Confidential Database Querying via Homomorphic Encryption and PIR

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Solution Overview

Problem

Existing methods for confidential database querying are either not scalable for large databases or require the exchange of private keys among users, which is insecure and inefficient.

Innovation Solution

A method using additive homomorphic encryption and Private Information Retrieval (PIR) protocol, where a first user with a stream cipher symmetric key authorizes a second user with an additive homomorphic cryptosystem to query a database by encrypting inverse masks and transmitting them to the server, allowing the second user to compute digital footprints and query the database without revealing sensitive information.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If Full Homomorphic Encryption (FHE) is used to authorize a wide variety of request types, then the versatility of querying is improved, but the scalability to large database sizes deteriorates due to unacceptable latency times

Engineering Contradiction:

Improverequest typesVSAvoidlatency time

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent segments the encryption approach by using additive homomorphic encryption instead of full homomorphic encryption. This allows the system to handle specific types of queries (presence queries) efficiently while maintaining scalability to large databases, thus resolving the contradiction between versatility and latency time.

Inventive Principle:

Principle #1Segmentation

2Loss of time

If additive homomorphic encryption is used to enable easy scaling to large databases, then the scalability is improved, but the versatility of request formats deteriorates to restricted formats only

Engineering Contradiction:

Improveresponse timeVSAvoidrequest format

Core Design Contradiction:

Loss of timeVSAdaptability or versatility

Solution Approach 1:

The patent introduces an intermediary transformation step where the database is reorganized into a specific format suitable for additive homomorphic encryption. This intermediary structure enables both fast scaling and versatile querying by mapping diverse query types onto the restricted format that additive homomorphic encryption handles efficiently.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If private keys are exchanged among users to enable multi-user access to databases, then the accessibility is improved, but the security deteriorates due to exposure of confidential information

Engineering Contradiction:

Improveuser accessVSAvoidconfidentiality

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent uses copying by creating multiple encrypted versions of the database, each encrypted with a different user's public key. This allows multiple users to access the database independently without exchanging private keys, as each user can decrypt their own copy using their private key, thus maintaining both accessibility and security.

Inventive Principle:

Principle #26Copying

4Reliability

If multiple private keys are created for multiple databases to enable user authorization, then the security control is improved, but the system complexity deteriorates due to multiplication of requests and key management

Engineering Contradiction:

Improveaccess controlVSAvoidkey management

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies universality by creating a unified system where a single database encrypted with multiple public keys can serve multiple users. This multi-functional approach eliminates the need for separate databases and key pairs for each user, reducing system complexity while maintaining secure access control through the homomorphic encryption framework.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12314270B2Method for multi-user confidential querying of the presence of a record in a database

Publication Date: 2025.05.27 COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES

AI summary

A method for confidentially querying the presence of a record in a database hosted by a server, the records being stored in the database in the form of digital footprints obtained by hashing a record by a public hash function. The footprints are masked by a stream cipher using a symmetric key of a first user. The first user may grant a second user authorisation to query the database by transmitting the inverse masks of various rows, encrypted by the public key of an additive homomorphic cryptosystem of the second user. The rows of the database are unmasked in the homomorphic domain and the second user transmits an encrypted request to query the base according to a PIR protocol. The second user can decrypt the response from the server using the private key of their homomorphic cryptosystem and determine whether the footprint sought is present in the response thus decrypted.