Secret Search Salt Selection for Frequency Attack Resistance

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing searchable encryption techniques face challenges in balancing the risk of frequency analysis attacks with the speed-up effect, particularly in probabilistic encryption, where longer disclosure bits reduce comparison space but increase attack risk, while shorter bits provide less speed-up.

Innovation Solution

A secret search system employs a probabilistic encryption technique with a registration client device that calculates disclosure bits using a salt, considering the existing distribution bias, eliminating the need for prior knowledge of keyword frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If longer disclosure bits are used in probabilistic encryption, then the speed-up effect is improved, but the risk of frequency analysis attack increases

Engineering Contradiction:

Improvesearch processing speedVSAvoidfrequency analysis attack risk

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the parameter of disclosure bit length dynamically based on the security level requirement and frequency distribution characteristics. By adjusting the disclosure bit length parameter, the system can optimize between search speed and security risk according to different scenarios

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent performs preliminary frequency analysis on the keyword distribution before setting the disclosure bit length. This preliminary action allows the system to pre-determine the optimal disclosure bit length that balances speed and security before actual search operations begin

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If shorter disclosure bits are used in probabilistic encryption, then the risk of frequency analysis attack is reduced, but the speed-up effect decreases

Engineering Contradiction:

Improvefrequency analysis attack riskVSAvoidsearch processing speed

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The system dynamically adjusts the disclosure bit length parameter based on the analyzed frequency distribution, finding the optimal balance point that provides sufficient speed-up while maintaining acceptable security levels

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces dynamic adjustment of disclosure bit length based on the actual frequency distribution characteristics of the data being searched. This allows the system to adaptively optimize the balance between speed and security rather than using a fixed length

Inventive Principle:

Principle #15Dynamics

3Object-affected harmful factors

If transformed keywords proportional to keyword occurrence frequency are prepared, then frequency analysis attack risk is reduced, but occurrence frequencies of keywords must be known in advance

Engineering Contradiction:

Improvefrequency analysis attack riskVSAvoidrequirement for prior knowledge

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system automatically analyzes the frequency distribution of keywords in the database and uses this information to determine the optimal disclosure bit length, eliminating the need for manual configuration or external knowledge of keyword frequencies

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS12475246B2Secret search system, secret search method, and non-transitory computer readable medium

Publication Date: 2025.11.18 MITSUBISHI ELECTRIC CORP

AI summary

In a secret search system based on probabilistic encryption, a registration client device (20) registers data (201) to be searched for in secrecy and a keyword (200) corresponding to the data (201) in a secret search server device, and discloses disclosure bits, which are data to be externally disclosed and are part of data calculated deterministically using each keyword (200) registered in the secret search server device and a salt corresponding to each keyword (200) registered in the secret search server device. The registration client device (20) includes a disclosure bit calculation unit (240) to determine, as a determined salt, a salt corresponding to a registration keyword, which is the keyword (200) to be registered in the secret search server device. The disclosure bit calculation unit (240) determines the determined salt, taking into consideration a size of a bias in a distribution composed of disclosure bits already disclosed by the registration client device (20) and disclosure bits calculated using the registration keyword and the determined salt.