FHE Key Provisioning with Server Bootstrapping Offload

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Solution Overview

Problem

Implementing fully homomorphic encryption algorithms is challenging due to the high computational requirements and large size of bootstrapping keys, which can exceed the storage and processing capabilities of electronic devices, and communicating the secret key to a server for key generation is insecure.

Innovation Solution

A method involving a computing device generating a secret key and a bootstrapping key, providing them securely to an electronic device and a server, enabling the electronic device to encrypt data using the secret key and perform fully homomorphic encryption, while the server processes the encrypted data using the bootstrapping key, and the electronic device decrypts the result using the secret key.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If bootstrapping key is stored on electronic device for fully homomorphic encryption, then noise reduction in computations is improved, but storage capacity and device complexity are exceeded

Engineering Contradiction:

Improvenoise reductionVSAvoidstorage capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The system segments the bootstrapping key management by separating it from the electronic device and placing it on the server. The electronic device only stores the secret key, while the bootstrapping key is generated and stored on the server, allowing the electronic device to perform fully homomorphic encryption without being burdened by the large bootstrapping key storage requirements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The server acts as an intermediary that holds and manages the bootstrapping key. The electronic device sends encrypted data to the server, which performs bootstrapping operations using the bootstrapping key, then returns the processed encrypted data to the electronic device for decryption.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If bootstrapping key is stored on electronic device, then computation quality is improved, but computational expense and processing capabilities are exceeded

Engineering Contradiction:

Improvecomputation qualityVSAvoidprocessing capabilities

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The computational workload is segmented between the electronic device and the server. The electronic device performs encryption and decryption operations, while the server performs the computationally intensive bootstrapping operations using the bootstrapping key, distributing the processing burden appropriately.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The server serves as a computational intermediary that handles the expensive bootstrapping operations. This allows the electronic device to benefit from high-quality noise reduction without needing to possess the computational resources to perform bootstrapping itself.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If secret key is provided to electronic device for encryption, then encryption capability is enabled, but key exposure risk increases

Engineering Contradiction:

Improveencryption capabilityVSAvoidkey exposure risk

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The key management is segmented into two parts: the secret key stored securely in the electronic device's secure element for encryption operations, and the bootstrapping key stored on the server. This segmentation limits the exposure risk of each key type to different environments.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The server acts as a secure intermediary that never receives the secret key but handles the bootstrapping key. The secret key remains confined to the electronic device's secure element, minimizing its exposure risk while still enabling full encryption functionality.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If bootstrapping key is generated on computing device, then key security is improved, but key management complexity increases

Engineering Contradiction:

Improvekey securityVSAvoidkey management complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The key generation process is segmented: the secret key is generated and stored in the electronic device's secure element, while the bootstrapping key is generated and stored on the server. This segmentation simplifies key management by placing each key type in the most appropriate environment.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system uses an intermediary key management architecture where the server generates and manages the bootstrapping key, while the electronic device generates and manages the secret key. This distributed key management approach balances security requirements with operational simplicity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12627462B2Secure provision of keys for fully homomorphic encryption

Publication Date: 2026.05.12 STMICROELECTRONICS SRL

AI summary

The present disclosure relates to a method including: the generation, by a computing device, of a first key and a bootstrapping key; the provision of the first key and an identifier of the bootstrapping key to an electronic device and the provision of the bootstrapping key and the identifier to a server; the fully homomorphic encryption, by the electronic device, of a first data value, stored in the electronic device, by using the first key; and the provision, by the electronic device, of the encrypted first data value and of the identifier, to the server.