File management technique using location authentication

Abstract

To safely deliver a file between users through a network.SOLUTION: There is provided a file management system enabling file transmission between a first information communication terminal device of a first user and a second information communication terminal device of a second user. The first information communication terminal device designates a file, a receiver-side user and file receiving place, encrypts the file to create an encryption file, and transmits the receiving place to a file management server. The second information communication terminal device acquires the encryption file and transmits position information acquired by a key terminal device of the second user to the file management server. On the basis of the receiving place, the file management server discriminates position authentication. When the position authentication is successful as a result of the discrimination, the second information communication terminal device decrypts the encryption file to acquire the original file.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a file management technology using location authentication, and more particularly to a file management system and method using location authentication utilizing encryption / decryption technology. [Background technology]

[0002] There are known file sharing services (sometimes called online storage services or cloud storage services) that allow users to back up their files to a file management server on a network so that they can be restored later or sent to other users.

[0003] For example, Patent Document 1 below discloses an online storage device in which hash data encrypted by encrypted data is stored together with a public key, and content is encrypted by the encrypted hash data.

[0004] Furthermore, public key cryptography can be used for encrypting / decrypting files. In public key cryptography, a key pair consisting of a private key and a public key is generated for a user. The public key is used to encrypt files and can be made public to other users. On the other hand, the private key is used to decrypt files and should be managed secretly by the user.

[0005] Furthermore, Non-Patent Document 1 below discloses a proxy re-encryption technology that enables a user Z other than user X and user Y to create an encrypted file B encrypted with the public key of user Y from an encrypted file A encrypted with the public key of user X, without knowing the private keys of user X and user Y. Information for converting encrypted file A into encrypted file B is sometimes called a proxy key. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2014-507841 [Non-patent literature]

[0007] [Non-Patent Document 1] Sherman SM CHOW, Weng JIAN, Yanjiang YANG, and Robert H. DENG. (2010). Efficient unidirectional proxy reencryption. Progress in Cryptology - AFRICACRYPT 2010: Third International Conference on Cryptology in Africa, Stellenbosch, South Africa, May 3-6: Proceedings. vol. 6055, pp. 316-332. Research Collection School Of Information Systems. (https: / / ink.library.smu.edu.sg / sis_research / 1316). May 2010 Summary of the Invention [Problem to be solved by the invention]

[0008] In public key cryptography and proxy re-encryption, the management of private keys is extremely important. For this reason, there is a strong demand for a technology that enables users to perform processes such as encryption / decryption and re-encryption of files while secretly managing their private keys in a specific device and without letting external devices know the keys.

[0009] In addition, a file transmission procedure has become widespread in which a user who wants to send a file to another user encrypts the file with a password, sends the file to the other user as an attachment to an email, and then sends the password in the body of the email. However, there is a risk that emails transmitted over a communication network may be leaked or intercepted, and as long as the password is sent in the body of the email, such a file transmission procedure cannot be said to be perfect in terms of security.

[0010] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a new file transmission scheme that enables a user to safely send a file to a desired recipient via a communication network.

[0011] More specifically, one of the objects of the present invention is to provide a file management service that enables a file encrypted by a sender user (first user) to be securely decrypted by a receiver user (second user) without transmitting the file encrypted with a password (encryption key) and the password as is over a communications network.

[0012] Another object of the present invention is to provide a file management service that enables a sending user to safely deliver an encrypted file to a recipient even if there is a risk that email transmitted over a communication network may be leaked or intercepted, and enables the recipient of the email (the recipient user) to safely decrypt the encrypted file. [Means for solving the problem]

[0013] The present invention for solving the above problems includes the following invention-specific matters or technical features.

[0014] That is, the present invention according to one aspect is a file management system that enables the transmission of a file between a first information communication terminal device of a first user and a second information communication terminal device of a second user. The file management system includes a file management server that is communicatively connected to each of the first information communication terminal device and the second information communication terminal device, and a key terminal device that is communicatively connected to the file management server and is capable of acquiring geographical location information. The file management server acquires destination information including at least an identifier of the second user and a receiving location of the file from the first information communication terminal device, receives a location authentication request including geographical location information from the key terminal device, determines whether location authentication is successful based on the receiving location included in the destination information and the geographical location information included in the location authentication request, and transmits the result of the determination to the second information communication terminal device, and the second information communication terminal device decrypts the encrypted file in which the file is encrypted when the result of the determination indicates that the location authentication is successful.

[0015] The first information communication terminal device generates a common key according to a predetermined function (for example, a random number function), and creates the encrypted file using the generated common key.

[0016] The first information communication terminal device uses a public key to generate a first ciphertext based on the common key and transmits the generated first ciphertext to the file management server. For example, the first ciphertext includes the common key encrypted using the public key.

[0017] The second information communication terminal device generates a temporary key pair consisting of a temporary private key and a temporary public key according to a predetermined key generation algorithm, and stores the temporary private key of the temporary key pair. The key terminal device stores the temporary public key of the temporary key pair. The file management server generates a second ciphertext using the temporary public key in cooperation with the key terminal device, and transmits the generated second ciphertext to the second information communication terminal device. For example, the file management server generates a proxy key using a master private key and the temporary public key held by the key terminal device, and generates the second ciphertext by applying the generated proxy key to the first ciphertext. Alternatively, the key terminal device obtains the common key by decrypting the first ciphertext using a master private key held by itself, and generates the second ciphertext by encrypting the common key using the temporary public key.

[0018] In order to obtain the common key, the second information communication terminal device decrypts the second ciphertext using the temporary private key, and decrypts the encrypted file using the common key obtained by decrypting the second ciphertext.

[0019] The file management server acquires the temporary public key from the second information communication terminal device, and transmits the acquired temporary public key to the key terminal device.

[0020] The file management server acquires the temporary public key during login authentication by the second information communication terminal device.

[0021] The file management server determines whether the login authentication has been successful by multi-factor authentication based on the possession or use of the key terminal device.

[0022] The receiving location is geographical location information designated by the first user, and the geographical location information is designated based on a geographical map displayed on a user interface of the first information communication terminal device.

[0023] The file management server determines whether the location authentication is successful based on the geographical location information of the second information communication terminal device. In this case, the file management server determines that the location authentication is successful when the geographical location information included in the location authentication request and the geographical location information of the second information communication terminal device each correspond to the receiving location included in the destination information.

[0024] The geographical location information of the second information communication terminal device is a GPS coordinate or a functional global IP address.

[0025] According to another aspect, the present invention is a file management server communicably connected to each of a first information communication terminal device of a first user, a second information communication terminal device of a second user, and a key terminal device 30. The file management server is configured to execute the following processes: acquiring destination information including at least an identifier of the second user and a file receiving location from the first information communication terminal device, receiving a location authentication request including geographical location information acquired by the key terminal device, determining whether location authentication is successful or not based on the receiving location included in the destination information and the geographical location information included in the location authentication request, and, if the location authentication is successful, transmitting to the second information communication terminal device a ciphertext used to decrypt an encrypted file in which the file was encrypted by the first information communication terminal device.

[0026] According to another aspect, the present invention is a file transmission method for enabling transmission of a file between a first information communication terminal device of a first user and a second information communication terminal device of a second user, the method including: specifying destination information including an identifier of the second user and a receiving location of the file in the first information communication terminal device; generating an encrypted file by encrypting the file in the first information communication terminal device; acquiring the receiving location designated in a file management server; storing the generated encrypted file in the second information communication terminal device; transmitting geographical location information acquired in a key terminal device possessed by the second user from the key terminal device to the file management server; determining in the file management server whether the geographical location information corresponds to the designated receiving location and transmitting the result of the determination to the second information communication terminal device; and, when the result of the determination indicates that the geographical location information corresponds to the designated receiving location, decrypting the encrypted file in the second information communication terminal device to acquire the original file.

[0027] Creating the encrypted file includes generating a common key according to a predetermined function (eg, a random number function) and creating the encrypted file using the generated common key.

[0028] The method further includes generating a first ciphertext based on the common key using the public key, and transmitting the generated first ciphertext to the file management server.

[0029] The method includes generating a temporary key pair consisting of a temporary private key and a temporary public key in accordance with a predetermined key generation algorithm in the second information communication terminal device, storing the temporary private key of the temporary key pair in the second information communication terminal device, storing the temporary public key of the temporary key pair in the key terminal device, generating a second ciphertext using the temporary public key by the file management server in cooperation with the key terminal device, and storing the generated second ciphertext in the second information communication terminal device.

[0030] The method further includes, in the second information communication terminal device, decrypting the generated second ciphertext using the temporary private key to obtain the common key. Decrypting the ciphertext includes decrypting the ciphertext using the common key obtained by decrypting the second ciphertext.

[0031] The method further includes, in the file management server, acquiring the temporary public key from the second information communication terminal device, and transmitting the acquired temporary public key to the key terminal device.

[0032] The method includes, in the file management server, acquiring the temporary public key during login authentication by the second information communication terminal device.

[0033] The method includes determining, in the file management server, whether the login authentication has been successful through multi-factor authentication based on possession or use of the key terminal device.

[0034] Also, the present invention according to another aspect is a file management method executed by a file management server communicably connected to each of a first information communication terminal device of a first user, a second information communication terminal device of a second user, and a key terminal device 30. The method includes: acquiring destination information including at least an identifier of the second user and a file receiving location from the first information communication terminal device; receiving a location authentication request including geographical location information acquired by the key terminal device; determining whether location authentication is successful or not based on the receiving location included in the destination information and the geographical location information included in the location authentication request; and, if the location authentication is successful, transmitting information (ciphertext) used to decrypt an encrypted file in which the file was encrypted by the first information communication terminal device to the second information communication terminal device.

[0035] Furthermore, the present invention according to another aspect may be a computer program for causing a computing device to execute the above-mentioned method, and a machine-readable recording medium non-transitoryly carrying the computer program.

[0036] In this disclosure, the present invention is described as a file management system and a file transmission system, but regardless of the name, it may also be understood as, for example, an encryption / decryption system and method.

[0037] In this disclosure, the term "means" does not simply mean a physical means, but also includes cases where the functions of the means are realized by software. Also, the functions of one means may be realized by two or more physical means, and the functions of two or more means may be realized by one physical means.

[0038] In addition, in this disclosure, a "system" includes a logical collection of multiple devices (or functional modules that realize a specific function), regardless of whether each device or functional module is physically configured as a single entity or as separate entities. Effect of the Invention

[0039] According to the present invention, a user can safely send a file to a desired recipient via a communication network. In particular, according to the present invention, a file encrypted by a sender user can be safely decrypted by a receiver user without transmitting the file encrypted by a password (encryption key) and the password as is over the communication network.

[0040] Furthermore, according to the present invention, even if there is a risk that email transmitted over a communication network may be leaked or intercepted, a file encrypted by a sending user can be safely delivered to a receiving user via a file management server, and the recipient of the email can safely decrypt the encrypted file.

[0041] Other technical features, objects, and operational effects or advantages of the present invention will become apparent from the following embodiments described with reference to the accompanying drawings. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 is a block diagram showing an example of a schematic configuration of a file management system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a sequence chart for explaining an example of a schematic process in the file management system according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a sequence chart for explaining an example of a schematic process in the file management system according to one embodiment of the present invention. [Figure 4] FIG. 4 is a sequence chart for explaining an example of a proxy re-encryption process in the file management system according to an embodiment of the present invention. [Diagram 5]FIG. 5 is a sequence chart for explaining an example of a process for creating a second ciphertext by a key terminal device in a file management system according to an embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart for explaining an example of a decryption process of an encrypted file in the file management system according to one embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing an example of a top screen displayed on a user interface of an information communication terminal device in a file management system according to an embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing an example of a destination selection screen displayed on a user interface of an information communication terminal device in a file management system according to an embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing an example of a receiving location registration screen displayed on a user interface of an information communication terminal device in a file management system according to an embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing an example of an encrypted file selection screen displayed on a user interface of an information communication terminal device in a file management system according to an embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing an example of a decryption file selection screen displayed on a user interface of an information communication terminal device in a file management system according to an embodiment of the present invention. [Figure 12] FIG. 12 is a flowchart for explaining an example of a location authentication process in the file management system according to an embodiment of the present invention. [Figure 13] FIG. 13 is a diagram showing an example of a hardware configuration of a computing device in a system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and application of techniques not specified below. The present invention can be implemented by various modifications (for example, combining the respective embodiments) within the scope of the gist of the present invention. In addition, in the following description of the drawings, the same or similar parts are represented by the same or similar reference numerals. The drawings are schematic and do not necessarily correspond to actual dimensions, ratios, etc. The drawings may also include parts with different dimensional relationships and ratios.

[0044] <First embodiment> This embodiment is characterized in that, when a file is transmitted between a first user and a second user, the first user who sends the file encrypts the file and designates a location where the file is to be received, and the file can be decrypted only when the second user who receives the file is in the designated location. Whether the second user is in the designated location is determined based on location information of, for example, a smartphone (hereinafter, described as a key terminal device) that functions as a key terminal device possessed by the second user.

[0045] Fig. 1 is a block diagram showing an example of a schematic configuration of a file management system according to an embodiment of the present invention. As shown in the figure, the file management system 1 of this embodiment includes a file management server 10, a plurality of information communication terminal devices 20, and a key terminal device 30, which are communicably connected to each other via a communication network N. The file management system 1 may also be configured to further include a key management server 40. The file management system 1 provides a so-called network storage service.

[0046] The file management server 10 is a computing device that provides a network storage service to a user. The hardware configuration of the file management server 10 is shown in Fig. 13, for example, but since such a configuration is known, a detailed description thereof will be omitted. The file management server 10 may be, for example, a storage system constructed by a SAN (Storage Area Network).

[0047] The information and communication terminal device 20 is a computing device operated by a user, and may be, but is not limited to, a desktop computer, a notebook computer, a tablet computer, a smartphone, a feature phone, or other intelligent devices. The information and communication terminal device 20 may be, for example, a computing device virtualized by desktop virtualization technology.

[0048] More specifically, the information communication terminal device 20 is composed of hardware resources such as a CPU (processor), chipset, memory, communication module, user interface, etc., and software resources such as an operating system (which may include, for example, a kernel, various device drivers, standard libraries, etc., hereinafter referred to as "OS"). Under the control of the processor, the information communication terminal device 20 executes various application programs on the OS to achieve desired functions. In the present disclosure, the information communication terminal device 20 implements, for example, a mail client program and an encryption / decryption client program that realize the function of sending and receiving mail. The information communication terminal device 20 may also implement a browser program that realizes a browser function.

[0049] In the present disclosure, one of the multiple information communication terminal devices 20 is a first information communication terminal device 20a operated by a first user (sender user) who is a sender of a file, and the other is a second information communication terminal device 20b operated by a second user (recipient user) who is a recipient of the file. That is, the sender user operates the first information communication terminal device 20a to upload a file to the file management server 10, and one or more recipient users designated by the sender user download the file to the second information communication terminal device 20b, thereby enabling the transmission (handover) of a file between the sender user and the recipient user. As will be described later, a master key pair including a master private key and a master public key is assigned to the second information communication terminal device 20b. That is, the recipient user is a key owner who possesses the master key pair. In the present disclosure, when the sender user designates a recipient user to whom he / she is going to send a file, the sender user designates a location where the recipient user should receive the file (reception location). For example, the sender user may specify a location such as the recipient user's office or home as the receiving location.

[0050] Furthermore, the second information communication terminal device 20b generates a temporary key pair for temporary use when downloading a file from the file management server 10. The generated temporary key pair consists of a temporary private key and a temporary public key. Typically, the second information communication terminal device 20b secretly stores (stores) the generated temporary private key in a memory. Secretly storing the temporary private key means that the temporary private key is never leaked outside the second information communication terminal device 20b. In other words, in the above-mentioned transfer of files via the communication network N, the temporary private key is not known by any device other than the second information communication terminal device 20b.

[0051] The sender user and the receiver user may be the same. For example, a user can use the file management system 1 for file backup. That is, a user can back up a file on a first information communication terminal device 20a to the file management system 1 and restore the file on a second information communication terminal device 20b. Alternatively, the first information communication terminal device 20a and the second information communication terminal device 20b may be the same.

[0052] The key terminal device 30 is a computing device operated by a recipient user, and may be, for example, a desktop computer, a notebook computer, a tablet computer, a smartphone, a feature phone, or other intelligent devices, but is not limited thereto. The key terminal device 30 may be, for example, a computing device virtualized by desktop virtualization technology. Alternatively, the key terminal device 30 may be a dedicated device that enables processing related to public key cryptography and management of key pairs. A mobile device such as a smartphone is one aspect of the key terminal device 30. In this disclosure, the key terminal device 30 has a function of acquiring geographical location information from, for example, a GPS system. In addition, the key terminal device 30 implements a key management client program that realizes functions based on the public key cryptography. The key terminal device 30 is associated with the second information communication terminal device 20b (encryption / decryption client program) via, for example, an identifier (for example, an email address) of the recipient user.

[0053] For example, the key terminal device 30 generates a master key pair consisting of a master private key and a master public key, and secretly stores the generated master private key in memory. For example, under the control of the processor, the key terminal device 30 executes a key management client program to generate a master key pair consisting of a master private key and a master public key, and stores the master private key in memory. In addition, the key terminal device 30 performs a predetermined exchange with the key management server 40 to register the generated public key in the key management server 40.

[0054] Storing the master private key in secret means that the master private key is never leaked outside the key terminal device 30. In other words, in the transfer of files as described above via the communication network N, the master private key is not known to any device other than the key terminal device 30.

[0055] The key management server 40 is a computing device having a database (not shown) that manages a public key (i.e., a master public key) for each user (whether a sender user or a receiver user). The key management server 40 can be, for example, a Web server computer that provides a Web API (Application Programming Interface) configured to output a public key in response to a user's inquiry, or a public key server computer conforming to OpenPKSD for publishing a public key based on the OpenPGP technology.

[0056] The key management server 40 typically receives the master public key transmitted from the key terminal device 30 and registers it in a database. In response to a query including a user's identifier, the key management server 40 refers to the database, extracts the public key assigned to the user according to the user's identifier, and outputs it.

[0057] A user identifier may be any information that can uniquely identify an individual user, such as an email address, address and name, social security number, tax number, national identification number, account names used for various public services, and various private services, or any combination thereof.

[0058] In addition, when key management server 40 receives an inquiry including an identifier of a user not registered in the database, it generates a temporary key pair consisting of a temporary private key and a temporary public key, associates the generated temporary key pair with the identifier of the user, temporarily registers the generated temporary key pair in the database, and transmits the temporary public key to the user.

[0059] When such an unregistered user registers the master public key of the master key pair generated in the key terminal device 30 in the key management server 40, the key management server 40 first transmits the interim key pair to the key terminal device 30 using a secure communication means. After the interim key pair is transmitted to the key management server 40, the key management server 40 invalidates the interim key pair. As described above, the key terminal device 30 generates a new master key pair and transmits the master public key of the master key pair to the key management server 40. When the key management server 40 receives the master public key from the key terminal device 30, it registers it in a database.

[0060] In this example, the file management server 10 and the key management server 40 are configured as separate computing devices, but the present invention is not limited to this and may be configured as a single computing device.

[0061] (File transfer procedure) 2 and 3 are sequence charts for explaining an example of a schematic process in a file management system according to an embodiment of the present invention. Specifically, Fig. 2 is a flowchart showing an example of an upload process in the file management system 1, and Fig. 3 is a flowchart showing an example of a download process in the file management system 1.

[0062] (File upload) As shown in FIG. 2, a sender user (first user) operates the first information communication terminal device 20a to specify or select one or more files to be backed up or handed over, one or more receiver users (second users) to receive the files, and information on the receiving location as destination information (S201). For example, an identifier such as a user ID or an email address may be used to specify the user. For example, geographical location information (GPS coordinates, etc.) may be used to specify the receiving location. In this case, from the viewpoint of usability, the receiving location may be a place name, address, and / or name (such as a building name, office, or home) associated with the GPS coordinates. For example, the receiving location may be a GPS coordinate obtained by geocoding via an external API from a point indicated by the user on a geographical map displayed on a user interface or an address entered by the user. The receiving location of the receiver user may be selected from those registered in advance.

[0063] Here, the sender user designates a file, a receiver user, and a receiving location to the first information communication terminal device 20a, but the present invention is not limited to this. For example, when backing up files stored in a specific folder periodically, the sender user may set his / her own identifier and receiving location in the first information communication terminal device 20a in advance, and use these when backing up. Also, the first information communication terminal device 20a may scan the files placed in the folder, extract the corresponding file, and designate it.

[0064] Next, the first information communication terminal device 20a transmits a query including the identifier of the specified recipient user to the key management server 40 in order to obtain key information (i.e., a public key) of the specified recipient user (S202). Upon receiving the query, the key management server 40 refers to a database to identify a public key associated with the identifier indicated by the query (S203), and transmits a response including the identified public key to the first information communication terminal device 20a (S204). Note that if the public key (master public key) of the recipient user is set in advance in the first information communication terminal device 20a via an information recording medium or the like, the above-mentioned exchange between the first information communication terminal device 20a and the key management server 40 is omitted.

[0065] Next, the first information communication terminal device 20a generates a common key according to a predetermined function (S205). The common key is a random value generated using, for example, a random number function, and preferably has a sufficient bit length. Next, the first information communication terminal device 20a encrypts the file using the generated common key to generate an encrypted file (hereinafter referred to as an "encrypted file") (S206).

[0066] A common key is a key shared by a sender user and a receiver user. That is, the common key is used to encrypt a file to generate an encrypted file, and is also used to decrypt the encrypted file to generate the original file. A common key is also called a symmetric key or a shared key. Various techniques can be applied to encryption / decryption processing using a common key, such as block encryption techniques such as IDEA, AES, and Camellia, and stream encryption techniques such as RC4, FISH, and MUGI.

[0067] The common key may be the same for multiple files, or may be different for each file. The common key may be newly generated each time a file is backed up or transferred. Alternatively, an expiration date may be set for the common key, and the same common key may be used during the expiration date instead of being generated each time.

[0068] Next, the first information communication terminal device 20a generates a first ciphertext by encrypting the generated common key using the acquired master public key (S207). The first information communication terminal device 20a may generate the first ciphertext by encrypting the common key and the receiving location together. The encryption process using the master public key is based on public key cryptography, and various techniques such as RSA cryptography, ElGamal cryptography, and elliptic curve cryptography can be applied.

[0069] Next, the first information communication terminal device 20a transmits a file upload request in which the encrypted file, the first ciphertext, and the receiving location are associated with the sender user to the file management server 10 (S208). As a result, the file management server 10 stores the encrypted file, the first ciphertext, and the receiving location in association with the sender user. Typically, the user operates the first information communication terminal device 20a to log in to the file management server 10 and uploads the encrypted file together with the first ciphertext and the receiving location to a predetermined storage area of ​​the file management server 10. This completes the process related to the file upload by the sender user, and therefore, in the subsequent processes, the sender user does not need to operate the first information communication terminal device 20a.

[0070] Alternatively, the first information communication terminal device 20a may send an email with the encrypted file attached to the designated email address of the sender user, and may also send the first ciphertext associated with the sender user and the receiving location to the file management server 10. In this case, the recipient user can obtain the encrypted file without operating the second information communication terminal device 20b to access the file management server 10.

[0071] As described above, the first information communication terminal device 20a can obtain the master public key from the key management server 40 or the like and can generate the common key as necessary, so there is no need for the first information communication terminal device 20a to continuously hold and manage the master public key and the common key. In addition, the first information communication terminal device 20a does not need to know the private key (master private key) assigned to the recipient user in order for the second information communication terminal device 20b to decrypt the file.

[0072] (download) Next, a description will be given of the download process in the file management system 1. As described above, the master private key of the recipient user is secretly stored in the key terminal device 30, and when downloading a file, the first information communication terminal device 20a, the second information communication terminal device 20b, and the file management server 10 do not need to know the master private key.

[0073] As shown in Fig. 3, the second information communication terminal device 20b generates a temporary key pair consisting of a temporary public key and a temporary private key (S301), and secretly stores the temporary private key in the second information communication terminal device 20b (S302). The temporary key pair may be generated by the same public key encryption algorithm as the master key pair assigned to the recipient user, or may be generated by a different public key encryption algorithm. The generated temporary key pair is used temporarily in the second information communication terminal device 20b, and may be generated every time a file is downloaded, or an expiration date may be set and the same temporary key pair may be used during the expiration date.

[0074] Next, the recipient user operates the second information communication terminal device 20b to request login authentication from the file management server 10 (S303). During login authentication, the file management server 10 acquires the recipient user's identifier / password and a temporary public key. In response, the file management server 10 performs login authentication processing for the user (S304). If authentication by the login authentication processing is successful, the file management server 10 may acquire the temporary public key from the second information communication terminal device 20b.

[0075] Here, the login authentication may be, for example, multi-factor authentication in which the possession or use of the key terminal device 30 by the recipient-side user is one of the authentication factors. That is, when the recipient-side user operates the second information communication terminal device 20b to request login authentication from the file management server 10, the recipient-side user executes a key management client program on the key terminal device 30. Typically, in the login authentication process, the file management server 10 may additionally determine whether or not the key management client program is being executed on the key terminal device 30 by acquiring an execution status transmitted from the key terminal device 30. Also, the key management client program may be configured to accept an authentication request from the file management server 10 only within a predetermined time period.

[0076] When the file management server 10 determines that the login authentication has been successful as a result of the authentication process for the login authentication request, it transmits an authentication result indicating that the login authentication has been successful to the second information communication terminal device 20b (S305). In addition, the file management server 10 transmits the temporary public key acquired from the second information communication terminal device 20b to the key terminal device 30 (S306), and in response, the key terminal device 30 stores the received temporary public key in memory (S307).

[0077] In the above example, the temporary public key of the temporary key pair generated by the second information communication terminal device 20b is transmitted to the key terminal device 30 via the file management server 10, but the present invention is not limited to this and may be transmitted to the key terminal device 30 using other secure transmission means. For example, the second information communication terminal device 20b may display a geometric pattern (e.g., a two-dimensional code) indicating the temporary public key on a user interface, and the user may operate the key terminal device 30 to read the displayed geometric pattern, thereby allowing the key terminal device 30 to obtain the temporary public key.

[0078] In addition, other multi-factor authentication methods may be adopted for login authentication. For example, the key terminal device 30 may transmit the temporary public key acquired from the second information communication terminal device 20b to the file management server 10, and the file management server 10 may perform login authentication processing based on the temporary public key acquired in response to the login authentication request from the second information communication terminal device 20b and the temporary public key acquired from the key terminal device 30. In this case, the key terminal device 30 may use the stored master private key to apply a digital signature to the acquired temporary public key, and then transmit the temporary public key together with the digital signature to the file management server 10, and in response, the file management server 10 may use the master public key to verify the validity of the received digital signature.

[0079] Alternatively, the second information communication terminal device 20b may transmit the temporary public key to the key terminal device 30 by, for example, short messaging or e-mail. Alternatively, the second information communication terminal device 20b may transmit the temporary public key to the key terminal device 30 by communication according to the Bluetooth (registered trademark) standard or the NFC (Near Field Communication) standard, communication using a USB cable, wired communication via a network cable, Wi-Fi communication via a wireless access point, mobile communication via a carrier network, or the like, or may supply the temporary public key to the key terminal device 30 via a physical device such as a USB memory device.

[0080] If the login authentication is successful, the file management server 10 and the key terminal device 30 cooperate with each other to generate a second ciphertext (S308). The second ciphertext corresponds to a common key encrypted using a temporary public key, and is information used to decrypt the encrypted file. That is, the second ciphertext is generated based on the master private key stored in the key terminal device 30, the temporary public key transmitted from the second information communication terminal device 20b, and the first ciphertext stored in the file management server 10. The details of the second ciphertext generation process will be described later.

[0081] On the other hand, the key terminal device 30 acquires its own geographical location information by executing the key management client program (S309). For example, the key terminal device 30 acquires the geographical location information by using the acquisition of the temporary public key as a trigger. The geographical location information is, for example, GPS coordinates acquired by using the GPS function of the key terminal device 30. Alternatively or in addition to this, the key terminal device 30 may use a location information service using WiFi (registered trademark). Then, the key terminal device 30 transmits a location authentication request including the acquired geographical location information to the file management server 10 (S310). Alternatively, the geographical location information may be transmitted from the key terminal device 30 to the file management server 10, for example, at the time of additional authentication of whether or not the key management client program is being executed on the key terminal device 30.

[0082] When the file management server 10 receives a location authentication request from the key terminal device 30, it judges whether the location authentication is successful or not by determining whether the geographical location information indicated by the location authentication request corresponds to the receiving location specified by the first information communication terminal device 20a (S311). For example, the file management server 10 judges that the location authentication is successful if the geographical location information is within a predetermined effective range from the receiving location specified by the sender user, taking into consideration an error in the geographical location information. Such an effective range can be arbitrarily set by the user, for example.

[0083] When the file management server 10 determines that the location authentication is successful, the file management server 10 transmits a determination result indicating that the location authentication is successful, including the generated second ciphertext, to the second information communication terminal device 20b (S312). That is, the file management server 10 transmits the second ciphertext used to decrypt the encrypted file to the second information communication terminal device 20b only when the location authentication is successful.

[0084] When the second information communication terminal device 20b receives the second ciphertext, it decrypts the second ciphertext using a temporary private key that it secretly stores to obtain the shared key (S313). Next, the file management server 10 transmits the encrypted file to the second information communication terminal device 20b (S314), and the second information communication terminal device 20b obtains the encrypted file and stores it in a specified folder (S315). The second information communication terminal device 20b may obtain the second ciphertext and the encrypted file together, rather than obtaining them separately.

[0085] Alternatively, the sender user may send an email with the encrypted file attached from the first information communication terminal device 20a to the recipient user's email address, and the recipient user may receive the email on the second information communication terminal device 20b and store it in a specified folder. In this case, the recipient user does not need to log in to the file management server 10 from the second information communication terminal device 20b and download the encrypted file.

[0086] Next, the second information communication terminal device 20b uses the decrypted common key to decrypt the obtained encrypted file, thereby obtaining the original file (S316). In this way, the file is safely transferred between the sender user and the receiver user.

[0087] If the file management server 10 determines that the location authentication has failed, the second information communication terminal device 20b cannot receive the second ciphertext, and instead receives a determination result indicating that the location authentication has failed. The second information communication terminal device 20b that has received the determination result indicating that the location authentication has failed stops the decryption process of the encrypted file and presents, for example, an error message to the user.

[0088] Thus, according to this embodiment, when the second ciphertext is generated, the common key remains secret from the file management server 10. Therefore, even the administrator of the file management server 10 cannot decrypt the encrypted file, which further improves the security of file transfer.

[0089] Furthermore, if the geographical location information acquired by the key terminal device 30 does not correspond to the receiving location specified by the sender user, the second information communication terminal device 20b cannot acquire the second ciphertext from the file management server 10, and therefore cannot acquire the common key and therefore cannot decrypt the encrypted file, thereby further improving the security of file transfer.

[0090] Next, the second ciphertext generation process (S308) will be described in detail. The second ciphertext generation process may be performed, for example, by using proxy re-encryption (see FIG. 4) or by performing decryption and encryption processes in the key terminal device 30 (see FIG. 5).

[0091] FIG. 4 is a sequence chart for explaining an example of a proxy re-encryption process in the file management system according to an embodiment of the present invention.

[0092] As shown in the figure, first, the key terminal device 30 generates a proxy key based on the master private key stored therein and the temporary public key transmitted from the second information communication terminal device 20b (S401). Note that here, it is assumed that the temporary public key is transmitted to the key terminal device 30 directly from the second information communication terminal device 20b, not via the file management server 10. Next, the key terminal device 30 transmits the generated proxy key to the file management server 10 (S402).

[0093] On the other hand, the file management server 10 generates a second ciphertext by re-encrypting the first ciphertext received from and stored in the first information communication terminal device 20a with the proxy key transmitted from the key terminal device 30 (S403). As described above, if the location authentication is successful, the file management server 10 transmits the generated second ciphertext to the second information communication terminal device 20b (S312 in FIG. 3).

[0094] In this way, a proxy re-encryption technique that can re-encrypt a ciphertext by a public key cryptosystem of a master key pair can be applied to the generation of a temporary key pair. For example, the master key pair public key cryptosystem AFGH06 described in the above-mentioned Non-Patent Document 1 can be applied to the present invention. In this method, the master key pair is based on a public key cryptosystem on an elliptic curve, but the temporary key pair is based on a public key cryptosystem over a finite field, and re-encryption can be performed only once.

[0095] In this disclosure, various proxy re-encryption techniques can be applied, including the proxy re-encryption technique disclosed in Non-Patent Document 1. Then, depending on the technique adopted, a master key pair and a temporary key pair are generated, encryption processing is performed using a public key, and decryption processing is performed using a private key.

[0096] FIG. 5 is a sequence chart for explaining an example of a process for creating a second ciphertext by a key terminal device in a file management system according to an embodiment of the present invention.

[0097] As shown in the figure, as described above, the key terminal device 30 acquires the temporary public key (S307). Note that in the figure, the temporary public key is assumed to have been transmitted directly from the second information communication terminal device 20b to the key terminal device 30, not via the file management server 10.

[0098] Moreover, the file management server 10 transmits a first ciphertext to the key terminal device 30 (S501), and the key terminal device 30 acquires the first ciphertext (S502). Next, the key terminal device 30 acquires the shared key by decrypting the first ciphertext acquired from the file management server 10 using the master private key stored in itself (S503).

[0099] Next, the key terminal device 30 generates a second ciphertext by encrypting the decrypted shared key using the temporary public key transmitted from the second information communication terminal device 20b (S504). Then, the key terminal device 30 transmits the generated second ciphertext to the file management server 10 (S505), and the file management server 10 acquires the second ciphertext (S506). As described above, if the location authentication is successful, the file management server 10 transmits the generated second ciphertext to the second information communication terminal device 20b (S312 in FIG. 3).

[0100] In the above example, the key terminal device 30 uses the master private key to decrypt the first ciphertext to generate the common key, and then uses the temporary public key to encrypt the common key to generate the second ciphertext. Therefore, various public key cryptosystems can be used depending on the performance and use of the device by using the master key pair and the temporary key pair.

[0101] The various pieces of information relating to the transfer of files as described above are organized as follows: (a) An encrypted file is information in which a file is encrypted with a common key. (b) The first ciphertext is information obtained by encrypting the common key with the master public key. (c) The first ciphertext is decrypted with the master private key to obtain the common key. (d) The second ciphertext is information obtained by encrypting the common key with the temporary public key. (e) A proxy key is derived from the temporary public key and the master private key. (f) By applying the proxy key to the first ciphertext, a second ciphertext is obtained while keeping the common key secret. (g) The second ciphertext is decrypted with the temporary private key to obtain the common key. (h) When the encrypted file is decrypted with the common key, the original file is obtained.

[0102] Thus, according to this embodiment, the master private key of the recipient user does not need to be output from the key terminal device 30 to the outside, and therefore can be safely managed without being exposed to a third party. In particular, according to this embodiment, the encrypted file can be decrypted only when the recipient user who possesses the key terminal device 30 operates the second information communication terminal device 20b at the receiving place designated by the sender user, and therefore the security of the file transfer can be further improved.

[0103] In addition, when a recipient user starts using the services of the file management system 1 of this embodiment, it is desirable that the key terminal device 30 installs a specified application program, and that the key terminal device 30, under the control of the processor, executes a specified key management client program to generate a master key pair consisting of a master public key and a master private key, and transmits the master public key to be registered in the key management server 40.

[0104] In addition, when a sender user is about to upload a file to the file management server 10, the receiver user may not have yet started using the services of the file management system 1 of the present disclosure. In such a case, the key management server 40 generates a master key pair on behalf of the receiver user, so that the sender user can upload the file in advance.

[0105] That is, the key management server 40 judges whether or not a public key associated with the identifier of the recipient user indicated by the inquiry sent from the first information communication terminal device 20a is registered, and if the key management server 40 judges that the public key is not registered, it generates a temporary key pair consisting of a temporary public key and a temporary private key, and registers the generated temporary public key in association with the identifier. When a user associated with the identifier (i.e., a recipient user) installs an application program on the key terminal device 30 and starts using the services of the file management system 1, the key management server 40 transmits the temporary private key to the key terminal device 30, and the key terminal device 30 stores it secretly as a master private key.

[0106] Therefore, even if the receiving user has not yet started using the services of the file management system 1, the sender user can store an encrypted file for the file to be sent to the receiving user in the file management server 10. On the other hand, if the receiving user starts using the services of the file management system 1 in response to a communication from the sender user to the receiving user by e-mail or the like, the receiving user can obtain the file by downloading it from the file management server 10.

[0107] After obtaining the encrypted file from the file management server 10 and decrypting the file, it is desirable for the recipient user to promptly generate a new master key pair in the key terminal device 30, transmit the master public key to the key management server 40, and update the master public key to the one he or she has generated.

[0108] In addition, when the key terminal device 30 installs a specified application program, the key terminal device 30 may immediately generate a new master key pair, and may use both the interim private key based on the interim key pair and the master private key related to the new master key pair for a certain period of time after the installation. (Decoding process) 6 is a flow chart for explaining an example of a decryption process of an encrypted file in a file management system according to an embodiment of the present invention. This process is realized by the second information communication terminal device 20b executing a decryption program under the control of a processor in cooperation with a predetermined hardware. In the following process, it is assumed that the second information communication terminal device 20b has already acquired the encrypted file designated by the sender user. It is also assumed that the key terminal device 30 has executed a key management client program and acquired a temporary public key.

[0109] That is, as shown in the figure, the second information communication terminal device 20b generates a temporary key pair consisting of a temporary public key and a temporary private key (S601) in response to an operation by the recipient user, and secretly stores the temporary private key in memory (S602).

[0110] Next, the recipient user operates the second information communication terminal device 20b to request login authentication to the file management server 10 and logs in (S603). During login authentication, the second information communication terminal device 20b transmits the recipient user's identifier / password and temporary public key to the file management server 10. In response to this, the file management server 10 performs login authentication processing. After login authentication, the file management server 10 cooperates with the key terminal device 30 to create a second ciphertext as described above.

[0111] Next, the receiver user operates the key terminal device 30 to execute the key management client program, and in response to this, the key terminal device 30 acquires its own geographical location information using, for example, a GPS function or the like (S604), and transmits a location authentication request including the acquired geographical location information to the file management server 10 (S605). In response to this, the file management server 10 judges whether the geographical location information indicated by the location authentication request corresponds to the receiving location designated by the sender user, and transmits the judgment result to the second information communication terminal device 20b. In this example, the judgment result indicating that the location authentication has been successful includes the second ciphertext. Therefore, only when the location authentication has been successful, the second information communication terminal device 20b can acquire the second ciphertext. Note that, in this example, the key terminal device 30 acquires the geographical location information and transmits it to the file management server 10, but this is not limited thereto, and the second information communication terminal device 20b may acquire the geographical location information and transmit it to the file management server 10.

[0112] Based on the determination result received from the file management server 10, the second information communication terminal device 20b determines whether the determination result indicates that the location authentication has been successful, that is, whether the determination result indicates that the second ciphertext has been acquired (S607). When the second information communication terminal device 20b determines that the second ciphertext has been acquired (Yes in S607), the second information communication terminal device 20b decrypts the second ciphertext using the temporary private key to acquire a common key (S608). Next, the second information communication terminal device 20b decrypts the encrypted file using the common key acquired by the decryption to acquire the original file (S609). This allows the file to be safely transferred between the sender user and the receiver user.

[0113] If the second information communication terminal device 20b determines that the determination result indicates that the location authentication has failed (No in S607), it determines that the decryption has failed, performs a predetermined error process, and ends the decryption process (S610).

[0114] (Specific examples) Next, a specific example of file transfer between a sender user and a receiver user in the above-described file management system will be described.

[0115] First, a sender user who wishes to safely deliver an arbitrary file to a recipient user operates the first information communication terminal device 20a to execute an encryption / decryption client program and log in to the file management server 10, whereby the first information communication terminal device 20a displays a top screen 700, for example, as shown in Fig. 7, on the user interface. The sender user selects an "encryption" icon 701 on the top screen 700. In response to this, the first information communication terminal device 20a displays a destination selection screen 800, for example, as shown in Fig. 8, on the user interface of the first information communication terminal device 20a.

[0116] Next, on the destination selection screen 800, the sender user specifies destination information to which the file is to be sent. That is, on the destination selection screen 800, the sender user checks the check box 801 to select a destination (the recipient user's email address) that has been registered in advance. If the recipient user is not registered, the sender user can select the "Add User" button 803 to display a user registration screen (not shown) and register the recipient user by inputting necessary information on the user registration screen.

[0117] In addition, the sender user specifies the location where the sender user should receive the file on the destination selection screen 800. For example, the sender user selects the file receiving location from a pull-down menu 802. In this case, the sender user selects "add receiving location" to display a receiving location registration screen 900 as shown in Fig. 9 on the user interface, and specifies the receiving location of the receiver user.

[0118] For example, on the receiving location registration screen 900, the sender user inputs the address of the recipient user's workplace in the address input field 901, and displays a geographical map of the surrounding area. That is, the first information communication terminal device 20a converts the input address into GPS coordinates using geocoding, and displays a pin 902a and an effective range 902b at a position corresponding to the address on the geographical map. The effective range 902b is a rough guideline range that takes into account errors in the GPS coordinates. Although not shown, the user may change the size of the effective range 902b, for example, in a setting menu. The sender user can select and confirm the receiving location by clicking the pin 902a on the geographical map. Although not shown, when the sender user clicks the pin 902a, the sender user can assign an arbitrary name (label), such as a building name, office, or home, to the receiving location and register it.

[0119] 8, the sender user selects a desired destination and receiving location on the destination selection screen 800, and then selects the "Next" button 804. In response to this, the first information communication terminal device 20a accesses the file management server 10, and the file management server 10 displays a file selection screen 1000, for example, as shown in FIG. 10, on the user interface of the first information communication terminal device 20a.

[0120] The sender user can select a file by dragging and dropping the desired file into the drag and drop area 1001 on the file selection screen 1000. Alternatively, the sender user may select a file from a file selection dialog box. The sender user can select multiple files. After selecting the desired file, the sender user selects the "Encrypt file" button 1002.

[0121] When the sender user selects the "Encrypt file" button 1002, the first information communication terminal device 20a starts generating an encrypted file and a first ciphertext. That is, as described above, the first information communication terminal device 20a generates a common key according to a predetermined function, and encrypts the selected file using the generated common key to generate an encrypted file. The first information communication terminal device 20a also obtains a master public key from the key management server 40, and encrypts the common key using the obtained master public key to generate a first ciphertext. Then, the first information communication terminal device 20a transmits a file upload request including the encrypted file, the first ciphertext, the destination, and the receiving location to the file management server 10. As a result, the file management server 10 stores the encrypted file, the first ciphertext, and the receiving location in association with the sender user.

[0122] The sender user may store the encrypted file in a storage device of the first information communication terminal device 20a in order to send the encrypted file by email, instead of uploading it to the file management server 10. The first information communication terminal device 20a may also open an email sending window in which the destination is specified as an email address and the encrypted file is specified as an attachment, by the encryption / decryption client program cooperating with the email client program.

[0123] Next, the reception of a file by a recipient user is described. The second information communication terminal device 20b of the recipient user is assumed to generate a temporary key pair and store the temporary private key. The key terminal device 30 of the recipient user is assumed to store the temporary public key.

[0124] First, a receiver user who wishes to receive a file from a sender user operates the second information communication terminal device 20b to log in to the file management server 10 and display a top screen 700, for example, as shown in FIG. 7, on the user interface. In this example, the layout of the top screen 700 is the same for the sender user and the receiver user. The receiver user selects the "Decrypt" icon 702 on the top screen 700. In response to this, the second information communication terminal device 20b accesses the file management server 10, and the file management server 10 displays a file selection screen 1100, for example, as shown in FIG. 11, on the user interface of the second information communication terminal device 20b.

[0125] The recipient user can select a file (encrypted file) by dragging and dropping a desired file to a drag and drop area 1101 on the file selection screen 1100. Alternatively, the recipient user may select an encrypted file from a file selection dialog box. The recipient user can select multiple encrypted files. For example, the second information communication terminal device 20b displays a list of encrypted files that the recipient user can receive in the file management server 10, and the recipient user can select a desired encrypted file from the list of encrypted files. Alternatively, the recipient user may open a folder in which the encrypted files received by the second mail are stored, and select a desired encrypted file. After selecting a desired encrypted file, the recipient user selects the "Encrypt file" button 1102.

[0126] Also, the receiver-side user selects the "Decrypt file" button 1102. At this time, for example, according to a message (not shown) additionally displayed on the file selection screen 1100, the receiver-side user operates the key terminal device 30 to execute the key management client program. As a result, the key terminal device 30 acquires its own geographical location information and transmits a location authentication request including the acquired geographical location information to the file management server 10. When the file management server 10 receives the location authentication request from the key terminal device 30, it determines whether the geographical location information indicated by the location authentication request corresponds to the designated receiving location, and transmits the determination result to the second information communication terminal device 20b. In this example, the determination result indicating that the location authentication was successful includes the second ciphertext. When the second information communication terminal device 20b acquires the second ciphertext from the file management server 10 due to the success of the location authentication, it decrypts the acquired second ciphertext using the temporary private key to generate a common key. Next, the second information communication terminal device 20b decrypts the encrypted file using the generated common key to acquire the original file. This allows files to be securely transferred between the sending user and the receiving user.

[0127] As described above, according to this embodiment, the master private key of the receiving user does not need to be output from the key terminal device 30 to the outside, and therefore can be safely managed without being exposed to a third party. In particular, according to this embodiment, the encrypted file can be decrypted only when the receiving user who possesses the key terminal device 30 operates the second information communication terminal device 20b at the receiving place designated by the sending user, and therefore the security of the file transfer can be further improved.

[0128] <Second embodiment> This embodiment is a modification of the first embodiment, and differs from the first embodiment in that the file can be decrypted only when both the information communication terminal device and the key terminal device of the second user who is the recipient of the file are present at the receiving location designated by the first user. In the following, detailed descriptions of the same matters as those in the first embodiment will be omitted as appropriate.

[0129] In order to estimate the geographical position of the second information communication terminal device 20b, the second information communication terminal device 20b itself may be equipped with a function for acquiring geographical position information. For example, the second information communication terminal device 20b may be equipped with a GPS function. Alternatively, the second information communication terminal device 20b may be connected to a USB standard device equipped with a GPS function. In such an embodiment, the second information communication terminal device 20b transmits the acquired geographical position information of itself after logging in to the file management server 10, for example.

[0130] On the other hand, when the second information communication terminal device 20b is a desktop computer or the like, it is often not equipped with a GPS function, and there may be little motivation to connect an external GPS device. Therefore, in such a case, for example, a global IP address assigned to a router in a LAN to which the second information communication terminal device 20b is connected can be used as the geographical location information of the second information communication terminal device 20b. That is, in network communication, since the communication data transmitted from the second information communication terminal device 20b includes a global IP address assigned to the router, the file management server 10 can extract the global IP address from the communication data and estimate the geographical location of the second information communication terminal device 20b by referring to an IP address database. In general, since there is a tendency for errors to be large in location estimation of a global IP address, it is preferable that the file management server 10 performs location authentication of the second user (the second information communication terminal device 20b) by expanding the allowable error range.

[0131] 12 is a flowchart for explaining an example of a location authentication process by a file management server in a file management system according to an embodiment of the present invention. In the following example, a global IP address is used for location estimation of the second information communication terminal device 20b.

[0132] As shown in the figure, the file management server 10 accepts a login authentication request transmitted from the second information communication terminal device 20b of the recipient user and performs the login authentication (S1201). During the login authentication, the file management server 10 obtains the identifier / password and temporary public key of the recipient user from the second information communication terminal device 20b (S1202). At this time, the file management server 10 obtains from the communication data a global IP address assigned to a router in the LAN to which the second information communication terminal device 20b is connected (S1203).

[0133] After the login authentication, the file management server 10 waits until it receives a location authentication request from the key terminal device 30 (S1204). When the file management server 10 receives the location authentication request from the key terminal device 30 (Yes in S1204), the file management server 10 judges whether the first location authentication process is successful or not based on the location authentication request (S1205). That is, the file management server 10 judges whether the geographical location information indicated by the location authentication request (hereinafter referred to as "first geographical location information") corresponds to the receiving location designated by the sender user. When the file management server 10 judges that the first geographical location information does not correspond to the designated receiving location (No in S1205), the file management server 10 transmits a judgment result indicating that the location authentication has failed to the second information communication terminal device 20b (S1210).

[0134] On the other hand, when the file management server 10 determines that the first geographical location information corresponds to the specified pick-up location (Yes in S1205), the file management server 10 refers to the IP address database based on the acquired global IP address and acquires the second geographical information (S1206). Next, the file management server 10 determines whether the second location authentication process is successful or not based on the acquired second geographical location information (S1207). In other words, the file management server 10 determines whether the acquired second geographical location information corresponds to the specified pick-up location.

[0135] When the file management server 10 determines that the second geographical location information does not correspond to the designated receiving location (No in S1207), the file management server 10 similarly transmits a determination result indicating that the location authentication has failed to the second information communication terminal device 20b (S1210). That is, in this embodiment, it is not enough for the key terminal device 30 to be present at the designated receiving location, but the second information communication terminal device 20b must also be present at the designated receiving location.

[0136] On the other hand, when the file management server 10 determines that the second geographical location information corresponds to the specified receiving location (Yes in S1207), the file management server 10 cooperates with the key terminal device 30 to generate a second ciphertext (S1208) as described above. Then, the file management server 10 transmits the generated second ciphertext to the second information communication terminal device 20b (S1209).

[0137] As described above, according to this embodiment, the same advantages or effects as those of the above-mentioned embodiment can be obtained. In particular, according to this embodiment, the determination of whether the receiver user is at the receiving location specified by the sender user is performed based on not only the first geographical location information indicated by the key terminal device 30 but also the second geographical location information indicated by the second information communication terminal device 20b, so that the security of the file transfer can be further improved. In other words, the sender user can decrypt the encrypted file only at a location where the receiver user has the key terminal device 30 and where the second information communication terminal device 20b used by the receiver user is installed, so that the security of the file transfer can be further improved.

[0138] (Modification) In the above example, the file management server 10 judges whether the location authentication is successful based on the second geographical location information of the second information communication terminal device 20b in addition to the first geographical location information acquired by the key terminal device 30. However, for example, the file management server 10 may judge whether the location authentication is successful based on whether the second information communication terminal device 20b and the key terminal device 30 are connected to a router in the same LAN.

[0139] For example, it is assumed that the key terminal device 30 can be connected to a WiFi (registered trademark) access point provided by a router in a LAN. When the recipient user decrypts the encrypted file, the key terminal device 30 switches the wireless communication connection from the carrier network to the access point. This allows the file management server 10 to obtain a global IP address assigned to the router in the LAN to which the key terminal device 30 is connected in network communication with the key terminal device 30.

[0140] That is, as described above, the file management server 10 obtains a global IP address from the second information communication terminal device 20b and obtains a global IP address from the key terminal device 30, and judges whether these global IP addresses match. The receiving user can decrypt the encrypted file only when the receiving user is at the receiving location specified by the sending user and the second information communication terminal device 20b and the key terminal device 30 are at that location (within the same LAN), so that the security of the file transfer can be further improved. In this case, the judgment based on the geographical location information from the GPS function of the key terminal device 30 may be performed or omitted.

[0141] Alternatively, it may be additionally determined whether the second information communication terminal device 20b and the key terminal device 30 are connected by Bluetooth (registered trademark) communication or near field communication (NFC). This allows the second information communication terminal device 20b and the key terminal device 30 to be estimated as being in the vicinity of the recipient user, and similarly increases the accuracy of determining whether the location authentication is successful. Alternatively, the second information communication terminal device 20b may display a geometric pattern (e.g., a two-dimensional code) indicating a one-time authentication code presented by the file management server 10 on a user interface, and the recipient user may operate the key terminal device 30 to read the displayed geometric pattern, thereby causing the key terminal device 30 to obtain the geometric pattern and transmit it to the file management server 10. In other words, since the key terminal device 30 is location-authenticated by geographical location information by the GPS function, it is possible to estimate that the second information communication terminal device 20b and the key terminal device 30 are in the vicinity of the recipient user through such a display on the user interface.

[0142] The above-described embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments. The present invention can be embodied in various forms without departing from the spirit of the present invention.

[0143] For example, in the above embodiment, the sender user registers the receiving location, but the present invention is not limited to this, and for example, a system administrator of a company or business may collectively specify the receiving locations when the employees of the company are the receiving users. This allows the company or business to improve the security of file transfer by specifying the receiving location of the files of employees as the office, and by setting a system policy that prohibits the files from being received anywhere other than the office.

[0144] In addition, in the methods disclosed herein, steps, operations, or functions may be performed in parallel or in a different order, provided that the results are not inconsistent. The steps, operations, and functions described are provided merely as examples, and some of the steps, operations, and functions may be omitted or combined into one, or other steps, operations, or functions may be added, without departing from the spirit of the invention.

[0145] In addition, although various embodiments are disclosed in this specification, specific features (technical matters) in one embodiment can be added to or replaced with specific features in other embodiments, with appropriate modifications, and such forms are also included in the spirit of the present invention. [Explanation of symbols]

[0146] 1. File management system 10...File management server 20...Information and communication terminal equipment 20a...first information communication terminal device 20b...Second information communication terminal device 30...Key terminal device 40...Key management server

Claims

1. A file management system that enables file transmission between a first information communication terminal device of a first user and a second information communication terminal device of a second user, comprising: a file management server communicably connected to each of the first information communication terminal device and the second information communication terminal device; a key terminal device communicably connected to the file management server, capable of generating a master key pair consisting of a master private key and a master public key, storing the master private key, and acquiring geographical location information; The file management server includes: acquiring, from the first information communication terminal device, at least an identifier of the second user, destination information including a receiving location of the file, and a first ciphertext obtained by encrypting a common key; receiving a location authentication request including geographical location information from the key terminal device; determining whether location authentication has been successful or not based on the receiving location included in the destination information and the geographical location information included in the location authentication request, and transmitting a result of the determination to the second information communication terminal device; a second ciphertext used by the second information communication terminal device to decrypt the encrypted file obtained by encrypting the file, the second ciphertext being generated from the common key obtained by using the master private key in cooperation with the key terminal device, and being transmitted to the second information communication terminal device; the second information communication terminal device decrypts the encrypted file using the common key obtained from the second ciphertext when the result of the determination indicates that the location authentication has been successful. File management system.

2. the first information communication terminal device generates the common key in accordance with a predetermined function; creating the encrypted file using the generated common key; The file management system according to claim 1 .

3. The first information communication terminal device generating the first ciphertext by encrypting the common key using the master public key; transmitting the generated first ciphertext to the file management server; The file management system according to claim 2 .

4. The second information communication terminal device generating a temporary key pair consisting of a temporary private key and a temporary public key in accordance with a predetermined key generation algorithm, and storing the temporary private key of the temporary key pair; the key terminal device stores the temporary public key of the temporary key pair; the file management server generates the second ciphertext from the common key by using the temporary public key in cooperation with the key terminal device; If the location authentication is successful, a result of the determination including the generated second ciphertext is transmitted to the second information communication terminal device. The file management system according to claim 3.

5. The second information communication terminal device decrypting the second ciphertext using the temporary private key to obtain the common key; decrypting the encrypted file using the common key obtained by decrypting the second ciphertext; The file management system according to claim 4.

6. The file management server includes: obtaining the temporary public key from the second information communication terminal device; Transmitting the obtained temporary public key to the key terminal device; 5. The file management system according to claim 4.

7. the file management server acquires the temporary public key when performing login authentication by the second information communication terminal device; The file management system according to claim 6.

8. the file management server determines whether the login authentication has been successful by multi-factor authentication based on the possession or use of the key terminal device. The file management system according to claim 7.

9. The receiving location is a geographic location specified by the first user. The file management system according to claim 1 .

10. the geographical location information specified by the first user is specified based on a geographical map displayed on a user interface of the first information communication terminal device; The file management system according to claim 9.

11. the file management server determines whether the location authentication has been successful based on the geographical location information of the second information communication terminal device; The file management system according to claim 1 .

12. the file management server determines that the location authentication has been successful when the geographical location information included in the location authentication request and the geographical location information of the second information communication terminal device each correspond to the receiving location included in the destination information. The file management system according to claim 11.

13. The geographical location information of the second information communication terminal device is a global IP address. The file management system according to claim 11.

14. A file management server communicably connected to each of a first information communication terminal device of a first user, a second information communication terminal device of a second user, and a key terminal device that generates a master key pair consisting of a master private key and a master public key and stores the master private key, A process of acquiring, from the first information communication terminal device, destination information including at least an identifier of the second user and a file receiving location, and a first ciphertext obtained by encrypting a common key; receiving a location authentication request including geographical location information acquired by the key terminal device; a process of determining whether location authentication has been successful or not based on the receiving location included in the destination information and the geographical location information included in the location authentication request; and if the location authentication is successful, a process of generating, in cooperation with the key terminal device, a second ciphertext used for decrypting an encrypted file obtained by encrypting the file by the first information communication terminal device from the common key obtained by using the master private key, and transmitting the second ciphertext to the second information communication terminal device. File management server.

15. 1. A file transmission method for enabling transmission of a file between a first information communication terminal device of a first user and a second information communication terminal device of a second user, comprising: Specifying destination information including an identifier of the second user and a location to receive the file in the first information communication terminal device; generating an encrypted file by encrypting the file using a common key in the first information communication terminal device; acquiring a first ciphertext obtained by encrypting the specified destination information and the common key in a file management server; storing the generated encrypted file in the second information communication terminal device; a key terminal device which is owned by the second user and which generates a master key pair consisting of a master private key and a master public key and stores the master private key, and transmits geographical location information obtained in the key terminal device to the file management server; In the file management server, determining whether or not the geographical location information corresponds to the receiving location of the specified destination information, and transmitting the result of the determination to the second information communication terminal device; generating a second ciphertext used for decrypting the encrypted file from the common key obtained by using the master private key in cooperation with the file management server and the key terminal device, and transmitting the second ciphertext to the second information communication terminal device; and when the result of the determination indicates that the geographical location information corresponds to the receiving location, decrypting the encrypted file using the common key obtained from the second ciphertext in the second information communication terminal device to obtain the original file. File transmission methods.

16. Creating the encryption file includes generating the common key according to a predetermined function; and creating the encrypted file using the generated common key. The file transmission method according to claim 15.

17. generating the first ciphertext by encrypting the common key using the master public key; and transmitting the generated first ciphertext to the file management server.

17. The file transmission method according to claim 16.

18. generating a temporary key pair including a temporary private key and a temporary public key in accordance with a predetermined key generation algorithm in the second information communication terminal device; storing the temporary private key of the temporary key pair in the second information communication terminal device; storing the temporary public key of the temporary key pair in the key terminal device; the file management server generating the second ciphertext from the common key by using the temporary public key in cooperation with the key terminal device; and storing the generated second ciphertext in the second information communication terminal device based on a result of the determination that the geographical location information corresponds to the receiving location.

18. The file transmission method according to claim 17.

19. The method further includes, in the second information communication terminal device, decrypting the second ciphertext using the temporary private key to obtain the common key; decrypting the encrypted file includes decrypting the encrypted file using the common key obtained by decrypting the second ciphertext.

20. The file transmission method according to claim 18.

20. In the file management server, acquiring the temporary public key from the second information communication terminal device; and transmitting the obtained temporary public key to the key terminal device.

20. The file transmission method according to claim 18.

21. The method further includes, in the file management server, acquiring the temporary public key when performing login authentication by the second information communication terminal device.

21. The file transmission method according to claim 20.

22. The method further includes determining whether the login authentication is successful or not by multi-factor authentication based on possession or use of the key terminal device in the file management server.

22. The file transmission method according to claim 21.

23. The receiving location is a geographic location specified by the first user. The file transmission method according to claim 15.

24. the geographical location information specified by the first user is specified based on a geographical map displayed on a user interface of the first information communication terminal device; 24. The file transmission method according to claim 23.

25. 1. A file management method executed by a file management server communicably connected to a first information communication terminal device of a first user, a second information communication terminal device of a second user, and a key terminal device that generates a master key pair consisting of a master private key and a master public key and stores the master private key, comprising: acquiring, from the first information communication terminal device, destination information including at least an identifier of the second user and a file receiving location, and a first ciphertext obtained by encrypting a common key; receiving a location authentication request including geographical location information obtained by the key terminal device; determining whether location authentication has been successful or not based on the receiving location included in the destination information and the geographical location information included in the location authentication request; generating, in cooperation with the key terminal device, a second ciphertext used for decrypting the encrypted file obtained by encrypting the file by the first information communication terminal device from the common key obtained by using the master private key, when the location authentication is successful, and transmitting the second ciphertext to the second information communication terminal device. How to manage files.

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