Homomorphic Threshold Encryption for Secure Message Authentication
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Solution Overview
Problem
Secure communication of messages between sender and receiver computers over insecure networks is challenging, especially when neither party has cryptographic key material, and existing solutions require pre-shared secrets or secure channels, which are inconvenient and insecure.
Innovation Solution
A system using multiple servers that store and manage receiver passwords via homomorphic threshold encryption, allowing secure message communication without pre-shared secrets, where each server contributes to decryption shares only if the password is correctly authenticated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a password is used to encrypt the message, then the message can be encrypted without requiring pre-shared secrets, but the password has low-entropy and is vulnerable to brute-force attacks
Solution Approach 1:
The secret key is segmented into multiple key shares distributed across different servers. Each server holds only a portion of the key material, and the complete key can be reconstructed only when a threshold number of servers cooperate. This segmentation prevents any single server from having full access to the password, thereby mitigating brute-force attack risks while maintaining ease of message encryption.
2Reliability
If the password is exchanged in advance between sender and receiver, then secure communication can be established, but this requires a secure channel beforehand which may not always be feasible
Solution Approach 1:
The system introduces server intermediaries that hold key shares and facilitate secure message transmission. Instead of requiring direct pre-shared secrets between sender and receiver, the servers act as intermediaries that enable authentication and decryption. The sender transmits messages to the server, and the receiver retrieves them using their password, eliminating the need for direct secure channels between communicating parties.
Solution Approach 2:
The key shares are preliminarily distributed to servers during system setup, and the receiver's password is preliminarily stored encrypted on the server. This preliminary action enables subsequent message transmission without requiring real-time secure channel establishment between sender and receiver, improving convenience while maintaining security.
3Ease of operation
If a corrupt server learns the password, then all message data sent using the password is compromised, but storing the password on the server is necessary for authentication
Solution Approach 1:
The password is segmented into multiple key shares distributed across different servers. Each server holds only a portion of the key material, and the complete key can be reconstructed only when a threshold number of servers cooperate. This segmentation ensures that a single corrupt server cannot learn the complete password, thereby protecting message data even if some servers are compromised.
Solution Approach 2:
Different servers have different roles and hold different key shares with specific properties. The system design ensures that no single server has complete access to the password, and each server's local knowledge is insufficient for breaking security. This local quality differentiation protects against server corruption while maintaining authentication capability.
4Reliability
If the sender chooses the password and transmits a message only once with this password, then security is maintained, but this is a considerable inconvenience and unrealistic for applications where senders may wish to send more than one message
Solution Approach 1:
The receiver's password is preliminarily stored in encrypted form on the server during setup. This preliminary action enables the sender to transmit multiple messages without repeatedly negotiating passwords or establishing secure channels. The server uses the pre-stored encrypted password to facilitate authentication and message retrieval, improving convenience for multiple message transmission while maintaining security through the threshold encryption scheme.
Data Source
AI summary
A method is provided for communicating messages between sender and receiver computers, connectable via a network to a system of servers, based on authentication of receiver passwords, associated with respective receiver IDs, by the system. A method is also provided for receiving a message from a sender based on authentication of a receiver password, associated with a receiver ID, by a system of servers, in a network, wherein each server stores for the ID a ciphertext produced by encrypting the receiver password under a public key via a homomorphic threshold encryption scheme having a threshold, and a key-share of a secret key corresponding to that public key, and stores an encrypted message from the sender encrypted under the public key. Systems are provided including servers, for communicating messages between sender and receiver computers based on authentication of receiver passwords, associated with respective receiver IDs, by the system.