Encrypted Keyword Indexing via Extractor Graphs for Frequency Masking
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Solution Overview
Problem
Electronic document management systems are vulnerable to frequency-based attacks due to their susceptibility to infer information from encrypted keyword indexes, which can compromise document security, especially when using 1:1 mappings and order-preserving encryption schemes.
Innovation Solution
The system employs an extractor graph to map keywords to buckets containing encrypted document identifiers, ensuring each keyword maps to approximately the same number of identifiers, and uses an order-preserving encryption scheme by generating a sequence of encrypted instances for ordered attribute values, allowing queries that rely on order while masking frequency information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a 1:1 mapping between keywords and encrypted keywords is used, then searching efficiency is improved, but security against frequency-based attacks deteriorates
Solution Approach 1:
The patent segments the encrypted keyword index into multiple encrypted keyword lists, where each list contains encrypted keywords for a subset of documents. This segmentation prevents attackers from analyzing the complete frequency distribution across all documents, as they can only observe partial distributions in each list. The encryption scheme maps each keyword to multiple encrypted representations distributed across different lists, breaking the direct 1:1 frequency correlation while maintaining search functionality.
Solution Approach 2:
The patent changes the parameter of keyword encryption from a deterministic 1:1 mapping to a probabilistic many-to-many mapping. Instead of each keyword mapping to a single encrypted value, the same keyword can map to multiple different encrypted values across different encrypted keyword lists. This parameter change in the encryption scheme obscures frequency information while allowing efficient search operations through the use of encryption keys.
2Adaptability or versatility
If order-preserving encryption is used for indexed attributes, then range query capability is improved, but security against frequency analysis deteriorates
Solution Approach 1:
The patent segments ordered attributes into multiple encrypted representations distributed across different encrypted keyword lists. Each list contains a subset of the encrypted attribute values, preventing attackers from observing the complete ordered distribution. This segmentation maintains range query capability through encrypted comparisons while obscuring frequency information that would otherwise be visible in a single comprehensive encrypted index.
Solution Approach 2:
The patent adds a dimensional aspect to order-preserving encryption by distributing encrypted attribute values across multiple lists rather than maintaining a single sequential encrypted structure. This dimensional change allows range queries to be performed within each list while the overall frequency distribution across all lists remains obscured, providing both query capability and security.
Data Source
AI summary
A method and system for cryptographically indexing, searching for, and retrieving documents is provided. In some embodiments, an encryption system is provided that generates a document index that allows users to retrieve documents by performing encrypted queries for keywords associated with the documents. In some embodiments, each keyword maps to the same number of encrypted document identifiers. In some embodiments, an extractor graph is employed to map an indication of each keyword to a number of buckets storing encrypted document identifiers. In some embodiments, an order-preserving encryption system is provided. The encryption system uses an ordered index that maps encrypted instances of ordered attribute values to documents that are associated with those values. The ordered index enables queries containing query operators that rely on order, such as less than (“<”) or greater than (“>”), to be successfully performed on encrypted attribute values.