Quantum networks are communication networks in which adjacent nodes enjoy perfectly secure channels thanks to quantum key distribution (QKD). Drawing end- to-end security from QKD-supported point-to-point security can be done by virtue of multipath transmission. This concept buys security at the cost of strongly connected networks and perfect routing. Particularly the latter is hard to ensure, since congestions or (passive) may cause QKD key- buffers to run empty, thus enforcing local re-routing of packets. Hence, the adversary may use not to extract information, but to redirect the information flow towards a relay-node that he controls. Such attacks can readily invalidate the stringent requirements of multipath transmission protocols and thus defeat any formal arguments for perfect secrecy. Moreover, this form of indirect eavesdropping seems to be unconsidered in the literature so far. We investigate whether or not unconditional security in a quantum network with non- reliable routing is possible. Using Markov-chains, we derive various sufficient criteria for retaining perfect secrecy under imperfect packet relay. In particular, we explicitly do not assume trusted relay or quantum repeaters available. Keywords-Quantum Cryptography, Markov-Chain, Secure
Quantum networks are communication networks in which adjacent nodes enjoy perfectly secure channels thanks to quantum key distribution (QKD). Drawing end- to-end security from QKD-supported point-to-point security can be done by virtue of multipath transmission. This concept buys security at the cost of strongly connected networks and perfect routing. Particularly the latter is hard to ensure, since congestions or (passive) may cause QKD key- buffers to run empty, thus enforcing local re-routing of packets. Hence, the adversary may use not to extract information, but to redirect the information flow towards a relay-node that he controls. Such attacks can readily invalidate the stringent requirements of multipath transmission protocols and thus defeat any formal arguments for perfect secrecy. Moreover, this form of indirect eavesdropping seems to be unconsidered in the literature so far. We investigate whether or not unconditional security in a quantum network with non- reliable routing is possible. Using Markov-chains, we derive various sufficient criteria for retaining perfect secrecy under imperfect packet relay. In particular, we explicitly do not assume trusted relay or quantum repeaters available. Keywords-Quantum Cryptography, Markov-Chain, Secure
Abstract—Quantum networks are communication networks in which adjacent nodes enjoy perfectly secure channels thanks to quantum key distribution (QKD). While QKD is renowned for perfect point-to-point security and its eavesdropping detec-tion capabilities, end-to-end security is nontrivial to achieve. More importantly, the eavesdropping detection can indeed be turned against the system itself. It is known that perfect end-to-end security can be created from point-to-point security by means of multipath transmission (in fact, there is no other way to do this, assuming no pre-shared secrets and avoiding public-key cryptography). However, multipath transmission requires node-disjoint paths, which in turn are to be assured by the underlying routing protocol. At this point, an active or passive adversary may intentionally eavesdrop on the QKD protocol to temporarily cut a channel and to cause key-buffers running empty and enforcing local rerouting of packets towards nodes under his control. Consequently, the multipath transmission channels might no longer be non-intersecting, thus defeating the overall security by exploiting QKD’s eavesdropping detec-tion facilities. Alternatively, an active adversary may as well insert bogus traff c to cause local congestion, thus even sparing the effort of eavesdropping on a QKD link. In this work, we use Markov chains to model a multipath transmission, and we discuss the extent to which secure multipath transmission is resilient against local congestions caused by an adversary. We argue that a protection against an active adversary who uses bogus traff c to f ddle with the routing, calls for additional security measures, perhaps even beyond the capabilities of QKD or multipath transmission. It turns out that robustness against passive and active adversaries can be retained as long as no bogus traff c is observed.
We study the significance of the common trusted relay assumption in quantum networks. While most practical implementations of quantum networks rely on trusted devices, the question of security without this assumption has been rarely addressed. Device independent security attempts to minimize the assumptions made on the quantum hardware, entanglement based methods try to avoid relays to the extent possible, and multipath transmission improves robustness and security by enforcing the attacker to conquer more than just a single intermediate node. Common to all these past studies is their focus on the physical layer and direct connections. We describe an attack from the networking and routing layer. Assuming at least one node that is not perfectly tamper-proof, meaning that an attacker has established a foothold to read traffic from the inside, we show how to exploit the eavesdropping detection mechanisms of the quantum key distribution (QKD) devices to cause traffic redirection over the vulnerable node, thus defeating security under the trusted node assumption. We experimentally demonstrate how the attack works on networks of different size and topology, and thereby further substantiate the significance of the trust assumptions for end-to-end security of QKD networks.
As a promising application of quantum information technology, Quantum Key Distribution (QKD) can provide information-theoretically secure key exchange for adjacent communication parties. To achieve long-distance secure communication and scale expansion against inherent channel loss, trusted relays, which are assumed to be absolutely secure, are introduced into QKD networks. However, in practice, trusted relays may be compromised by attacks from ubiquitous eavesdroppers even protected by powerful hardware. Thus, how to ensure the security of end-to-end key distribution in partially-trusted relay QKD networks with the coexistence of trusted relays and untrusted relays becomes a challenging but urgent problem to be solved. To address this critical problem, in this article, we design a segment-based multipath key distribution method. The basic idea of the method is to maximize the security of the end-to-end key distribution through the segment-based multipath key distribution. Under the premise of security level requirements, we further propose a flexible key reconstruction scheme to improve the efficiency of key distribution and obtain available secret keys as many as possible. The extensive simulations are conducted and the results reveal that our method significantly outperforms the traditional multipath QKD method in terms of both security and efficiency.
Quantum key distribution (QKD) protocols generate a same secret key at two nodes which are at different locations. Such key is used to encrypt and decrypt messages for unconditionally secure communications through a classical channel. Originally, QKD protocols are designed to work between two nodes which are directly connected through a point-to-point quantum channel. Currently, commercial QKD systems have limited range and key rate. To increase key rate and extend range, the key generated by QKD at one end node is relayed hop-by-hop to the other end node through multiple trusted nodes. In a QKD network with multiple pairs of communicating nodes, routing deals with the issue of deciding for each pair, which trusted nodes are used to form a path connecting the end nodes. This paper presents an overview of QKD and highlights the differences between QKD routing as compared to classical routing. The challenges of QKD routing are presented. Existing works dealing with the challenges are surveyed. This paper ends with a discussion on remaining research issues.
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.
Current quantum communication protocols rely heavily on classical authentication for message origin verification, leaving them vulnerable to evolving attacks that exploit classical trust assumptions. In this work, we propose a novel framework for secure quantum relay networks that completely avoids classical authentication. Instead, we leverage pre-distributed entanglement graphs and non-classical correlation-assisted decoding to enable exclusive message retrieval by designated nodes without broadcasting any key or handshake. The system routes messages across multiple relay nodes, yet ensures that no intermediate node can access the message unless it possesses the entangled state partner. We demonstrate that even in multi-path scenarios with asynchronous entanglement distribution, the protocol guarantees quantum-forward secrecy and end-to-end origin integrity without trusted intermediaries. Simulation results confirm both functionality and robustness under entanglement loss and imperfect detection. This architecture paves the way for scalable quantum communication systems where physical quantum states replace classical authentication mechanisms entirely.