MULTI-PHOTON TOLERANT QUANTUM KEY DISTRIBUTION PROTOCOLS FOR SECURED GLOBAL COMMUNICATION

This dissertation investigates the potential of multi-photon tolerant protocols for satellite-aided global quantum key distribution (QKD). Recent investigations like braided single-stage protocol and the implementation of the three-stage protocol in fiber have indicated that multi-photon tolerant protocols have wide-ranging capabilities for increasing the distance and speed of quantum-secure communication. This dissertation proposes satellite-based network multicasting and its operation that can profitably use multi-photon tolerant protocols for quantum-secure global communication. With a growingly interconnected world and an increasing need for security in communication, communication satellites at Lower Earth Orbits (LEO), Medium Earth Orbit (MEO) and Geostationary Earth Orbit (GEO) have a potential role in serving as a means to distribute secure keys for encryption among distant endpoints. This dissertation systematically evaluates such a role. The dissertation proposes a layered framework using satellites and fiber optic links that can form a composite system for carrying the information payload and distributing quantum-secure keys for encrypting information in transit. Quantum communications links are currently point-to-point. Considering the concept of global QKD network, there is need for multicast quantum links. Multi casting can be achieved in quantum networks by (a) using multiple wavelengths, or (b) using use specific set of bases. In efforts to develop a composite quantum secure global communication system; this dissertation also introduces the concept of multi-photon tolerant quantum threshold cryptography. The motivation for development of threshold cryptography is that a secret can be encrypted with multiple users and requires multiple users to decrypt. The quantum threshold cryptography is proposed by using idea of multiple bases. This can be considered as step forward towards multiparty quantum communication. This dissertation also proposed layered architecture for key distribution. Concisely, this dissertation proposes the techniques like multicasting in quantum scenario, quantum threshold cryptography to achieve the goal of secured global communication

QUANTUM SECURE COMMUNICATION USING POLARIZATION HOPPING MULTI-STAGE PROTOCOLS

This dissertation presents a study of the security and performance of a quantum communication system using multi-stage multi-photon tolerant protocols. Multi-stage protocols are a generalization of the three-stage protocol proposed in 2006 by Subhash Kak. Multi-stage protocols use “Polarization Hopping,” which is the process of changing the polarization state at each stage of transmission. During the execution of a multi-stage protocol, the message transfer always starts by encoding a bit of information in a polarization state; for example, bit 0 is encoded using state |0⟩ and bit 1 is encoded using state|1⟩ whereas, on the channel, the state of polarization is given by α|├ 0⟩┤+β|├ 1⟩┤. In the following α and β are restricted to the real numbers i.e., the polarization stays on the equator of the Poincare sphere. A transformation applied by one communicating party at a given stage will result in new values of α and β. This dissertation analyzes the security of multi-stage, multi-photon tolerant protocols and proposes an upper bound on the average number of photons per pulse in the cases where Fock states and the cases where coherent states are used in the implementation of the three-stage protocol. The derived average number of photons is the maximum limit at which the three-stage protocol can operate at a quantum secure level while operating in a multi-photon domain. In addition, this dissertation studies the vulnerability of the multi-stage protocol to the Trojan horse attack, Photon Number splitting attack (PNS), Amplification attack, as well as the man-in-the middle attack. Moreover, this dissertation proposes a modified version of the multi-stage protocol. This modified version uses an initialization vector and implements a chaining mode between consecutive implementations of the protocol. The modified version is proposed in the case of the three-stage protocol and named a key/message expansion four variables three-stage protocol. The proposed nomenclature is based on the fact that an additional variable is added to secure the three-stage protocol. The introduction of this additional variable has the potential to secure the multi-stage protocol in the multi-photon regime. It results in the eavesdropper having a set of simultaneous equations where the number of variables exceeds the number of equations. The dissertation also addresses the performance of the multi-stage, multi-photon tolerant protocol. An average photon number of 1.5 photon/stage is used to calculate the maximum achievable distance and key transfer rates while using the single-stage protocol over fiber optic cables. We compute the increase in distance as well as data transfer rate while using the single-stage protocol. Channel losses as well as the detector losses are accounted for. Finally, an application of the multi-stage protocol in IEEE 802.11 is proposed. This application provides wireless networks with a quantum-level of security. It proposes the integration of multi-stage protocols into the four-way handshake of IEEE 802.11