Theoretical uncertainties associated with the measurement of quantum bits have made Quantum Key Distribution (QKD) an attractive research topic for secure communication systems. Recent research in this area has focused on using weak coherent laser pulses as the carrier instead of the traditional approach of using single photon carriers. This opens the possibility to implement QKD infrastructure that is compatible with the existing optical fiber communication network. In this work, we report a theoretical study of a new approach that utilizes the Quantum Public Key Envelope (QPKE) based on the randomized Glauber states in a classical coherent optical communication system to obtain a secure communication. We verify the efficacy of the system using numerical simulation. We also study the possible approaches for an eavesdropper to test the degree of security enhancement of the proposed system at bitrate of 56 Gb/s. Two eavesdropping techniques are proposed for security analysis. A set of security parameters are used to simulate the variety of eavesdropping schemes.
Theoretical uncertainties associated with the measurement of quantum bits have made Quantum Key Distribution (QKD) an attractive research topic for secure communication systems. Recent research in this area has focused on using weak coherent laser pulses as the carrier instead of the traditional approach of using single photon carriers. This opens the possibility to implement QKD infrastructure that is compatible with the existing optical fiber communication network. In this work, we report a theoretical study of a new approach that utilizes the Quantum Public Key Envelope (QPKE) based on the randomized Glauber states in a classical coherent optical communication system to obtain a secure communication. We verify the efficacy of the system using numerical simulation. We also study the possible approaches for an eavesdropper to test the degree of security enhancement of the proposed system at bitrate of 56 Gb/s. Two eavesdropping techniques are proposed for security analysis. A set of security parameters are used to simulate the variety of eavesdropping schemes.
State-of-the-art Quantum Key Distribution (QKD) is based on the uncertainty principle of qubits on quantum measurements and is theoretically proven to be unconditionally secure. Over the past three decades, QKD has been explored with single photons as the information carrier. More recently, attention has shifted towards using weak coherent laser pulses as the information carrier. In this paper, we propose a novel quantum key distribution mechanism over a pure optical channel using randomized Glauber states. The proposed mechanism closely resembles a quantum mechanical implementation of the public key envelope idea. The core idea can be described in five steps as follows: 1. A user (Bob) generates a Glauber state as a quantum public key envelope (QPKE) by randomly modulating a secret phase φr, known only to Bob, and transmits it over an optical channel to the other user (Alice). 2. Alice modulates a key phase φk into the QPKE based on a random key and selected modulation scheme and returns it to Bob. 3. For the returning QPKE, Bob derandomizes it with his private key or the phase -φr and then 4. passes it to a coherent receiver to measure the key phase φk. 5. For better security, differential phase-shift keying (DPSK) technique with a reference list is applied to extract keys. For the proposed solution, we explore physical countermeasures to provide path authentication and to avoid man-in-the-middle attacks. Other attack vectors can also be effectively mitigated by leveraging the QPKE, the uncertainty principle and the DPSK modulation technique.
Twin-field quantum key distribution (TF-QKD) has recently attracted attention for its ability to overcome the fundamental limits of secret key rate for point-to-point connectivity without quantum repeaters in QKD. Coherent-based TF-QKD or CTF-QKD, which utilizes coherent states for both transmissions and detections, has allowed systems to be designed for existing optical fiber communication networks allowing for improved performance compared to conventional QKD. Here, we report a theoretical study of CTF-QKD security from an eavesdropper. Compared to conventional QKD and TF-QKD systems, CTF-QKD system is not limited to using only single photon sources/detectors allowing this system to have comparable performance and range as current optical fiber networks. Using commercially available simulation software, we verify the efficacy by studying three different preventative measures for different modulation formats to prevent an eavesdropper from obtaining any secret key information. Results show that parameters can be limited to prevent an eavesdropper from obtaining any information. The simulation also demonstrates that the photon number-phase uncertainty principle for coherent states starts to play major role of security at 128-QAM modulation. Additional security measures are also described to detect the presence of an eavesdropper and improve the system integrity.
Presently, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are very different communication modalities. Dedicated devices are commonly required to implement QKD. In this paper, we propose a scheme which allows classical communication and QKD to be implemented simultaneously using the same communication infrastructure. More specially, we propose a coherent communication scheme where both the bits for classical communication and the Gaussian distributed random numbers for QKD are encoded on the same weak coherent pulse and decoded by the same coherent receiver. Simulation results based on practical system parameters show that both deterministic classical communication with a bit error rate of ${10}^{\ensuremath{-}9}$ and secure key distribution could be achieved over tens of kilometers of single-mode fibers. It is conceivable that in the future coherent optical communication network, QKD will be operated in the background of classical communication at a minimal cost.
The secure distribution of the secret random bit sequences known as `key' material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is an emerging technology for secure key distribution with single-photon transmissions: Heisenburg's uncertainty principle ensures that an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non-orthogonal single-photon states to generate shared key material over multi-kilometer optical fiber paths and over line-of-sight links. In both cases, key material is built up using the transmission of a single- photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. In our optical fiber experiment we have performed quantum key distribution over 24-km of underground optical fiber using single-photon interference states, demonstrating that secure, real-time key generation over `open' multi-km node-to-node optical fiber communications links is possible.
The burgeoning Internet and Internet-of-Things (IoT) sectors necessitate robust cryptographic methods to ensure data security, integrity, and authentication over unsecured networks. Traditional public key cryptography, reliant on computationally hard problems, faces threats from quantum computing advancements. Quantum Key Distribution (QKD) presents a solution through the generation of unconditionally secure cryptographic keys using quantum mechanics. This paper explores the enhancement of QKD protocols to establish secure end-to-end communication in photonic networks. The proposed method involves a QKD system that generates two types of weak quantum signals: one with randomly varied intensity, polarization, or phase, and another with random frequency fluctuations. These signals are used to establish a shared key between a transmitter (Alice) and multiple receivers (Bobs) by measuring the quantum states. This dual signal approach enhances protection against Photon Number Splitting attacks and improves key length. Key Management Agents (KMAs) securely handle QKD-generated keys for data encryption before transmission, ensuring only intended recipients can decrypt the messages. The system leverages optical fiber or free-space optical links to transmit weak quantum signals and synchronization signals, facilitating key distribution even under existing network constraints. The proposed architecture allows for the secure exchange of cryptographic keys between Alice and multiple Bobs, ensuring private and authenticated communication over public channels. The approach mitigates potential eavesdropping by enabling the detection of any interception attempts through Quantum Bit Error Rate (QBER) estimation. This study underscores the promise of QKD as a foundational element of future communication systems, providing uncrackable quantum keys and paving the way for secure photonic networks. Incremental advancements in quantum devices, networking, and infrastructure are essential to fully realize QKD's potential for robust cryptographic security.
Optical key distribution (OKD) protects the physical layer of communication links by taking advantage of the inherent noise present in the photodetection process. It allows for efficient generation of a shared random key between two distant users that is secure against passive eavesdropping and can be subsequently used for cryptographic purposes. Moreover, it can be straightforwardly implemented over standard intensity modulation and direct detection links, making it an attractive alternative to quantum key distribution. Here we present a comprehensive security analysis against more powerful eavesdroppers possessing the ability to perform either coherent detection, or even quantum-optimal measurements on the intercepted transmission.