Ciphertext-Policy Attribute-Based Encryption for Conjunctive Normal Form Expressions
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Solution Overview
Problem
Current attribute-based encryption (ABE) schemes primarily support disjunctive normal form (DNF) expressions and are limited to monotonic logical expressions, failing to efficiently manage ciphertext-policy ABE for conjunctive normal form (CNF) expressions with logical ANDs, ORs, and NOTs.
Innovation Solution
A method for attribute-based encryption that generates key pairs and encryption keys using bilinear maps, allowing for efficient ciphertext-policy ABE schemes that support CNF expressions by using a key generation engine, encryption engine, and decryption engine to create and manage decryption keys for attributes and clauses within a CNF expression, ensuring attribute-collusion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ABE schemes use DNF expressions with fixed number of clauses or attributes, then the scheme is simpler to implement, but the expressiveness and flexibility of access policies are limited
Solution Approach 1:
The patent segments the CNF expression into multiple clauses, where each clause can be independently processed. The encryption scheme divides the access policy into N clauses β1, β2, ..., βN, each representing a disjunction of attributes. This segmentation allows the system to handle complex CNF expressions by breaking them down into manageable units while maintaining overall expressiveness.
Solution Approach 2:
The patent transitions from the traditional DNF form to CNF form, representing a dimensional change in the logical structure of access policies. By using CNF (conjunction of disjunctions) instead of DNF (disjunction of conjunctions), the scheme enables new dimensions of policy expression including logical NOT operations, thereby increasing versatility without proportionally increasing complexity.
2Adaptability or versatility
If ABE schemes support arbitrary number of clauses and attributes in CNF expressions, then the flexibility of access policies increases, but the computational overhead and key size increase
Solution Approach 1:
The patent changes the structural parameters of the encryption scheme to accommodate CNF expressions. The encryption key includes parameters N (number of clauses) and the ability to handle arbitrary numbers of attributes per clause. This parameter change enables flexible access policies while the bilinear map-based construction keeps the computational overhead manageable through efficient pairing operations.
Solution Approach 2:
The patent creates a universal ABE scheme that can handle both DNF and CNF expressions, as well as monotonic and non-monotonic policies with logical NOT operations. The encryption and decryption mechanisms are designed to be multi-functional, working with any CNF expression structure without requiring separate specialized schemes, thereby achieving flexibility without proportional increases in complexity.
3Adaptability or versatility
If ABE schemes implement CNF expressions with logical NOT operations, then the expressiveness of access policies improves, but the attribute-collusion resistance becomes more difficult to maintain
Solution Approach 1:
The patent introduces bilinear maps as an intermediary mechanism to maintain attribute-collusion resistance in the presence of logical NOT operations. The pairing-based cryptography provides a mathematical intermediary that ensures security properties are preserved even when dealing with complex CNF expressions including negations. The decryption key structure uses bilinear pairings to verify attribute compliance without revealing individual attributes, thereby maintaining collusion resistance.
Solution Approach 2:
The patent modifies the decryption key parameters to include components that specifically address CNF expression evaluation. The key structure incorporates elements that enable the decryption algorithm to evaluate clauses with logical NOT operations while maintaining security. The parameter changes in the key generation and decryption processes ensure that attribute-collusion resistance is preserved despite the increased expressiveness.
Data Source
Figure 1~2
AI summary
The aim of the present invention is to propose a method for providing attribute-based encryption for conjunctive normal form (CNF) expressions, the said CNF expression comprising at least one clause over a set of attributes, the said method using a key generation engine, an encryption engine and a decryption engine.