Abstract: A communication terminal shares a session key with and sends cipher text to another communication terminal via a server device, including: a common key cipher text obtaining unit that encrypts a message based on a common key to obtain common key cipher text; a function computation result obtaining unit that computes the common key and the session key based on a predetermined first function to obtain a function computation result; a public key cipher text obtaining unit that encrypts the function computation result based on a public key to obtain public key cipher text; and a cipher text sending unit that sends the common key cipher text and the public key cipher text to the server device. The communication terminal can update data previously saved in a server to data that can be decrypted on the communication terminal side using an updated session key, without the server decrypting the data.

Abstract: There is provided a data sharing technique in which it is possible to update data stored in a server before to such data that is decryptable on the communication terminal side using an updated session key without the data being decrypted on the server side, and a deleted user cannot decrypt the decryptable data. There are included: a generation identifier generation step of a data sharing server generating a generation identifier showing a generation of a group; a session key encryption step of a communication terminal to perform encrypted session key update using the generation identifier received from the data sharing server and a public parameter and a session key recorded in a recording part to generate an encrypted session key, which is a session key encrypted; and an encrypted session key management step of the data sharing server recording the encrypted session key received from the communication terminal to perform encrypted session key update as a currently valid encrypted session key.

Abstract: Plurality of users share a common key while permitting change of members sharing the common key and computational complexity required for key exchange is reduced. Ri and ci are computed based on a twisted pseudo-random function in a first key generation step. sid is generated based on a target-collision resistant hash function and (sid, R?, R?) is transmitted to communication devices Ui in a session ID generation step. T1 and T? are computed based on a pseudo-random function in a representative second key generation step. Tj is computed based on the pseudo-random function in a general second key generation step. k? is computed based on the twisted pseudo-random function and T?j is computed with respect to each j in a third key generation step. K11 and k1 are computed in a first session key generation step. A common key K2 is generated based on the pseudo-random function in a second session key generation step.

Abstract: A communication terminal which is capable of reducing load of a server apparatus by reutilizing a message key to be used for encrypting a message is provided.

Abstract: A communication device includes a signature encryption unit that encrypts input information with a secret key and transmits the information to a server device if the communication device belongs to a group, and a signature decryption unit that downloads, from the server device, encrypted n?1 pieces of the input information transmitted from other communication devices and decrypts the encrypted n?1 pieces of input information with the secret key if the communication device belongs to a group. The communication device transmits session key generation information to the server device via the signature encryption unit, generates a session key using n?1 pieces of session key generation information acquired via the signature decryption unit and session key generation information of the communication device, transmits a cipher text encrypted with the session key via the signature encryption unit to the server device, and decrypts n?1 cipher texts acquired via the signature decryption unit with the session key.

Abstract: A client apparatus converts second input authentication information having a data content compliant with a second authentication method different from a first authentication method into authentication target information in a data format compliant with the first authentication method and transmits information corresponding to the authentication target information to a communication server apparatus. A server apparatus is capable of carrying out both a first process of providing a first authentication server apparatus that carries out an authentication process compliant with the first authentication method with first information corresponding to the authentication target information and a second process of providing a second authentication server apparatus that carries out an authentication process compliant with the second authentication method with second information corresponding to the authentication target information.

Abstract: An encrypted communication is correctly decrypted even when key exchange completion notification is delayed. A key storage (10) stores at least one common key which is shared with another encrypted communication device. A key selecting unit (11) selects an encryption key from the at least one common key stored in the key storage (10). An encrypting unit (12) generates encrypted data by encrypting, by using the encryption key, data to be transmitted to the other encrypted communication device. A transmitting unit (13) transmits, to the other encrypted communication device, the encrypted data with a key index, by which the encryption key is uniquely identified, added thereto. A receiving unit (14) receives the encrypted data with the key index added thereto from the other encrypted communication device. A key obtaining unit (15) obtains, from the at least one common key stored in the key storage (10), a decryption key corresponding to the key index added to the encrypted data.

Abstract: With respect to a key distribution system including N terminal devices Ui and a key distribution server used for exchanging a session key, the key distribution system includes an isogeny calculating unit configured to calculate a first public value using a basis of a first torsion subgroup of a predetermined elliptic curve at an odd-numbered terminal device Ui and calculate a second public value using a basis of a second torsion subgroup of the predetermined elliptic curve at an even-numbered terminal device Ui, when N is an even number, a distributing unit configured to distribute the first public value calculated at the odd-numbered terminal device Ui to a terminal device Ui?1 and a terminal device Ui+1, and distribute the second public value calculated at the even-numbered terminal device Ui to a terminal device Ui?1 and a terminal device Ui+1, from the key distribution server, a key generating unit configured to use second public values distributed by the distributing unit to generate the session key at t

Abstract: There is provided a data sharing technique in which it is possible to update data stored in a server before to such data that is decryptable on the communication terminal side using an updated session key without the data being decrypted on the server side, and a deleted user cannot decrypt the decryptable data. There are included: a generation identifier generation step of a data sharing server generating a generation identifier showing a generation of a group; a session key encryption step of a communication terminal to perform encrypted session key update using the generation identifier received from the data sharing server and a public parameter and a session key recorded in a recording part to generate an encrypted session key, which is a session key encrypted; and an encrypted session key management step of the data sharing server recording the encrypted session key received from the communication terminal to perform encrypted session key update as a currently valid encrypted session key.

Abstract: A key exchange technique of performing a key exchange among N (?2) parties, which can conceal metadata on communication, is provided. A key exchange method includes: a first key generation step in which a communication device Ui generates a first key; a first anonymous broadcast step in which the communication device Ui anonymously broadcasts the first key with a set R?{Ui} being designated for i?{1, . . . , n} and the communication device Ui anonymously broadcasts the first key with ? being designated for i?{n+1, . . . , N}; a second key generation step in which the communication device Ui generates a second key; a second anonymous broadcast step in which the communication device Ui anonymously broadcasts the second key with the set R?{Ui} being designated for i?{1, . . . , n} and the communication device Ui anonymously broadcasts the second key with ? being designated for i?{n+1, . . . , N}; and a session key generation step in which the communication device Ui generates a session key SK for i?{1, . . .

Abstract: On the assumption that i?s, j is the number of times a key exchange is performed, and k is any one of integers greater than or equal to 0 and less than j, a key exchange device includes: a shared secret key storage in which shared secret information mkik which is information different from a secret key of the key exchange device is stored; an authentication information addition unit that generates authentication information ?i, by which authentication is performed and falsification is detected, for key exchange information ei, which is output to the outside, by using the shared secret information mkik; and an authentication information verification unit that receives key exchange information es and authentication information ?s corresponding to the key exchange information es from the outside, verifies the authentication information ?s using the shared secret information mkik, and, if the authentication information ?s is not successfully verified, stops a key exchange, and the shared secret information mkik i

Abstract: Plurality of users share a common key while permitting change of members sharing the common key and computational complexity required for key exchange is reduced. Ri and ci are computed based on a twisted pseudo-random function in a first key generation step. sid is generated based on a target-collision resistant hash function and (sid, R?, R?) is transmitted to communication devices Ui in a session ID generation step. T1 and T? are computed based on a pseudo-random function in a representative second key generation step. Tj is computed based on the pseudo-random function in a general second key generation step. k? is computed based on the twisted pseudo-random function and T?j is computed with respect to each j in a third key generation step. K11 and k1 are computed in a first session key generation step. A common key K2 is generated based on the pseudo-random function in a second session key generation step.

Abstract: Registered network-based identification corresponding to any of networks is stored in a key device 12. A terminal device 11 sends ciphertext and network-based identification to the key device 12, using a network. The key device 12 receives the sent ciphertext and network-based identification and outputs response information corresponding to a decrypted value of the ciphertext when the network-based identification corresponds to the registered network-based identification. The terminal device 11 obtains the decrypted value from the response information.

Abstract: A server sends a key update request for requesting updating of the key, to a client terminal. The client terminal sends, to a key delivery server, a key delivery request for requesting the delivery of a key to the client terminal. The key delivery server delivers a key to the client terminal. The client terminal sends, to the server, a key reception notice indicating that the delivered key was received. The server sends, to the client terminal, a key-use start notice indicating that the client terminal starts data transmission and reception by using the delivered key with a different client terminal from the aforementioned client terminal. The client terminal performs data transmission and reception with the different client terminal by using the delivered key.

Abstract: A key distribution system includes a representative user terminal 2p, a server apparatus 3, and an (n+1)-th user terminal 2n+1. The representative user terminal 2p uses a public key for the (n+1)-th user terminal 2n+1 and information for identifying the (n+1)-th user terminal 2n+1 to encrypt key information with a predetermined encryption function in Certificate-less Encryption to obtain ciphertext. The server apparatus 3 sends the ciphertext to the (n+1)-th user terminal 2n+1 when the (n+1)-th user terminal 2n+1 is added. The (n+1)-th user terminal 2n+1 uses a complete secret key for the (n+1)-th user terminal 2n+1 and the information for identifying the (n+1)-th user terminal 2n+1 to decrypt the ciphertext with a predetermined decryption function to obtain the key information.

Abstract: Plurality of users share a common key while permitting dynamic member change and computational complexity required for key exchange is reduced. The first key generation unit 212 of the communication devices Ui computes Ri and ci, or ci based on a twisted pseudo-random function. A session ID generation unit 113 of a key distribution device S generates sid based on a target-collision resistant hash function and transmits sid to the communication devices Ui. A second key generation unit 214 of the communication devices Ui computes Ti based on a pseudo-random function. A third key generation unit 115 of the key distribution device S computes k? and T?i based on the twisted pseudo-random function. A session key generation unit 217 of the communication devices Ui generates the common key K2 based on a pseudo-random function.

Abstract: The present invention makes it possible to improve confidentiality. A communication terminal stores a session key shared with other communication terminals (S3). The communication terminal makes a pair of an index generated by using the session key for a character string relating to a message and a message identifier, and transmits it to a server apparatus (S4). The server apparatus stores the pair of the index and the message identifier (S5). The communication terminal generates, when the session key is updated, a re-encryption key with a session key before update and a session key after update (S8). The server apparatus updates, by using the re-encryption key, the stored index to an index generated by using the session key after update (S9). The communication terminal encrypts a search keyword with the session key to generate a search query (S10). The server apparatus extracts a message identifier of which the index matches the search query (S11).

Abstract: A leakage prevention apparatus stores an assumed use permission range, stores an information asset caused to be in an unavailable state by encryption, stores an information asset caused to be in an available state by decryption, and stores an information asset caused to be in a leakage-concerned state. When use of an information asset in the unavailable state is requested by an application corresponding to the use permission range, the information asset is decrypted to cause the information asset to be in the available state. When the use of the information asset in the available state by the application ends, the information asset is encrypted to cause the information asset to be in the unavailable state. When use of an information asset in the unavailable state is requested by an application not corresponding to the use permission range, the information asset is caused to be in the leakage-concerned state.

Abstract: A random number generating unit generates random numbers s1, s2, s?1, and s?2. A public keys randomizing unit generates first randomized public keys information obtained by randomizing public keys using the random number s1 and second randomized public keys information obtained by randomizing the public keys using the random number s2. A proxy calculation unit calculates a first commission result by using a secret key and calculates a second commission result by using the secret key. A verification unit calculates a first verification value by using the random number s2, calculates a second verification value by using the random number s1, and verifies whether or not the first verification value and the second verification value coincide with each other. A common key calculation unit calculates a common key by using the random numbers s?1 and s?2 if the first verification value and the second verification value coincide with each other.

Abstract: A communication terminal shares a session key with and sends cipher text to another communication terminal via a server device, including: a common key cipher text obtaining unit that encrypts a message based on a common key to obtain common key cipher text; a function computation result obtaining unit that computes the common key and the session key based on a predetermined first function to obtain a function computation result; a public key cipher text obtaining unit that encrypts the function computation result based on a public key to obtain public key cipher text; and a cipher text sending unit that sends the common key cipher text and the public key cipher text to the server device. The communication terminal can update data previously saved in a server to data that can be decrypted on the communication terminal side using an updated session key, without the server decrypting the data.