Encrypted database system, client terminal, encrypted database server, natural joining method, and program

A client terminal constituting an encrypted database system by being mutually connected to an encrypted database server, the client terminal comprising:

• a recording module which records an encryption key in advance;
• a column encryption unit which encrypts data on an a-th column of a first table and data on a b-th column of a second table inputted from outside, and outputs the encrypted data to the outside;
• and
• an encrypted table natural joining request unit which outputs a natural joining request text for requesting natural joining of the a-th column and the b-th column of the encrypted first table and second tables, generates a table joining key containing a column public key and a column private key generated by the encryption key from table identifiers of the first and the second tables and column identifiers of the a-th and b-th columns, and outputs the generated key by including it in the natural joining request text.

A natural joining method used in an encrypted database system constituted with a client terminal and an encrypted database server mutually connected to each other, wherein:

• an encryption key is stored in advance to a recording module of the client terminal;
• the recording module of the client terminal encrypts data on an a-th column of a first table and data on a b-th column of a second table inputted from outside by using the encryption key, and outputs the encrypted data to the outside;
• a data reception unit of the encrypted database server receives and records the encrypted first and second tables;
• an encrypted table natural joining request unit of the client terminal generates a table joining key containing a column public key and a column private key generated by the encryption key from table identifiers of the first and the second tables and column identifiers of the a-th and b-th columns;
• the encrypted table natural joining unit of the client terminal outputs the table joining key by including it in a natural joining request text for requesting natural joining of the a-th column and the b-th column of the encrypted first table and second tables;
• an encrypted table natural joining unit of the encrypted database server executes the natural joining of the encrypted first and second tables according to the natural joining request text by employing the table joining key;
• and
• the encrypted table joining unit of the encrypted database server returns a result of the natural joining to the client terminal.

A non-transitory computer readable recording medium storing a natural joining program used in an encrypted database system constituted with a client terminal having an encryption key stored in advance and an encrypted database server mutually connected to each other, the program causing a computer provided to the client terminal to execute:

• a procedure for encrypting data on an a-th column of a first table and data on a b-th column of a second table inputted from outside by using the encryption key, and outputting the encrypted data to the outside;
• a procedure for generating a table joining key containing a column public key and a column private key generated by the encryption key from table identifiers of the first and the second tables and column identifiers of the a-th and b-th columns;
• and
• a procedure for outputting the table joining key by including it in a natural joining request text for requesting natural joining of the a-th column and the b-th column of the encrypted first table and second tables.

An encrypted database system constituted with a client terminal and an encrypted database server mutually connected to each other, wherein

• the client terminal comprises:
• recording means for recording an encryption key in advance;
• column encryption means for encrypting data on an a-th column of a first table and data on a b-th column of a second table inputted from outside by using the encryption key, and outputting the encrypted data to the outside;
• and
• encrypted table natural joining request means for outputting a natural joining request text for requesting natural joining of the a-th column and the b-th column of the encrypted first table and second tables, generating a table joining key containing a column public key and a column private key generated by the encryption key from table identifiers of the first and the second tables and column identifiers of the a-th and b-th columns, and outputting the generated key by including it in the natural joining request text, and
• the encrypted database server comprises:
• data reception means for receiving and recording the encrypted first and second tables;
• and
• encrypted table natural joining means for executing the natural joining of the encrypted first and second tables according to the natural joining request text by employing the table joining key.

A client terminal constituting an encrypted database system by being mutually connected to an encrypted database server, the client terminal comprising:

• recording means for recording an encryption key in advance;
• column encryption means for encrypting data on an a-th column of a first table and data on a b-th column of a second table inputted from outside, and outputting the encrypted data to the outside;
• and
• encrypted table natural joining request means for outputting a natural joining request text for requesting natural joining of the a-th column and the b-th column of the encrypted first table and second tables, generating a table joining key containing a column public key and a column private key generated by the encryption key from table identifiers of the first and the second tables and column identifiers of the a-th and b-th columns, and outputting the generated key by including it in the natural joining request text.