Proxy Re-Encryption Key Update Without Administrator Private Key
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Solution Overview
Problem
In file sharing systems, existing proxy re-encryption systems require the group administrator's private key to update re-encryption keys, making it impossible to update keys without the administrator's presence or if user private keys are not disclosed.
Innovation Solution
A server apparatus that generates and updates re-encryption keys without decrypting ciphertext data, using a random number to calculate new re-encryption key data and transmit it to user apparatuses for updating, allowing re-encryption key updates even when the group administrator is absent and user private keys are not disclosed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the group administrator's private key is used to update re-encryption keys, then re-encryption key updates can be performed, but the system requires the administrator's presence and may expose private keys
Solution Approach 1:
The patent extracts the re-encryption key update capability from the group administrator's private key. Instead of requiring the administrator to directly update keys using their private key, the system uses a re-encryption key that can be updated autonomously by the server apparatus without exposing or requiring the administrator's private key, thus separating the update function from the administrator's secret key
Solution Approach 2:
The patent introduces a re-encryption key as an intermediary between the administrator's private key and the users' ciphertext. This re-encryption key serves as a mediator that enables key updates without requiring the administrator's private key to be exposed or used directly in the update process, enhancing security while maintaining functionality
2Reliability
If individual encryption keys are used for each user, then file security is maintained, but the system becomes complex and troublesome when adding new users
Solution Approach 1:
The patent implements a universal re-encryption key that serves multiple users simultaneously. Instead of managing separate encryption keys for each user, the system uses a single re-encryption key that can re-encrypt ciphertext for any user in the group, simplifying key management while maintaining individual user security through their respective private keys
3Device complexity
If a common encryption key is shared among users, then key management is simplified, but security is compromised if the key leaks
Solution Approach 1:
The patent segments the encryption functionality into two separate key components: a common re-encryption key for managing file access and individual user private keys for decrypting files. This segmentation allows the re-encryption key to be updated independently without affecting user private keys, maintaining both simplicity and security
Solution Approach 2:
The patent employs asymmetric cryptography where the re-encryption key and user private keys have different functions and security requirements. The re-encryption key is designed for key management operations while user private keys are designed for file decryption, creating an asymmetric key management system that balances simplicity and security
Data Source
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AI summary
A server apparatus according to an embodiment generates a random number on receiving from a user apparatus a notification showing that a re-encryption key should be updated, and calculates re-encryption key data on the basis of the re-encryption key stored and the random number generated. The server apparatus transmits the re-encryption key to the user apparatus and receives, from the user apparatus, the user private key not updated yet and re-encryption key updating data calculated from the re-encryption key data on the basis of the user private key updated. The server apparatus calculates the re-encryption key updated, on the basis of the re-encryption key updating data and the random number, and replaces the re-encryption key stored in the storage device with the updated re-encryption key.