Vulnerability of the Synchronization Process in the Quantum Key Distribution System

A typical structure of an auto-compensation system for quantum key distribution is given. The principle of operation of a fiber-optic system for the distribution of quantum keys with phase coding of photon states is described. The operation of the system in the synchronization mode and the formation of quantum keys was investigated. The process of detecting a time interval with an optical synchronization pulse is analyzed. The structural scheme of the experimental stand of the quantum-cryptographic network is given. Data are obtained that attest to the presence of a multiphoton signal during the transmission of sync pulses from the transceiver station to the coding and backward direction. The results of experimental studies are presented, which prove the existence of a vulnerability in the process of synchronization of the quantum key distribution system. It is shown that the use of a multiphoton optical pulse as a sync signal makes it possible for an attacker to unauthorized access to a quantum communication channel. The experimental results show that tapping a portion of the optical power from the quantum communication channel during the synchronization process allows an attacker to remain unnoticed while the quantum protocol is operating. Experimentally proved the possibility of introducing malfunctions into the operation of the quantum communication system at the stage of key formation, while remaining invisible for control means.

Vulnerability of the Synchronization Process in the Quantum Key Distribution System

A typical structure of an auto-compensation system for quantum key distribution is given. The principle of operation of a fiber-optic system for the distribution of quantum keys with phase coding of photon states is described. The operation of the system in the synchronization mode and the formation of quantum keys was investigated. The process of detecting a time interval with an optical synchronization pulse is analyzed. The structural scheme of the experimental stand of the quantum-cryptographic network is given. Data are obtained that attest to the presence of a multiphoton signal during the transmission of sync pulses from the transceiver station to the coding and backward direction. The results of experimental studies are presented, which prove the existence of a vulnerability in the process of synchronization of the quantum key distribution system. It is shown that the use of a multiphoton optical pulse as a sync signal makes it possible for an attacker to unauthorized access to a quantum communication channel. The experimental results show that tapping a portion of the optical power from the quantum communication channel during the synchronization process allows an attacker to remain unnoticed while the quantum protocol is operating. Experimentally proved the possibility of introducing malfunctions into the operation of the quantum communication system at the stage of key formation, while remaining invisible for control means.

Manipulation of Quantum Communication Channel via Two-Level Atom Interacting with Caving Fields

Base on the dispersive atom-cavity field interaction, the scheme for preparing the entangled coherent state is discussed. An experimentally feasible protocol for realizing entanglement concentration of the entangled coherent states by using a two-level atom interacting with caving fields is proposed. In this protocol, the entanglement between two coherent states, and , with the same amplitude but a phase difference is utilized as the quantum communication channel. The process of the entanglement concentration is implemented by using a two-level atom interacting with caving fields and two-modes orthogonal states measurement. With the present development of cavity quantum electrodynamics (QED) techniques, the scheme can be achieved.

Semi-loss-tolerant strong coin flipping protocol using EPR pairs

In this paper, we present a quantum strong coin flipping protocol. In this protocol, an EPR pair and a quantum memory storage are made use of, and losses in the quantum communication channel and quantum memory storage are all analyzed. We obtain the bias in the fair scenario as a function of $p$, where $p$ is the probability that the particle in Bob's quantum memory storage is lost, which means our bias varies as the degree of losses in the quantum memory storage changes. Therefore we call our protocol semi-loss-tolerant. We also show that the bias decreases with decreasing $p$. When $p$ approaches $0$, the bias approaches 0.3536, which is less than that of all the previous loss-tolerant protocols. Details of both parties' optimal cheating strategies are also given and analyzed. What's more, experimental feasibility is discussed and demonstrated. Compared with previous qubit-based loss-tolerant SCF protocols, we introduce the EPR pair to keep our protocol loss-tolerant while trying to push down the bias. In addition, a quantum memory storage is used and the losses in it has been taken into account. We obtain the bias in the fair scenario as a function of $p$, where $p$ is the probability that the particle in Bob's quantum memory storage is lost, which means our bias varies as the degree of losses in the quantum memory storage changes. We also show that the bias decreases with decreasing $p$. When $p$ approaches $0$, the bias approaches 0.3536, which is less than that of all the previous loss-tolerant protocols. Details of both parties' optimal cheating strategies are also given and analyzed. Besides, experimental feasibility is discussed and demonstrated.

AUTHENTICATED QUANTUM KEY DISTRIBUTION WITHOUT CLASSICAL COMMUNICATION

The aim of quantum key distribution protocols is to establish a secret key among two parties with high security confidence. Such algorithms generally require a quantum channel and an authenticated classical channel. This paper presents a totally new perception of communication in such protocols. The quantum communication alone satisfies all needs of array communication between the two parties. Even so, the quantum communication channel does not need to be protected or authenticated whatsoever. As such, our algorithm is a purely quantum key distribution algorithm. The only certain identification of the two parties is through public keys.