Homomorphic Encryption Key Segmentation for Multi-User Confidentiality
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Solution Overview
Problem
Homomorphic encryption with deniability disclosed in existing literature requires sharing a key between users, compromising data confidentiality when conducting analysis processing using data from various users in a cloud service.
Innovation Solution
A confidential information processing system that generates encryption, decryption, and homomorphic operation keys, enabling encryption with different keys for each user, and includes devices for encryption, denial random number generation, homomorphic operation, and decryption to ensure data confidentiality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If homomorphic encryption with deniability is used to allow analysis processing on encrypted data, then data security against forced disclosure is improved, but user data confidentiality is compromised because the same key must be shared among all users
Solution Approach 1:
The patent segments the key management system by introducing user-specific key pairs (public key PK_i and secret key SK_i) for each user i, while maintaining a shared trapdoor key TD. This allows each user to encrypt data with their own public key, ensuring that only the legitimate owner can decrypt their data, thus preserving user data confidentiality while still enabling the deniability property through the shared trapdoor mechanism.
Solution Approach 2:
The patent introduces a cloud server as an intermediary that performs homomorphic operations on ciphertexts encrypted with different user keys. The cloud server does not need any secret keys, allowing it to process encrypted data from multiple users without compromising their confidentiality. The trapdoor key serves as an intermediary mechanism that enables the deniability property without requiring users to share their secret keys.
2Adaptability or versatility
If different encryption keys are used by each user to ensure data confidentiality, then user data confidentiality is improved, but the ability to perform homomorphic operations between users' data is lost
Solution Approach 1:
The patent creates a universal homomorphic encryption system where ciphertexts encrypted with different user-specific public keys can still undergo homomorphic operations. The system maintains multi-functionality by supporting both user-specific encryption for confidentiality and cross-user homomorphic operations for productivity, with the trapdoor key enabling the bridge between these two requirements.
Solution Approach 2:
The trapdoor key acts as an intermediary that enables homomorphic operations between ciphertexts encrypted with different user keys. The cloud server uses the trapdoor key to perform conversions and operations that would otherwise be impossible between differently-encoded ciphertexts, thus maintaining productivity while preserving user-specific key confidentiality.
3Productivity
If a shared key is used among all users for homomorphic encryption, then homomorphic operation capability is maintained, but user data confidentiality deteriorates because any user can potentially access other users' data
Solution Approach 1:
The patent segments the encryption keys into user-specific public keys (PK_i) and secret keys (SK_i), eliminating the need for users to share a common secret key. Each user's data is encrypted with their own public key, creating isolated confidentiality zones while still allowing homomorphic operations through the trapdoor mechanism. This segmentation removes the data access vulnerability inherent in shared-key systems.
Solution Approach 2:
The trapdoor key serves as a mediator that enables homomorphic operations between user-specific ciphertexts without requiring users to share their secret keys. The cloud server can perform operations on encrypted data from multiple users using the trapdoor key, maintaining productivity while the user-specific key structure prevents unauthorized data access.
Data Source
AI summary
A key generation device (200) generates an encryption key PK, a decryption key SK and a homomorphic operation key EVK. An encryption device (300) generates ciphertext data CDPK (m) by encrypting plaintext data m with the encryption key PK. A denial random number generation device (400) takes the encryption key PK and the ciphertext data CDPK (m) as input to generate denial random number data r* for denying the disclosure of plaintext data m. A homomorphic operation device (500) generates post-homomorphic operation ciphertext data CMPK (M) by performing a homomorphic operation on the calculation result of the plaintext data with the homomorphic operation key EVK. A decryption device (600) decrypts the post-homomorphic operation ciphertext data CMPK (M).