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Covert communication is achieved when a transmitter Alice can successfully transmit a message to a receiver Bob without being detected by an attentive and capable adversary Willie. Early results demonstrated the difficulty of the covert communications problem: with AWGN discrete-time channels between all parties, only O(sqrt(n)) bits can be sent in n channel uses. But it was soon recognized that uncertainty about the environment at Willie, for example, uncertainty in his own noise statistics, could allow for a positive rate: O(n) bits can be sent covertly in n channel uses. However, most covert communication results, including this promising positive rate result, have been obtained for a discrete-time communications channel. Here, we demonstrate that the assumption of a discrete-time channel is problematic when trying to exploit Willie's noise uncertainty. In particular, we demonstrate that if Alice transmits ω(sqrt(T)) bits in a length T interval to Bob on a continuous-time channel, then there exists a detector at Willie that can detect her transmission, as the probability of false alarm and missed detection PMD+PFA→0 as T→∞. In other words, the communication is not covert, unlike the case of a discrete-time channel.
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This content will become publicly available on October 14, 2025
Security of partially corrupted quantum repeater networks
Abstract Quantum Key Distribution allows two parties to establish a secret key that is secure against computationally unbounded adversaries. To extend the distance between parties, quantum networks are vital. Typically, security in such scenarios assumes the absolute worst case: namely, an adversary has complete control over all repeaters and fiber links in a network and is able to replace them with perfect devices, thus allowing her to hide her attack within the expected natural noise. In a large-scale network, however, such a powerful attack may be infeasible. In this paper, we analyze the case where the adversary can only corrupt a subset of the repeater network connecting Alice and Bob, while some portion of the network near Alice and Bob may be considered safe from attack (though still noisy). We derive a rigorous finite key proof of security assuming this attack model, and show that improved performance and noise tolerances are possible. Our proof methods may be useful to other researchers investigating partially corrupted quantum networks, and our main result may be beneficial to future network operators.
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- Award ID(s):
- 2143644
- PAR ID:
- 10572623
- Publisher / Repository:
- IOP Science
- Date Published:
- Journal Name:
- Quantum Science and Technology
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2058-9565
- Page Range / eLocation ID:
- 015005
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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