Communication Terminal Session Key Update Encryption
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Solution Overview
Problem
Existing cloud-based message transmission systems face challenges in updating previously saved data on a server device to be decrypted using an updated session key without decrypting it on the server side, especially when users join or leave, making it difficult to apply end-to-end encryption protocols effectively.
Innovation Solution
The implementation of communication terminals equipped with public key encryption schemes, such as RSA or elliptic curve ElGamal, that allow for key updates without revealing the new session key to the server device, by using functions that mask and unmask cipher texts in a way that ensures only the communication terminals can decrypt messages using the updated key.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If end-to-end encryption is implemented with session key sharing among communication terminals, then message security against server device is improved, but the ability to update previously saved message data with new session keys deteriorates
Solution Approach 1:
The encryption system is segmented into multiple encryption layers: initial encryption with first session keys, and update encryption with second session keys. The update encryption unit applies a second encryption scheme that operates independently on the already encrypted data, allowing key rotation without decrypting the original data on the server.
Solution Approach 2:
The system performs preliminary encryption of message data with first session keys before transmission and storage. When updating keys, the system preliminarily prepares second session keys and applies them to the existing encrypted data through update encryption, ensuring continuous security without exposing plaintext.
2Object-affected harmful factors
If messages are saved in encrypted form on server device, then security against external attacks is improved, but vulnerability to internal fraud by server administrators remains
Solution Approach 1:
The system uses asymmetric session key distribution where communication terminals hold the ability to encrypt and decrypt messages, while the server device only performs update encryption using second session keys. This asymmetric arrangement ensures that even server administrators cannot decrypt messages, as the decryption capability remains exclusively with the communication terminals.
3Reliability
If session keys are updated when users join or leave, then message security is maintained, but complexity of key management increases
Solution Approach 1:
Communication terminals autonomously generate and manage their own session keys (both first and second types) without requiring complex centralized key management. Each terminal independently performs update encryption using its own second session keys, eliminating the need for complex key distribution and management infrastructure on the server side.
Data Source
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AI summary
The present invention provides a communication terminal that can update data that was previously saved in a server device to data that can be decrypted on the communication terminal side using an updated session key, without the data being decrypted on the server device side. A communication terminal that shares a session key with another communication terminal and sends cipher text to the other communication terminal via a server device, includes: a common key cipher text obtaining unit that encrypts a message based on a common key to obtain common key cipher text; a function computation result obtaining unit that computes the common key and the session key based on a predetermined first function to obtain a function computation result; a public key cipher text obtaining unit that encrypts the function computation result based on a public key to obtain public key cipher text; and a cipher text sending unit that sends the common key cipher text and the public key cipher text to the server device.