Searchable encryption system, data management device, searchable encryption method, and computer readable medium

A data management device comprising:

• processing circuitry to acquire a registration auxiliary key EK2 of a registration secret key EK, a public parameter, and encrypted data that is plaintext data encrypted using a registration key EK1 of the registration secret key EK and the public parameter, transform the encrypted data using the registration auxiliary key EK2 and the public parameter, and register transformed encrypted data obtained by transformation in a registration database in association with an identifier that identifies the plaintext data, the registration secret key EK being generated using a master key and the public parameter, and being composed of the registration key EK1 used for encrypting data and the registration auxiliary key EK2 used for transforming encrypted data, the registration key EK1 being EK1=G{circumflex over ( )}ek1 mod N, where G, ek1, and N are positive integers obtained based on the master key and the public parameter, the registration auxiliary key EK2 being an integer from 1 to (Z−1) with which X=ek1*EK2 mod Z, where X and Z are positive integers obtained based on the master key and the public parameter.

A searchable encryption method comprising:

• acquiring a registration key EK1 of a registration secret key EK, plaintext data, and a public parameter, and encrypting the plaintext data using the registration key EK1 and the public parameter so as to generate encrypted data, the registration secret key EK being generated using a master key and the public parameter, and being composed of the registration key EK1 used for encrypting data and a registration auxiliary key EK2 used for transforming encrypted data, the registration key EK1 being EK1=G{circumflex over ( )}ek1 mod N, where G, ek1, and N are positive integers obtained based on the master key and the public parameter, the registration auxiliary key EK2 being an integer from 1 to (Z−1) with which X=ek1*EK2 mod Z, where X and Z are positive integers obtained based on the master key and the public parameter;
• and
• acquiring the registration auxiliary key EK2, the public parameter, and the encrypted data, transforming the encrypted data using the registration auxiliary key EK2 and the public parameter, and registering transformed encrypted data obtained by transformation in a registration database in association with an identifier that identifies the plaintext data.

A non-transitory computer readable medium storing a searchable encryption program that causes a computer to execute:

• a registration request process of acquiring a registration key EK1 of a registration secret key EK, plaintext data, and a public parameter, and encrypting the plaintext data using the registration key EK1 and the public parameter so as to generate encrypted data, the registration secret key EK being generated using a master key and the public parameter, and being composed of the registration key EK1 used for encrypting data and a registration auxiliary key EK2 used for transforming encrypted data, the registration key EK1 being EK1=G{circumflex over ( )}ek1 mod N, where G, ek1, and N are positive integers obtained based on the master key and the public parameter, the registration auxiliary key EK2 being an integer from 1 to (Z−1) with which X=ek1*EK2 mod Z, where X and Z are positive integers obtained based on the master key and the public parameter;
• and
• a data management process of acquiring the registration auxiliary key EK2, the public parameter, and the encrypted data, transforming the encrypted data using the registration auxiliary key EK2 and the public parameter, and registering transformed encrypted data obtained by transformation in a registration database in association with an identifier that identifies the plaintext data.