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IEEE Globecom Workshops (GC Wkshps)

Secure Key Throughput of Intermittent Trusted-Relay QKD Protocols

Stefano Guerrini, Marco Chiani, Andrea Conti

Published Dec 1, 2018• 26 citations
Publisher

Abstract

Quantum key distribution (QKD) protocols are designed to distribute secure keys between two remote parties. Current QKD systems require the presence of a trusted relay to distribute the keys over intercontinental distances, due to technological limitations. When the trusted relay is intermittently available to the end parties, as in the case of low Earth orbit (LEO) satellites, the QKD system undergoes a severe reduction in the amount of exchangeable secret bits. This paper proposes a new way to analyze the performance of QKD systems under these premises. It is shown that the secret key rate is not the most important figure of merit in the design of QKD protocols with intermittent relays, despite its importance for standard QKD links.

DOI
10.1109/glocomw.2018.8644402

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Quantum key distribution (QKD) protocols are designed to distribute secure keys between two remote parties. Current QKD systems require the presence of a trusted relay to distribute the keys over intercontinental distances, due to technological limitations. When the trusted relay is intermittently available to the end parties, as in the case of low Earth orbit (LEO) satellites, the QKD system undergoes a severe reduction in the amount of exchangeable secret bits. This paper proposes a new way to analyze the performance of QKD systems under these premises. It is shown that the secret key rate is not the most important figure of merit in the design of QKD protocols with intermittent relays, despite its importance for standard QKD links.
Quantum Key Distribution (QKD) is a technology that enables the exchange of private encryption keys between two legitimate parties, using protocols that involve quantum mechanics principles. The rate at which secret keys can be exchanged depends on the attenuation that is experienced. Therefore, it is more convenient to replace many terrestrial fiber segments (and repeaters) by just few optical satellite links that would enable flexible global coverage. Then, the satellite nodes can take the role of trusted-relays, forwarding the secret keys from source to destination. However, since the rate at which secret keys can be generated in each quantum link is limited, it is very important to select the intermediate satellite nodes to inter-connect ground stations efficiently. This paper studies the most convenient allocation of resources in a QKD network that combines complementary connectivity services of GEO and LEO satellites. The aim of the centralized routing algorithm is to select the most convenient trusted-relays to forward the secret keys between pairs of ground stations, verifying the constraints that satellite-to-ground and inter-satellite quantum channels have.
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.
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) is a revolutionary technology which leverages the laws of quantum mechanics to distribute cryptographic keying material between two parties with theoretically unconditional security. Terrestrial QKD systems are limited to distances of <;200 km in both optical fiber and line-of-sight free-space configurations due to severe losses during single photon propagation and the curvature of the Earth. Thus, the feasibility of fielding a low Earth orbit (LEO) QKD satellite to overcome this limitation is being explored. Moreover, in August 2016, the Chinese Academy of Sciences successfully launched the world's first QKD satellite. However, many of the practical engineering performance and security tradeoffs associated with space-based QKD are not well understood for global secure key distribution. This paper presents several system-level considerations for modeling and studying space-based QKD architectures and systems. More specifically, this paper explores the behaviors and requirements that researchers must examine to develop a model for studying the effectiveness of QKD between LEO satellites and ground stations.
This paper presents a method for performance evaluation of quantum key distribution (QKD) based on satellites using thetrusted node repeater strategy. Evaluation is focused on low Earth orbits satellites to illustrate the effective secure key distribution to remote terrestrial nodes. QKD generates the secure key material at link level (satellite and ground station point-to-point connection), whose performance evaluation is already covered in several studies. In this work we focus on a second evaluation level corresponding to the secure key effectively distributed to the remote terrestrial nodes. This corresponds to the performance of key-relay capacity per pair of distant ground nodes willing to connect securely. Here the satellite acts as a flying trusted node, performing a public-XOR-key scheme: the composition of xored key material is produced on the satellite and published to the remote pair of ground QKD nodes to obtain the other side QKD key. Key-relay capacity is tied to the rate generation at link level but also depends on other parameters, such as differences in key rate generation per QKD segment, the chosen strategy of generation and distribution of composed key material, or the satellite and terrestrial network topology (e.g. number and localization of nodes). These different aspects condition and may lower the secret key material effectively distributed remotely. Then, a model for generation and distribution of keys is described and implemented in a simulation tool, allowing the understanding of the system and its performance evaluation under different circumstances. Results confirm the key-relay performance per node is upbounded by twice the generation at link level, and how different aspects may lower it.