# US 11,451,372 B2 · Privacy-preserving analysis device, privacy-preserving analysis system, privacy-preserving analysis method, and computer readable medium

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- Number: US 11,451,372 B2
- Document ID: US11451372B2
- Status: Granted
- Kind: B2
- Application number: 16/767,018
- Filed: 2018-01-17
- Published: 2021-01-14
- Granted: 2022-09-20
- Earliest claimed: 2018-01-17
- Assignees: Mitsubishi Electric Corporation
- Applicants: Mitsubishi Electric Corporation
- Inventors: Yutaka Kawai; Takato Hirano; Yoshihiro Koseki
- Web page: https://patentgrep.com/patent/US11451372B2

## CPC

- H04L 9/0618: {Block ciphers, i.e. encrypting groups of characters of a plain text message using fixed encryption transformation}
- H04L 9/0894: {Escrow, recovery or storing of secret information, e.g. secret key escrow or cryptographic key storage}
- 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 9/0662: {with particular pseudorandom sequence generator}
- H04L 9/0861: {Generation of secret information including derivation or calculation of cryptographic keys or passwords}
- H04L 9/3213: {using tickets or tokens, e.g. Kerberos (network architectures or network communication protocols for entities authentication using tickets in a packet data network H04L63/0807)}
- 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

An encryption device (50) generates a ciphertext ct encrypted from information x with using an encryption token etk. A decryption key generation device (60) generates a decryption key dk from a user secret key sk in which a vector y is set, with using a decryption token dtk corresponding to the encryption token etk. A privacy-preserving analysis device (70) decrypts the ciphertext ct generated by the encryption device (50), by means of the decryption key dk generated by the decryption key generation device (60), so as to generate a result of computation over the vector x and the vector y.

## Claims

### Claim 1

A privacy-preserving analysis device comprising:
processing circuitry
to acquire, for each integer i of i=1 . . . , n concerning an integer n of 1 or more, a ciphertext cti encrypted from a sum mi of an encryption token etki, being a vector ui, and information xi;
to acquire a decryption key dk generated with using a decryption token dtk and a user secret key ski, the decryption token dtk including the vector ui for each integer i, the user secret key ski being set with information yi for each integer i, the decryption key dk including a sum z of inner product of the vector ui and the information yi for each integer i;
to decrypt the ciphertext cti for each integer i, using a decryption algorithm in a cryptography that calculates inner product of information being set in the ciphertext and information being set in the user secret key; and
to generate decryption data Di, and to subtract the sum z included in the decryption key dk from a sum of the decryption data Di for each integer i, thereby calculating a sum of inner product of the information xi and the information yi for each integer i, wherein
the decryption token dtk corresponds to the encryption token etki for each integer i of i=1 . . . , n.

### Claim 2

A privacy-preserving analysis system comprising:
a first processing circuitry to generate, for each integer i of i=1 n concerning an integer n of 1 or more, a ciphertext cti encrypted from a sum mi of an encryption token etki, being a vector ui, and information xi;
a second processing circuitry to generate a decryption key dk, with using a decryption token dtk and a user secret key ski, the decryption token dtk including the vector ui for each integer i, the user secret key ski being set with information yi for each integer i, the decryption key dk including a sum z of inner product of the vector ui and the information yi for each integer i; and
a third processing circuitry to decrypt the ciphertext cti for each integer i, the ciphertext cti being generated by the encryption device, using a decryption algorithm in a cryptography that calculates inner product of information being set in the ciphertext and information being set in the user secret key, wherein
the third processing circuitry generates decryption data Di and subtracts the sum z included in the decryption key dk generated by the decryption key generation device, from a sum of the decryption data Di for each integer i, thereby calculating a sum of inner product of the information xi and the information y for each integer i, and
the decryption token dtk corresponds to the encryption token etki for each integer i of i=1 . . . , n.

### Claim 3

A privacy-preserving analysis method comprising:
acquiring, for each integer i of i=1 . . . , n concerning an integer n of 1 or more, a ciphertext ct encrypted from a sum mi of an encryption token etki, being a vector ui, and information xi;
acquiring a decryption key dk generated with using a decryption token dtk and a user secret key ski, the decryption token dtk including the vector for each integer i, the user secret key ski being set with information yi for each integer i, the decryption key dk including a sum z of inner product of the vector ui and the information yi for each integer i;
decrypting the ciphertext cti for each integer i, using a decryption algorithm in a cryptography that calculates inner product of information being set in the ciphertext and information being set in the user secret key; and
generating decryption data Di and subtracting the sum z included in the decryption key dk from a sum of the decryption data Di for each integer, thereby calculating a sum of inner product of the information xi and the information yi for each integer, wherein
the decryption token dtk corresponds to the encryption token etki for each integer i of i=1 . . . , n.

### Claim 4

A non-transitory computer readable medium storing a privacy-preserving analysis program which causes a computer to execute:
a ciphertext acquisition process of acquiring, for each integer i of i=1 . . . , n concerning an integer n of 1 or more, a ciphertext cti encrypted from a sum mi of an encryption token etki, being a vector ui, and information xi;
a decryption key acquisition process of acquiring a decryption key dk generated with using a decryption token dtk and a user secret key ski, the decryption token dtk including the vector ui for each integer i, the user secret key ski being set with information yi for each integer i, the decryption key dk including a sum z of inner product of the vector ui and the information yi for each integer i; and
a decryption process of decrypting the ciphertext cti for each integer i, using a decryption algorithm in a cryptography that calculates inner product of information being set in the ciphertext and information being set in the user secret key, wherein
the decryption process generates decryption data Di and subtracts the sum z included in the decryption key dk from a sum of the decryption data Di for each integer, thereby calculating a sum of inner product of the information xi and the information yi for each integer, and
the decryption token dtk corresponds to the encryption token etki for each integer i of i=1 . . . , n.