Quantum Group Key Sharing Without a Trusted Intermediary

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Solution Overview

Problem

Existing quantum key distribution (QKD) systems face challenges in securely sharing group keys among multiple endpoints without relying on a fully trusted intermediary device, as the intermediary may gain access to the shared key, posing security risks, especially in group messaging scenarios.

Innovation Solution

A method for generating group keys using quantum and classical communication channels, where each endpoint device receives a randomly encoded encryption key and basis information, allowing endpoints to agree on a group key while ensuring the intermediary lacks sufficient information to derive or determine the key, thus maintaining security.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a single group key is shared among multiple endpoints through an intermediary device, then key distribution efficiency is improved, but security is worsened because the intermediary device gains access to the shared key

Engineering Contradiction:

Improvekey distribution efficiencyVSAvoidsecurity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent segments the single group key into multiple pairwise keys, where each endpoint shares a separate key with the intermediary device. This eliminates the security vulnerability of a single shared key while maintaining efficient key distribution through the intermediary.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each endpoint device receives a uniquely encoded encryption key tailored to its specific communication needs with the intermediary. The basis information is locally processed at each endpoint to generate its specific pairwise key, ensuring that no single endpoint or the intermediary possesses a universal group key.

Inventive Principle:

Principle #3Local quality

2Device complexity

If an intermediary device distributes cryptographic keys to multiple receivers, then key management is simplified, but trust requirements are worsened because the intermediary must be fully trusted

Engineering Contradiction:

Improvekey management complexityVSAvoidtrust model flexibility

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent divides the trust model by creating separate pairwise keys for each endpoint-intermediary communication channel. This segmentation allows the system to maintain simplified key management through the intermediary while reducing trust requirements, as the intermediary cannot derive other endpoints' keys from its own pairwise key.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The intermediary device acts as a mediator that facilitates key distribution without possessing a master group key. It uses its pairwise keys to securely communicate key material to endpoints and to verify their identities, enabling trusted key management without requiring the intermediary to be fully trusted with all group keys.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If quantum key distribution is used for group key sharing, then security is improved, but system complexity is worsened due to multiple quantum channels and authentication processes

Engineering Contradiction:

ImprovesecurityVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges multiple quantum key distribution processes into a unified group key sharing protocol. The intermediary device coordinates quantum channel establishment and authentication for multiple endpoints in a single integrated process, maintaining high security while reducing the operational complexity of managing separate QKD sessions for each endpoint pair.

Inventive Principle:

Principle #5Merging (Combining)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Ensures secure group key sharing among multiple endpoints without compromising security, as the intermediary device cannot derive the group key, enhancing trust and reducing vulnerabilities in group communication systems.

Implementation Method 1

The sender device and receiver device are connected by a quantum communication channel that allows quantum information such as quantum states to be transmitted

Methodology Applied

Scientific EffectQuantum state transmission:

Implementation Method 2

The BB84 QKD protocol uses a set of bases including at least two pairs of conjugate photon polarisation bases—for example a set of bases including a rectilinear photon basis (e.g. vertical) (0° and horizontal) (90° polarisations) and a diagonal photon basis (e.g. 45° and 135° polarisations)

Methodology Applied

Scientific EffectPhoton polarisation: Polarisation

Data Source

PatentUS20250358105A1Group key sharing

Publication Date: 2025.11.20 ARQIT LTD

AI summary

The present disclosure provides methods systems and apparatuses for use in the secure agreement of group keys in which the group key(s) are shared between multiple end-point devices, said multiple-endpoint devices being used to create the group key(s) that is/are distributed in such a manner that no other untrusted part of the system has access to sufficient information to be able to derive or determine the group key(s) and/or portions of said group key(s). This is achieved by pairs of endpoint devices agreeing pairwise keys between themselves, wherein an intermediary device that distributes encryption keys to the endpoint devices over quantum communication channels does not have sufficient information to be able to derive the identity of the pairwise keys.