JP4921899B2 - ENCRYPTION DEVICE, DECRYPTION DEVICE, AND ENCRYPTION KEY UPDATE METHOD - Google Patents

Description

  The present invention relates to an encryption device that encrypts data such as video and audio, a decryption device that decrypts encrypted data, and an encryption key update method that updates an encryption key for encrypting data.

  In recent years, IP (Internet Protocol) multicast has attracted attention as a new usage of the Internet. IP multicast is a data transfer method capable of delivering the same data to a large number of recipients, and data distribution services such as video and audio have begun to appear in earnest using IP multicast. Compared to IP unicast, which distributes data to a specific partner by specifying a single address, IP multicast reduces the processing load on servers and networks by copying packets containing data at the router, and by parallel distribution Advantages such as simultaneity and shortening of delivery time can be obtained, so it can be said that it is suitable for broadcast delivery to multiple addresses.

  By the way, when realizing communication via the Internet by IP multicast, security must be taken into consideration. In order to realize secure communication, it is indispensable to encrypt data and guarantee the validity of the data. Among them, it is particularly important how to distribute and update keys used for data encryption and decryption processing.

  In the encryption technique for data distribution by IP multicast, for example, the ones shown in Non-Patent Documents 1 to 3 are known as key distribution and update methods.

  First, in Non-Patent Document 1, data is encrypted with a common key to generate encrypted data, and the common key is encrypted for each authorized user using an individual encryption key. By generating an encrypted common key and streaming the encrypted common key together with the encrypted data, the authorized user decrypts the encrypted common key with a unique encryption key and encrypts it with the extracted common key Data can be decrypted, and a user without usage authority cannot decrypt the data.

  Next, what is shown in Non-Patent Document 2 is distributed different for each user as an encryption key for decoding the same encryption stream distributed to each terminal, and this encryption key has an expiration date, Each user communicates with the server to periodically update the key. By observing this key update on the server side, it is possible to know when, who, and how much the IP multicast broadcast was viewed, and the encryption key update should be canceled according to the user's contract conditions. Thus, it is possible to control whether or not each user can view the content from the server side.

Furthermore, what is shown in Non-Patent Document 3 realizes copyright protection by embedding different electronic fingerprints for each user in encrypted data distributed using IP multicast, and uses a web client in advance. The data is decrypted with the authentication key delivered individually to each user.
“Developing network security technology to realize advanced commercial services over IPv6”, [online], June 1, 2001, Nippon Telegraph and Telephone Corporation, [July 19, 2006 search], Internet <URL: http: // www. ntt. co. jp / news / news01 / 0106/010601. html> Koji Hiraoka et al., “Efforts of IPv6 in OKI MediaServer V5”, Oki Technical Review No. 197 Vol. 71 no. 1. January 2004 Katsushi Yamaoka et al., “Research and Development on Audience-Limited Digital Broadcasting Platform Using Software”, 1st Strategic Information and Communication Research and Development Promotion Results Presentation, Session 7: Preliminary Collection of Young Advanced IT Researcher Development Research and Development 1 June 2005

  However, the ones shown in Non-Patent Documents 1 to 3 are configured to distribute a key for decrypting encrypted data to all users, which increases the processing load on servers and networks. There was a problem.

  The present invention has been made to solve the conventional problems, and provides an encryption device, a decryption device, and an encryption key update method capable of reducing the processing load of a server and a network as compared with the conventional one. For the purpose.

An encryption apparatus according to the present invention is an encryption apparatus that transmits encrypted data to a decryption apparatus, and stores a first encryption key storage that stores a first encryption key that is updated every predetermined first period. Means, second encryption key storage means for storing a second encryption key updated every second predetermined period longer than the first period, and a third encryption key shared with the decryption device A third encryption key storage means for storing data, and a data encryption that obtains the latest first encryption key from the first encryption key storage means and encrypts the data with the latest first encryption key to generate encrypted data Obtaining the latest second encryption key from the encryption means and the second encryption key storage means, and encrypting the latest first encryption key with the latest second encryption key to generate an encrypted first encryption key a first encryption key encryption means, the encrypted data, the encrypted first encryption key and, When the second encryption key is updated, a transmission means for transmitting the latest second encryption key encrypted with the second encryption key before the update to the decryption device, and a second acquired in advance by the decryption device Request information sent by the decryption device to request the latest second encryption key when decryption of the encrypted first encryption key fails using an encryption key, the decryption Successful authentication of the transmission source, encryption request information receiving means for receiving the encryption request information encrypted by the device with the third encryption key, transmission source authentication means for authenticating the transmission source of the encryption request information, and A second encryption key encryption unit for each source that encrypts the latest second encryption key with the third encryption key, and the latest second encryption key encrypted with the third encryption key. It has the structure provided with the after-update 2nd encryption key transmission means transmitted originally .

  With this configuration, the encryption device of the present invention allows only the user who has the second encryption key before the update, that is, the authorized user who has previously signed a contract, to decrypt the encrypted first encryption key, Since the encrypted data can be decrypted with the decrypted first encryption key, there is no need to distribute a key for decrypting the encrypted data to all users unlike the conventional one. The processing load on the server and the network can be reduced as compared with the conventional one.

Also, with this configuration, the encryption device of the present invention authenticates the user who requested the updated second encryption key, and encrypts the updated second encryption key with the third encryption key when the authentication is successful. Since it can be provided to the user, even if the authorized user does not acquire the updated second encryption key for some reason, the updated second encryption key can be provided in response to the request of the authorized user. .

  Further, in the encryption device according to the present invention, the encryption request information includes either a message authentication code or electronic signature information, and the transmission source authentication means includes at least one of the message authentication code and the electronic signature information. Based on this, the transmission source is authenticated.

  With this configuration, the encryption apparatus of the present invention authenticates the user who requested the updated second encryption key based on at least one of the message authentication code and the electronic signature information, and therefore requested the updated second encryption key. The accuracy of user authentication can be improved.

  Further, in the encryption device according to the present invention, the encryption request information receiving means receives the encryption request information from the transmission source via a communication network, and the encryption request information indicates a generated date and time. It has a configuration including at least one of generation date and time information, location information indicating the location of the transmission source on the communication network, and an identifier for identifying the transmission source.

  With this configuration, the encryption apparatus according to the present invention has at least one of the generation date / time information of the encryption request information, the position information indicating the position of the transmission source on the network, and the identifier for identifying the transmission source. Is used to authenticate the user who requested the updated second encryption key, so that it is possible to further increase the accuracy of the authentication of the user who requested the updated second encryption key.

The decryption device of the present invention is a decryption device for decrypting encrypted data encrypted by an encryption device, wherein the encrypted data, the encrypted first encryption key, and the second encryption key are Receiving means for receiving the latest second encryption key encrypted with the second encryption key before update when updated, and after the update for decrypting the latest second encryption key with the second encryption key before update Second encryption key decryption means; second encryption key storage means for storing the decrypted second encryption key; third encryption key storage means for storing a third encryption key shared with the encryption device; First encryption key decryption means for decrypting the encrypted first encryption key with the second encryption key acquired from the second encryption key storage means to generate a decrypted first encryption key, and the decrypted first encryption key The data decrypting means for decrypting the encrypted data and the first encryption key decrypting means A request to output the encryption request information encrypted with the third encryption key, which is request information for requesting the encryption device the latest second encryption key when the decryption of the first encryption key fails. Information output means, encryption request information transmission means for transmitting the encryption request information to the encryption apparatus, and the latest second encryption key encrypted with the third encryption key is received from the encryption apparatus. A second encrypted key receiving means after update, and a second received encryption key decrypting means for decrypting the latest second encryption key received by the updated second encryption key receiving means with the third encryption key . It has a configuration.

  With this configuration, the decryption device of the present invention allows only authorized users who have the second encryption key before update to decrypt the encrypted first encryption key, and decrypts the encrypted data. Therefore, it is not necessary to distribute a key for decrypting encrypted data to all users unlike the conventional one, and the processing load on the server and network is reduced. It can be reduced more than the conventional one.

Also, with this configuration, the decryption device of the present invention requests the updated second encryption key from the encryption device, and then after the update encrypted with the third encryption key when the encryption device succeeds in authentication. Since the second encryption key can be acquired, the updated second encryption key is provided in response to a request from the authorized user even when the authorized user does not acquire the updated second encryption key for some reason. be able to.

  Furthermore, in the decryption device of the present invention, the encryption request information includes either a message authentication code or electronic signature information, and the updated second encryption key receiving means includes the message authentication code in the encryption device. When the authentication based on at least one of the electronic signature information is successful, the updated second encryption key is received from the encryption device.

  With this configuration, the decryption apparatus of the present invention causes the encryption apparatus to authenticate the user based on at least one of the message authentication code and the electronic signature information. Therefore, the authentication of the user who requested the second encryption key after the update is high. Accuracy can be improved.

  Furthermore, in the decryption device of the present invention, the encryption request information transmission means transmits the encryption request information to the encryption device via a communication network, and the encryption request information indicates the date and time when it was generated. It includes a configuration including at least one of generation date / time information to be displayed, position information indicating the position of the own apparatus on the communication network, and an identifier for identifying the own apparatus.

  With this configuration, the decryption device of the present invention includes the generation date / time information indicating the generation date / time of the latest work key request message, the position information indicating the position of the transmission source on the network, and the identifier for identifying the transmission source. Since the encryption device performs authentication of the user who requested the updated second encryption key using at least one of them, the authentication of the user who requested the updated second encryption key is further improved in accuracy. Can do.

In the encryption key update method of the present invention, a first encryption key storage step in which an encryption device that transmits encrypted data to a decryption device stores a first encryption key that is updated every predetermined first period. A second encryption key storage step for storing a second encryption key updated every second predetermined period longer than the first period, and a third encryption key shared with the decryption device A third encryption key storing step for storing, and data encryption for obtaining the latest first encryption key in the first encryption key storing step and encrypting data with the latest first encryption key to generate encrypted data And obtaining the latest second encryption key in the second encryption key storage step, and encrypting the latest first encryption key with the latest second encryption key to generate an encrypted first encryption key. An encryption key encryption step, the encrypted data, the encrypted first encryption key, And transmitting the latest second encryption key encrypted with the second encryption key before update to the decryption device when the second encryption key is updated, and the decryption device previously acquired Request information transmitted by the decryption device to request the latest second encryption key when the decryption of the encrypted first encryption key fails using a second encryption key, An encryption request information receiving step in which the decryption device receives the encryption request information encrypted with the third encryption key; a source authentication step of authenticating a source of the encryption request information; and authentication of the source A second encryption key encryption step by source for encrypting the latest second encryption key with the third encryption key when successful, and a latest second encryption key encrypted with the third encryption key. have the configuration for performing the second encryption key transmitting step updated to be transmitted to the sender .

  With this configuration, the encryption key update method of the present invention enables only authorized users to decrypt the encrypted first encryption key, and encrypts the encrypted data with the decrypted first encryption key. Since it can be decrypted, there is no need to distribute a key for decrypting encrypted data to all users unlike the conventional one, and the processing load on the server and network is reduced compared to the conventional one. be able to.

  The present invention can provide an encryption device, a decryption device, and an encryption key update method that have the effect of reducing the processing load on a server or a network as compared with the conventional one.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. An example in which the encryption apparatus and the decryption apparatus of the present invention are applied to a content distribution system that distributes data such as video, audio, text, and still images (hereinafter referred to as “content”) by IP multicast will be described. To do.

  First, the configuration of the content distribution system 10 in the present embodiment will be described.

  As shown in FIG. 1, a content distribution system 10 according to the present embodiment includes a content providing device 20 that provides content, a content distribution device 100 that distributes content, and a receiving device that receives content via a communication network 30. 200. As will be described later, the content distribution device 100 transmits the encrypted content and a key related to the encryption of the content to the reception device 200 via the communication network 30, and the reception device 200 needs the latest work key. At that time, a message to that effect is transmitted to the content distribution apparatus 100.

  Note that, as a form of the receiving device 200, for example, a fixed receiver 201 installed and used in the home of the user A who has contracted the content distribution service, a mobile phone 202 carried by the user B, and a user C Examples thereof include a personal digital assistant 203 which is a personal electronic device called PDA (Personal Digital Assistants).

  The content providing device 20 includes content providing devices 21 to 23. The content providing devices 21 to 23 are provided in different content providers, and transmit the content produced by each content provider to the content distribution device 100 based on a predetermined contract. Yes. Note that the number of content providing devices 20 is not limited to three.

  The communication network 30 includes a plurality of routers 31. For example, the router 31 transfers an IP multicast packet to a predetermined receiving device 200 based on destination information.

  The content distribution device 100 is configured to accumulate and manage content received from the content providing device 20. The configuration of the content distribution apparatus 100 is, for example, as shown in FIG. 2, and a packet including destination information is encrypted by IP multicast via the communication network 30 and the content is encrypted to the receiving apparatus 200 of a user who has subscribed to the content distribution service. To be delivered. In the present embodiment, as keys for content encryption, there are a session key Ks, a work key Kw, and a master key Km. Each of these keys is data composed of a character string of a predetermined number of bits, including generation date / time information indicating the generated date / time. This will be specifically described below.

  First, the session key Ks is a key used for content encryption and decryption, and is updated, for example, about every second in order to prevent unauthorized reception of content. Next, the work key Kw is a key used for encryption and decryption of the session key Ks, and is updated about every month, for example. Furthermore, the master key Km is a key that the user of the receiving device 200 acquires when contracting for the content distribution service, and is a key used for encryption and decryption of the work key Kw. The master key Km is stored in an IC card such as a CAS (Conditional Access Systems) card.

  After the user of the receiving device 200 contracts with the content distribution service and acquires the master key Km, for example, the work key Kw is distributed to the receiving device 200 by requesting the work key Kw from the content distribution device 100. Therefore, in the content distribution system 10, even when the work key Kw is updated, when the work key Kw is updated, for example, when the power of the receiving apparatus 200 is turned off or the power is turned on. Even if the latest work key Kw could not be acquired due to the inability to communicate, the user of the receiving device 200 is regarded as a legitimate user if the work key Kw before update is available. Can do.

  The session key Ks, the work key Kw, and the master key Km correspond to the first encryption key, the second encryption key, and the third encryption key described in the claims, respectively. Here, the session key Ks may be referred to as a shared key or a scramble key. The master key Km may be referred to as an individual key.

  Next, a detailed configuration of the content distribution apparatus 100 will be described.

  As shown in FIG. 2, the content distribution device 100 is a server device 110 that manages content and each key, an encryption device 120 that performs processing related to encryption of the content and each key, and a transmission / reception that communicates with the reception device 200. Device 130.

  The server apparatus 110 includes a content management server 111 that manages content, a session key management server 112 that manages a session key Ks, a work key management server 113 that manages a work key Kw, and a master key management that manages a master key Km. Server 114. Note that the content and each key may be managed by one server.

  Although not shown in the figure, a registration device for each key is connected to the session key management server 112, the work key management server 113, and the master key management server 114, and each key is registered by this registration device. It has become.

  The encryption device 120 includes a content encryption unit 121 that encrypts content, a latest session key storage unit 122 that stores the latest session key Ks, a session key encryption unit 123 that encrypts the session key Ks, a work A work key update determination unit 124 that determines whether or not the key Kw has been updated, a latest work key storage unit 125 that stores the latest work key Kw, and an updated work key encryption that encrypts the updated work key Kw. Unit 126, a user-specific updated work key encryption unit 127 that encrypts the updated work key Kw for each user, and a user authentication unit 128 that performs user authentication.

  The transmission / reception apparatus 130 receives a reception unit 131 that transmits content and each key and a message for requesting the latest work key Kw transmitted by the reception apparatus 200 (hereinafter referred to as “latest work key request message”). Part 132. The encryption device 120 corresponds to the encryption device of the present invention.

  The content management server 111 receives each content from the content providing device 20, accumulates, registers, and manages the received content. For example, the received content is registered and managed based on the content and a content ID (Identification) for identifying the content and the business providing the content.

  Each of the session key management server 112, the work key management server 113, and the master key management server 114 accumulates each key registered by each key registration device (not shown), for example, to the key number assigned to each key. Each key is managed based on this.

  The content encryption unit 121 receives content from the content management server 111 and encrypts the content using the latest session key Ks stored in the latest session key storage unit 122. For example, the content encryption unit 121 divides the input content into blocks having a certain number of bits based on the block encryption method, and encrypts the content using the latest session key Ks. The content encryption unit 121 constitutes a data encryption unit of the present invention.

  The latest session key storage unit 122 acquires and stores the updated session key Ks updated from the session key management server 112 when the session key Ks is updated.

  The session key encryption unit 123 uses the latest work key Kw stored in the latest work key storage unit 125 to encrypt the latest session key Ks extracted from the latest session key storage unit 122. . The session key encryption unit 123 constitutes a first encryption key encryption unit of the present invention.

  The work key update determination unit 124 determines whether or not the work key Kw has been updated. Specifically, for example, when the work key Kw is registered in the work key management server 113, the work key update determination unit 124 receives a signal from the work key management server 113 that the work key Kw has been registered. It has become. At that time, the work key update determination unit 124 uses the work key Kw newly registered in the work key management server 113 and the work key Kw stored in the latest work key storage unit 125, for example, each work key Kw By comparing the generated generation date and time information, it is determined whether or not the work key Kw has been updated.

  When the work key update determination unit 124 determines that the work key Kw has been updated, the work key update determination unit 124 acquires the updated work key Kw from the work key management server 113, and the latest work key storage unit 125 stores the work key Kw. It is like that.

In this specification, when a work key is referred to without being distinguished before and after updating, it is simply expressed as “work key Kw”. On the other hand, when it is necessary to distinguish the work key Kw before and after the update, the symbol “t” indicating the update status in time series is added to the symbol “Kw” indicating the work key, and expressed as the work key Kw _t. those for key Kw _t been updated n times referred to as "the work key _{Kw t + n".} For example, a work key Kw _t updated once is represented as a work key Kw _{t + 1} .

The updated work key encryption unit 126 encrypts the updated work key Kw with the work key Kw immediately before the update. Specifically, when the work key Kw _t becomes work key _{Kw t + 1} is updated, update work key encryption unit 126 is configured to encrypt the work key _{Kw t + 1} in the work key Kw _t. Here, the encryption of the updated work key Kw is not limited to the work key Kw immediately before the update, and for example, a structure using the update key before the update may be used. Further, the updated work key encryption unit 126 constitutes an updated second encryption key encryption unit of the present invention.

  When receiving the latest work key request message from the receiving device 200, the user-specific update work key encryption unit 127 acquires the latest work key Kw from the latest work key storage unit 125 and stores it in the master key management server 114. The latest work key Kw is encrypted with the master key Km and output to the transmission unit 131. The user-specific update work key encryption unit 127 constitutes a second encryption key encryption unit for each transmission source according to the present invention.

  When receiving the latest work key request message from the receiving apparatus 200, the user authenticating unit 128 authenticates the user of the receiving apparatus 200 that is the transmission source. The user authentication unit 128 constitutes a transmission source authentication unit of the present invention.

  The transmission unit 131 includes, for example, a packet generation unit that encapsulates encrypted content into an IP packet, and a network card that transmits the IP packet. For example, the transmission unit 131 encapsulates content encrypted as data in a transstream format conforming to the MPEG (Moving Picture Experts Group) -2 standard into an IP packet, and transmits the packet to the reception device 200 by IP multicast. It has become.

  Further, the transmission unit 131 encrypts the session key Ks encrypted by the session key encryption unit 123, the work key Kw encrypted by the updated work key encryption unit 126, and the user-specific updated work key encryption unit 127. The transmitted work key Kw is transmitted. Each key may be transmitted separately from the content, or may be transmitted after being multiplexed with the content. As a technique for multiplexing each key with content and transmitting it, for example, ECM (Entimental Control Message) in “access control method in digital broadcasting” (standard number ARIB STD-B25) standardized by ARIB (Radio Industry Association). ) And EMM (Entitlement Management Message) methods. The transmission unit 131 constitutes an updated second encryption key transmission unit of the present invention.

  The receiving unit 132 includes, for example, a network card that receives an IP packet, and receives the latest work key request message transmitted from the receiving device 200 using the IP packet. The receiving unit 132 constitutes an encryption request information receiving unit of the present invention.

  Next, a detailed configuration of the receiving apparatus 200 will be described.

  As shown in FIG. 3, the receiving apparatus 200 includes a receiving unit 210 that receives content, and a transmitting unit 220 that transmits a latest work key request message. Note that the receiving device 200 corresponds to the decoding device of the present invention.

  The receiving unit 210 includes a receiving unit 211 that receives the encrypted content and each key, a content decrypting unit 212 that decrypts the encrypted content, and a content storage unit 213 that stores the decrypted content. The content output unit 214 that outputs the content, the session key decryption unit 215 that decrypts the session key Ks, the session key storage unit 216 that stores the decrypted session key Ks, and the work key that decrypts the work key Kw The decryption unit 217 includes a work key update determination unit 218 that determines whether or not the work key Kw has been updated, and a latest work key storage unit 219 that stores the latest work key Kw.

  The transmission means 220 includes a master key storage unit 221 that stores the master key Km, a request message generation unit 222 that generates the latest work key request message, and a request message encryption unit 223 that encrypts the generated latest work key request message. A MAC generation unit 224 that generates a digest of a message for performing user authentication (hereinafter referred to as a “MAC (Message Authentication Code)”), and a transmission unit 225 that transmits the encrypted message and the MAC. And.

  The receiving unit 211 includes, for example, a network card that receives IP packets, receives IP packets including encrypted content from the content distribution apparatus 100 via the communication network 30, and outputs the IP packets to the content decrypting unit 212. It has become. The receiving unit 211 constitutes encrypted data input means and updated second encryption key receiving means of the present invention.

  The content decryption unit 212 decrypts the received content using the session key Ks stored in the session key storage unit 216 and outputs the decrypted content to the content storage unit 213.

  The content storage unit 213 is configured by, for example, a hard disk drive, and stores received content. In addition, the content storage unit 213 generates menu information for selecting content when storing the content, and outputs the menu information to the content output unit 214.

  The content output unit 214 is connected to a content playback device (not shown) that plays back video and audio, and outputs content in a playback format corresponding to the playback device. In addition, the content output unit 214 displays the menu information acquired from the content storage unit 213 on the playback device, thereby allowing the user to select content desired by the user via, for example, a remote control device.

  The session key decryption unit 215 decrypts the session key Ks received by the reception unit 211 using the work key Kw stored in the latest work key storage unit 219. If the session key decryption unit 215 fails to decrypt the received session key Ks, the session key decryption unit 215 outputs a signal indicating that to the work key update determination unit 218. The session key decryption unit 215 constitutes a first encryption key decryption unit of the present invention.

  As described above, since the session key Ks is encrypted with the work key Kw, the work key Kw stored in the latest work key storage unit 125 of the content distribution apparatus 100 and the latest work key storage unit 219 of the reception apparatus 200 are stored. If the stored work key Kw is the same, the decryption is successful, but if the two are different, the decryption fails. For example, when the power of the receiving apparatus 200 is turned off when the work key Kw is updated and distributed, the work key Kw of both is different, so that the decryption of the session key Ks fails. In this case, the receiving device 200 requests the latest work key Kw by transmitting a latest work key request message to the content distribution device 100 as described later.

  The session key storage unit 216 stores the session key Ks decrypted by the session key decryption unit 215.

  The work key decryption unit 217 receives and decrypts the work key Kw when the work key Kw is updated in the content distribution apparatus 100 and the updated work key Kw is distributed. The work key decryption unit 217 outputs information related to the success or failure of decryption of the received work key Kw to the work key update determination unit 218. The work key decryption unit 217 constitutes the updated second encryption key decryption means and the received second encryption key decryption means of the present invention.

  Here, the work key decryption unit 217 decrypts the work key Kw when the work key Kw updated by the content distribution apparatus 100 is broadcast by IP multicast and when the reception apparatus 200 receives the work key Kw. After the latest work key request message is transmitted to the content distribution apparatus 100, the updated work key Kw may be individually distributed by IP unicast by the content distribution apparatus 100.

  First, when the updated work key Kw is broadcast, the work key decryption unit 217 uses the work key Kw stored in the latest work key storage unit 219 to receive the work received by the reception unit 211. The key Kw is decrypted.

In the present embodiment, the updated work key encryption unit 126 (see FIG. 2) of the content distribution apparatus 100 encrypts the updated work key Kw with the previous work key Kw. If the work key Kw used for encryption by the updated work key encryption unit 126 is the same as the work key Kw stored in the latest work key storage unit 219 of the receiving apparatus 200, the decryption is successful. . For example, when the content distribution apparatus 100 updates the work key Kw _{t + 1} to the work key Kw _{t + 2} , the content distribution apparatus 100 encrypts and distributes the work key Kw _{t + 2} with the work key Kw _{t + 1} by the updated work key encryption unit 126. Therefore, when the work key Kw _{t + 1} is stored in the latest work key storage unit 219 of the receiving apparatus 200, the receiving apparatus 200 succeeds in decrypting the work key Kw _{t + 2} . In this case, the work key decryption unit 217 outputs a signal indicating that the work key Kw _{t + 2} has been successfully decrypted to the work key update determination unit 218.

On the other hand, when the work key Kw is updated in the content distribution apparatus 100 and distributed by IP multicast, the update is performed when the receiving apparatus 200 cannot receive the work key Kw, for example, when the power is turned off. Since the work key Kw used for encryption by the work key encryption unit 126 is different from the work key Kw stored in the latest work key storage unit 219, the decryption fails. For example, even when the content distribution apparatus 100 updates the work key Kw _{t + 1} to the work key Kw _{t + 2} , the receiving apparatus 200 does not perform the update, and the latest work key storage unit 219 stores the work key Kw _t . Since the content distribution apparatus 100 encrypts and distributes the work key Kw _{t + 2} with the work key Kw _{t + 1} by the updated work key encryption unit 126, the reception apparatus 200 fails to decrypt the work key Kw _{t + 2} . In this case, the work key decryption unit 217 outputs a signal indicating that the decryption has failed to the work key update determination unit 218 after attempting to decrypt the encrypted work key Kw _{t + 2} .

  Second, the work key decryption unit 217 individually distributes the updated work key Kw by IP unicast after the receiving device 200 transmits the latest work key request message to the content distribution device 100. In this case, the work key Kw received by the receiving unit 211 is decrypted using the master key Km stored in the master key storage unit 221.

  The work key update determination unit 218 receives information related to success or failure of decryption of the received work key Kw from the work key decryption unit 217, and determines whether or not the work key Kw has been updated based on this information. It has become. The work key update determination unit 218 stores the decrypted work key Kw in the latest work key storage unit 219 when the generation date and time of the decrypted work key Kw is new.

  Specifically, when the work key update determination unit 218 receives a signal indicating that the decryption is successful from the work key decryption unit 217, the work key Kw decrypted by the work key decryption unit 217, The work key Kw stored in the latest work key storage unit 219 is compared. When the generation date / time of the decrypted work key Kw is new, the decrypted work key Kw is stored in the latest work key storage unit 219. It is like that.

  When the work key update determination unit 218 receives a signal indicating that the decryption has failed from the work key decryption unit 217, the work key update determination unit 218 determines that the work key Kw has been updated, and requests to generate the latest work key request message. A control signal is output to the message generator 222.

  Similarly, when the work key update determining unit 218 receives a signal from the session key decrypting unit 215 indicating that the decryption of the session key Ks has failed, it determines that the work key Kw has been updated, and requests the latest work key request. A control signal is output to the request message generator 222 so as to generate a message.

  The latest work key storage unit 219 stores the latest work key Kw decrypted by the work key decryption unit 217.

  The master key storage unit 221 stores the master key Km stored in the CAS card via, for example, an interface (not shown) for reading data from the CAS card.

  When the work key update determination unit 218 determines that the work key Kw has been updated, the request message generation unit 222 generates the latest work key request message to be transmitted to the content distribution apparatus 100, and the request message encryption unit 223 and the MAC The data is output to the generation unit 224.

  The request message encryption unit 223 receives the latest work key request message from the request message generation unit 222, encrypts the latest work key request message using the master key Km stored in the master key storage unit 221, and transmits the transmission unit 225. To output. The request message encryption unit 223 constitutes request information output means of the present invention.

  The MAC generation unit 224 receives the latest work key request message from the request message generation unit 222 and uses the master key Km stored in the master key storage unit 221 and the MAC of the latest work key request message, for example, using a hash function. It is generated and output to the transmission unit 225. For example, AES (Advanced Encryption Standard) is used for generating the MAC. The MAC generation unit 224 constitutes request information output means of the present invention.

  The transmission unit 225 includes, for example, a packet generation unit that generates an IP packet and a network card that transmits the IP packet, and the content of the IP packet obtained by adding the MAC to the latest work key request message encrypted via the communication network 30 The data is transmitted to the distribution apparatus 100. The transmission unit 225 constitutes the encryption request information transmission unit of the present invention.

  Next, the operation of the content distribution system 10 in the present embodiment will be described.

  First, operations related to content distribution in the content distribution system 10 will be described with reference to FIGS. FIG. 4 is a flowchart showing each step related to content distribution. Steps S11 to 15 show each step in the content distribution device 100, and steps S16 to 19 show each step in the reception device 200. Yes.

  First, in the content distribution device 100, the content encryption unit 121 acquires the session key Ks from the latest session key storage unit 122 (step S11). The session key Ks acquired here is the latest one input from the session key management server 112 to the latest session key storage unit 122.

  Next, the content encryption unit 121 acquires the content from the content management server 111, encrypts the content using the session key Ks (step S12), and outputs the encrypted content to the transmission unit 131.

  Further, the work key Kw is acquired from the latest work key storage unit 125 by the session key encryption unit 123 (step S13).

  Subsequently, the session key encryption unit 123 acquires the session key Ks from the latest session key storage unit 122, encrypts the session key Ks using the work key Kw (step S14), and encrypts the session key Ks. Is output to the transmission unit 131.

  Then, the transmission unit 131 transmits the encrypted content and the session key Ks to the reception device 200 via the communication network 30 by IP multicast (step S15).

  Next, in the receiving device 200, first, the receiving unit 211 receives the encrypted content and the session key Ks (step S16).

  Next, the session key decryption unit 215 obtains the work key Kw from the latest work key storage unit 219, decrypts the session key Ks using the work key Kw (step S17), and decrypts the decrypted session key Ks. Is stored in the session key storage unit 216. In step S17, if the decryption of the session key Ks fails, the session key decryption unit 215 outputs a signal indicating that to the work key update determination unit 218, and the work key update determination unit 218 The latest work key request process described later is executed.

  Further, the content decrypting unit 212 acquires the encrypted content from the receiving unit 211, and decrypts the encrypted content using the session key Ks stored in the session key storage unit 216 (step S18). ). The decrypted content is output to the content storage unit 213.

  Then, the content output unit 214 displays the menu information of the content stored in the content storage unit 213 on the content playback device (not shown), and the content selected by the user is displayed on the content playback device (step S19).

  Next, each step relating to the broadcast distribution of the work key Kw in the content distribution system 10 will be described with reference to FIGS. FIG. 5 is a flowchart showing an operation related to the broadcast distribution of the work key Kw. Steps S21 to S24 indicate each step in the content distribution apparatus 100, and steps S25 to S29 indicate each step in the reception apparatus 200. Is shown.

First, in the content distribution apparatus 100, the work key update determination unit 124 determines whether or not the work key Kw has been updated (step S21). For example, when the work key update determination unit 124 receives a signal indicating that the work key Kw has been registered from the work key management server 113, the work key Kw registered in the work key management server 113 and the latest work key storage are stored. It is determined whether or not the work key Kw has been updated by comparing the work key Kw stored in the unit 125 with the generation date and time information, for example. In the following description, what is newly registered in the work key management server 113 is a work key Kw _{t + 3,} and what is stored in the latest work key storage unit 125 is a work key Kw _{t + 2} .

Next, the work key update determination unit 124 stores the work key Kw _{t + 3} in the latest work key storage unit 125 (step S22), and outputs the work key Kw _{t + 2} and the work key Kw _{t + 3} to the updated work key encryption unit 126. .

Further, the updated work key encryption unit 126 encrypts the work key Kw _{t + 3} with the work key Kw _{t + 2} (step S23) and outputs it to the transmission unit 131. This step S23 constitutes the encryption key encryption step of the present invention.

Then, the transmission unit 131 transmits the encrypted work key Kw _{t + 3} to the reception device 200 via the communication network 30 by IP multicast (step S24).

Next, in the receiving device 200, first, the receiving unit 211 receives the encrypted work key Kw _{t + 3} (step S25).

Next, the work key decryption unit 217 decrypts the encrypted work key Kw _{t + 3} (step S26), and determines whether the decryption is successful (step S27).

In step S26, the work key decryption unit 217 reads the work key Kw from the latest work key storage unit 219 and decrypts the work key Kw _{t + 3. The} work key stored in the latest work key storage unit 219 is the work key. If it is Kw _{t + 2} , the work key Kw _{t + 3} is successfully decrypted, and the work key decryption unit 217 stores the work key Kw _{t + 3} in the latest work key storage unit 219 (step S29).

On the other hand, if what is stored in the latest work key storage unit 219 is not the work key Kw _{t + 2} in step S26, for example, if the work key Kw _{t + 1} , the work key Kw _{t + 3} fails to be decrypted. The update determination unit 218 determines that the work key Kw has been updated, and proceeds to the latest work key request process (step S28).

  Next, the latest work key request process will be described with reference to FIGS. FIG. 6 is a flowchart showing each step related to the processing of the latest work key request message. Steps S31 to 33 and Steps S41 to 43 show each step in the receiving device 200, and Steps S34 to 40 are contents. Each step in the distribution apparatus 100 is shown. In FIG. 6, the latest work key request message is abbreviated as “request m”.

  First, in the receiving apparatus 200, when the work key update determination unit 218 determines that the work key Kw has been updated, the request message generation unit 222 generates the latest work key request message (step S31), and the request message encryption unit 223 and the MAC generation unit 224.

  Next, the request message encryption unit 223 acquires the master key Km from the master key storage unit 221, and the latest work key request message is encrypted using the master key Km (step S32).

  Similarly, the MAC generation unit 224 acquires the master key Km from the master key storage unit 221, and generates the MAC of the latest work key request message using the master key Km (step S33).

  Then, the transmission unit 225 adds the MAC to the encrypted latest work key request message, transmits the message to the content distribution device 100, receives it by the reception unit 132 of the content distribution device 100, and outputs it to the user authentication unit 128. . Note that illustration of this step is omitted.

  Subsequently, the user authentication unit 128 acquires the master key Km from the master key management server 114 (step S34), and decrypts the latest work key request message using the master key Km (step S35).

  Further, the MAC of the latest work key request message is generated by the user authentication unit 128 using the master key Km (step S36).

  Subsequently, the MAC received by the receiving unit 132 by the user authentication unit 128, that is, the MAC generated in step S33 (hereinafter referred to as “first MAC”) and the MAC generated in step S36 (hereinafter referred to as “second MAC”). .) Is collated (step S37).

  Then, the user authentication unit 128 determines whether or not the first MAC and the second MAC match (step S38).

If it is determined in step S38 that the first MAC and the second MAC match, the user who has requested the latest work key request message is regarded as a legitimate user and is updated by the user-specific update work key encryption unit 127. The work key Kw _{t + 3} is acquired from the latest work key storage unit 125 (step S39), and the work key Kw _{t + 3} is encrypted using the master key Km of the user acquired from the master key management server 114 (step S40). .

  If it is determined in step S38 that the first MAC and the second MAC do not match, the user who has requested the latest work key request message is not regarded as a regular user, and the latest work key request process is terminated.

Following step S _< b _> 40, the transmission unit 131 transmits the encrypted work key Kw _{t + 3} to the reception device 200, receives it by the reception unit 211 of the reception device 200, and outputs it to the work key decryption unit 217. Note that illustration of this step is omitted.

Next, the work key decryption unit 217 acquires the master key Km from the master key storage unit 221 and decrypts the encrypted work key Kw _{t + 3} using the master key Km (step S41).

Further, the work key update determination unit 218 determines whether or not the decrypted work key has been updated (step S42). In the present embodiment, what is stored in the latest work key storage unit 219 is the work key Kw _{t + 2} , and is the one immediately before the update of the latest work key Kw _{t + 3} updated in the content distribution apparatus 100. In step S42, it is determined that the work key has been updated, the work key Kw _{t + 3} is stored in the latest work key storage unit 219 (step S43), and the latest work key request process is terminated.

  On the other hand, if it is not determined in step S42 that the decrypted work key has been updated, the latest work key request process is terminated.

  It should be noted that by programming each step shown in FIG. 6, the computer can execute the encryption key update method according to the present invention.

  Further, in the above-described embodiment, the configuration in which the authentication of the reception device 200 is performed by the MAC has been described as an example. However, the present invention is not limited to this, and the reception device 200 may be, for example, the reception device 200. Instead of the MAC generation unit 224, an electronic signature information generation unit for generating electronic signature information is provided, and the latest work key request message with the electronic signature information added is transmitted to the content distribution apparatus 100, and the content distribution apparatus 100 receives the electronic signature information. A similar effect can be obtained by authenticating the receiving apparatus 200 based on the above. Here, RSA, DSA, etc. are mentioned as a method of producing | generating electronic signature information, for example.

  Further, generation date / time information indicating the date / time when the latest work key request message was generated, position information indicating a position on the communication network 30 of the transmission source of the latest work key request message, and an identifier for identifying the transmission source By adopting a configuration in which at least one of them is included in the latest work key request message, it is possible to further increase the accuracy of authentication of the user who requested the updated work key Kw.

  In the above-described embodiment, the configuration in which content is distributed by IP multicast has been described as an example. However, the present invention is not limited to this, and content is distributed by a communication method other than IP multicast. If it is a thing, the same effect is acquired. Further, the present invention can be applied without depending on the form of content distribution service, the type of communication line (for example, optical fiber, wireless line, etc.), the type of receiving apparatus, and the like.

  In the above-described embodiment, the content distribution system 10 that distributes content has been described as an example. However, the present invention is not limited to this. For example, application data is encrypted instead of content. The same effect can be obtained when the configuration is applied to a distribution system. Further, the same effect can be obtained when the encryption key update method according to the present invention is applied to a storage device that encrypts and stores data.

  As described above, according to the content distribution system 10 in the present embodiment, only the authorized user who has signed a contract in advance can decrypt the encrypted session key Ks, and the decrypted session key Since the content encrypted with Ks is decrypted, there is no need to distribute the session key Ks for decrypting the encrypted content to all users unlike the conventional one, and the server and network The processing load can be reduced compared to the conventional one, and the content is protected from threats to the content distribution service, such as content tampering, impersonation of legitimate users, and denial of service (DoS: Denial of Services) attacks. can do.

  Further, according to the encryption device 120 in the present embodiment, the content encryption unit 121 that outputs encrypted data encrypted with the session key Ks, and the session key encryption that encrypts the session key Ks with the work key Kw. Unit 123 and an updated work key encryption unit 126 that encrypts the work key Kw updated when the work key Kw is updated with the pre-update work key Kw. Since the encrypted session key Ks can be decrypted and the content encrypted with the decrypted session key Ks is decrypted, the work key Kw is an individual key as in the prior art. Compared to the case where encryption is performed using the master key Km and the work key Kw is distributed to all users individually, the processing load on the server and the network can be reduced.

  Moreover, according to the encryption apparatus 120 in this Embodiment, the receiving part 132 which receives the newest work key request message which the receiving apparatus 200 transmitted, the user authentication part 128 which authenticates the transmission source of the newest work key request message, Since the configuration includes the user-specific updated work key encryption unit 127 that encrypts the updated work key Kw with the master key Km when the transmission source authentication is successful, the latest work key request message is transmitted. Since the user can be authenticated and the updated work key Kw can be encrypted with the master key Km and provided to the user when the authentication is successful, the authorized user can obtain the updated work key Kw for some reason. Even if it is not, the updated work key Kw can be provided in response to a request from a legitimate user.

  Furthermore, according to the encryption device 120 in the present embodiment, the latest work key request message includes either the message authentication code or the electronic signature information, and the user authentication unit 128 includes at least the message authentication code and the electronic signature information. Since the configuration is such that the sender of the latest work key request message is authenticated based on one of them, it is possible to increase the accuracy of the authentication of the user who requested the updated work key Kw.

  Furthermore, according to the encryption device 120 of the present embodiment, the latest work key request message indicates generation date / time information indicating the date / time generated and the position on the communication network 30 of the transmission source of the latest work key request message. Since the configuration includes at least one of the position information and the identifier for identifying the transmission source, it is possible to further increase the accuracy of the authentication of the user who requested the updated work key Kw. .

  In addition, according to the receiving device 200 as the decryption device of the present invention, the reception unit 211 that inputs content encrypted with the session key Ks, and the session that decrypts the session key Ks encrypted with the work key Kw. Since the configuration includes the key decryption unit 215 and the work key decryption unit 217 that decrypts the updated work key Kw with the pre-update work key Kw when the work key Kw is updated. Only a legitimate user having the work key Kw can decrypt the encrypted session key Ks and decrypt the encrypted data with the decrypted first encryption key. In this way, it is possible to reduce the processing load on the server and the network as compared with the case where the work key Kw is encrypted with the master key Km, which is an individual key, and the work key Kw is distributed to all users individually. That.

  Furthermore, according to the receiving apparatus 200 of the present invention, the request message encryption unit 223 that encrypts the latest work key request message with the master key Km, and the transmission unit 225 that transmits the latest work key request message to the content distribution apparatus 100, A receiving unit 211 that receives the updated work key Kw encrypted with the master key Km from the content distribution apparatus 100, and a work key decrypting unit that decrypts the received updated work key Kw with the master key Km. Therefore, even if a legitimate user does not acquire the updated work key Kw for some reason, the updated work key Kw can be provided in response to a request from the legitimate user. it can.

  Furthermore, according to the receiving apparatus 200 of the present invention, the latest work key request message includes either the message authentication code or the electronic signature information, and the receiving unit 211 receives the message authentication code and the electronic signature information in the content distribution apparatus 100. Since the updated work key Kw is received from the content distribution apparatus 100 when the authentication of the own apparatus is successful based on at least one of them, the accuracy of the authentication of the user who requested the updated work key Kw is improved. You can plan.

  Furthermore, according to the receiving apparatus 200 of the present invention, the latest work key request message identifies the generated date / time information indicating the generated date / time, the position information indicating the position of the own apparatus on the communication network 30, and the own apparatus. Therefore, it is possible to further improve the accuracy of the authentication of the user who requested the updated work key Kw.

  As described above, the encryption device, the decryption device, and the encryption key update method according to the present invention have the effect that the processing load on the server and the network can be reduced as compared with the conventional ones, such as video and audio. The present invention is useful as an encryption device that encrypts data, a decryption device that decrypts encrypted data, an encryption key update method that updates an encryption key for encrypting data, and the like.

The conceptual diagram which shows the outline | summary of a structure of the content delivery system in one embodiment of this invention. The block diagram which shows the outline | summary of the content delivery apparatus which concerns on the content delivery system in one embodiment of this invention The block diagram which shows the outline | summary of the receiver which concerns on the content delivery system in one embodiment of this invention The flowchart which shows each step which concerns on the delivery of the content of the content delivery system in one embodiment of this invention The flowchart which shows each step which concerns on the broadcast delivery of the work key of the content delivery system in one embodiment of this invention The flowchart which shows each step which concerns on the newest work key request | requirement process of the content delivery system in one embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Content distribution system 20 (21-23) Content provision apparatus 30 Communication network 31 Router 100 Content distribution apparatus 110 Server apparatus 111 Content management server 112 Session key management server 113 Work key management server 114 Master key management server 120 Encryption apparatus 121 Content Encryption section (data encryption means)
122 Latest session key storage unit 123 Session key encryption unit (first encryption key encryption unit)
124 work key update determination unit 125 latest work key storage unit 126 updated work key encryption unit (updated second encryption key encryption unit)
127 Update work key encryption unit for each user (second encryption key encryption means for each transmission source)
128 User authentication section (source authentication means)
130 Transmitter / Receiver 131 Transmitter (Updated Second Encryption Key Transmitter)
132 Receiving section (encryption request information receiving means)
DESCRIPTION OF SYMBOLS 200 Receiver 201 Fixed type receiver 202 Mobile phone 203 Personal digital assistant 210 Receiving means 211 Receiving part (encrypted data input means, updated second encryption key receiving means)
212 content decryption unit 213 content storage unit 214 content output unit 215 session key decryption unit (first encryption key decryption means)
216 Session key storage unit 217 Work key decryption unit (updated second encryption key decryption unit, reception second encryption key decryption unit)
218 Work key update determination unit 219 Latest work key storage unit 220 Transmission unit 221 Master key storage unit 222 Request message generation unit 223 Request message encryption unit (request information output unit)
224 MAC generator (request information output means)
225 Transmitter (encryption request information transmission means)

Claims (7)

An encryption device for transmitting encrypted data to a decryption device,
First encryption key storage means for storing a first encryption key that is updated every predetermined first period;
Second encryption key storage means for storing a second encryption key updated every second predetermined period longer than the first period;
Third encryption key storage means for storing a third encryption key shared with the decryption device;
Data encryption means for obtaining the latest first encryption key from the first encryption key storage means and encrypting data with the latest first encryption key to generate encrypted data ;
A first encryption key that obtains the latest second encryption key from the second encryption key storage unit and encrypts the latest first encryption key with the latest second encryption key to generate an encrypted first encryption key; Encryption means;
When the encrypted data, the encrypted first encryption key, and the second encryption key are updated, the latest second encryption key encrypted with the second encryption key before update is transmitted to the decryption device. Sending means to
When the decryption device fails to decrypt the encrypted first encryption key using the second encryption key acquired in advance, the decryption device transmits to request the latest second encryption key Encryption request information receiving means for receiving the encryption request information encrypted with the third encryption key by the decryption device;
Source authentication means for authenticating the source of the encryption request information;
Source-specific second encryption key encryption means for encrypting the latest second encryption key with the third encryption key when authentication of the source is successful;
An encrypted apparatus comprising: an updated second encryption key transmission unit configured to transmit the latest second encryption key encrypted with the third encryption key to the transmission source . The encryption request information includes either a message authentication code or electronic signature information,
2. The encryption apparatus according to claim 1, wherein the transmission source authentication unit authenticates the transmission source based on at least one of the message authentication code and the electronic signature information . The encryption request information receiving means receives the encryption request information from the transmission source via a communication network,
The encryption request information includes at least one of generation date / time information indicating a generated date / time, position information indicating a position of the transmission source on the communication network, and an identifier for identifying the transmission source. encryption device according to claim 1 or claim 2, characterized in that it comprises a. A decryption device for decrypting encrypted data encrypted by the encryption device according to any one of claims 1 to 3,
Receiving means for receiving the latest second encryption key encrypted with the second encryption key before update when the encrypted data, the encrypted first encryption key, and the second encryption key are updated;
Updated second encryption key decryption means for decrypting the latest second encryption key with the second encryption key before update;
Second encryption key storage means for storing the decrypted second encryption key;
Third encryption key storage means for storing a third encryption key shared with the encryption device;
First encryption key decryption means for decrypting the encrypted first encryption key with the second encryption key acquired from the second encryption key storage means and generating a decrypted first encryption key;
Data decryption means for decrypting the encrypted data with the decryption first encryption key;
Request information for requesting the encryption device to request the latest second encryption key when the first encryption key decryption unit fails to decrypt the encrypted first encryption key, and the third encryption key Request information output means for outputting the encryption request information encrypted with
Encryption request information transmitting means for transmitting the encryption request information to the encryption device;
Updated second encryption key receiving means for receiving the latest second encryption key encrypted with the third encryption key from the encryption device;
A decryption apparatus comprising: a received second encryption key decryption unit configured to decrypt the latest second encryption key received by the updated second encryption key reception unit with the third encryption key. The encryption request information includes either a message authentication code or electronic signature information,
The updated second encryption key receiving means receives the updated second encryption key from the encryption device when authentication based on at least one of the message authentication code and the electronic signature information is successful in the encryption device. The decoding device according to claim 4, wherein: The encryption request information transmitting means transmits the encryption request information to the encryption device via a communication network,
The encryption request information includes at least one of generation date / time information indicating a generated date / time, position information indicating a position of the own device on the communication network, and an identifier for identifying the own device. 6. The decoding device according to claim 4 or 5, wherein An encryption device that transmits encrypted data to a decryption device is:
A first encryption key storing step of storing a first encryption key updated every predetermined first period;
A second encryption key storing step of storing a second encryption key updated every predetermined second period longer than the first period;
A third encryption key storage step of storing a third encryption key shared with the decryption device;
A data encryption step of obtaining the latest first encryption key in the first encryption key storage step and encrypting data with the latest first encryption key to generate encrypted data;
A first encryption key that obtains the latest second encryption key in the second encryption key storage step and encrypts the latest first encryption key with the latest second encryption key to generate an encrypted first encryption key Encryption process;
When the encrypted data, the encrypted first encryption key, and the second encryption key are updated, the latest second encryption key encrypted with the second encryption key before update is transmitted to the decryption device. A transmission process to
When the decryption device fails to decrypt the encrypted first encryption key using the second encryption key acquired in advance, the decryption device transmits to request the latest second encryption key Encryption request information receiving step for receiving the encryption request information encrypted with the third encryption key by the decryption device;
A sender authentication step for authenticating the sender of the encryption request information;
A source-specific second encryption key encryption step of encrypting the latest second encryption key with the third encryption key when authentication of the source is successful;
A method of updating an encryption key, comprising: performing an updated second encryption key transmission step of transmitting the latest second encryption key encrypted with the third encryption key to the transmission source.

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