Nippon Telegraph and Telephone Corporation

Reo Yoshida

Tetsutaro Kobayashi

Hitoshi Fuji

Yuto Kawahara

Yuki Okano

Kazuki Yoneyama

Tomohide Yamamoto

Go Yamamoto

Ryo Nishimaki

Tomoaki Washio

Tsuyoshi Miyamoto

Hironobu Okuyama

Junya Akiba

Masahiro Matsui

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 Ugenerates a first key; a first anonymous broadcast step in which the communication device Uanonymously broadcasts the first key with a set R-{U} being designated for i∈{1, . . . , n} and the communication device Uanonymously broadcasts the first key with φ being designated for i∈{n+1, . . . , N}; a second key generation step in which the communication device Ugenerates a second key; a second anonymous broadcast step in which the communication device Uanonymously broadcasts the second key with the set R-{U} being designated for i∈{1, . . . , n} and the communication device Uanonymously broadcasts the second key with φ being designated for i∈{n+1, . . . , N}; and a session key generation step in which the communication device Ugenerates a session key SK for i∈{1, . . . , n} if a predetermined condition is satisfied.

Anonymous broadcast method, key exchange method, anonymous broadcast system, key exchange system, communication device, and program

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 Ugenerates a first key; a first anonymous broadcast step in which the communication device Uanonymously broadcasts the first key with a set R−{U} being designated for i∈{1, . . . , n} and the communication device Uanonymously broadcasts the first key with φ being designated for i∈{n+1, . . . , N}; a second key generation step in which the communication device Ugenerates a second key; a second anonymous broadcast step in which the communication device Uanonymously broadcasts the second key with the set R−{U} being designated for i∈{1, . . . , n} and the communication device Uanonymously broadcasts the second key with φ being designated for i∈{n+1, . . . , N}; and a session key generation step in which the communication device Ugenerates a session key SK for i∈{1, . . . , n} if a predetermined condition is satisfied.

A server device includes a memory and a processor to execute saving an encrypted text of a message generated by encrypting the message with a message key generated from a shared key and a group identifier, by using a message key identifier as an identifier of the message key as a key; saving an encrypted text of the message key generated by encrypting the message key to be re-encryptable by using the shared key, by using the message key identifier as a key; and receiving, after update of the shared key, a re-encryption key from a communication terminal that has generated the re-encryption key by using the shared key and the updated shared key, using the re-encryption key to generate a re-encrypted encrypted text of the message key, and overwriting the encrypted text of the message key before re-encryption with the re-encrypted encrypted text of the message key.

Server device, communication terminal, communication system, and program

The present invention makes it possible to improve confidentiality. A communication terminal stores a session key shared with other communication terminals (S). 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 (S). The server apparatus stores the pair of the index and the message identifier (S). 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 (S). The server apparatus updates, by using the re-encryption key, the stored index to an index generated by using the session key after update (S). The communication terminal encrypts a search keyword with the session key to generate a search query (S). The server apparatus extracts a message identifier of which the index matches the search query (S).

Message transmission system, communication terminal, server apparatus, message transmission method, and program

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. Rand care 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 Uin a session ID generation step. Tand T' are computed based on a pseudo-random function in a representative second key generation step. Tis computed based on the pseudo-random function in a general second key generation step. k&#x2032; is computed based on the twisted pseudo-random function and T&#x2032;is computed with respect to each j in a third key generation step. Kand kare computed in a first session key generation step. A common key Kis generated based on the pseudo-random function in a second session key generation step.

Key exchange method and key exchange system

To provide a terminal device that can share a session key for use in encryption communication with multiple terminal devices at a certain timing without relying on an existing server device. The terminal device includes: a list/request sending unit that, when the terminal device operates as an owner device, generates a key distribution request, signs the key distribution request, and transmits the key distribution request to a key distribution management device; a participation request sending unit that, when the terminal device operates as a general device, generates a participation request, signs the participation request, and transmits the participation request to the key distribution management device; a session key generating unit that executes an authentication-based multipoint key distribution algorithm of server-client type in cooperation with another terminal device participating in the session and with the key distribution management device to generate a session key; and a post-confirmation unit that, when the session key has been normally generated, transmits a success notice to the key distribution management device and receives a collective notice from the key distribution management device.

Terminal device, key distribution management device, server-client system, communication method, and programs

A key exchange device is provided that includes: a shared secret key storage in which shared secret information mkwhich is information different from a secret key of the key exchange device is stored; an authentication information addition unit that generates authentication information &#x3c3;, by which authentication is performed and falsification is detected, for key exchange information e, which is output to the outside, by using the shared secret information mk; and an authentication information verification unit that receives key exchange information eand authentication information &#x3c3;corresponding to the key exchange information efrom the outside, verifies the authentication information &#x3c3;using the shared secret information mk, and, if the authentication information &#x3c3;is not successfully verified, stops a key exchange, and the shared secret information mkis a value that is used in a generation process in a key exchange.

Key exchange device, key exchange system, key exchange method, and key exchange program for exchanging a key with another device

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&#x2212;1 pieces of the input information transmitted from other communication devices and decrypts the encrypted n&#x2212;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&#x2212;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&#x2212;1 cipher texts acquired via the signature decryption unit with the session key.

Communication device, server device, concealed communication system, methods for the same, and program

With respect to a key distribution system including N terminal devices Uand 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 Uand calculate a second public value using a basis of a second torsion subgroup of the predetermined elliptic curve at an even-numbered terminal device U, when N is an even number, a distributing unit configured to distribute the first public value calculated at the odd-numbered terminal device Uto a terminal device Uand a terminal device U, and distribute the second public value calculated at the even-numbered terminal device Uto a terminal device Uand a terminal device U, 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 the odd-numbered terminal device U, and use first public values distributed by the distributing unit to generate the session key at the even-numbered terminal device U, wherein the isogeny calculating unit calculates the first public value using the basis of the first torsion subgroup and the second public value using the basis of the second torsion subgroup at a predetermined terminal device Uamong the terminal devices U, when N is an odd number.

Key distribution system, terminal device, key distribution method, and program

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

Encrypted communication device, encrypted communication system, encrypted communication method, and program

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. The communication terminal includes a session key storage part which stores a session key which is shared with another communication terminal and which is not shared with the server apparatus, a message key generating part which generates a message key, a message key storage part which stores the message key to be reutilized in association with a message key identifier, a message encrypting part which generates a message encrypted text based on a common key cryptosystem using the message and the message key, a message key encrypting part which generates a message key encrypted text based on a common key cryptosystem which can perform re-encryption using the session key and the message key, and an encrypted text transmitting part which transmits a group identifier which is an identifier of a group to which an own terminal belongs, the message key encrypted text or the message key identifier, and the message encrypted text to the server apparatus.

Communication terminal, server apparatus, and program

A key distribution system includes a representative user terminal, a server apparatus, and an (n+1)-th user terminal. The representative user terminaluses a public key for the (n+1)-th user terminaland information for identifying the (n+1)-th user terminalto encrypt key information with a predetermined encryption function in Certificate-less Encryption to obtain ciphertext. The server apparatussends the ciphertext to the (n+1)-th user terminalwhen the (n+1)-th user terminalis added. The (n+1)-th user terminaluses a complete secret key for the (n+1)-th user terminaland the information for identifying the (n+1)-th user terminalto decrypt the ciphertext with a predetermined decryption function to obtain the key information.

Key distribution system and method, key generation apparatus, representative user terminal, server apparatus, user terminal, and program

There is provided an encrypted message search technique making it difficult to, at the time of searching for a message in a state of being encrypted, guess content of the search and a result of the search. There are included: an encrypted search secret key transmission step of a terminal generating an encrypted search secret key from a search secret key generated each time an update interval set in advance elapses and transmitting the encrypted search secret key to a server; a search secret key decryption step of the terminal decrypting the encrypted search secret key acquired from the server to obtain the search secret key; an encrypted message transmission step of the terminal transmitting an index set generated using information related to a message and a newest search secret key, and an encrypted message to the server; a query transmission step of the terminal transmitting a query set generated using a message search character string and the search secret key; and an encrypted message returning step of the server transmitting an encrypted message including elements of an index set corresponding to an element of the query set.

Encrypted message search method, message transmission/reception system, server, terminal and program

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.

Growing community of inventors

Musashino, Japan

Reo Yoshida