Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

The Security of Simplified Trusted Relays

William Stacey

Published Aug 27, 2014• 0 citations
OpenAlex

Abstract

This thesis examines the security of performing quantum key distribution (QKD) with a simplified trusted relay (STR). The protocol carries out the quantum phase of a conventional trusted relay, however, reduces the required complexity of the nodes by carrying out an altered classical phase. Rather than announcing the parity of the final keys, the simplified trusted relay announces the parity of the keys before error correction and privacy amplification. As a result, the majority of the post-processing is left to the end users. \n \nSpecifically, we examine the security of an STR protocol which carries out the quantum phase of the BB84 protocol. Through two different methods, we derive qubit key rates. For the first method, we require that the basis choice is equally weighted. Furthermore, we limit the relay to a single node. This proof has the benefit that it easily generalizes to an alternate protocol where a node may generate error correcting information. In the second security proof, we derive a key rate for an arbitrary number of nodes with an arbitrary basis weighting. \n \nWe further extend our analysis to realistic scenarios in which the legitimate parties use weak coherent pulses to transmit signal states over a lossy channel. We provide a framework for generalizing decoy state methods to STR protocols.

Related papers

Security of quantum key distribution using a simplified trusted relay

William Stacey, Razieh Annabestani, Xiongfeng Ma +1 more

We propose a QKD protocol for trusted node relays. Our protocol shifts the communication and computational weight of classical postprocessing to the end users by reassigning the roles of error correction and privacy amplification, while leaving the exchange of quantum signals untouched. We perform a security analysis for this protocol based on the Bennett-Brassard 1984 protocol on the level of infinite key formulas, taking into account weak coherent implementations involving decoy analysis.

arXiv:1408.4426•Physical Review A•Jan 28, 2015•26 citations

Finite Key Security of Simplified Trusted Node Networks

Walter O. Krawec, Bing Wang, Ryan Brown

Simplified trusted nodes (STNs) are a form of trusted node for quantum key distribution (QKD) networks which do not require running a full QKD stack every instance (i.e., they do not need to run error correction and privacy amplification each session). Such systems hold the advantage that they may be implemented with weaker computational abilities, than regular TNs, while still keeping up with key generation rate demands. The downside is that noise tolerance is lower. However, to get a better understanding of their suitability in various scenarios, one requires practical, finite-key security bounds for STN networks. So far, only theoretical asymptotic bounds are known. In this work we derive a new proof of security for STN chains in the finite key setting. We also derive a novel cost function allowing us to evaluate when STNs would be beneficial from a computational cost perspective, compared with regular TN networks.

arXiv:2404.17420•IEEE International Conference on Quantum Computing and Engineering (QCE)•Sep 15, 2024•2 citations

A Novel Scheme With Honest Relay for Secret Key Distribution

Peng‐Yong Kong

Original quantum key distribution (QKD) protocols operate on a peer-to-peer basis between two adjacent nodes, which are directly connected through a quantum channel. Such protocols are severely distance limited. To extend the range, existing schemes use trusted nodes to relay in a hop-by-hop manner, secret key generated at one end node to the other end node. It is difficult to ensure node trustworthiness and more trusted nodes will lead to an enlarged attack surface. This paper proposes a scheme called honest relay key distribution (HRKD) that does not require relays be trusted. Specifically, HRKD removes the trusted node requirement by distilling a secret key directly between end nodes which are separated by multiple hops and imposing strict timing requirements on quantum state bases announcement and key usage. We have analyzed HRKD to show that its key secrecy protection can be as good as BB84 in some cases and is better than trusted node key relaying. We have derived its secret key rate as a function of distance between two end nodes. We have verified the key rate accuracy through extensive simulations. Evaluation results have also confirmed that with an increase in the distance between two end nodes, HRKD requires a maximum of two physical honest relays regardless of the distance while trusted node key relaying requires an increasing number of relays.

IEEE Access•Jan 1, 2026•0 citations

Secret Key Rate Over Multiple Relays in Quantum Key Distribution for Cyber–Physical Systems

Peng‐Yong Kong

In a cyber–physical system, quantum key distribution (QKD) protocols can provide a continuous supply of common secret key bits for secure communications between the control center and a remote device. QKD protocols operate on a peer-to-peer basis between two adjacent nodes and are distance-limited. Hence, trusted nodes are installed between two communicating end nodes for a better QKD range and key rate. These trusted nodes relay in a hop-by-hop manner, key bits generated in the first hop to the other end node. At each trusted node, the first hop key bits are encrypted by other locally generated key bits before being relayed. Since QKD process is stochastic, secret key bits are generated at different rates at different hops. Thus, buffer is needed at a trusted node to temporally hold some key bits while waiting for other key bits. There is no existing work that accounts for such a realistic relaying operation in deriving the key rate. This article contributes to developing a key rate model to determine accurately the end-to-end rates across multiple trusted nodes. We have evaluated accuracy of the proposed model through extensive simulations. The results show that there exist an optimal number of trusted nodes for a given distance between two end nodes. For example, the optimal number of relays increases from four for 100 km to six for 200 km.

IEEE Transactions on Industrial Informatics•Apr 23, 2024•13 citations

On the QKD relaying models

Quoc‐Cuong Le, Patrick Bellot

We investigate Quantum Key Distribution (QKD) relaying models. Firstly, we propose a novel quasi-trusted QKD relaying model. The quasi-trusted relays are defined as follows: (i) being honest enough to correctly follow a given multi-party finite-time communication protocol; (ii) however, being under the monitoring of eavesdroppers. We develop a simple 3-party quasi-trusted model, called Quantum Quasi-Trusted Bridge (QQTB) model, to show that we could securely extend up to two times the limited range of single-photon based QKD schemes. We also develop the Quantum Quasi-Trusted Relay (QQTR) model to show that we could securely distribute QKD keys over arbitrarily long distances. The QQTR model requires EPR pair sources, but does not use entanglement swapping and entanglement purification schemes. Secondly, we show that our quasi-trusted models could be improved to become untrusted models in which the security is not compromised even though attackers have full controls over some relaying nodes. We call our two improved models the Quantum Untrusted Bridge (QUB) and Quantum Untrusted Relay (QUR) ones. The QUB model works on single photons and allows securely extend up to two times the limited QKD range. The QUR model works on entangled photons but does not use entanglement swapping and entanglement purification operations. This model allows securely transmit shared keys over arbitrarily long distances without dramatically decreasing the key rate of the original QKD schemes.

arXiv:0803.3699•Mar 26, 2008•0 citations

On the security of the BB84 quantum key distribution protocol

Cannings, Richard

The BB84 quantum key distribution (QKD) protocol enables two authenticated parties to generate a secret key over an insecure quantum channel. Using a standardized security definition, we prove that BB84 is secure and include explicit bounds on its security. Furthermore, our use of quantum circuit diagrams simplify the Shor-Preskill proof. Namely, we can reduce the Modified Lo-Chau QKD to a practical version of BB84 using the observation from Shor and Preskill that one may ignore a correctable number of phase errors, and the fact that computational basis measurements commute with controls of CNOT operations. The first four chapters provide the required background material on quantum computing, information theory, cryptography, coding theory, and quantum error correcting codes. Chapter 5 presents protocols for entanglement purification. Chapter 6 reduces an entanglement purification protocol to the Modified Lo-Chau QKD, and proves that it is secure. Finally, a reduction from the Modified Lo-Chau QKD to BB84 establishes the security of the latter.

•Jan 1, 2004•0 citations
This thesis examines the security of performing quantum key distribution (QKD) with a simplified trusted relay (STR). The protocol carries out the quantum phase of a conventional trusted relay, however, reduces the required complexity of the nodes by carrying out an altered classical phase. Rather than announcing the parity of the final keys, the simplified trusted relay announces the parity of the keys before error correction and privacy amplification. As a result, the majority of the post-processing is left to the end users. \n \nSpecifically, we examine the security of an STR protocol which carries out the quantum phase of the BB84 protocol. Through two different methods, we derive qubit key rates. For the first method, we require that the basis choice is equally weighted. Furthermore, we limit the relay to a single node. This proof has the benefit that it easily generalizes to an alternate protocol where a node may generate error correcting information. In the second security proof, we derive a key rate for an arbitrary number of nodes with an arbitrary basis weighting. \n \nWe further extend our analysis to realistic scenarios in which the legitimate parties use weak coherent pulses to transmit signal states over a lossy channel. We provide a framework for generalizing decoy state methods to STR protocols.
Simplified trusted nodes (STNs) are a form of trusted node for quantum key distribution (QKD) networks which do not require running a full QKD stack every instance (i.e., they do not need to run error correction and privacy amplification each session). Such systems hold the advantage that they may be implemented with weaker computational abilities, than regular TNs, while still keeping up with key generation rate demands. The downside is that noise tolerance is lower. However, to get a better understanding of their suitability in various scenarios, one requires practical, finite-key security bounds for STN networks. So far, only theoretical asymptotic bounds are known. In this work we derive a new proof of security for STN chains in the finite key setting. We also derive a novel cost function allowing us to evaluate when STNs would be beneficial from a computational cost perspective, compared with regular TN networks.
Original quantum key distribution (QKD) protocols operate on a peer-to-peer basis between two adjacent nodes, which are directly connected through a quantum channel. Such protocols are severely distance limited. To extend the range, existing schemes use trusted nodes to relay in a hop-by-hop manner, secret key generated at one end node to the other end node. It is difficult to ensure node trustworthiness and more trusted nodes will lead to an enlarged attack surface. This paper proposes a scheme called honest relay key distribution (HRKD) that does not require relays be trusted. Specifically, HRKD removes the trusted node requirement by distilling a secret key directly between end nodes which are separated by multiple hops and imposing strict timing requirements on quantum state bases announcement and key usage. We have analyzed HRKD to show that its key secrecy protection can be as good as BB84 in some cases and is better than trusted node key relaying. We have derived its secret key rate as a function of distance between two end nodes. We have verified the key rate accuracy through extensive simulations. Evaluation results have also confirmed that with an increase in the distance between two end nodes, HRKD requires a maximum of two physical honest relays regardless of the distance while trusted node key relaying requires an increasing number of relays.
In a cyber–physical system, quantum key distribution (QKD) protocols can provide a continuous supply of common secret key bits for secure communications between the control center and a remote device. QKD protocols operate on a peer-to-peer basis between two adjacent nodes and are distance-limited. Hence, trusted nodes are installed between two communicating end nodes for a better QKD range and key rate. These trusted nodes relay in a hop-by-hop manner, key bits generated in the first hop to the other end node. At each trusted node, the first hop key bits are encrypted by other locally generated key bits before being relayed. Since QKD process is stochastic, secret key bits are generated at different rates at different hops. Thus, buffer is needed at a trusted node to temporally hold some key bits while waiting for other key bits. There is no existing work that accounts for such a realistic relaying operation in deriving the key rate. This article contributes to developing a key rate model to determine accurately the end-to-end rates across multiple trusted nodes. We have evaluated accuracy of the proposed model through extensive simulations. The results show that there exist an optimal number of trusted nodes for a given distance between two end nodes. For example, the optimal number of relays increases from four for 100 km to six for 200 km.
We investigate Quantum Key Distribution (QKD) relaying models. Firstly, we propose a novel quasi-trusted QKD relaying model. The quasi-trusted relays are defined as follows: (i) being honest enough to correctly follow a given multi-party finite-time communication protocol; (ii) however, being under the monitoring of eavesdroppers. We develop a simple 3-party quasi-trusted model, called Quantum Quasi-Trusted Bridge (QQTB) model, to show that we could securely extend up to two times the limited range of single-photon based QKD schemes. We also develop the Quantum Quasi-Trusted Relay (QQTR) model to show that we could securely distribute QKD keys over arbitrarily long distances. The QQTR model requires EPR pair sources, but does not use entanglement swapping and entanglement purification schemes. Secondly, we show that our quasi-trusted models could be improved to become untrusted models in which the security is not compromised even though attackers have full controls over some relaying nodes. We call our two improved models the Quantum Untrusted Bridge (QUB) and Quantum Untrusted Relay (QUR) ones. The QUB model works on single photons and allows securely extend up to two times the limited QKD range. The QUR model works on entangled photons but does not use entanglement swapping and entanglement purification operations. This model allows securely transmit shared keys over arbitrarily long distances without dramatically decreasing the key rate of the original QKD schemes.
The BB84 quantum key distribution (QKD) protocol enables two authenticated parties to generate a secret key over an insecure quantum channel. Using a standardized security definition, we prove that BB84 is secure and include explicit bounds on its security. Furthermore, our use of quantum circuit diagrams simplify the Shor-Preskill proof. Namely, we can reduce the Modified Lo-Chau QKD to a practical version of BB84 using the observation from Shor and Preskill that one may ignore a correctable number of phase errors, and the fact that computational basis measurements commute with controls of CNOT operations. The first four chapters provide the required background material on quantum computing, information theory, cryptography, coding theory, and quantum error correcting codes. Chapter 5 presents protocols for entanglement purification. Chapter 6 reduces an entanglement purification protocol to the Modified Lo-Chau QKD, and proves that it is secure. Finally, a reduction from the Modified Lo-Chau QKD to BB84 establishes the security of the latter.