Delegatable Pseudorandom Function for Encrypted Search
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Solution Overview
Problem
Existing searchable encryption schemes suffer from zero-day attacks and file-injection attacks, which reveal information to untrusted servers before any search queries are processed, and they struggle to maintain privacy and security while allowing efficient search functionality.
Innovation Solution
The implementation of delegatable pseudorandom functions (DPRF) generates a binary tree-based pseudorandom function that minimizes information leakage by delegating a portion of the function to an untrusted storage device, allowing it to access an encrypted search index without revealing frequency tables or document identifiers until a search query is processed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional searchable encryption is used to enable search functionality on encrypted documents, then search efficiency is improved, but information leakage occurs before search queries are processed
Solution Approach 1:
The system performs preliminary actions by generating the DPRF binary tree structure and storing encrypted search indices before any search queries are executed. The frequency table is encrypted and stored in advance, but remains unusable for information leakage until the DPRF is evaluated with a actual search query. This preliminary setup enables fast search execution without pre-exposing sensitive information.
Solution Approach 2:
The DPRF (Delegatable Pseudorandom Function) acts as an intermediary between the encrypted frequency table and the search queries. It transforms the encrypted frequency table into a form that can be searched without revealing the underlying document identifiers or frequency information to the untrusted server. The DPRF evaluation serves as a mediator that enables search functionality while maintaining security.
2Productivity
If frequency tables are stored to enable efficient search, then search performance is improved, but zero-day attacks can exploit them to reveal information
Solution Approach 1:
The system changes the parameter state of the frequency table by encrypting it using DPRF before storage. Instead of storing plain frequency counts that are vulnerable to zero-day attacks, the frequency table is transformed into an encrypted form that maintains its utility for search operations while becoming resistant to exploitation. The encryption parameter change ensures that even if attackers access the stored data, they cannot extract meaningful information without the DPRF evaluation.
3Ease of operation
If encrypted search indices are made accessible to untrusted servers, then search functionality is enabled, but privacy and security are compromised
Solution Approach 1:
The search system is segmented into multiple components with different security requirements: the DPRF binary tree structure is evaluated locally on the user device, while only the encrypted search indices are stored on the untrusted server. This segmentation allows the untrusted server to provide search functionality without having access to the sensitive DPRF evaluation process, thereby maintaining privacy and security while enabling ease of operation.
Data Source
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AI summary
A method (900) for providing encrypted search includes receiving, at a user device (10) associated with a user (12), a search query (122) for a keyword (32) that appears in one or more encrypted documents (152) stored on an untrusted storage device (150) and accessing a count table (210) to obtain a count (212) of documents that include the keyword. The method also includes generating a delegatable pseudorandom function (DPRF) (126) based on the keyword, a private cryptographic key (124), and the count of documents. The method also includes evaluating a first portion of the DPRF (126A) and delegating a second portion of the DPRF (126B) to the untrusted storage device which causes the untrusted storage device to evaluate the DPRF and access an encrypted search index (160). The untrusted storage device determines one or more encrypted documents associated with DPRF and returns an identifier (154) for each encrypted document.