Unlike classical bits, quantum bits cannot be duplicated and the quantum-entangled states cannot be identified. This property of quantum information was used to suggest an information-theoretic secure cryptography-quantum cryptography. This paper concentrates on quantum key distribution over a long-distance quantum network, it has many nodes and control centers which are connected by quantum channels. Quantum bits are storage on the quantum control centers and using entanglement states swapping to transfer over large distances between nodes and centers. An eavesdropper will inevitably increase the quantum bit error rate and the legitimate users will detect the eavesdropper and hence not use the key.
Unlike classical bits, quantum bits cannot be duplicated and the quantum-entangled states cannot be identified. This property of quantum information was used to suggest an information-theoretic secure cryptography-quantum cryptography. This paper concentrates on quantum key distribution over a long-distance quantum network, it has many nodes and control centers which are connected by quantum channels. Quantum bits are storage on the quantum control centers and using entanglement states swapping to transfer over large distances between nodes and centers. An eavesdropper will inevitably increase the quantum bit error rate and the legitimate users will detect the eavesdropper and hence not use the key.
Quantum cryptography was designed to provide a new approach to the problem of distributing keys for private-key cryptography. The principal idea is that security can be ensured by exploiting the laws of quantum physics and, in particular, by the fact that any attempt to measure a quantum state will change it uncontrollably. This change can be detected by the legitimate users of the communication channel and so reveal to them the presence of an eavesdropper. In this paper I explain (briefly) how quantum key distribution works and some of the progress that has been made towards making this a viable technology. With the principles of quantum communication and quantum key distribution firmly established, it is perhaps time to consider how efficient it can be made. It is interesting to ask, in particular, how many bits of information might reasonably be encoded securely on each photon. The use of photons entangled in their time of arrival might make it possible to achieve data rates in excess of 10 bits per photon.
Quantum cryptography is based on quantum mechanics to guarantee secure communication.It allows two parties to produce a shared random bit string known only to them.These random bits can be used as a key to encrypt and decrypt messages.The most important and unique property of quantum cryptography is the ability of the two communicating users to detect the presence of any third party trying to gain knowledge of the key.It is based on fundamental aspects of quantum mechanics.By using quantum entanglement or quantum super positions and transmitting information in quantum states, a communication system can be implemented which detects eavesdropping.Quantum cryptography is used to produce and distribute a key, not to transmit any message data.This key along with certain encryption algorithm, is used to encrypt (and decrypt) a message, which can then be transmitted over a standard communication channel.This paper concentrates on comparison between classical and quantum cryptography as well as survey on various quantum key distribution protocols used to generate and distribute the key among communicating parties.
Quantum communication represents a revolutionary advancement over classical information theory, which leverages unique quantum mechanics properties like entanglement to achieve unprecedented capabilities in secure and efficient information transmission. Unlike bits in classical communication, quantum communication utilizes qubits in superposition states, allowing for novel information storage and processing. Entanglement, a key quantum phenomenon, enables advanced protocols with enhanced security and processing power. This paper provides a comprehensive overview of quantum communication, emphasizing the role of entanglement in theoretical foundations, practical protocols, experimental progress, and security implications. It contrasts quantum communications potential applications with classical networks, identifying areas where entanglement offers significant advantages. The paper explores the fundamentals of quantum mechanics in communication, the physical realization of quantum information, and the formation of secure quantum networks through entanglement-based strategies like Quantum Key Distribution (QKD) and teleportation. It addresses the challenges of long-distance quantum communication, the role of quantum repeaters in scaling networks, and the conceptualization of interconnected quantum networks. Additionally, it discusses strides towards the Quantum Internet, Quantum Error-Correcting codes, and quantum cryptographys role in ensuring secure communication. By highlighting the role of entanglement, this paper aims to inspire further research and innovation in secure and efficient information exchange within quantum networks.
Quantum Cryptography is a novel approach to make the information and network world more secure. Unlike classical cryptography, quantum cryptography ensures the security of communication because it is based on the laws of Quantum Mechanics; a branch of physics that deals with the fundamental behavior of matter and their energies to the levels of subatomic particles. These particles and their intrinsic properties such as photon polarization and entanglement allow us to develop an unbreakable system of cryptographic information. Conventionally, the security has been primarily concerned with the secured distribution of secret key carried over an insecure channel. However, in Quantum Cryptographic systems the transmission of secret key is done using aforementioned laws of nature through a secured quantum channel highly susceptible to intrusion detection. Consequently, the Quantum Key Distribution (QKD), in conjunction with protocols such as BB84 protocol has emerged as an ultimate modern secured communication system. This article concentrates on briefly reviewing quantum cryptography, some recent developments and reports of its vulnerabilities.
We present a protocol for quantum cryptographic network consisting of a quantum network center and many users, in which any pair of parties with members chosen from the whole users on request can secure a quantum key distribution by help of the center. The protocol is based on the quantum authentication scheme given by Barnum et al. [Proc. 43rd IEEE Symp. FOCS'02, p. 449 (2002)]. We show that exploiting the quantum authentication scheme the center can safely make two parties share nearly perfect entangled states used in the quantum key distribution. This implies that the quantum cryptographic network protocol is secure against all kinds of eavesdropping.
[Shortened abstract:] This thesis investigates the importance of quantum memory in quantum cryptography, concentrating on quantum key distribution schemes. In the hands of an eavesdropper -- a quantum memory is a powerful tool, putting in question the security of quantum cryptography; Classical privacy amplification techniques, used to prove security against less powerful eavesdroppers, might not be effective when the eavesdropper can keep quantum states for a long time. In this work we suggest a possible direction for approaching this problem. We define strong attacks of this type, and show security against them, suggesting that quantum cryptography is secure. We start with a complete analysis regarding the information about a parity bit (since parity bits are used for privacy amplification). We use the results regarding the information on parity bits to prove security against very strong eavesdropping attacks, which uses quantum memories and all classical data (including error correction codes) to attack the final key directly. In the hands of the legitimate users, a quantum memory is also a useful tool. We suggest a new type of quantum key distribution scheme where quantum memories are used instead of quantum channels. This scheme is especially adequate for networks of many users. The use of quantum memory also allows reducing the error rate to improve large scale quantum cryptography, and to enable the legitimate users to work with reasonable error rate.