# US 2022/0286271 A1 · Registration device, search operation device, and data management device

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- Number: US 2022/0286271 A1
- Document ID: US20220286271A1
- Status: Published application
- Kind: A1
- Application number: 17/750,902
- Filed: 2022-05-23
- Published: 2022-09-08
- Earliest claimed: 2020-01-14
- Assignees: Mitsubishi Electric Corporation
- Applicants: Mitsubishi Electric Corporation
- Inventors: Takato HIRANO; Yutaka KAWAI; Yoshihiro KOSEKI; Satoshi YASUDA
- Web page: https://patentgrep.com/patent/US20220286271A1

## CPC

- H04L 9/0618: {Block ciphers, i.e. encrypting groups of characters of a plain text message using fixed encryption transformation}
- H04L 9/0643: {Hash functions, e.g. MD5, SHA, HMAC or f9 MAC}
- G09C 1/00: Apparatus or methods whereby a given sequence of signs, e.g. an intelligible text, is transformed into an unintelligible sequence of signs by transposing the signs or groups of signs or by replacing them by others according to a predetermined system (cryptographic typewriters G09C3/00)
- H04L 9/065: {Encryption by serially and continuously modifying data stream elements, e.g. stream cipher systems, RC4, SEAL or A5/3}
- H04L 9/0819: {Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s) (network architectures or network communication protocols for key distribution in a packet data network H04L63/062)}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- G09C: CIPHERING OR DECIPHERING APPARATUS FOR CRYPTOGRAPHIC OR OTHER PURPOSES INVOLVING THE NEED FOR SECRECY

## Abstract

A registration device (500) accepts plaintext, attribute information of a user having an authority of referring to the plaintext, and a registration key for use in generating a user key for generating a search query. The registration device generates aggregate information indicating one or more aggregate values, by aggregating a plurality of attribute values included in the attribute information. The registration device generates generalized information indicating a plurality of generalized values for each aggregate value by generalizing each aggregate value included in the aggregate information. The registration device generates ciphertext data including the plaintext encrypted, by using the plaintext, the attribute information, the generalized information, and the registration key. The registration device registers the ciphertext data in a database.

## Claims

### Claim 1

A registration device comprising:
processing circuitry
to accept plaintext, attribute information indicating a plurality of attribute values which identify a plurality of attributes of a user having an authority of referring to the plaintext, and a registration key identical to a key for use in generating a user key for generating a search query;
to generate aggregate information indicating one or more aggregate values each configured of one or more attribute values, by aggregating the plurality of attribute values included in the attribute information;
to generate, for each of the aggregate values included in the aggregate information, a plurality of generalized values each configured of zero or more wildcards which replace zero or more attribute values in the aggregate value and remaining attribute values in the aggregate value and to generate generalized information indicating the plurality of generalized values for each of the aggregate values included in the aggregate information;
to generate ciphertext data including the plaintext encrypted, by using the plaintext, the attribute information, the generalized information, and the registration key;
to generate, by using a keyword regarding the plaintext, the attribute information, the generalized information, and the registration key, an encrypted tag including the keyword encrypted; and
to register a set of the ciphertext data and the encrypted tag in a database.

### Claim 2

A search operation device comprising:
processing circuitry
to accept a search keyword and a user key; and
to generate a search query by using the search keyword and a user tag key included in the user key, wherein
the user tag key has a plurality of flag values based on a plurality of attribute values which identify a plurality of attributes of a user and one or more tag attribute keys based on one or more aggregate values generated by aggregating the plurality of attribute values, and
the processing circuitry
generates a search-purpose aggregate flag indicating one or more aggregate values each configured of one or more flag values, by aggregating the plurality of flag values included in the user tag key,
generates, by using the search-purpose aggregate flag, search position information which identifies one or more attribute elements for use in searching among a plurality of attribute elements included in an encrypted tag registered together with ciphertext data in a database, and
generates the search query by using the search keyword, the one or more tag attribute keys included in the user tag key, and the search position information.

### Claim 3 (depends on 2)

The search operation device according to claim 2,
wherein the processing circuitry
transmits the search query and receives an encrypted search result including ciphertext data matching the search query; and
decodes the ciphertext data included in the encrypted search result into plaintext by using a user data key included in the user key,
wherein the user data key has a plurality of flag values based on the plurality of attribute values and one or more data attribute keys based on one or more aggregate values generated by aggregating the plurality of attribute values, and
wherein the processing circuitry
generates a decoding-purpose aggregate flag indicating one or more aggregate values each configured of one or more flag values, by aggregating the plurality of flag values included in the user data key,
generates, by using the decoding-purpose aggregate flag, decoding position information which identifies one or more attribute elements for use in decoding among a plurality of attribute elements included in the ciphertext data in the encrypted search result, and
decodes the ciphertext data included in the encrypted search result into the plaintext by using the one or more data attribute keys included in the user data key and the decoding position information.

### Claim 4

A data management device to manage a database having registered therein a plurality of sets of ciphertext data and an encrypted tag having a plurality of attribute elements, the data management device comprising:
processing circuitry
to receive a search query having an encrypted keyword and search position information;
to collate the search query with each encrypted tag, and
to transmit an encrypted search result including ciphertext data corresponding to an encrypted tag matching the search query,
wherein the search position information is information which identifies one or more attribute elements for use in searching among the plurality of attribute elements included in each encrypted tag, and
wherein the processing circuitry selects, from each encrypted tag, one or more attribute elements identified by the search position information, and collates the search query with each encrypted tag by using one or more attribute elements selected from each encrypted tag and the encrypted keyword included in the search query.