K m . Here, K b  meets a formula such as K b =H[ID b  ⊕ H[auth.tab], K m ].  
         [0017]     After K b  is created, the server encrypts the content using a title key (hereinafter, referred to as “K t ”) for protecting the content (S 222 ). Meanwhile, each piece of content contains usage rule (UR) information including copy control information, information on whether the content is allowed to be distributed to the outside, a right to use the content, a valid use period, and the like. The UR information and K t  are encrypted using K b  to produce E(K t  ⊕ H[UR]K b ) (S 224 ).  
         [0018]     Meanwhile, the device receives the “auth.tab” from the server, and K b  is obtained from K b =H[ID b  ⊕ H[auth.tab], K m ] using the previously extracted K m  and ID b  (S 230 ). Further, after K t  is extracted from E(K t  ⊕ H[UR]K b ) (S 232 ), the content received from the server is decrypted using the extracted K t  (S 234 ).  
         [0019]     In the xCp cluster protocol operating as described above, all devices capable of communicating with the server can automatically join a domain without the process of selecting devices that will join the domain. Further, since ID b  is fixed, the values of K b , K t , and the like can be calculated even when the device is put outside the domain. However, there is inconvenience in that whenever each device creates its new K b , the device should receive the auth.tab from the server to calculate the new K b . Accordingly, there is a need for more secure protection of content through construction of a unique home domain and involvement of a user in device authentication.  
         [0020]     Meanwhile, DRM serves as an essential component in the development of the digital industry and also plays an essential role in a home network. Accordingly, an increased need exists for implementing the domain management model described above in the home network. As described above, the related art for applying the domain management technique to a home network uses a direct communication scheme between the master and slave devices in the home network, as shown in  FIG. 1 . This scheme needs to develop communication protocols adapted for respective domain management. Thus, there is a problem in that compatibility with respective devices is deteriorated. Accordingly, measures to efficiently solve the problem are required. Recently, a lot of companies all over the world have been interested in UPnP (Universal Plug and Play), which has emerged as home network middleware, and produce many products supporting UPnP. UPnP has many advantages in that it can be smoothly incorporated into existing networks due to the use of conventional standard Internet protocols and does not depend on specific operating systems, physical media, or the like. However, since a method of implementing domain management through UPnP remains unknown, there is a need for a method of effectively implementing domain management using UPnP.  
       SUMMARY OF THE INVENTION  
       [0021]     The present invention is conceived to solve the problems in the related art. An object of the present invention is to provide a method of more safely constructing a domain independent of the outside through the direct involvement of a user in constructing the domain, and preventing content from being illegally used by a third person.  
         [0022]     Another object of the present invention is to provide a method of implementing more efficient domain management using UPnP when the domain-constructing method is applied to a home network.  
         [0023]     According to an aspect of the present invention for achieving the objects, there is provided a method of constructing a domain based on a public key and implementing the domain through UPnP so that a unique domain can be constructed to allow only an authorized user to use content in a public-key based architecture in a home network, comprising a first step of selecting one of controlled devices that are operable as a master device and determining the selected device as the master device; a second step of performing device authentication in such a manner that other controlled devices receive a secret information block from the determined master device and create certificates; and a third step of determining slave devices by selecting one or more devices among the authenticated controlled devices.  
         [0024]     The first step may comprise the steps of: notifying a control point that the controlled devices are connected; obtaining, by the control point, device information and DRM information of the controlled devices; selecting the master device among the controlled devices by using the DRM information; and setting the controlled device selected as the master device to a master mode and providing a list of devices to the controlled devices.  
         [0025]     The second step may comprise the steps of: receiving, by the determined master device, the secret information block from an external server; delivering the received secret information block to the controlled devices except the master device; extracting secret values and creating the certificates using the delivered secret information block; and verifying the certificates and preparing a list of authenticated devices by using the created certificates, device IDs and public keys.  
         [0026]     The third step may comprise the steps of: if the devices authenticated in the second step have no domain attributes, displaying a list of these devices to the user; selecting the slave devices among the listed devices; receiving a list of selected slave devices and creating a domain ID and a domain key; and encrypting the domain ID and the domain key using public keys.  
         [0027]     In the method, important ones of functions of the control point in UPnP may be taken over by the master device and the control point deals with tasks related to user interfaces.  
         [0028]     Further, the master device and the slave devices may be determined after manager authentication is performed by obtaining manager authentication information from the master device.  
         [0029]     Moreover, selecting the master device and the slave devices may be performed by means of user selection through user interfaces. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0031]      FIG. 1  shows a conventional domain management configuration;  
         [0032]      FIG. 2  is a flowchart illustrating the process of reproducing content based on ‘xCP Cluster Protocol’ in accordance with a conventional master-slave configuration;  
         [0033]      FIG. 3  illustrates a method of constructing a domain in a public key-based architecture according to the present invention;  
         [0034]      FIG. 4  is a block diagram showing an example in which the domain-constructing method of the present invention is applied to UPnP;  
         [0035]      FIG. 5  illustrates a general UPnP operation performed between a control point and controlled devices;  
         [0036]      FIG. 6  illustrates the process of determining a master device according to a first embodiment of the present invention;  
         [0037]      FIG. 7  illustrates a device-authenticating process performed subsequent to the process illustrated in  FIG. 6  according to the first embodiment of the present invention;  
         [0038]      FIG. 8  illustrates the process of determining a slave device that is performed subsequent to the process illustrated in  FIG. 7  according to the first embodiment of the present invention;  
         [0039]      FIG. 9A  shows a user interface for receiving a user&#39;s selection to select a master device;  
         [0040]      FIG. 9B  shows a user interface for receiving a manager ID and password from a user to authenticate a manager;  
         [0041]      FIG. 9C  shows a user interface for receiving a user&#39;s selection to select a slave device;  
         [0042]      FIG. 10  illustrates the process of determining a master device according to a second embodiment of the present invention;  
         [0043]      FIG. 11  illustrates a device-authenticating process performed subsequent to the process illustrated in  FIG. 10  according to the second embodiment of the present invention; and  
         [0044]      FIG. 12  illustrates the process of determining a slave device that is performed subsequent to the process illustrated in  FIG. 11  according to the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0046]      FIG. 3  illustrates a method of constructing a domain in a public key-based architecture according to the present invention.  
         [0047]     For the sake of convenience of description of the present invention, it is assumed that each device requesting a master device, which provides content, to transmit content thereto has a set of unique secret keys and a public key or a public key-creating function upon manufacture of the device. At this time, the set of secret keys are used to extract a secret value from a secret information block (hereinafter, referred to as “SIB”) provided in a broadcast encryption manner. The SIB is information for verifying the revocation of devices. Revoked devices cannot extract an intended secret value from the SIB, whereas legitimate devices can extract a common secret value.  
         [0048]     In a single domain, there is a master  320  involved in constructing a domain. The master  320  receives a SIB from an external server  310  in a broadcast encryption manner (S 332 ). Thereafter, the master  320  recognizes the presence of devices  330  in the domain in such a manner that the devices  330  inform the server that they exist in the domain or the master itself  320  discovers the devices  330  through a wired or wireless network (S 334 ).  
         [0049]     When the master  320  provides a user with the devices  330 , which have been recognized by the master, by displaying them on a display unit of the master, the user selects devices  330  that the user wants to register with the domain among the displayed devices (S 336 ). Then, the master  320  sends the SIB, which have been already received from the external server  310 , to the devices  330  selected by the user (S 338 ). Each of the devices  330  that have received the SIB extracts a secret value from the SIB (S 340 ), and prepares a certificate for its own public key using the extracted secret value (S 342 ).  
         [0050]     When each of the devices  330  sends its own certificate, unique identifier (ID) and public key to the master  320  (S 344 ), the master  320  verifies the certificate in order to verify that the device is a legitimate device (S 346 ). Then, the master  320  prepares an authentication list in which unique identifiers (IDs) and public keys of authenticated devices are recorded (S 348 ). The number of devices that can be authenticated is limited by a user.  
         [0051]     After the master  320  prepares the authentication list, the master creates a unique domain ID and a domain key using information on the devices included in the authentication list and a random number created by the master itself (S 350 ). The domain ID is a secret key shared among only devices belonging to a domain formed by the user&#39;s selection and is simultaneously changed whenever there are changes in members constituting the domain. The domain ID is used as a discriminator for distinguishing a domain from other domains.  
         [0052]     The master  320  encrypts the domain ID and the domain key using respective public keys of the authenticated devices  330  present in the domain and then transmits the encrypted domain ID and domain key to the authenticated devices  330 . The devices  330  restore the domain key using their own secret keys (S 354 ). Thus, the domain for using the content is finally formed. When the domain for sharing the content is formed, the master  320  encrypts the content using a content key that in turn is encrypted using the domain key. When the devices, which want to use the content, decrypt the encrypted content using the domain key, the devices can use the content.  
         [0053]      FIG. 4  is a block diagram showing an example in which the domain-constructing method of the present invention is applied to UPnP.  
         [0054]     Each of controlled devices  110  to  160  receives/sends commands and also provides their own services under the control of a control point  190 . A domain is constructed by designating one device of the controlled devices as a master device  110  and designating devices  120 ,  130  and  140 , which have been selected by a user, among the remaining devices, as slave devices. Among the controlled devices, the devices  150  and  160  that have been not designated as master or slave devices, i.e. the ones that have not been included in the domain are called guest devices. The master device  110  and the slave devices  120  to  140  construct an authenticated home domain, and the control point  190  and the controlled devices  110  to  160  constructs a home network  200  as a whole.  
         [0055]      FIG. 5  illustrates a general UPnP operation performed between the control point and the controlled devices. First, an addressing step is performed. UPnP networking is based on a TCP/IP protocol of which an essential point is an addressing function. Each device should have a dynamic host configuration protocol (DHCP) client. When the device is first connected to a network, the device searches for a DHCP server. If there is a DHCP server, the device uses an IP address allocated thereto. If there is no available DHCP server, the device uses an “auto IP” to secure an address.  
         [0056]     Next, a discovery step is performed. Once the device is connected to the network and a proper address is allocated thereto, a discovery operation can be performed. The discovery operation is processed using a simple service discovery protocol (SSDP). When the device is added to the network, the SSDP functions to notify the control point present in the network of services provided by the device.  
         [0057]     Next, a description step is performed subsequent to the UPnP networking. Although the control point has discovered the device, the control point still has little information on the device. If the control point intends to obtain detailed information on the device and its function and cooperates with the device, the control point should check a description of the device from a discovery message and a URL provided by the relevant device. The UPnP description of the device is expressed in XML, and includes unique manufacture information of the manufacturer of the device (for example, model name, serial number, manufacturer&#39;s name, manufacturer&#39;s URL, etc). Further, this description also includes lists of embedded devices and services as well as URLs for control, eventing and presentation.  
         [0058]     After the aforementioned steps of addressing, discovery and description, a UPnP step is substantially performed. The UPnP step is performed through operations for control, eventing, presentation and the like. In the control operation, the control point secures a description of the device and then performs indispensable tasks for control of the device. In order to control the device, the control point sends an operation command to the device for a service provided by the device. To this end, the control point sends a proper control message to a control URL (available from the device description) for the device&#39;s service. The control message is also expressed in XML using a simple object access protocol (SOAP). In response to the control message, the relevant service then provides a specific operation value or a fault code.  
         [0059]     In the eventing operation, when each device is subjected to a change in its status due to the reception of the command, it notifies the control point of the status change through an event message. The event message includes the names of one or more status variables and the current values of these variables, and is expressed in XML and formatted using a generic event notification architecture (GENA). The contents of the event are periodically updated and the control point is continuously notified of the updated contents of the event. Further, a subscription may be canceled using the GENA.  
         [0060]     As for the presentation operation, if the device has a URL for presentation, the control point can search a page through the URL and load the page in a browser. Users can control the device or refer to the status of the device using the page. The level at which these functions can be performed depends on the presentation page and a specific function of the device.  
         [0061]     FIGS.  6  to  8  illustrate processes performed according to a first embodiment of the present invention. Among the figures,  FIG. 6  illustrates the process of determining a master device. First, all the controlled devices  110  to  160  notify the control point  190  that they have been connected to the home network by using the SSDP (S 601 ). Then, the control point  190  obtains device information and DRM information from the devices  110  to  160  (S 602 ) through a HTTP. Here, device information means general device information for use in UPnP, and DRM information means a device attribute and a device mode. The device attribute is a value for use in determining whether the controlled device can be operated as a master device in the domain. Further, the device mode is a value enabling determination on whether the device is currently operated as a master, slave or guest. All the controlled devices are initially set as guests. Thereafter, if the devices are set as a master or slaves, the value of the device mode may be changed.  
         [0062]     It is determined from the device mode of the DRM information whether there is a controlled device operating as a master. If there is no device operating as a master, one of the controlled devices that can be operated as a master device, is selected (S 603 ). Setting a device as a master in such a manner is accomplished by means of user selection through a user interface of the control point  190 . An example of the user interface is shown in  FIG. 9   a.  In the user interface, there are shown “main nexus” and “sub nexus” which are operable as a master and currently set as guests. In order to select a master, a user simply marks a check for one of the devices that the user desires to designate as the master. In the present example, controlled device  1   110  is selected as the master.  
         [0063]     Next, the control point  190  obtains manager authentication information of controlled device  1   110  set as the master through SOAP. Such manager authentication information may be retrieved from a smart card of the master and is required for a procedure of confirming whether the user that has selected the master is a legitimate manager. The control point  190  performs manager authentication by outputting a user interface using the manager authentication information and receiving a manager&#39;s ID and password from the user (S 605 ).  FIG. 9   b  shows one example of such a user interface.  
         [0064]     After the manager authentication, the control point  190  sets controlled device  1   110  as a domain master and then provides controlled device  1   110  with a list of devices that the control point  190  possesses (S 606 ). Thereafter, the device mode value of controlled device  1   110  becomes “master.” Controlled device  1   110  set as the master initially creates a new domain with only the device itself as a member (S 607 ).  
         [0065]      FIG. 7  illustrates a device-authenticating process performed subsequent to the process illustrated in  FIG. 6  according to the first embodiment of the present invention. First, the domain master  110  receives a new SIB through an external server in such a manner illustrated in  FIG. 3  (S 611 ). The control point  190  then delivers URL information with the SIB stored therein to the remaining controlled devices  120  to  160  by using SOAP (S 612 ). The remaining controlled devices  120  to  160  obtain the SIB present in the URL through HTTP (S 613 ). Then, the controlled devices extract secret values using the obtained SIB, and create certificates using the secret values and their own IDs and public keys (S 614 ). These certificates are used for discriminating illegal devices from legitimate devices. For example, if an authentication policy in which only devices produced by specific manufacturers are approved as legitimate devices is enforced, devices produced by other manufacturers except the specific manufacturers would be treated as illegal devices.  
         [0066]     Thereafter, when the control point  190  sends URL information containing the certificates to the master device  110  through SOAP (S 615 ), the master device  110  obtains the certificates, device IDs and public keys from the remaining controlled devices  120  to  160  by using HTTP (S 615 ). Further, the master device  110  verifies the obtained certificates and prepares a list of authenticated devices (S 617 ). Devices classified into illegal devices through certificate verification are subsequently excluded from the domain, and there is no possibility for them to be designated as slave devices.  
         [0067]      FIG. 8  illustrates the process of determining a slave device that is performed subsequent to the process illustrated in  FIG. 7  according to the first embodiment of the present invention. First, the control point  190  verifies domain attributes for the devices  120  to  140  approved as legitimate devices according to the results of the certificate verification by using SOAP (S 621 ). Each domain attribute may include a domain key, the names of devices belonging to a domain, the number of devices belonging to the domain, and the like. If the devices have no domain attributes, the control point  190  displays a list of these devices through a user interface (S 622 ) and allows the user to select slave devices (S 623 ).  FIG. 9   c  illustrates an example of a user interface showing a list of the legitimate devices  120  to  140 . The user marks checks for devices that the user wishes to include in the domain among the listed devices to select slave devices. Contrary to the selection of the master, the user can select a plurality of devices as slave devices. Thereafter, in the same manner as the master-selecting process illustrated in  FIG. 6 , manager authentication information is obtained (S 624 ) and the manager-authenticating process is performed (S 625 ).  
         [0068]     Next, the control point  190  delivers a list of the slave devices selected among the listed devices to the master device  110  through SOAP (S 626 ), and sets the selected devices to the slave mode through SOAP (S 627 ). The devices that have been set to the slave mode have “slave” as their device mode values. Then, the master device  110  creates a domain ID and a domain key using the list of slave devices (S 628 ). The master device encrypts the domain ID and domain key using public keys for the slave devices (S 629 ).  
         [0069]     Next, the control point  190  delivers the URL information containing the domain attribute value from the master device to the slave devices through SOAP (S 630 ). Then, the slave devices obtain the domain attribute present in the URL via HTTP (S 631 ). The domain attribute includes the domain key, the names of the devices belonging to the domain, the number of the devices belonging to the domain, and the like.  
         [0070]     FIGS.  10  to  12  illustrate processes according to a second embodiment of the present invention. The second embodiment is different from the first embodiment in that important ones of the functions of the control point  190  are taken over by the master device  110 . The control point  190  deals with tasks related to user interfaces. As a result, the master device  110  has functions of a controlled device as well as functions of a control point except the residual function of the control point  190 . Accordingly, loads on the control point  190  are greatly reduced. Further, problems do not occur in view of security even though the control point  190  is an illegal device. Moreover, there are no problems even though the master device has no user interface.  
         [0071]     Among these figures,  FIG. 10  illustrates the process of determining a master device, wherein device  1   110  is operated only as a controlled device (CD). Therefore, this process is identical to the process of determining the master device illustrated in  FIG. 6  according to the first embodiment. Thus, iterative description thereof will be omitted.  
         [0072]      FIG. 11  illustrates a device-authenticating process performed subsequent to the process illustrated in  FIG. 10  according to the second embodiment of the present invention. First, the control point  190  notifies the master device  110  through SOAP that the device-authenticating process starts (S 711 ). During this process, the master device is operated as a CD. Then, the master device  110  (operating as a CD) delivers the SIB directly to the remaining controlled devices  120  to  160  using SOAP. Then, the remaining controlled devices  120  to  160  extract secret values using the received SIB, and create certificates using the secrete values and their own device IDs and public keys (S 713 ).  
         [0073]     Subsequently, the remaining controlled devices  120  to  160  deliver their certificates, device IDs and public keys directly to the master device  100  (operating as a control point) through SOAP (S 714 ). Then, the master device  110  verifies the received certificates and prepares a list of authentication devices (S 715 ). Devices classified as illegal devices through the certificate verification are subsequently excluded from the domain, and there is no possibility for them to be designated as slave devices. Then, the master device  110  (operating as a CD) notifies the control point  190  of device IDs of the verified devices by means of an event message by using GENA (S 716 ). Then, the control point  190  obtains the results of the verification of the devices from the master device  110  (operating as a CD) using SOAP (S 717 ), and then displays, through a user interface, the verification results on whether the devices are illegal or legitimate devices (S 718 ).  
         [0074]      FIG. 12  illustrates the process of determining a slave device that is performed subsequent to the process illustrated in  FIG. 11  according to the second embodiment of the present invention. First, the control point  190  verifies domain attributes for the devices  120  to  140  approved as legitimate devices according to the results of certificate verification by using SOAP (S 721 ). If the devices have no domain attributes, the control point  190  displays a list of these devices through a user interface (S 722 ), and allows the user to select slave devices (S 723 ).  FIG. 9   c  illustrates an example of the user interface showing a list of legitimate devices  120  to  140 . The user marks checks for devices that the user wishes to include in the domain among the listed devices to select slave devices. Thereafter, in the same manner as the master-selecting process illustrated in  FIG. 6 , the manager authentication information is obtained (S 724 ) and the manager-authenticating process is performed (S 725 ).  
         [0075]     Next, the control point  190  delivers a list of slave devices  120  to  140  selected among the listed devices to the master device  110  (operating as a CD) through SOAP (S 726 ). Then, the master device  110  creates a domain ID and a domain key using the list of slave devices (S 727 ). Then, the master device encrypts the domain ID and domain key using public keys for the slave devices (S 728 ). The master device  110  (operating as a control point) directly sets the selected devices to the slave mode through SOAP, and then delivers the domain attributes of the set devices (S 729 ).  
         [0076]     According to the present invention, there are advantages in that it possible to construct a domain independent of the outside by using a public key-based architecture in which a user is directly involved in constructing the domain, and a domain key is created using a authentication list and a random number as input values and thus varies depending on changes in members belonging to the domain, thereby more safely limiting the use of content.  
         [0077]     Further, according to the present invention, there is an advantage in that since a communication method implemented in UPnP can be used as it is in applying domain management techniques to a home network, it is not necessary to develop a new communication method among members in a domain. Further, the present invention has advantages in that devices included in a home network can be more easily authenticated, smooth incorporation into conventional networks can be made without depending on specific operating systems or physical media by using a standard Internet protocol, and compatibility with all devices supporting UPnP can be achieved.  
         [0078]     Although the embodiments of the present invention have been described with reference to the accompanying drawings, it can be understood by those skilled in the art that the present invention can be implemented in other specific forms without modifying or changing the technical spirit and essential features thereof. Therefore, it should be understood that the aforementioned embodiments are not limitative but illustrative in all aspects. The scope of the present invention should be defined by the appended claims, and all changes or modifications made from the spirit and scope of the invention and equivalents thereof should be construed as falling within the scope of the invention.