Nippon Telegraph and Telephone Corporation

Kazuki Yoneyama

Tetsutaro Kobayashi

Reo Yoshida

Hitoshi Fuji

Yuto Kawahara

Tomohide Yamamoto

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.

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

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

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

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 unitof the communication devices Ucomputes Rand c, or cbased on a twisted pseudo-random function. A session ID generation unitof a key distribution device S generates sid based on a target-collision resistant hash function and transmits sid to the communication devices U. A second key generation unitof the communication devices Ucomputes Tbased on a pseudo-random function. A third key generation unitof the key distribution device S computes k' and T&#x2032;based on the twisted pseudo-random function. A session key generation unitof the communication devices Ugenerates the common key Kbased on a pseudo-random function.

Key exchange method, key exchange system, communication device and storage medium therefore

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 computes Rand cbased on a twisted pseudo-random function. A session ID generation unit generates sid based on a target-collision resistant hash function and transmits (sid, R, R) to communication devices U. A second key generation unit of a representative communication device Ucomputes Tbased on a pseudo-random function. A second key generation unit of general communication devices Ucomputes Tbased on the pseudo-random function. A third key generation unit computes k' based on the twisted pseudo-random function and computes T&#x2032;with respect to each j. A session key generation unit of the general communication devices Ucomputes Kand k. The session key generation unit generates a common key Kbased on the pseudo-random function.

Growing community of inventors

Hitachi, Japan

Kazuki Yoneyama