Homomorphic Encryption System for Cloud Data Privacy

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Solution Overview

Problem

Current encryption systems, particularly in cloud storage, face challenges with efficient computation on encrypted data without decryption and ensure data privacy, as fully-homomorphic encryption schemes are impractical due to large key and ciphertext sizes and security risks when the cloud possesses the decryption key.

Innovation Solution

A method providing user-specific encryption keys, computing a common decryption key, and encrypting plaintexts to create homomorphic ciphertexts that support poly-many additions and a single multiplication, ensuring encryption is efficient, secure, and verifiable, with compact key and ciphertext sizes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If fully-homomorphic encryption schemes are used to enable computation on encrypted data, then computation capability on encrypted data is improved, but key and ciphertext sizes become excessively large

Engineering Contradiction:

Improvecomputation capability on encrypted dataVSAvoidkey and ciphertext sizes

Core Design Contradiction:

Adaptability or versatilityVSQuantity of substance

Solution Approach 1:

The patent segments the homomorphic encryption scheme into two distinct parts: a key-homomorphic component for computing decryption keys from encrypted inputs, and a message-homomorphic component for computing encrypted outputs from encrypted inputs. This segmentation allows each component to be optimized independently, avoiding the need for fully-homomorphic encryption and its associated large key and ciphertext sizes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements partial homomorphic encryption rather than full homomorphic encryption. Specifically, it provides homomorphic evaluation for addition operations and key-homomorphic evaluation, which is sufficient for many practical applications without requiring the full functionality of FHE. This partial action approach achieves computational capability on encrypted data while keeping key and ciphertext sizes manageable.

Inventive Principle:

Principle #16Partial or excessive action

2Speed

If the cloud possesses the decryption key to enable efficient decryption, then decryption efficiency is improved, but data privacy security deteriorates due to potential misuse by the cloud provider

Engineering Contradiction:

Improvedecryption efficiencyVSAvoiddata privacy security

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent segments the decryption key into multiple user-specific decryption key components, each held by different users. The cloud never possesses the complete decryption key. Instead, the cloud computes intermediate values from encrypted inputs, and only when all users contribute their decryption key components can the final plaintext be decrypted. This segmentation eliminates the need for the cloud to have the full decryption key while maintaining decryption efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces user-specific decryption key components as intermediaries between the encrypted data and the final plaintext. These intermediate key components are distributed to users rather than centralized in the cloud. The cloud acts as a mediator that combines encrypted inputs with these intermediate key components to produce decrypted outputs, ensuring that no single party (including the cloud) possesses the complete decryption capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Quantity of substance

If somewhat homomorphic encryption schemes are used to reduce key sizes, then key and ciphertext sizes are reduced, but the number of multiplication operations is limited by a fixed upper bound

Engineering Contradiction:

Improvekey and ciphertext sizesVSAvoidnumber of multiplication operations

Core Design Contradiction:

Quantity of substanceVSAdaptability or versatility

Solution Approach 1:

The patent provides key-homomorphic evaluation capability without limiting the number of multiplication operations. By focusing on key-homomorphic properties rather than full message-homomorphic properties, the scheme achieves unbounded key computation capability while maintaining reasonable key and ciphertext sizes. This partial homomorphic approach in the key domain solves the limitation of fixed multiplication bounds in traditional somewhat homomorphic schemes.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS10938547B2Method and system for providing encrypted data

Publication Date: 2021.03.02 NEC CORP

AI summary

A method for providing encrypted data on a client, a cloud or the like includes, providing, for each user, a user-specific encryption key for encrypting user-specific plaintext. A common decryption key is computed with a pre-determined f netion using the user-specific encryption keys as input for the function, The function is a polysized function supporting poly-many additions and a single multiplication. Each user-specific plaintext is encrypted with the corresponding user-specific encryption key resulting in user-specific ciphertexts, The encrypting is performed such that encryption is homomorphic in the user-specific plaintext as well in the user-specific encryption keys. A. common ciphertext is computed with the function using the user-specific ciphertexts as input for the function. The common ciphertext and the common decryption key are provided for decryption.