QKD Intermediary Node Synchronization Without Trusted Key Storage

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Solution Overview

Problem

Existing QKD networks face limitations in distance due to the need to trust intermediate nodes, which store final keys and are prone to security risks, and implementations like MDI and TF QKD are impractical due to stringent synchronization requirements and hardware complexity.

Innovation Solution

The use of Minimally Trusted Nodes (MTNs) that minimize the trust required by ensuring sensitive information is only temporarily stored in low-level electronics and erased quickly, using a Synchronizing Processing Unit (SPU) to process and synchronize quantum state preparation and measurement data without storing raw keys, and a Synchronizing Exclusive OR (SXOR) to establish secure keys.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If Trusted Nodes are used to extend QKD distance, then the distance between remote QKD modules is extended, but security risk increases due to key storage at intermediate nodes

Engineering Contradiction:
Improvedistance between QKD modulesVSAvoidsecurity of key distribution
Core Design Contradiction:
Length of stationary objectVSReliability

Solution Approach 1:

The patent extracts the key material from the intermediate node's storage system, processing it immediately upon receipt and forwarding only the final authenticated key to the remote node. This eliminates the security vulnerability of storing key material at intermediate Trusted Nodes while maintaining the distance extension capability.

Inventive Principle:
Principle #2Taking out (Extraction)

Solution Approach 2:

The patent implements rapid processing of key material through the intermediate node without storage delays. The key material is processed, authenticated, and forwarded in real-time, minimizing the time key material exists at intermediate nodes and effectively 'skipping' the storage step that creates security risks.

Inventive Principle:
Principle #21Skipping (Rushing through)

2Reliability

If MDI or TF QKD is implemented to avoid key storage at intermediate nodes, then security risk is reduced, but hardware complexity and synchronization requirements increase

Engineering Contradiction:
Improvesecurity of key distributionVSAvoidhardware complexity
Core Design Contradiction:
ReliabilityVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary processing mechanism at the intermediate node that handles key material authentication and forwarding without requiring the complex hardware modifications of MDI or TF QKD. This mediator approach achieves security without the stringent synchronization and hardware complexity of those protocols.

Inventive Principle:
Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the operational parameters of the intermediate node to process and authenticate key material in real-time without storage, transforming the node from a key storage device to a key processing pipeline. This parameter change reduces security risks while avoiding the hardware complexity of alternative protocols.

Inventive Principle:
Principle #35Parameter changes

3Adaptability or versatility

If key material is stored at Trusted Nodes for key management, then key distribution flexibility is improved, but security vulnerability increases due to potential attacks on stored keys

Engineering Contradiction:
Improvekey distribution flexibilityVSAvoidsecurity attacks on stored keys
Core Design Contradiction:
Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts key material from long-term storage and processes it immediately for distribution. By eliminating the storage step, the system removes the target for security attacks while maintaining the flexibility to distribute keys on-demand through real-time processing.

Inventive Principle:
Principle #2Taking out (Extraction)

Solution Approach 2:

The intermediate node performs self-service authentication and processing of key material without requiring storage capabilities. The node autonomously verifies and forwards keys in real-time, eliminating security vulnerabilities associated with stored key materials while maintaining distribution flexibility.

Inventive Principle:
Principle #25Self-service

Data Source

PatentEP4125238B1System and method using minimally trusted nodes over a QKD network
Publication Date: 2026.01.28 ID QUANTIQUE SA
  • EP4125238B1 patent drawingFigure 1~2B
  • EP4125238B1 patent drawingFigure 3(a)~5A
  • EP4125238B1 patent drawingFigure 5B~6A

AI summary

The invention relates to a QKD Communication intermediary component adapted to be placed between two remote QKD modules that are adapted to respectively send and/or receive quantum states to said QKD Communication intermediary component. Said QKD Communication intermediary component comprising: a post-processing unit, a synchronizing processing unit, at least two independent optical modules being adapted to prepare or measure the quantum states, which comprise raw key material to be exchanged with the two remote QKD modules, wherein the at least two independent optical modules send the information corresponding to the prepared and measured quantum states to the synchronizing processing unit, characterized in that the synchronizing processing unit is arranged to operate simultaneously with the first and second remote optical modules and the at least two independent optical modules so as to process said information received from the at least two independent optical modules and comprises at least one memory adapted to temporarily store data coming from one of the at least two optical modules until the data from the other optical module(s) is input in the synchronizing processing unit and is adapted to erase the said at least one memory in the timescale of two consecutive detection events after outputting necessary information to enable a key establishment at the two remote QKD modules.