Colin V. McLaughlin

Performance Evaluations of Quantum Key Distribution System Architectures

Quantum key distribution (QKD) exploits the laws of quantum physics to generate shared secret cryptographic keys and can detect eavesdroppers during the key generation process. However, previous QKD research has focused more on theory than practice.

A Modeling Framework for Studying Quantum Key Distribution System Implementation Nonidealities

Quantum key distribution (QKD) is an innovative technology that exploits the laws of quantum mechanics to generate and distribute unconditionally secure shared key for use in cryptographic applications. However, QKD is a relatively nascent technology where real-world system implementations differ significantly from their ideal theoretical representations. In this paper, we introduce a modeling framework built upon the OMNeT++ discrete event simulation framework to study the impact of implementation nonidealities on QKD system performance and security. Specifically, we demonstrate the capability to study the device imperfections and practical engineering limitations through the modeling and simulation of a polarization-based, prepare and measure BB84 QKD reference architecture. The reference architecture allows users to model and study complex interactions between physical phenomenon and system-level behaviors representative of real-world design and implementation tradeoffs. Our results demonstrate the flexibility of the framework to simulate and evaluate current, future, and notional QKD protocols and components.

Basis Mismatch in a Compressively Sampled Photonic Link

To accurately reproduce an incoming signal, compressive sampling requires that the signal have a sparse representation from within a finite basis or dictionary of vectors. If the incoming signal cannot be sparsely represented by vectors within the given basis or dictionary-a situation sometimes termed basis mismatch-then reconstruction error or failure is likely. In this letter, we present both simulated and experimental results showing the influence of basis mismatch on the ability of a photonic compressive sampling system to accurately reconstruct harmonic signals. Our reconstruction algorithm utilizes gradient projection for sparse reconstruction coupled with a discrete Fourier basis.

Polarization in Phase Modulated Optical Links: Jones- and Generalized Stokes-Space Analysis

Component birefringence can cause signal impairments in phase modulated optical links. At the transmitter, imperfect launch conditions couple phase modulation to unintended polarization modulation. At the receiver, polarization modulation creates spurious photocurrents due to birefringence in, and time delays between, interferometric paths. In this paper, we analyze such systems, and develop a formula for the photocurrent as a function of 11 system parameters. We utilize both the Jones description and our recent generalization of the Stokes description that includes optical phase, examine several special cases for phase modulated RF optical links, and evaluate some typical system performance issues.

Quantum key distribution: examination of the decoy state protocol

Quantum key distribution (QKD) is an innovative technology that exploits the laws of quantum mechanics to generate and distribute a shared cryptographic key for secure communications. The unique nature of QKD ensures that eavesdropping on quantum communications necessarily introduces detectable errors which is desirable for high-security environments. QKD systems have been demonstrated in both freespace and optical fiber configurations, gaining global interest from national laboratories, commercial entities, and the U.S. Department of Defense. However, QKD is a nascent technology where realized systems are constructed from non-ideal components, which can significantly impact system performance and security. In this article, we describe QKD technology as part of a secure communications solution and identify vulnerabilities associated with practical network architectures. In particular, we examine the performance of decoy state enabled QKD systems against a modeled photon number splitting attack and suggest an improvement to the decoy state protocol security condition that does not assume a priori knowledge of the QKD channel efficiency.

Using Modeling and Simulation to Study Photon Number Splitting Attacks

Quantum key distribution (QKD) is an innovative technology, which exploits the laws of quantum mechanics to generate and distribute unconditionally secure shared cryptographic keying material between two geographically separated parties. The unique nature of QKD that ensures eavesdropping on the key distribution channel necessarily introduces detectable errors and shows promise for high-security environments, such as banking, government, and military. However, QKD systems are vulnerable to advanced theoretical and experimental attacks. In this paper, the photon number splitting (PNS) attack is studied in a specialized QKD modeling and simulation framework. First, a detailed treatment of the PNS attack is provided with emphasis on practical considerations, such as performance limitations and realistic sources of error. Second, ideal and non-ideal variations of the PNS attack are studied to measure the eavesdroppers information gain on the QKD-generated secret key bits and examine the detectability of PNS attacks with respect to both quantum bit error rate and the decoy state protocol. Finally, this paper provides a repeatable methodology for efficiently studying advanced attacks, both realized and notional, against QKD systems and more generally quantum communication protocols.

Using the Discrete Event System Specification to model Quantum Key Distribution system components

In this paper, we present modeling a Quantum Key Distribution (QKD) system with its components using the Discrete Event System Specification (DEVS) formalism. The DEVS formalism assures the developed component models are composable and exhibit well-defined temporal behavior independent of the simulation environment. These attributes enable users to assemble a valid simulation using any collection of compatible components to represent complete QKD system architectures. To illustrate the approach, we introduce a prototypical “prepare and measure” QKD system, decompose one of its subsystems, and present the detailed modeling of the subsystem using the DEVS formalism. The developed models are provably composable and exhibit behavior suitable for the intended analytic purpose, thus improving the validity of the simulation. Finally, we examine issues identified during the verification of the conceptual DEVS model and discuss the impact of these findings on implementing a hybrid QKD simulation framework.

Implementing the decoy state protocol in a practically oriented Quantum Key Distribution system-level model

Quantum Key Distribution (QKD) is an emerging cybersecurity technology that exploits the laws of quantum mechanics to generate unconditionally secure symmetric cryptographic keying material. The unique nature of QKD shows promise for high-security environments such as those found in banking, government, and the military. However, QKD systems often have implementation non-idealities that can negatively impact their performance and security. This article describes the development of a system-level model designed to study implementation non-idealities in commercially available decoy state enabled QKD systems. Specifically, this paper provides a detailed discussion of the decoy state protocol, its implementation, and its usage to detect sophisticated attacks, such as the photon number splitting attack. In addition, this work suggests an efficient and repeatable systems engineering methodology for understanding and studying communications protocols, architectures, operational configurations, and implementation tradeoffs in complex cyber systems.

A module-based simulation framework to facilitate the modeling of Quantum Key Distribution system post-processing functionalities:

Quantum Key Distribution (QKD) systems are a novel technology that exploits the laws of quantum mechanics to generate and distribute unconditionally secure cryptographic keys between two geographically separated parties. They are suitable for use in applications where high levels of secrecy are required, such as banking, government, and military environments. In this paper, we describe the development of a module-based QKD simulation framework that facilitates the modeling of QKD post-processing functionalities. We highlight design choices made to improve upon an initial design, which included the segmentation of functionalities associated with various phases of QKD post-processing into discrete modules implementing abstract interfaces. In addition, communication between modules was improved by implementing observers to share data, and a specific strategy for dealing with post-processing synchronization and configuration activities was designed. Collectively, these improvements resulted in a significantly enhanced analysis capability to model and study the security and performance characteristics associated with specific QKD system designs.

Reconfigurable liquid metal fiber-optic mirror for continuous, widely-tunable true-time-delay

This paper reports the demonstration of a widely-translatable fiber-optic mirror based on the motion of liquid metal through the hollow core of a photonic bandgap fiber. By moving a liquid metal mirror within the hollow core of an optical fiber, large, continuous changes in optical path length are achieved in a comparatively small package. A fiber-optic device is demonstrated which provided a continuously-variable optical path length of over 3.6 meters, without the use of free-space optics or resonant optical techniques (i.e. slow light). This change in path length corresponds to a continuously-variable true-time delay of over 12 ns, or 120 periods at a modulation frequency of 10 GHz. Wavelength dependence was shown to be negligible across the C and L bands.