Patent Publication Number: US-10785023-B2

Title: Apparatus and method for managing metering information

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2017-0144490, filed Nov. 1, 2017, which is hereby incorporated by reference in its entirety into this application. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to Internet-of-Things (IoT) technology, smart grid technology, and remote metering technology, and more particularly to a meter data management method for encrypting, storing, and transmitting data in a remote metering service in an IoT environment or a smart grid environment. 
     2. Description of Related Art 
     In an IoT environment, various kinds of IoT devices are connected with each other, thereby forming a network. Here, IoT devices in the lowest layer may transmit data sensed by themselves to a server in the highest layer, and the server in the highest layer processes data received from the multiple IoT devices, thereby providing an IoT service. 
     Therefore, only when the data sensed by the IoT devices in the lowest layer are securely transmitted to the server in the highest layer via multiple networks may the desired IoT service be securely provided in the IoT environment. 
     In order to securely provide an IoT service, security functions, such as mutual authentication between IoT devices, encryption of data, and the like, are necessary. For example, data may be encrypted using a symmetric key cryptography algorithm in which a private key is shared in advance between a device in the lowest layer and a device in the highest layer. Alternatively, in the state in which a private key is not shared in advance, the private key may be exchanged using a public key cryptography algorithm or a key exchange algorithm, and data may be encrypted using the shared private key. 
     Also, because a security method using hardware may provide stronger security functions than a security method using software, a hardware security chip may be used. However, the security method using hardware may incur additional costs for hardware security chips, and it is difficult to apply the same to existing IoT devices. 
     Furthermore, the security methods using software or hardware are problematic in that the server in the highest layer is required to store and manage multiple private keys that are identical to the private keys of IoT devices in the lowest layer in order to decrypt data, encrypted and transmitted by the respective IoT devices. 
     Recently, such security functions are required for a remote metering service, in which electricity information is exchanged in real time in order to charge for electricity consumption. 
     The remote metering service is configured such that information about electricity is exchanged in real time, departing from merely checking electricity consumption using unidirectional communication, whereby electric meters may be controlled and information about electricity consumption may be provided to an electricity supply service provider. 
     Here, the remote metering service may be provided in a smart grid environment, and the electricity supply service provider may remotely read meter data using a wired and wireless communication network without the need for a meterman to personally visit a user&#39;s place in order to read an electric meter. 
     However, such a remote metering service may cause a security problem. 
     Particularly, information about the amount of electricity, gas, water, hot water, and heating energy used by a person may be sensitive information from which private information may be inferred. When such private information is leaked or exposed to third parties, it may constitute an invasion of privacy. 
     Also, when incorrect control information and falsified meter data are transmitted to an electricity supply service provider, the remote metering service may cause a big problem. 
     Meanwhile, Korean Patent No. 10-1317806, titled “Apparatus and method for encrypting meter data in advanced metering infrastructure”, relates to an apparatus and method for encrypting data in a smart grid environment and a system for the same, and discloses an apparatus and method for providing security by encrypting meter data in a smart grid environment and a system for the same. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to guarantee end-to-end security between a device in the lowest layer and a device in the highest layer and to prevent information from being leaked to third parties. 
     Another object of the present invention is to enable a device in the lowest layer to encrypt sensitive and important data, such as private information and the like, before the data are stored, and to transmit the encrypted data to a device in the highest layer, whereby data stored in the devices may be securely protected. 
     A further object of the present invention is to provide secure encryption and decryption functions in the state in which a device in the highest layer does not manage keys for respective devices in the lowest layer. 
     Yet another object of the present invention is to securely protect meter data using a private key that is newly created in response to a request by a device in the highest layer and to optimally acquire meter data using an updated metering interval. 
     In order to accomplish the above objects, a method for managing meter data, in which a meter data management apparatus is used, according to an embodiment of the present invention includes acquiring first time information by decrypting an encrypted message received from a server device; acquiring meter data from a target device using the first time information; creating a first private key using the first time information; encrypting the meter data using the first private key; acquiring second time information by decrypting an encrypted metering request message, which is received from the server device; and transmitting the meter data based on the first time information and the second time information to the server device. 
     Here, acquiring the first time information may be configured such that the meter data management apparatus creates a registration request message that includes an identifier thereof and transmits the registration request message to the server device, and such that the server device creates an initial private key that is identical to an initial private key stored in advance in the meter data management apparatus using the identifier included in the registration request message. 
     Here, acquiring the first time information may be configured to create the encrypted registration completion message in which the first time information is encrypted using the initial private key. 
     Here, acquiring the first time information may be configured such that the server device creates the registration completion message so as to include a metering period of the first time information, which is created based on at least one of an amount of memory in a device for storing meter data and a change in usage by the target device. 
     Here, acquiring the meter data may be configured to acquire the meter data from the target device from a metering start time of the first time information. 
     Here, creating the first private key may be configured such that the meter data management apparatus and the server device create the same first private key by taking the first time information as input. 
     Here, creating the first private key may be configured to create the first private key by taking the metering period and the metering start time of the first time information as input. 
     Here, acquiring the second time information may be configured such that the server device creates the metering request message in which a metering period and a metering request time of the second time information are encrypted using the first private key. 
     Here, acquiring the second time information may be configured such that the server device creates the metering request message so as to include the metering period of the second time information, which is created based on at least one of the amount of memory in the device for storing meter data and the change in usage by the target device. 
     Here, acquiring the second time information may be configured such that the meter data management apparatus selects the metering period of the second time information when a metering period is determined to be changed as a result of comparison of the metering period of the first time information with that of the second time information. 
     Here, transmitting the meter data may be configured to transmit the meter data read from the metering start time of the first time information to the metering request time of the second time information. 
     Also, in order to accomplish the above objects, a method for managing meter data, in which a meter data management apparatus is used, according to an embodiment of the present invention includes acquiring time information by decrypting an encrypted message received from a server device; transmitting first meter data of a target device to the server device based on the time information; creating a private key using the time information; and encrypting second meter data using the private key. 
     Here, acquiring the time information may be configured such that the server device creates the encrypted message including the time information using an initial private key and transmits the encrypted message to the meter data management apparatus and such that the meter data management apparatus acquires the time information by decrypting the encrypted message using an initial private key stored in advance, which is identical to the initial private key created by the server device. 
     Here, acquiring the time information may be configured such that the server device creates the encrypted message so as to include a metering period of the time information, which is created based on at least one of an amount of memory in a device for storing meter data and a change in usage by the target device. 
     Here, transmitting the first meter data may be configured to transmit the first meter data, read by a metering request time of the time information, to the server device. 
     Here, creating the private key may be configured to acquire the second meter data from the target device using the metering period of the time information when a metering period is determined to be changed as a result of comparison of the metering period of the time information with a metering period that is used when the first meter data are acquired. 
     Here, creating the private key may be configured to create the private key by taking as input at least one of the metering period and the metering request time of the time information. 
     Here, encrypting the second meter data may be configured to encrypt the second meter data, which are acquired from the target device after the private key is created, using the private key. 
     Here, the method may further include decrypting, by the server device, the first meter data using the private key after creating the private key, and decrypting the first meter data may be configured to provide a metering service to users using the first meter data. 
     Also, in order to accomplish the above objects, an apparatus for managing meter data according to an embodiment of the present invention includes a metering unit for acquiring meter data from a target device based on time information; a communication unit for receiving a message including the time information from a server device and transmitting the meter data to the server device; and a security unit for creating a private key using the time information and encrypting the meter data using the private key. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view that shows a remote metering service in an IoT environment according to an embodiment of the present invention; 
         FIG. 2  is a view that shows a remote metering service using a smart meter that stores meter data according to an embodiment of the present invention; 
         FIG. 3  is a view that shows a remote metering service using a smart meter, in which a data concentration unit stores meter data, according to an embodiment of the present invention; 
         FIG. 4  is a block diagram that shows a metering management system according to an embodiment of the present invention; 
         FIG. 5  is a block diagram that specifically shows an example of the meter data management apparatus illustrated in  FIG. 4 ; 
         FIG. 6  is a block diagram that specifically shows an example of the gateway device illustrated in  FIG. 4 ; 
         FIG. 7  is a block diagram that specifically shows an example of the server device illustrated in  FIG. 4 ; 
         FIG. 8  and  FIG. 9  are sequence diagrams that show a meter data management method in which a meter data management apparatus stores meter data according to an embodiment of the present invention; 
         FIG. 10  and  FIG. 11  are sequence diagrams that show a meter data management method in which a gateway device stores meter data according to an embodiment of the present invention; and 
         FIG. 12  is a block diagram that shows a computer system according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in detail below with reference to the accompanying drawings. Repeated descriptions and descriptions of known functions and configurations which have been deemed to make the gist of the present invention unnecessarily obscure will be omitted below. The embodiments of the present invention are intended to fully describe the present invention to a person having ordinary knowledge in the art to which the present invention pertains. Accordingly, the shapes, sizes, etc. of components in the drawings may be exaggerated in order to make the description clearer. 
     Throughout this specification, the terms “comprises” and/or “comprising”, and “includes” and/or “including” specify the presence of stated elements but do not preclude the presence or addition of one or more other elements unless otherwise specified. 
     For the convenience of description, an apparatus and method for managing meter data according to an embodiment of the present invention may be described by illustrating a remote metering service in an IoT environment or a remote metering service using smart meters in a smart grid environment as an example. However, the present invention is not limited to a remote metering service in an IoT environment or in a smart grid environment, and the present invention may be applied to various systems and services, such as data management services, remote metering services, and metering management systems. 
     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a view that shows a remote metering service in an IoT environment according to an embodiment of the present invention. 
     Referring to  FIG. 1 , a remote metering service in an IoT environment according to an embodiment of the present invention may be configured such that IoT devices  100 - 1  in the lowest layer may be connected with an IoT service provision server device  30 - 1  via a gateway device  20 - 1 . 
     Here, the IoT devices  100 - 1  may be directly connected with the IoT service provision server device  30 - 1  in the highest layer without a relay device, such as the gateway device  20 - 1  or the like, therebetween. 
     The IoT devices  100 - 1  in the lowest layer and the gateway device  20 - 1  having various wireless communication functions (Wi-Fi, Zigbee, BLE, and the like) may form a local network in most IoT environments. 
     Here, the IoT service provision server device  30 - 1  may be connected with the gateway device  20 - 1  through wired and wireless communication. 
     The IoT devices  100 - 1  may communicate with each other, and may transmit sensing data (meter data) when a request to transmit data is made by the IoT service provision server device  30 - 1 . 
     Here, the IoT devices  100 - 1  may sense data using information provided by the IoT service provision server device  30 - 1 . 
     Here, the data may be various kinds of data that are required to be read because the values thereof change in real time, such as the amount of electricity consumed by the IoT devices or the like. 
     Here, the IoT devices  100 - 1  may encrypt sensing data using information provided by the IoT service provision server device  30 - 1  and transmit the encrypted sensing data to the IoT service provision server device  30 - 1 . 
     The IoT service provision server device  30 - 1  may decrypt the received encrypted data. 
     Here, the IoT service provision server device  30 - 1  may provide users with an IoT service based on the decrypted data. 
     The IoT devices  100 - 1  may include meter data storage for storing sensing data, or may have a minimal amount of memory when not including meter data storage. 
     The gateway device  20 - 1  may include meter data storage for storing data received from the IoT devices  100 - 1 , or may have a minimal amount of memory when it does not include meter data storage. 
       FIG. 2  is a view that shows a remote metering service using a smart meter that stores meter data according to an embodiment of the present invention.  FIG. 3  is a view that shows a remote metering service using a smart meter, in which a data concentration unit stores meter data, according to an embodiment of the present invention. 
       FIG. 2  and  FIG. 3  show a remote metering service using a smart meter according to an embodiment of the present invention. 
     Smart meters  100 - 2  may read meter data, such as the amount of electricity consumed by home appliances  10 - 2 . 
     Here, when the smart meters  100 - 2  include meter data storage, as illustrated in  FIG. 2 , the smart meters  100 - 2  may encrypt meter data before storing the meter data. 
     Here, the smart meters  100 - 2  may correspond to the IoT devices  100 - 1  for sensing data illustrated in  FIG. 1 . 
     A Data Concentration Unit (DCU)  20 - 2  may request the encrypted meter data, which are stored in the smart meters, and may transmit the received meter data to a server system  30 - 2 . 
     Here, the DCU  20 - 2  may correspond to the gateway device  20 - 1  illustrated in  FIG. 1 , which may relay data between the smart meters  100 - 2  and the server system  30 - 2 . 
     Here, the DCU  20 - 2  may include meter data storage, as illustrated in  FIG. 3 . 
     Here, the DCU  20 - 2  may receive and store meter data that are read and encrypted by the smart meters  100 - 2 . 
     Here, the DCU  20 - 2  may transmit the stored meter data to the server system  30 - 2  when a request for meter data is made by the server system  30 - 2 . 
     The server system  30 - 2  may include both a remote metering server device for providing a remote metering service and an authentication server device for authenticating an electricity supply service provider. 
     Here, the server system  30 - 2  may correspond to the IoT service provision server device  30 - 1  illustrated in  FIG. 1 . 
     Here, the server system  30 - 2  may decrypt the received encrypted meter data. 
     Here, the server system  30 - 2  may provide the decrypted meter data to the electricity supply service provider. 
       FIG. 4  is a block diagram that shows a metering management system according to an embodiment of the present invention. 
     Referring to  FIG. 4 , a metering management system according to an embodiment of the present invention may include a target device  10 , a gateway device  20 , a server device  30 , and a meter data management apparatus  100 . 
     The target device  10  may correspond to the home appliance  10 - 2  or  10 - 3 , of which the amount of electricity consumed thereby is to be measured, illustrated in  FIG. 2  or  FIG. 3 . 
     The meter data management apparatus  100  may correspond to the smart meter  100 - 2  or  100 - 3  for reading information about the amount of electricity consumed by the home appliances illustrated in  FIG. 2  or  FIG. 3 . 
     Also, in the IoT environment, the IoT device  100 - 1  may sense its data (i.e., measure the amount of electricity consumed by itself) and transmit the data to the server device, as illustrated in  FIG. 1 . Accordingly, the IoT device  100 - 1  may include both the target device  10  and the meter data management apparatus  100  therein. 
     Here, the meter data management apparatus  100  may acquire meter data by reading information about the amount of electricity consumed by the target device. 
     Also, in the IoT environment illustrated in  FIG. 1 , the meter data management apparatus  100  shown in  FIG. 4  may not be separate from the IoT device  100 - 1 , in which case the IoT device  100 - 1  may correspond to the target device  10  that is formed in such a way that the home appliance  10 - 2  or  10 - 3  shown in  FIG. 2  or  FIG. 3  includes the meter data management apparatus  100 . 
     Here, the target device  10  may acquire meter data by autonomously reading information about the amount of electricity consumed by itself, encrypt the meter data, and store and transmit the encrypted meter data. 
     The gateway device  20  may relay data between the meter data management apparatus  100  and the server device  30 . 
     Here, the gateway device  20  may correspond to the gateway device  20 - 1  in the IoT environment illustrated in  FIG. 1  or the DCU  20 - 2  in the remote metering service illustrated in  FIG. 2  or  FIG. 3 . 
     The server device  30  may request meter data from the meter data management apparatus  100  and may receive encrypted meter data and decrypt the same. 
     Here, the server device  30  may provide a remote metering service to users using the decrypted meter data. 
     Also, the meter data management apparatus  100  may register itself in the server device  30 . 
     Here, the meter data management apparatus  100  may transmit a registration request message that includes the identifier thereof to the server device  30 . 
     Here, using the identifier of the meter data management apparatus  100 , which is included in the registration request message, the server device  30  may create an initial private key that is the same as the initial private key possessed by the meter data management apparatus  100 . 
     Here, the server device  30  may transmit a registration completion message, in which time information including metering configurations is encrypted using the initial private key, to the meter data management apparatus  100 . 
     Also, the meter data management apparatus  100  may acquire meter data by reading information about the amount of electricity consumed by the target device  10  depending on the metering configurations of the server device  30 . 
     That is, the meter data management apparatus  100  may decrypt the registration completion message, received from the server device  30 , using the initial private key. 
     Here, the meter data management apparatus  100  may acquire the time information including metering configurations by decrypting the registration completion message. 
     Here, the meter data management apparatus  100  may read information about the amount of electricity consumed by the target device  10  using a metering period and a metering start time included in the time information. 
     Here, the meter data management apparatus  100  may read information about the amount of electricity consumed by the target device  10  at time intervals of the metering period from the metering start time. 
     Also, the meter data management apparatus  100  may create a private key using the time information. 
     Here, the meter data management apparatus  100  may create a private key by taking the metering period and the metering start time as input. 
     Here, the meter data management apparatus  100  may encrypt the meter data using the private key and store the encrypted meter data. 
     Here, if the meter data management apparatus  100  includes storage for storing meter data, the meter data are stored therein. However, if the meter data management apparatus  100  does not include storage and the gateway device  20  includes storage, the meter data management apparatus  100  may transmit the encrypted meter data to the gateway device  20  so that the gateway device  20  may store the encrypted meter data therein. 
     Similarly, the server device  30  may create a private key that is the same as the private key created by the meter data management apparatus  100  by taking the metering period and the metering start time as input. 
     Here, the server device  30  may create a meter data request message in which time information including new metering configurations is encrypted using the private key, and may transmit the meter data request message to the meter data management apparatus  100 . 
     Here, the meter data management apparatus  100  may decrypt the meter data request message using the private key, thereby acquiring a metering period and a metering request time. 
     Here, when the metering period is determined to be changed as the result of comparison of the previous metering period with the newly acquired metering period, the meter data management apparatus  100  may select the newly acquired metering period. 
     Here, the meter data management apparatus  100  may transmit meter data, in which meter data from the metering start time to the metering request time are encrypted and saved, to the server device  30 . 
     Here, if the meter data are stored in the gateway device  20 , the meter data management apparatus  100  may approve transmission of the meter data by the gateway device  20 . 
     The server device  30  may decrypt the received meter data using the private key, and may provide users with a metering service using the decrypted meter data. 
     Also, the meter data management apparatus  100  may create a new private key by taking the new metering period and the metering request time as input, and may encrypt meter data using the new private key and store the encrypted meter data. 
     The server device  30  may repeatedly create a new private key by taking a new metering period and a metering request time as input, and may repeatedly create a meter data request message using the new private key, thereby requesting meter data. 
     As described above, the meter data management apparatus  100  and the server device  30  repeatedly create new private keys by taking a new metering period and a new metering request time as input, encrypt meter data using the private key and store the encrypted meter data, and provide service by decrypting the meter data using the private key, thereby maximizing the security of meter data acquired from the target device  10 . 
     Also, in the IoT environment and the remote metering service illustrated in  FIGS. 1 to 3 , data acquired by sensing the IoT devices  100 - 1  and meter data acquired by the smart meters  100 - 2  or  100 - 3  may be effectively and securely managed through the above-described method. 
     Hereinafter, the components of each of the devices included in the metering management system illustrated in  FIG. 4  will be described in detail. 
       FIG. 5  is a block diagram that specifically shows an example of the meter data management apparatus illustrated in  FIG. 4 . 
     Referring to  FIG. 5 , a meter data management apparatus  100  according to an embodiment of the present invention includes a metering unit  110 , a security unit  120  and a communication unit  130 . Here, the meter data management apparatus  100  may further include a meter data storage unit  140 . 
     The metering unit  110  acquires meter data from a target device  10  based on time information. 
     The time information may include metering configuration information set by a server device  30 . 
     That is, the time information may include at least one of a metering period, a metering start time, and a metering request time. 
     The meter data may be the amount of electricity consumed by the target device  10 . 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Here, when it receives the metering period and the metering start time, the metering unit  110  may read the meter data of the target device  10  at time intervals of the metering period from the metering start time. 
     Here, when it receives a new metering period, the metering unit  110  may change the metering period and read the meter data of the target device  10  based on the changed metering period. 
     Here, when the meter data management apparatus  100  is connected with multiple target devices  10 , the metering unit  110  may set the metering period and the metering start time to different values for the respective target devices  10 . 
     Here, the metering unit  110  may read meter data based on the metering period and the metering start time, which are different for the respective target devices  10 . 
     The security unit  120  may create a private key using time information, and may encrypt meter data using the private key. 
     First, the security unit  120  may create a registration request message for registering the meter data management apparatus  100  in the server device  30 . 
     Here, the security unit  120  may create a registration request message that includes the address of a destination, the address of an origin, and the identifier (ID) of the meter data management apparatus  100 , which is the unique information thereof. 
     Here, information about the amount of memory for storing meter data in the meter data management apparatus  100  may be further included in the registration request message. 
     The information about the amount of memory may be used as a reference when the server device  30  sets a metering period to be included in a registration completion message or a meter data request message. 
     Here, the security unit  120  may contain an initial private key to be used for the registration process. 
     Also, the security unit  120  may decrypt a registration completion message, received from the server device  30 , using the initial private key. 
     Here, the security unit  120  may acquire first time information by decrypting the registration completion message. 
     Here, the security unit  120  may deliver a metering period and a metering start time included in the first time information, which is acquired by decrypting the registration completion message, to the metering unit  110 . 
     Here, the security unit  120  may create a first private key by taking the metering period and the metering start time, included in the first time information, as input, the first time information being acquired by decrypting the registration completion message. 
     Here, the security unit  120  may encrypt meter data, acquired by the metering unit  110  from the metering start time, using the first private key, and may transmit the encrypted meter data to the meter data storage unit  140  or the gateway device  20  for storing meter data. 
     Also, the security unit  120  may decrypt a first meter data request message, received from the server device  30 , using the first private key. 
     Here, the security unit  120  may acquire second time information by decrypting the first meter data request message. 
     Here, the security unit  120  may deliver a metering period and a first metering request time included in the second time information, which is acquired by decrypting the first meter data request message, to the meter data storage unit  140  or the gateway device  20 . 
     Also, the security unit  120  may select the metering period of the second time information when the metering period is determined to be changed as the result of comparison of the metering period of the first time information with that of the second time information. 
     Here, when it sets a new metering period, the security unit  120  may deliver the new metering period to the metering unit  110 , and the metering unit  110  may acquire meter data based on the new metering period. 
     Also, the security unit  120  may create a second private key by taking the metering period and the first metering request time, included in the second time information, as input, the second time information being acquired by decrypting the first meter data request message. 
     Here, the security unit  120  may create a second private key using the second time information, and may encrypt meter data, acquired after the first meter data request message is received, using the second private key. 
     Here, the security unit  120  may encrypt meter data, acquired by the metering unit  110 , using the second private key, and may deliver the encrypted meter data to the meter data storage unit  140  or the gateway device  20  for storing meter data. 
     Also, the security unit  120  may decrypt a second meter data request message, received from the server device  30 , using the second private key. 
     Here, the security unit  120  may acquire third time information by decrypting the second meter data request message. 
     Here, the security unit  120  may deliver a metering period and a second metering request time included in the third time information, which is acquired by decrypting the second meter data request message, to the meter data storage unit  140  or the gateway device  20 . 
     Also, the security unit  120  may select the metering period of the third time information when the metering period is determined to be changed as the result of comparison of the metering period of the second time information with that of the third time information. 
     Here, when it selects a new metering period, the security unit  120  may deliver the new metering period to the metering unit  110 , and the metering unit  110  may acquire meter data based on the new metering period. 
     Also, the security unit  120  may create a third private key by taking the metering period and the second metering request time, included in the third time information, as input, the third time information being acquired by decrypting the second meter data request message. 
     Here, the security unit  120  may create a third private key using the third time information, and may encrypt meter data, acquired after the second meter data request message is received, using the third private key. 
     Here, the security unit  120  may encrypt the meter data, acquired by the metering unit  110 , using the third private key, and may deliver the encrypted meter data to the meter data storage unit  140  or the gateway device  20  for storing meter data. 
     As described above, the security unit  120  may create a new private key whenever it receives a new meter data request message from the server device  30 . 
     Here, the security unit  120  may create a new private key using a new meter data request message, encrypt meter data, acquired after the meter data request message is received, using the new private key, and store the encrypted meter data. 
     Also, the security unit  120  may use an operation mode that includes confidentiality and message authentication through a lightweight symmetric key cryptography algorithm. 
     For example, the security unit  120  may provide only confidentiality, or both confidentiality and integrity depending on the resources of a smart meter in the lowest layer or on the data transmission speed thereof. 
     Accordingly, the encrypted meter data stored in the meter data storage unit  140  or the gateway device  20  may include the identifier of the meter data management apparatus  100 , the date and time at which meter data are read, and information about electricity consumption. 
     For example, the encrypted meter data may be configured in the form of “Enc[smart meter ID (SM_ID)∥the date and time at which meter data are read (YYMMDD-HHMM)∥electricity consumption]”, and the integrity value may be further included therein. 
     The communication unit  130  may receive a message that includes time information from the server device  30 , and may transmit meter data to the server device  30 . 
     Here, the communication unit  130  may communicate with the server device  30  via the gateway device  20 . 
     Here, the communication unit  130  may transmit the registration request message created by the security unit  120  to the gateway device  20  or the server device  30 . 
     Here, the communication unit  130  may transmit the meter data stored in the meter data storage unit  140  to the gateway device  20  or the server device  30  in response to a request by the security unit  120 . 
     Here, the communication unit  130  may transmit a message for approving the transmission of meter data to the gateway device  20  in response to a request by the security unit  120 . 
     Here, the communication unit  130  may receive a registration completion message or a meter data request message from the gateway device  20  or the server device  30 . 
     The meter data storage unit  140  may store meter data encrypted by the security unit  120 . 
     Here, the meter data management apparatus  100  may not include the meter data storage unit  140  when the meter data management apparatus  100  is a low-specification device having no storage. 
     Here, the meter data storage unit  140  may transmit meter data, in which meter data from the metering start time to the metering request time are encrypted and saved, to the communication unit  130  in response to a request by the security unit  120 . 
     Here, the meter data storage unit  140  may transmit meter data, in which meter data from the first metering request time to the second metering request time are encrypted and saved, to the communication unit  130  in response to a request by the security unit  120 . 
       FIG. 6  is a block diagram that specifically shows an example of the gateway device illustrated in  FIG. 4 . 
     Referring to  FIG. 6 , the gateway device  20  according to an embodiment of the present invention may include a gateway communication unit  21  and a gateway meter data storage unit  22 . 
     The gateway communication unit  21  may relay communication between the meter data management apparatus  100  and the server device  30 . 
     The gateway communication unit  21  may receive a message that includes time information from the server device  30 , and may transmit meter data to the server device  30 . 
     Here, the gateway communication unit  21  may transmit the registration request message, transmitted from the meter data management apparatus  100 , to the server device  30 . 
     Here, the gateway communication unit  21  may transmit meter data stored in the gateway meter data storage unit  22  to the server device  30  in response to a request by the meter data management apparatus  100 . 
     Here, the gateway communication unit  21  may receive a message for approving the transmission of meter data from the meter data management apparatus  100 . 
     Here, the gateway communication unit  21  may receive a registration completion message or a meter data request message from the server device  30 . 
     The gateway meter data storage unit  22  may store the meter data received from the meter data management apparatus  100 . 
     Here, the gateway meter data storage unit  22  may transmit meter data, in which meter data from the metering start time to the metering request time are encrypted and saved, to the gateway communication unit  21  in response to a request by the meter data management apparatus  100 . 
     Here, the gateway meter data storage unit  22  may transmit meter data, in which meter data from the first metering request time to the second metering request time are encrypted and saved, to the gateway communication unit  21  in response to a request by the meter data management apparatus  100 . 
       FIG. 7  is a block diagram that specifically shows an example of the server device illustrated in  FIG. 4 . 
     Referring to  FIG. 7 , the server device  30  according to an embodiment of the present invention may include a server communication unit  31 , a server security unit  32 , and a service execution unit  33 . 
     The server communication unit  31  may receive a registration request message and deliver the same to the server security unit  32 . 
     The server security unit  32  may acquire the identifier of the meter data management apparatus  100  included in the registration request message. 
     Here, the server security unit  32  may create an initial private key using the identifier of the meter data management apparatus  100 , included in the registration request message, and secret information about the server device  30 . 
     Here, the server security unit  32  may register the meter data management apparatus  100  by checking the identifier of the meter data management apparatus  100 , which is included in the registration request message. 
     Here, the server security unit  32  may contain the secret information of the server device  30  therein. 
     Here, the initial private key created by the server device  30  may match the initial private key created by the security unit  120  of the meter data management apparatus  100 . 
     Accordingly, without the need to manage secret information of multiple meter data management apparatuses  100 , the server device  30  may create a private key that matches the initial private key contained in each of the meter data management apparatuses  100  using the secret information of the server device  30  and the identifier of each of the meter data management apparatuses  100  received therefrom. 
     Also, the server security unit  32  may create a registration completion message in which first time information is encrypted using the initial private key. 
     Here, the server security unit  32  may create a registration completion message in which a metering period and a metering start time included in the first time information are encrypted using the initial private key. 
     Here, the metering period may be set depending on the characteristics of a service or information about the amount of memory for storing meter data in the meter data management apparatus  100  or the gateway device  20 , which is included in the registration request message. 
     Here, the server security unit  32  may set the metering period to be inversely proportional to the amount of memory for storing meter data in the meter data management apparatus  100  or the gateway device  20 . 
     For example, the server security unit  32  may set the metering period to be shorter as the amount of memory in the meter data management apparatus  100  or the gateway device  20  is larger, and conversely may set the metering period to be longer as the amount of memory is smaller. 
     Also, the server security unit  32  may set the metering period to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, the server security unit  32  may set the metering period to be shorter as the change in the amount of electricity consumed by the target device  10  is larger, but may set the metering period to be longer as the change in the amount of electricity consumed by the target device  10  is smaller. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Here, the server communication unit  31  may transmit the created registration completion message to the meter data management apparatus  100 . 
     Also, the server security unit  32  may create a first private key by taking the metering period and the metering start time, included in the first time information, as input. 
     Here, the server security unit  32  may create a first meter data request message in which second time information is encrypted using the first private key. 
     Also, the server security unit  32  may create a first meter data request message in which the metering period and the first metering request time included in the second time information are encrypted using the first private key. 
     Here, the server security unit  32  may set the metering period of the second time information to be the same as that of the first time information, or may change the metering period. 
     That is, the server security unit  32  may set the metering period by changing the previous metering period depending on the characteristics of the metering service to be provided or on information about the amount of memory for storing meter data in the meter data management apparatus  100 , which is included in the registration request message. 
     Here, the server security unit  32  may set the metering period to be inversely proportional to the amount of memory for storing meter data in the meter data management apparatus  100  or the gateway device  20 . 
     For example, the server security unit  32  may set the metering period to be shorter as the amount of memory in the meter data management apparatus  100  or the gateway device  20  is larger, but may set the metering period to be longer as the amount of memory is smaller. 
     Also, the server security unit  32  may set the metering period to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, the server security unit  32  may set the metering period to be shorter as the change in the amount of electricity consumed by the target device  10  is larger, but may set the metering period to be longer as the change in the amount of electricity consumed by the target device  10  is smaller. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Here, the server security unit  32  may transmit the created first meter data request message to the meter data management apparatus  100 . 
     Here, the server security unit  32  may decrypt the encrypted first meter data, received from the meter data management apparatus  100 , using the first private key. 
     Here, the first meter data may be meter data read from the metering start time to the first metering request time. 
     Here, because the first meter data are encrypted by the meter data management apparatus  100  using the first private key, which is created by taking the metering period and the metering start time as input, the server security unit  32  may decrypt the encrypted first meter data using the first private key. 
     Here, the server security unit  32  may deliver the decrypted first meter data to the service execution unit  33 . 
     Here, the service execution unit  33  may provide users with a metering service using the decrypted first meter data. 
     Also, the server security unit  32  may create a second private key by taking the metering period and the first metering request time, included in the second time information, as input. 
     Here, the server security unit  32  may create a second meter data request message in which third time information is encrypted using the second private key. 
     Here, the server security unit  32  may create a second meter data request message in which the metering period and the second metering request time included in the third time information are encrypted using the second private key. 
     Here, the server security unit  32  may transmit the created second meter data request message to the meter data management apparatus  100 . 
     Also, the server security unit  32  may decrypt the encrypted second meter data, received from the meter data management apparatus  100 , using the second private key. 
     Here, the second meter data may be meter data read from the first metering request time to the second metering request time. 
     Here, because the second meter data are encrypted by the meter data management apparatus  100  using the second private key, which is created by taking the metering period and the second metering request time as input, the server security unit  32  may decrypt the encrypted second meter data using the second private key. 
     Here, the server security unit  32  may deliver the decrypted second meter data to the service execution unit  33 . 
     Here, the service execution unit  33  may provide users with a metering service using the decrypted second meter data. 
     As described above, the server security unit  32  may create a new private key whenever it transmits a new meter data request message to the meter data management apparatus  100 . 
     Here, the server security unit  32  may transmit a new meter data request message, in which new time information for new metering configurations is encrypted using a new private key, to the meter data management apparatus  100 . 
     Also, the server security unit  32  may use an operation mode that includes confidentiality and message authentication through a lightweight symmetric key cryptography algorithm. 
     For example, the server security unit  32  may provide only confidentiality or both confidentiality and integrity depending on the resources of a smart meter in the lowest layer or on the data transmission speed thereof. 
     Accordingly, the encrypted meter data stored in the meter data management apparatus  100  or the gateway device  20  may include the identifier of the meter data management apparatus  100 , the date and time at which meter data are read, and information about electricity consumption. 
     For example, meter data may be configured in the form of “Enc[smart meter ID (SM_ID)∥the date and time at which meter data are read (YYMMDD-HHMM)∥electricity consumption]” and may further include an integrity value. 
       FIG. 8  and  FIG. 9  are sequence diagrams that show a meter data management method in which a meter data management apparatus stores meter data according to an embodiment of the present invention. 
     Referring to  FIG. 8 , in the meter data management method according to an embodiment of the present invention, first, a registration request message may be transmitted at step S 210 . 
     Here, the meter data management apparatus  100  may transmit a registration request message to the server device  30  at step S 210 . 
     Here, the meter data management apparatus  100  may create a registration request message for registering itself in the server device  30  at step S 210 . 
     Here, at step S 210 , the meter data management apparatus  100  may create a registration request message that includes the address of a destination, the address of an origin, and the identifier of the meter data management apparatus  100 , which is the unique information thereof. 
     Here, the registration request message may further include information about the amount of memory for storing meter data in the meter data management apparatus  100 . 
     The information about the amount of memory may be used as a reference when the server device  30  sets a metering period to be included in a registration completion message or a meter data request message. 
     Also, in the meter data management method according to an embodiment of the present invention, an initial private key may be created at step S 220 . 
     That is, at step S 220 , the server device  30  may create an initial private key using the identifier of the meter data management apparatus  100 , which is acquired from the registration request message. 
     Here, the server device  30  may acquire the identifier of the meter data management apparatus  100  at step S 220  by receiving the registration request message. 
     Here, the server device  30  may create an initial private key using the secret information thereof and the identifier of the meter data management apparatus  100 , which is included in the registration request message, at step S 220 . 
     Here, the server device  30  registers the meter data management apparatus  100  at step S 220  by checking the identifier of the meter data management apparatus  100  included in the registration request message. 
     Here, the initial private key created by the server device  30  may match the initial private key created by the security unit  120  of the meter data management apparatus  100 . 
     Accordingly, without the need to manage secret information of multiple meter data management apparatuses  100 , the server device  30  may create a private key that matches the initial private key contained in each of the meter data management apparatuses  100  using the secret information of the server device  30  and the identifier of each of the meter data management apparatuses  100  received therefrom at step S 220 . 
     Also, in the meter data management method according to an embodiment of the present invention, an encrypted registration completion message may be created at step S 230 . 
     That is, at step S 230 , the server device  30  may create a registration completion message in which first time information is encrypted using the initial private key. 
     Here, at step S 230 , the server device  30  may create a registration completion message in which a metering period and a metering start time included in the first time information are encrypted using the initial private key. 
     Here, the metering period may be set depending on service characteristics or information about the amount of memory for storing meter data in the meter data management apparatus  100 , which is included in the registration request message. 
     Here, at step S 230 , the metering period may be set to be inversely proportional to the amount of memory for storing meter data in the meter data management apparatus  100 . 
     For example, at step S 230 , the larger the amount of memory in the meter data management apparatus  100 , the shorter the metering period may be set. Conversely, the smaller the amount of memory in the meter data management apparatus  100 , the longer the metering period may be set. 
     Also, at step S 230 , the metering period may be set to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, at step S 230 , the larger the change in the amount of electricity consumed by the target device  10 , the shorter the metering period may be set. Conversely, the smaller the change in the amount of electricity consumed by the target device  10 , the longer the metering period may be set. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Also, in the meter data management method according to an embodiment of the present invention, the encrypted registration completion message may be transmitted at step S 240 . 
     That is, the server device  30  may transmit the created registration completion message to the meter data management apparatus  100  at step S 240 . 
     Also, in the meter data management method according to an embodiment of the present invention, the registration completion message may be decrypted at step S 250 . 
     That is, the meter data management apparatus  100  may decrypt the registration completion message, received from the server device  30 , using the initial private key at step S 250 . 
     Here, the meter data management apparatus  100  may acquire the first time information at step S 250  by decrypting the registration completion message. 
     Here, at step S 250 , the meter data management apparatus  100  may acquire meter data from the target device using the metering period and the metering start time of the first time information, which is acquired by decrypting the registration completion message. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data management apparatus  100  may create a first private key at step S 260 . 
     That is, at step S 260 , the meter data management apparatus  100  may create a first private key by taking the metering period and the metering start time, included in the first time information, as input, the first time information being acquired by decrypting the registration completion message. 
     Also, in the meter data management method according to an embodiment of the present invention, meter data may be encrypted and stored at step S 270 . 
     That is, at step S 270 , the meter data management apparatus  100  may encrypt meter data, which are read at time intervals of the metering period of the first time information from the metering start time, using the first private key, and may store the encrypted meter data. 
     Also, in the meter data management method according to an embodiment of the present invention, the server device  30  may create a first private key at step S 280 . 
     Here, at step S 280 , the server device  30  may create a first private key by taking the metering period and the metering start time, included in the first time information, as input, the first time information being acquired by decrypting the registration completion message. 
     Here, step S 280  may be performed before step S 250 . 
     Also, in the meter data management method according to an embodiment of the present invention, an encrypted meter data request message may be created at step S 290 . 
     That is, at step S 290 , the server device  30  may create a first meter data request message in which second time information is encrypted using the first private key. 
     Here, at step S 290 , the server device  30  may create a first meter data request message in which the metering period and a first metering request time included in the second time information are encrypted using the first private key. 
     Here, at step S 290 , the server device  30  may set the metering period of the second time information to be the same as the metering period of the first time information, which is set at step S 230 , or may change the metering period. 
     That is, the metering period may be set by changing the previous metering period depending on the characteristics of the metering service to be provided or information about the amount of memory for storing the meter data in the meter data management apparatus  100 , which is included in the registration request message. 
     Here, at step S 290 , the metering period may be set to be inversely proportional to the amount of memory for storing the meter data in the meter data management apparatus  100 . 
     For example, at step S 290 , the larger the amount of memory in the meter data management apparatus  100 , the shorter the metering period may be set. Conversely, the smaller the amount of memory in the meter data management apparatus  100 , the longer the metering period may be set. 
     Also, at step S 290 , the metering period may be set to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, at step S 290 , the larger the change in the amount of electricity consumed by the target device  10 , the shorter the metering period may be set. Conversely, the smaller the change in the amount of electricity consumed by the target device  10 , the longer the metering period may be set. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be transmitted at step S 300 . 
     That is, the server device  30  may transmit the created first meter data request message to the meter data management apparatus  100  at step S 300 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be decrypted at step S 310 . 
     That is, the meter data management apparatus  100  may decrypt the first meter data request message, received from the server device  30 , using the first private key at step S 310 . 
     Here, the meter data management apparatus  100  may acquire the second time information at step S 310  by decrypting the first meter data request message. 
     Here, at step S 310 , the meter data management apparatus  100  may acquire the metering period and the first metering request time included in the second time information by decrypting the first meter data request message. 
     Here, at step S 310 , when the metering period is determined to be changed as the result of comparison of the metering period of the first time information with that of the second time information, the metering period of the second time information may be selected. 
     Here, at step S 310 , when the new metering period is set, the meter data management apparatus  100  may acquire meter data based on the new metering period. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be transmitted at step S 320 . 
     That is, at step S 320 , the meter data management apparatus  100  may transmit the first meter data, in which meter data from the metering start time of the first time information to the first metering request time of the second time information are encrypted and saved, to the server device  30 . 
     Also, in the meter data management method according to an embodiment of the present invention, the first meter data may be decrypted at step S 330 . 
     That is, at step S 330 , the server device  30  may decrypt the encrypted first meter data, received from the meter data management apparatus  100 , using the first private key. 
     Here, the first meter data may be meter data read from the metering start time to the first metering request time. 
     Here, because the first meter data are encrypted by the meter data management apparatus  100  using the first private key, which is created by taking the metering period and the metering start time as input, the server device  30  may decrypt the encrypted first meter data using the first private key at step S 330 . 
     Here, the server device  30  may provide users with a metering service using the decrypted first meter data at step S 330 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data management apparatus  100  may create a second private key at step S 340 . 
     That is, at step S 340 , the meter data management apparatus  100  may create a second private key by taking the metering period and the first metering request time, included in the second time information, as input, the second time information being acquired by decrypting the first meter data request message. 
     Here, step S 340  may be performed before step S 330 . 
     Here, at step S 340 , the meter data management apparatus  100  may acquire meter data depending on a new metering period when the new metering period is selected. That is, when the metering period of the first time information differs from that of the second time information, meter data may be acquired based on the metering period of the second time information. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be encrypted and stored at step S 350 . 
     That is, at step S 350 , the meter data management apparatus  100  may encrypt meter data, which are read at time intervals of the metering period of the second time information from the first metering request time, using the second private key, and may store the encrypted meter data. 
     Referring to  FIG. 9 , in the meter data management method according to an embodiment of the present invention, the server device  30  may create a second private key at step S 360 . 
     That is, at step S 360 , the server device  30  may create a second private key by taking the metering period and the first metering request time, included in the second time information, as input. 
     Also, in the meter data management method according to an embodiment of the present invention, an encrypted meter data request message may be created at step S 370 . 
     That is, at step S 370 , the server device  30  may create a second meter data request message in which third time information is encrypted using the second private key. 
     Here, at step S 370 , the server device  30  may create a second meter data request message in which the metering period and the second metering request time included in the third time information are encrypted using the second private key. 
     Here, at step S 370 , the server device  30  may set the metering period of the third time information to be the same as that of the second time information, which is set at step S 290 , or may change the metering period. 
     That is, at step S 370 , the metering period may be changed depending on the characteristics of the metering service to be provided or information about the amount of memory for storing the meter data in the meter data management apparatus  100 , which is included in the registration request message. 
     Here, at step S 370 , the metering period may be set to be inversely proportional to the amount of memory for storing meter data in the meter data management apparatus  100 . 
     For example, at step S 370 , the larger the amount of memory in the meter data management apparatus  100 , the shorter the metering period may be set. Conversely, the smaller the amount of memory in the meter data management apparatus  100 , the longer the metering period may be set. 
     Also, at step S 370 , the metering period may be set to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, at step S 370 , the larger the change in the amount of electricity consumed by the target device  10 , the shorter the metering period may be set. Conversely, the smaller the change in the amount of electricity consumed by the target device  10 , the longer the metering period may be set. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be transmitted at step S 380 . 
     That is, the server device  30  may transmit the created second meter data request message to the meter data management apparatus  100  at step S 380 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be decrypted at step S 390 . 
     That is, the meter data management apparatus  100  may decrypt the second meter data request message, received form the server device  30 , using the second private key at step S 390 . 
     Here, the meter data management apparatus  100  may acquire the third time information at step S 390  by decrypting the second meter data request message. 
     Here, at step S 390 , the meter data management apparatus  100  may acquire the metering period and the second metering request time included in the third time information by decrypting the second meter data request message. 
     Here, at step S 390 , when the metering period is determined to be changed as the result of comparison of the metering period of the second time information with that of the third time information, the metering period of the third time information may be selected. 
     Here, at step S 390 , when the new metering period is selected, the meter data management apparatus  100  may acquire meter data based on the new metering period. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be transmitted at step S 400 . 
     That is, at step S 400 , the meter data management apparatus  100  may transmit second meter data, in which meter data from the first metering request time of the second time information to the second metering request time of the third time information are saved, to the server device  30 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be decrypted at step S 410 . 
     That is, the server device  30  may decrypt the encrypted second meter data, received from the meter data management apparatus  100 , using the second private key at step S 410 . 
     Here, the second meter data may be meter data read from the first metering request time to the second metering request time. 
     Here, because the second meter data are encrypted by the meter data management apparatus  100  using the second private key, which is created by taking the metering period and the second metering request time as input, the server device  30  may decrypt the encrypted second meter data using the second private key at step S 410 . 
     Here, the server device  30  may provide users with a metering service using the decrypted second meter data at step S 410 . 
     Also, in the meter data management method according to an embodiment of the present invention, a third private key may be created at step S 420 . 
     That is, at step S 420 , the meter data management apparatus  100  may create a third private key by taking the metering period and the second metering request time, included in the third time information, as input, the third time information being acquired by decrypting the second meter data request message. 
     Here, step S 420  may be performed before step S 410 . 
     Here, at step  420 , the meter data management apparatus  100  may acquire meter data based on a new metering period when the new metering period is selected. That is, when the metering period of the second time information is determined to differ from that of the third time information, meter data may be acquired based on the metering period of the third time information. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be encrypted at step S 430 . 
     That is, at step S 430 , the meter data management apparatus  100  may encrypt meter data, which are read at time intervals of the metering period of the third time information from the second metering request time, using the third private key, and may store the encrypted meter data. 
     In the meter data management method, when the meter data management apparatus  100  and the server device  30  respectively create new private keys at the same time, the new private keys may be the same as each other. 
     Also, in the meter data management method, the meter data management apparatus  100  and the server device  30  may use an operation mode that includes confidentiality and message authentication using a lightweight symmetric key cryptography algorithm. 
     For example, in the meter data management method, the meter data management apparatus  100  and the server device  30  may provide only confidentiality or both confidentiality and integrity depending on the resources of the smart meter in the lowest layer or on the data transmission speed thereof. 
     Accordingly, in the meter data management method, encrypted meter data stored in the meter data management apparatus  100  or the gateway device  20  may include the identifier of the meter data management apparatus  100 , the date and time at which meter data are read, and information about electricity consumption. 
     For example, meter data may be configured in the form of “Enc[smart meter ID (SM_ID)∥the date and time at which meter data are read (YYMMDD-HHMM)∥electricity consumption]”, and may further include an integrity value. 
     Also, in the meter data management method, the server device  30  may create a new private key whenever it transmits a new meter data request message to the meter data management apparatus  100 , and the meter data management apparatus  100  may create a new private key whenever it receives the new meter data request message through the above-described steps S 360  to S 430 . 
     That is, in the meter data management method according to an embodiment of the present invention, steps S 360  to S 430  may be repeatedly performed, whereby meter data may be securely protected using a private key, which is newly created in response to a request by the server device  30 , and meter data may be optimally acquired using a changed metering period. 
       FIG. 10  and  FIG. 11  are sequence diagrams that show a meter data management method in which a gateway device stores meter data according to an embodiment of the present invention. 
     Referring to  FIG. 10 , in the meter data management method according to an embodiment of the present invention, first, a registration request message may be transmitted at step S 510 . 
     That is, the meter data management apparatus  100  may transmit a registration request message to the server device  30  at step S 510 . 
     Here, the meter data management apparatus  100  may create a registration request message for registering itself in the server device  30  at step S 510 . 
     Here, at step S 510 , the meter data management device  100  may create a registration request message that includes the address of a destination, the address of an origin, and the identifier of the meter data management apparatus  100 , which is the unique information thereof. 
     Here, the registration request message may further include information about the amount of memory for storing meter data in the gateway device  20 . 
     The information about the amount of memory may be used as a reference when the server device  30  sets a metering period to be included in a registration completion message or a meter data request message. 
     Also, in the meter data management method according to an embodiment of the present invention, an initial private key may be created at step S 520 . 
     That is, at step S 520 , the server device  30  may create an initial private key using the identifier of the meter data management apparatus  100 , which is acquired from the registration request message. 
     Here, the server device  30  may acquire the identifier of the meter data management apparatus  100  at step S 520  by receiving the registration request message. 
     Here, at step S 520 , the server device  30  may create an initial private key using the secret information about the server device  30  and the identifier of the meter data management apparatus  100 , which is included in the registration request message. 
     Here, the server device  30  may register the meter data management apparatus  100  at step S 520  by checking the identifier of the meter data management apparatus  100 , which is included in the registration request message. 
     Here, the initial private key created by the server device  30  may match the initial private key created by the security unit  120  of the meter data management apparatus  100 . 
     Accordingly, without the need to manage secret information of multiple meter data management apparatuses  100 , the server device  30  may create a private key that matches the initial private key contained in each of the meter data management apparatuses  100  using the secret information thereof and the identifier of each of the meter data management apparatuses  100  received therefrom at step S 520 . 
     Also, in the meter data management method according to an embodiment of the present invention, an encrypted registration completion message may be created at step S 530 . 
     That is, at step S 530 , the server device  30  may create a registration completion message in which first time information is encrypted using the initial private key. 
     Here, at step S 530 , the server device  30  may create a registration completion message in which the metering period and the metering start time included in the first time information are encrypted using the initial private key. 
     Here, the metering period may be set depending on service characteristics or information about the amount of memory for storing meter data in the gateway device  20 , which is included in the registration request message. 
     Here, at step S 530 , the metering period may be set to be inversely proportional to the amount of memory for storing meter data in the gateway device  20 . 
     For example, at step S 530 , the larger the amount of memory in the gateway device  20 , the shorter the metering period may be set. Conversely, the smaller the amount of memory in the gateway device  20 , the longer the metering period may be set. 
     Also, at step S 530 , the metering period may be set to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, at step S 530 , the larger the change in the amount of electricity consumed by the target device  10 , the shorter the metering period may be set. Conversely, the smaller the change in the amount of electricity consumed by the target device  10 , the longer the metering period may be set. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Also, in the meter data management method according to an embodiment of the present invention, the encrypted registration completion message may be transmitted at step S 540 . 
     That is, the server device  30  may transmit the created registration completion message to the meter data management apparatus  100  at step S 540 . 
     Also, in the meter data management method according to an embodiment of the present invention, the registration completion message may be decrypted at step S 550 . 
     That is, the meter data management apparatus  100  may decrypt the registration completion message, received from the server device  30 , using the initial private key at step S 550 . 
     Here, the meter data management apparatus  100  may acquire the first time information at step S 550  by decrypting the registration completion message. 
     Here, at step S 550 , the meter data management apparatus  100  may acquire meter data from the target device using the metering period and the metering start time of the first time information, which are acquired by decrypting the registration completion message. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data management apparatus  100  may create a first private key at step S 560 . 
     That is, at step S 560 , the meter data management apparatus  100  may create a first private key by taking the metering period and the metering start time, included in the first time information, as input, the first time information being acquired by decrypting the registration completion message. 
     Also, in the meter data management method according to an embodiment of the present invention, meter data may be encrypted and transmitted at step S 570 . 
     That is, at step S 570 , the meter data management apparatus  100  may encrypt meter data, which are read at time intervals of the metering period of the first time information from the metering start time, using the first private key, and may transmit the encrypted meter data to the gateway device  20 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be stored at step S 580 . 
     That is, at step S 580 , the gateway device  20  may store the meter data received from the meter data management apparatus  100 . 
     Also, in the meter data management method according to an embodiment of the present invention, the server device  30  may create a first private key at step S 590 . 
     That is, at step S 590 , the server device  30  may create a first private key by taking the metering period and the metering start time, included in the first time information, as input, the first time information being acquired by decrypting the registration completion message. 
     Here, step S 590  may be performed before step S 550 . 
     Also, in the meter data management method according to an embodiment of the present invention, an encrypted meter data request message may be created at step S 600 . 
     That is, the server device  30  may create a first meter data request message in which second time information is encrypted using the first private key at step S 600 . 
     Here, at step S 600 , the server device  30  may create a first meter data request message in which the metering period and the first metering request time included in the second time information are encrypted using the first private key. 
     Here, at step S 600 , the server device  30  may set the metering period of the second time information to be the same as that of the first time information, which is set at step S 530 , or may change the metering period. 
     That is, at step S 600 , the metering period may be set by changing the previous metering period depending on the characteristics of the metering service to be provided or information about the amount of memory for storing meter data in the gateway device  20 , which is included in the registration request message. 
     Here, at step S 600 , the metering period may be set to be inversely proportional to the amount of memory for storing meter data in the gateway device  20 . 
     For example, at step S 600 , the larger the amount of memory in the gateway device  20 , the shorter the metering period may be set. Conversely, the smaller the amount of memory in the gateway device  20 , the longer the metering period may be set. 
     Also, at step S 600 , the metering period may be set to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, at step S 600 , the larger the change in the amount of electricity consumed by the target device  10 , the shorter the metering period may be set. Conversely, the smaller the change in the amount of electricity consumed by the target device  10 , the longer the metering period may be set. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be transmitted at step S 610 . 
     That is, the server device  30  may transmit the created first meter data request message to the meter data management apparatus  100  at step S 610 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be decrypted at step S 620 . 
     That is, the meter data management apparatus  100  may decrypt the first meter data request message, received from the server device  30 , using the first private key at step S 620 . 
     Here, the meter data management apparatus  100  may acquire the second time information at step S 620  by decrypting the first meter data request message. 
     Here, at step  620 , the meter data management apparatus  100  may acquire the metering period and the first metering request time included in the second time information by decrypting the first meter data request message. 
     Here, at step S 620 , when the metering period is determined to be changed as the result of comparison of the metering period of the first time information with that of the second time information, the metering period of the second time information may be selected. 
     Here, at step S 620 , when the new metering period is set, the meter data management apparatus  100  may acquire meter data based on the new metering period. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be transmitted at step S 630 . 
     That is, at step S 630 , the meter data management apparatus  100  may request the gateway device  20  to transmit first meter data, in which meter data from the metering start time of the first time information to the first metering request time of the second time information are encrypted and saved, to the server device  30 . 
     Here, at step S 630 , the gateway device  20  may transmit the first meter data, in which meter data from the metering start time of the first time information to the first metering request time of the second time information are encrypted and saved, to the server device  30 . 
     Also, in the meter data management method according to an embodiment of the present invention, the first meter data may be decrypted at step S 640 . 
     That is, the server device  30  may decrypt the encrypted first meter data, received from the gateway device  20 , using the first private key at step S 640 . 
     Here, the first meter data may be meter data read from the metering start time to the first metering request time. 
     Here, because the first meter data are encrypted by the meter data management apparatus  100  using the first private key, which is created by taking the metering period and the metering start time as input, the server device  30  may decrypt the encrypted first meter data using the first private key at step S 640 . 
     Here, the server device  30  may provide users with a metering service using the decrypted first meter data at step S 640 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data management device  100  may create a second private key at step S 650 . 
     That is, the meter data management apparatus  100  may create a second private key at step S 650  by taking the metering period and the first metering request time, included in the second time information, as input, the second time information being acquired by decrypting the first meter data request message. 
     Here, step S 650  may be performed before step S 640 . 
     Here, at step S 650 , the meter data management apparatus  100  may acquire meter data based on a new metering period when the new metering period is selected. That is, when the metering period of the first time information is determined to differ from that of the second time information, meter data may be acquired based on the metering period of the second time information. 
     Also, in the meter data management method according to an embodiment of the present invention, meter data may be encrypted and transmitted at step S 660 . 
     That is, at step S 660 , the meter data management apparatus  100  may encrypt meter data, acquired at time intervals of the metering period of the second time information from the first metering request time, using the second private key, and may transmit the encrypted meter data to the gateway device  20 . 
     Also, in the meter data management method according to an embodiment of the present invention, the encrypted meter data may be stored at step S 670 . 
     That is, at step S 670 , the gateway device  20  may store the encrypted meter data received from the meter data management apparatus  100 . 
     Referring to  FIG. 11 , in the meter data management method according to an embodiment of the present invention, the server device  30  may create a second private key at step S 680 . 
     That is, at step S 680 , the server device  30  may create a second private key by taking the metering period and the first metering request time, included in the second time information, as input. 
     Also, in the meter data management method according to an embodiment of the present invention, an encrypted meter data request message may be created at step S 690 . 
     That is, at step S 690 , the server device  30  may create a second meter data request message in which third time information is encrypted using the second private key. 
     Here, at step S 690 , the server device  30  may create a second meter data request message in which the metering period and the second metering request time included in the third time information are encrypted using the second private key. 
     Here, at step S 690 , the server device  30  may set the metering period of the third time information to be the same as that of the second time information, which is set at step S 600 , or may change the metering period. 
     That is, at step S 690 , the metering period may be set by changing the previous metering period depending on the characteristics of the metering service to be provided or information about the amount of memory for storing meter data in the gateway device  20 , which is included in the registration request message. 
     Here, at step S 690 , the metering period may be set to be inversely proportional to the amount of memory for storing meter data in the gateway device  20 . 
     For example, at step S 690 , the larger the amount of memory in the gateway device  20 , the shorter the metering period may be set. Conversely, the smaller the amount of memory in the gateway device  20 , the longer the metering period may be set. 
     Also, at step S 690 , the metering period may be set to be inversely proportional to a change in the amount of electricity consumed by the target device  10  depending on the service characteristics. 
     For example, at step S 690 , the larger the change in the amount of electricity consumed by the target device  10 , the shorter the metering period may be set. Conversely, the smaller the change in the amount of electricity consumed by the target device  10 , the longer the metering period may be set. 
     For example, the metering period may be set in units of minutes to, for example, one minute, five minutes, ten minutes, fifteen minutes, thirty minutes, sixty minutes, or the like. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be transmitted at step S 700 . 
     That is, the server device  30  may transmit the created second meter data request message to the meter data management apparatus  100  at step S 700 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data request message may be decrypted at step S 710 . 
     That is, the meter data management apparatus  100  may decrypt the second meter data request message, received from the server device  30 , using the second private key at step S 710 . 
     Here, the meter data management apparatus  100  may acquire the third time information at step S 710  by decrypting the second meter data request message. 
     Here, at step S 710 , the meter data management apparatus  100  may acquire the metering period and the second metering request time included in the third time information by decrypting the second meter data request message. 
     Here, at step S 710 , when the metering period is determined to be changed as the result of comparison of the metering period of the second time information with that of the third time information, the metering period of the third time information may be selected. 
     Here, at step S 710 , when the new metering period is set, the meter data management apparatus  100  may acquire meter data based on the new metering period. 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be transmitted at step S 720 . 
     That is, at step S 720 , the meter data management apparatus  100  may request the gateway device  20  to transmit second meter data, in which meter data from the first metering request time of the second time information to the second metering request time of the third time information are saved, to the server device  30 . 
     Here, at step S 720 , the gateway device  20  may transmit the second meter data, in which meter data from the first metering request time of the second time information to the second metering request time of the third time information are saved, to the server device  30 . 
     Also, in the meter data management method according to an embodiment of the present invention, the meter data may be decrypted at step S 730 . 
     That is, the server device  30  may decrypt the encrypted second meter data, received from the gateway device  20 , using the second private key at step S 730 . 
     Here, the second meter data may be meter data read from the first metering request time to the second metering request time. 
     Here, because the second meter data are encrypted by the meter data management apparatus  100  using the second private key, which is created by taking the metering period and the second metering request time as input, the server device  30  may decrypt the encrypted second meter data using the second private key at step S 730 . 
     Here, at step S 730 , the server device  30  may provide users with a metering service using the decrypted second meter data. 
     Also, in the meter data management method according to an embodiment of the present invention, a third private key may be created at step S 740 . 
     That is, at step S 740 , the meter data management apparatus  100  may create a third private key by taking the metering period and the second metering request time, included in the third time information, as input, the third time information being acquired by decrypting the second meter data request message. 
     Here, step S 740  may be performed before step S 730 . 
     Here, at step S 740 , the meter data management apparatus  100  may acquire meter data based on a new metering period when the new metering period is selected. That is, when the metering period of the second time information is determined to differ from that of the third time information, meter data may be acquired based on the metering period of the third time information. 
     Also, in the meter data management method according to an embodiment of the present invention, meter data may be encrypted and transmitted at step S 750 . 
     That is, at step S 750 , the meter data management apparatus  100  may encrypt meter data, acquired at time intervals of the metering period of the third time information from the second metering request time, using the third private key, and may transmit the encrypted meter data to the gateway device  20 . 
     Also, in the meter data management method according to an embodiment of the present invention, the encrypted meter data may be stored at step S 760 . 
     That is, at step S 760 , the gateway device  20  may store the encrypted meter data received from the meter data management apparatus  100 . 
     In the meter data management method, when the meter data management apparatus  100  and the server device  30  respectively create new private keys at the same time, the new private keys may be the same as each other. 
     Also, in the meter data management method, the meter data management apparatus  100  and the server device  30  may use an operation mode that includes confidentiality and message authentication using a lightweight symmetric key cryptography algorithm. 
     For example, in the meter data management method, the meter data management apparatus  100  and the server device  30  may provide only confidentiality or both confidentiality and integrity depending on the resources of a smart meter in the lowest layer and on the data transmission speed thereof. 
     Accordingly, in the meter data management method, encrypted meter data stored in the meter data management apparatus  100  or the gateway device  20  may include the identifier of the meter data management apparatus  100 , the date and time at which meter data are read, and information about electricity consumption. 
     For example, meter data may be configured in the form of “Enc[smart meter ID (SM_ID)∥the date and time at which meter data are read (YYMMDD-HHMM)∥electricity consumption]”, and may further include an integrity value. 
     Also, in the meter data management method, the server device  30  may create a new private key whenever it transmits a new meter data request message to the meter data management apparatus  100 , and the meter data management apparatus  100  may create a new private key whenever it receives the new meter data request message through the above-described steps S 680  to S 760 . 
     That is, in the meter data management method according to an embodiment of the present invention, steps S 680  to S 760  may be repeatedly performed, whereby meter data may be securely protected using a private key newly created in response to a request by the server device  30  and meter data may be optimally acquired using a changed metering period. 
       FIG. 12  is a block diagram that shows a computer system according to an embodiment of the present invention. 
     Referring to  FIG. 12 , the target device  10 , the gateway device  20 , the server device  30 , and the meter data management apparatus  100  according to an embodiment of the present invention may be implemented in a computer system  1100  including a computer-readable recording medium. As illustrated in  FIG. 12 , the computer system  1100  may include one or more processors  1110 , memory  1130 , a user interface input device  1140 , a user interface output device  1150 , and storage  1160 , which communicate with each other via a bus  1120 . Also, the computer system  1100  may further include a network interface  1170  connected to a network  1180 . The processor  1110  may be a central processing unit or a semiconductor device for executing processing instructions stored in the memory  1130  or the storage  1160 . The memory  1130  and the storage  1160  may be various types of volatile or nonvolatile storage media. For example, the memory may include ROM  1131  or RAM  1132 . 
     According to the present invention, end-to-end security between a device in the lowest layer and a device in the highest layer may be guaranteed, and information may be prevented from being leaked to third parties. 
     Also, according to the present invention, a device in the lowest layer may encrypt sensitive and important data, such as private information and the like, before the data are stored, and may transmit the encrypted data to a device in the highest layer, whereby data stored in the devices may be securely protected. 
     Also, according to the present invention, secure encryption and decryption functions may be provided in the state in which a device in the highest layer does not manage keys for respective devices in the lowest layer. 
     Also, according to the present invention, meter data may be securely protected using a private key that is newly created in response to a request by a device in the highest layer, and meter data may be optimally acquired using an updated metering interval. 
     As described above, the apparatus and method for managing meter data according to the present invention are not limitedly applied to the configurations and operations of the above-described embodiments, but all or some of the embodiments may be selectively combined and configured, so that the embodiments may be modified in various ways.