Server apparatus, search system, terminal apparatus, search method, non-transitory computer readable medium storing server program, and non-transitory computer readable medium storing terminal program

A server apparatus comprising processing circuitry

• to store a plurality of pieces of encrypted data,
• to store, as an index, a data structure which is for performing search with using a function that outputs a unique numeric value in response to an inputted keyword, the data structure having a plurality of storage areas corresponding, in one-to-one relation, to numeric values outputted from the function, and storing, for a plurality of keywords corresponding to plaintext data being pre-encryption data of one of the plurality of pieces of encrypted data, an identifier of encrypted data being post-encryption data of the plaintext data to which each keyword corresponds, in a storage area corresponding to a numeric value outputted from the function when said each keyword is inputted,
• to receive one of the plurality of keywords from a terminal apparatus, and
• to input the received keyword to the function, identify a storage area corresponding to a numeric value outputted from the function, from the index, and acquire encrypted data corresponding to the identifier stored in the identified storage area.

A terminal apparatus comprising a processing circuitry

• to generate a plurality of pieces of encrypted data by encrypting a plurality of pieces of plaintext data with using an encryption key,
• to generate, as an index, a data structure which is for performing search with using a function that outputs a unique numeric value in response to an inputted keyword, the data structure having a plurality of storage areas corresponding, in one-to-one relation, to numeric values outputted from the function, and storing, for a plurality of keywords corresponding to one of the plurality of pieces of plaintext data, an identifier of encrypted data being post-encryption data of the plaintext data to which each keyword corresponds, in a storage area corresponding to a numeric value outputted from the function when said each keyword is inputted, and
• to transmit the plurality of pieces of encrypted data generated and the generated index to a server apparatus,
• the processing circuitry transmitting one of the plurality of keywords to the server apparatus, and receiving, from the server apparatus, encrypted data which the server apparatus has acquired by inputting the transmitted keyword to the function and searching the index based on a numeric value outputted from the function.

A search method in which used are:

• a data storage part to store a plurality of pieces of encrypted data;
• and
• an index storage part to store, as an index, a data structure which is for performing search with using a function that outputs a unique numeric value in response to an inputted keyword, the data structure having a plurality of storage areas corresponding, in one-to-one relation, to numeric values outputted from the function, and storing, for a plurality of keywords corresponding to plaintext data being pre-encryption data of one of the plurality of pieces of encrypted data, an identifier of encrypted data being post-encryption data of the plaintext data to which each keyword corresponds, in a storage area corresponding to a numeric value outputted from the function when said each keyword is inputted,
• the search method comprising:
• receiving one of the plurality of keywords from a terminal apparatus;
• and
• inputting the received keyword to the function, identifying a storage area corresponding to a numeric value outputted from the function, from the index, and acquiring encrypted data corresponding to the identifier stored in the identified storage area, from the data storage part.

A non-transitory computer readable medium storing a server program that causes a computer which includes:

• a data storage part to store a plurality of pieces of encrypted data;
• and
• an index storage part to store, as an index, a data structure which is for performing search with using a function that outputs a unique numeric value in response to an inputted keyword, the data structure having a plurality of storage areas corresponding, in one-to-one relation, to numeric values outputted from the function, and storing, for a plurality of keywords corresponding to plaintext data being pre-encryption data of one of the plurality of pieces of encrypted data, an identifier of encrypted data being post-encryption data of the plaintext data to which each keyword corresponds, in a storage area corresponding to a numeric value outputted from the function when said each keyword is inputted,
• to execute:
• a communication process of receiving one of the plurality of keywords from a terminal apparatus;
• and
• a search process of inputting the keyword received by the communication process to the function, identifying a storage area corresponding to a numeric value outputted from the function, from the index, and acquiring encrypted data corresponding to the identifier stored in the identified storage area, from the data storage part.

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

• a data encryption process of generating a plurality of pieces of encrypted data by encrypting a plurality of pieces of plaintext data with using an encryption key;
• an index generation process of generating, as an index, a data structure which is for performing search with using a function that outputs a unique numeric value in response to an inputted keyword, the data structure having a plurality of storage areas corresponding, in one-to-one relation, to numeric values outputted from the function, and storing, for a plurality of keywords corresponding to one of the plurality of pieces of plaintext data, an identifier of encrypted data being post-encryption data of the plaintext data to which each keyword corresponds, in a storage area corresponding to a numeric value outputted from the function when said each keyword is inputted;
• and
• a communication process of transmitting the plurality of pieces of encrypted data generated by the data encryption process and the index generated by the index generation process to a server apparatus,
• the communication process transmitting one of the plurality of keywords to the server apparatus, and receiving, from the server apparatus, encrypted data which the server apparatus has acquired by inputting the transmitted keyword to the function and searching the index based on a numeric value outputted from the function.