Multi-Recipient Key Encapsulation for Bandwidth-Efficient Key Sharing
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Solution Overview
Problem
Existing secure group messaging protocols face scalability and bandwidth efficiency issues, particularly under post-quantum assumptions, due to the need for large ciphertext and digital signature sizes, which are exacerbated by the use of active servers and asynchronous messaging.
Innovation Solution
A method and system for sharing symmetric cryptographic keys using an augmented multi-recipient key encapsulation mechanism (mKEM) that includes an encapsulation function to generate a cryptographic commitment token and a multi-recipient ciphertext, allowing for reduced data transmission and authentication, while ensuring post-quantum security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full ciphertexts are transmitted to each device for key sharing, then security is maintained, but bandwidth requirements increase significantly
Solution Approach 1:
The ciphertext is divided into multiple portions, each encrypted under a different encapsulation key corresponding to a specific device. Only the relevant portion is transmitted to each device instead of the full ciphertext, reducing bandwidth while maintaining security.
Solution Approach 2:
Each device receives only the ciphertext portion encrypted under its specific encapsulation key, tailored to its local requirements. This allows each device to process only the necessary data for its security needs without receiving unnecessary data for other devices.
2Reliability
If different authentication data is generated for each receiving device, then authentication security is improved, but computational load and bandwidth increase
Solution Approach 1:
A single authentication token is generated that serves as the authentication data for all devices. This universal token can be verified by any device using its own decapsulation key, eliminating the need to generate separate authentication data for each device while maintaining security.
Solution Approach 2:
The authentication token acts as an intermediary that mediates between the sender and multiple receivers. Instead of directly generating device-specific authentication data, the system uses this intermediate token that can be universally verified, reducing computational complexity.
3Reliability
If post-quantum secure authentication methods are used, then security under quantum attacks is improved, but ciphertext and signature sizes increase
Solution Approach 1:
The large post-quantum ciphertext is segmented into multiple smaller portions, each encrypted under a specific encapsulation key. This allows the total data transmitted to be reduced while maintaining post-quantum security guarantees for each portion.
Solution Approach 2:
The system changes the parameter of using multiple smaller encrypted portions instead of one large ciphertext. This parameter change allows the system to maintain security level while reducing the effective data size transmitted to each device.
Data Source
AI summary
A method includes, at a first communications device: processing encapsulation keys of a plurality of second communications devices using an encapsulation function to generate a symmetric key, an authenticable token, and a ciphertext; and transmitting, to each of the second communications devices, the token and a respective portion of the ciphertext depending on the respective encapsulation key of that second communications device. The token is a cryptographic commitment of the symmetric key, and the ciphertext is a multi-recipient encapsulation of the symmetric key under the encapsulation keys of the second communications devices. The method further includes, at each second communications device: processing the respective decapsulation key and the respective portion of the ciphertext using a decapsulation function to generate a respective candidate copy of the symmetric key; authenticating the token, whereby to determine that the respective candidate copy of the symmetric key corresponds to the symmetric key.