Cryptographic Keys With Shared Digits for Efficient TFHE Computation

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Solution Overview

Problem

Existing TFHE-based encrypted computation techniques face inefficiencies in computational efficiency, storage requirements, and flexibility in cryptographic parameters.

Innovation Solution

The method involves forming encryption keys with common digits and predefined values, allowing for improved efficiency and reduced storage by sharing encryptions and eliminating unnecessary operations, particularly through optimized key switching and sample extraction processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If traditional TFHE-based encrypted computation techniques are used, then security is maintained, but computational efficiency is poor and storage requirements are high

Engineering Contradiction:
Improvecomputational efficiencyVSAvoidstorage requirements
Core Design Contradiction:
ProductivityVSQuantity of substance

Solution Approach 1:

The patent merges multiple encryption keys that share common digits into a single unified key structure. By identifying and combining redundant key components across different encryption operations, the system reduces the total number of stored keys while maintaining security. This merging approach directly addresses the contradiction by decreasing storage requirements without compromising computational efficiency.

Inventive Principle:
Principle #5Merging (Combining)

Solution Approach 2:

The patent creates universal key structures that can serve multiple encryption and decryption functions simultaneously. By designing keys with shared common digits that can be reused across different ciphertext operations, the system eliminates the need for separate dedicated keys for each operation. This multi-functionality reduces storage requirements while maintaining computational efficiency through key reuse.

Inventive Principle:
Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If encryption keys are designed with more flexibility in cryptographic parameters, then adaptability improves, but system complexity increases

Engineering Contradiction:
Improveflexibility in cryptographic parametersVSAvoidsystem complexity
Core Design Contradiction:
Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments encryption keys into distinct components: common digits that are shared across multiple keys and unique digits that provide individual key specificity. This segmentation allows flexible configuration of cryptographic parameters while managing complexity by organizing keys into reusable modular components. The segmented structure enables adaptability without proportionally increasing system complexity.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent enables dynamic adjustment of cryptographic parameters such as key length, digit distribution, and sharing patterns. By allowing these parameters to be changed based on security requirements and performance needs, the system achieves high adaptability. The parameter changes are managed through structured key generation processes that maintain consistency, preventing complexity from escalating uncontrollably.

Inventive Principle:
Principle #35Parameter changes

3Measurement precision

If noise reduction techniques are applied during encrypted computations, then computation accuracy improves, but additional computational overhead is introduced

Engineering Contradiction:
Improvecomputation accuracyVSAvoidcomputational overhead
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies noise reduction techniques at predetermined stages during the encrypted computation process, before noise accumulation becomes problematic. By performing bootstrapping and noise management operations in advance rather than reactively, the system maintains computation accuracy without requiring excessive computational overhead during critical calculation phases. The preliminary action approach optimizes the balance between accuracy and overhead.

Inventive Principle:
Principle #10Preliminary action

Data Source

PatentEP4573693B1Keys with special digits
Publication Date: 2025.10.15 ZAMA SAS
  • EP4573693B1 patent drawingFigure 1A~1B
  • EP4573693B1 patent drawingFigure 2~3
  • EP4573693B1 patent drawingFigure 4A~4B

AI summary

Some embodiments are directed to a cryptographic method (600) of performing an encrypted computation. A blind rotation can be applied to an input value encrypted under a blind rotation input key to obtain a rotation polynomial encrypted under a blind rotation output key of the key set. Further, a sample extraction can be applied to a polynomial encrypted under a sample extraction input key to obtain an encrypted coefficient of the polynomial, and/or a key switching can be applied to a value or polynomial encrypted under a key switching input key to obtain a key switching output encrypted under a key switching output key. The keys are defined such that at least some keys have digits in common, and/or at least some keys have more digits with predefined values.