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.
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.
We propose a new definition for quasi-trusted relays. Our quasi-trusted relays are defined as follows: (1) being honest enough to correctly follow a given multi-party finitetime communication protocol; (2) however, being under the monitoring of eavesdroppers. From the new definition, we first develop a simple 3-party quasi-trusted model called Quantum Quasi-Trusted Bridge (QQTB) model. In this model, the origin Alice and the destination Bob are assumed out of range of Quantum Key Distribution (QKD). Carol is a quasi-trusted relay that can share QKD links with Alice and Bob. We show that QQTB protocol allows Alice and Bob, in cooperation with Carol, to securely establish secret keys. The originality of QQTB protocol is that we do not need invoke entangled photon pairs. Then, we extend QQTB model to Quantum Quasi-Trusted Relay (QQTR) model that is capable of securely distributing secret keys over arbitrarily long distances. Although QQTB model requires entangled photon sources, the originality is that we do not invoke entanglement swapping and entanglement purification as in [5, 6, 15]. Keywords: Controlled-NOT (C-NOT) gate, quantum circuit, quantum Key Distribution (QKD), QKD relaying model, quasi-trusted model, unconditional security 1
We investigate a quasi-trusted QKD relaying model. This is a three-party communication model. Two nodes Alice and Bob want to establish a secret key. However, the distance between them exceeds the limited range of QKD. Carol is a intermediate node that could share QKD links with Alice and Bob. Carol is assumed to be quasi-trusted: she correctly follows the given three-party protocol. However, she may be eavesdropped by the malicious person Eve. We propose two single-photon based protocols that allow Alice, Carol and Bob to achieve the goal. As a result, these protocols could be applied to securely extend up to two times the limited range of QKD without invoking entangled photons.
Quantum Key Distribution (QKD) is a promising technology that provides proven unconditional security based on fundamentals of quantum physics, especially for point-to-point communications. It could be applied in large-scale optical networks for long-distance key provisioning mainly by three relaying methods: quantum-repeater-based QKD, trusted-relay-based QKD, and measurement-device-independent QKD (MDI-QKD). However, quantum-repeater-based QKD is still under study because of the immature technologies such as the preliminary quantum memory. The trusted-relay-based QKD is vulnerable since insecurity of non-ideal single-photon sources and detectors cannot be ignored in practical applications. On the other hand, for MDI-QKD, there exists a limitation on its key rate under long-distance communications. According to these limitations, embedding protocols like MDI-QKD into the existing trusted-relay-based QKD secured optical networks (QKD-ON) with usage of untrusted relays is a promising key-provisioning scheme. In this paper, we study such partially-trusted relay scenarios and focus on its routing of keys in different kinds of typical network topologies. A partially-trusted-relay-based QKD method is described, which can allow a pair of optical nodes sharing secret keys under the coexistence of trusted relays and untrusted relays. The secret-key provisioning with collaborative routing (SKP-CR) algorithm is proposed to search for the optimal key-relay routing path. We perform the simulations with different proportion of trusted relays versus untrusted relays, initial secret keys in the quantum key pools (QKPs), and traffic load. The simulations verify that theSKP-CRalgorithm can significantly outperform the conventional trusted-relay-based scheme in terms of key-distribution success rate with an improvement of up to62%with a mesh topology.
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.
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.