Re-encryption Key Generator Preventing Unauthorized Transfer
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Solution Overview
Problem
Existing file sharing systems face challenges in managing re-encryption keys, particularly when the server and users collude, leading to unauthorized decryption key re-delegation, which compromises security and key management efficiency.
Innovation Solution
A re-encryption key generator that generates re-encryption keys without decrypting ciphertext, using a first private key, a second public key, and a random number, ensuring that re-encryption occurs without permission from the transfer source, thereby preventing unauthorized decryption authority transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the server and users collude to generate re-encryption keys, then key management flexibility is improved, but security is worsened due to unauthorized decryption authority transfer
Solution Approach 1:
The patent introduces a re-encryption key generator as an intermediary component that mediates between the server and users. This generator creates re-encryption keys based on the user's public key and a master key, preventing direct collusion between server and users from compromising security. The intermediary ensures that even if the server and users collude, they cannot generate valid re-encryption keys without the master key.
Solution Approach 2:
The patent extracts the security-critical master key management from the server and places it in a separate, secure location. The server only holds the public key, while the master key is used exclusively by the re-encryption key generator. This separation ensures that even if the server is compromised or colludes with users, the core security mechanism remains protected.
2Reliability
If strict server management is implemented to prevent collusion, then security is improved, but device complexity and management overhead are worsened
Solution Approach 1:
The re-encryption key generator operates autonomously using the master key and user public keys to generate re-encryption keys. It does not require continuous human intervention or complex server management protocols. The system essentially manages itself by automatically generating keys when needed, reducing the burden of strict server management while maintaining security.
Solution Approach 2:
The re-encryption key generator serves as an intermediary that simplifies the security model. Instead of requiring the server to directly manage user decryption authorities, the generator handles key creation automatically, reducing management overhead while maintaining security through its automated, rule-based operation.
3Ease of operation
If re-encryption keys are stored on the server for easy access, then ease of operation is improved, but security is worsened due to potential leakage
Solution Approach 1:
The patent extracts the master key from the server's storage and uses it only for generating re-encryption keys. The server stores only the public key and generated re-encryption keys, not the master key itself. This extraction ensures that even if server storage is compromised, the core security mechanism (master key) remains protected while maintaining operational ease through automated key generation.
Data Source
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AI summary
A re-encryption key generator according to an embodiment generates a re-encryption key required to re-encrypt, without decrypting, ciphertext data obtained by encrypting plaintext data by means of a first public key of a first user device to obtain re-encrypted text data which can be decrypted by a second private key of a second user device. The first storage device stores a first private key corresponding to the first public key. The second storage device stores a second public key corresponding to the second private key. The re-encryption key generation means generates the re-encryption key based on the first private key, the second public key, and the first random number.