Multikey Homomorphic Encryption for Private Search
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Solution Overview
Problem
Conventional searchable encryption schemes reveal search patterns to servers, compromising user privacy, as they allow servers to infer information about the content or type of files based on search queries, even though the keywords themselves remain encrypted.
Innovation Solution
A method using multikey homomorphic encryption that generates merged secret keys for each file, allowing secure and private searches by encrypting search queries and data, ensuring that only the files containing the searched information are decrypted and returned to the client, while keeping the search pattern hidden from the server.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional searchable encryption schemes are used, then data privacy is protected through encryption, but search patterns are leaked to the server
Solution Approach 1:
The patent segments the search process into multiple encrypted operations: the search query is transformed into an encrypted circuit representation, and the database is organized with encrypted tags. This segmentation allows the server to process encrypted components separately without revealing the overall search pattern, thereby protecting search privacy while maintaining data privacy protection.
Solution Approach 2:
The patent introduces an intermediary cryptographic mechanism (encrypted circuits and tags) that mediates between the client's search intent and the server's data storage. This intermediary layer allows the server to perform search operations on encrypted data without learning the search pattern, effectively hiding information from the server while enabling functional search capability.
2Ease of operation
If searchable encryption is implemented, then users can search encrypted data without decryption, but the server can still infer information about file content and type from search queries
Solution Approach 1:
The patent transforms the search parameter from plain text keywords into encrypted circuit representations. By changing the parameter form from readable search terms to encrypted computational circuits, the system enables search functionality while preventing the server from inferring file content or type, thus maintaining file content privacy while preserving search capability.
Solution Approach 2:
The patent moves the search operation from the semantic dimension (where servers can understand keywords and infer meaning) to the cryptographic dimension (where operations occur on encrypted representations). This dimensional change allows search functionality while eliminating the server's ability to infer information about file content and type.
3Loss of information
If multikey homomorphic encryption is used, then search patterns remain hidden from the server, but computational complexity increases
Solution Approach 1:
The patent performs preliminary actions during the setup phase by pre-generating key triples and pre-encrypting database tags with appropriate encryption keys. This preliminary preparation reduces the computational complexity during actual search operations, as the heavy cryptographic setup is done in advance rather than during each search, thereby managing device complexity while maintaining search pattern privacy.
Solution Approach 2:
The patent uses key triples that generate multiple related keys (public key, secret key, evaluation key) from a single seed. This copying mechanism allows the system to derive multiple cryptographic parameters without independently generating each one, reducing the overall complexity of the multikey homomorphic encryption scheme while preserving search pattern privacy.
Data Source
AI summary
A method is performed by a server for searching for information contained in encrypted data without revealing the information to the server. The server receives from a client: an encrypted matrix containing the information to be searched for in files and linking the information to the files; for each of the files, a merged secret key; and an encrypted vector having a length corresponding to a number of the information. The encrypted data is evaluated by performing a multiplication of the matrix with entries in the vector using a multikey homomorphic encryption scheme. For each of the files, a value of the multiplication of the matrix is decrypted using the corresponding merged secret key so as to determine which of the files contains the information. The files containing the information are sent to the client.