Nippon Telegraph and Telephone Corporation

Miyako Ohkubo

Masayuki Abe

Koutarou Suzuki

Atsushi Fujioka

Shingo Kinoshita

Fumitaka Hoshino

A tag device causes a second calculator to read a confidential value from a confidential value memory and to apply a second function Fwhich disturbs a relationship between elements of a definition domain and a mapping thereof to generate tag output information. The tag device delivers the tag output information to a backend apparatus. Subsequently, a first calculator reads out at least part of elements of the confidential value from the confidential value memory, and applies a first function F, an inverse image of which is difficult to obtain, and a result of such calculation is used to update a confidential value in the confidential value memory by overwriting.

Tag privacy protection method, tag device, backend apparatus, updater, update solicitor and record medium carrying such programs in storage

Two El Gamal ciphertexts, which are input to a two-input two-output unit switching gates SW forming a permutation network, are randomized with a random number and randomly permuted, and a zero-knowledge proof, which proves the correspondence between the inputs and outputs of the switching gates SW, is output to a verifier without revealing the random number and the random permutation. A decryption unit decrypts ciphertexts from a unit switching gate SW in he last column through the use of a secret key, and proves in zero-knowledge the validity of the decryption without revealing the secret key. A verification unit verifies the proof of each unit switching gate and the proof of the decryption unit.

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Kanagawa, Japan

Miyako Ohkubo