Implementation of Quantum Cryptography Protocol

The main goals of cryptography are the encryption of messages to render them unintelligible to third parties and the authentication of messages to certify that they have not been modified. These goals can be accomplished if the sender ("Alice") and recipient ("Bob") both possess a secret random binary digit (bit) known as "key". It is essential that Alice and Bob acquire the key material with a high level of confidence that any third party ("Eve") does not have even partial information about the random bit sequence. If Alice and Bob communicate solely through classical messages (as opposed to Quantum cryptography), it is impossible for them to generate a certifiably secret key. QKD are the new generation of cryptographic systems which allow two remote parties (Alice and Bob) to generate a secret key with privacy guaranteed by quantum mechanics. They generate a random key securely over an optical fiber connection (also known as Quantum channel). This random key is then used for encryption and decryption of confidential messages, which then can be sent in encrypted form over any non-secure communication channel. In this thesis, we study two fiber-based QKD systems namely "oneway" and "two-way". Both systems have their unique advantage which distinguish them to one another. In one-way, the complexity of the electronic system may reduce. However more attention has to be made on the optical setup due to the requirement of active compensation. In the two-way, the requirement of optical setup may reduce but the attention moves to the electronic system which requires precise and short pulse especially for high speed in Alice system configuration. Our developed prototype is capable to support either one-way and two-way QKD system. We also solved some of the issues from the previous prototype Kumar [2008] which limited the system to be used in high speed. For instance: the synchronization system now uses a single synchronization signal per frame; the frame initialization time delay is reduced to 140ms per frame; pulse shaping distortion due to current consumption. We also introduced the security perspective for B92 protocol with uninformative states. This is done by utilizing the security analysis for BB84 such as entanglement distillation protocol (EDP) [...], smooth Ra'©nyi entropy [...] and composable security [...]. Numerous proposal on smooth Ra'©nyi entropy as general case [...] either for finite security analysis [...] or in asymptotic limit [...] assist us to deduce finite security perspective for B92 with uninformative states. [...] This thesis is organized as follow, initially starts with a general introduction to the cryptography and its relation with quantum cryptography. This is elaborated in Chapter One. In the Second Chapter we will go through the background of quantum mechanics and quantum information and introduce some parameters and theory mostly used in Quantum Key Distribution. These include quantum measurement, state behavior and the security analysis parameters. The second chapter will give the background concepts for the QKD in perspective of quantum information. The Third Chapter will explore more detailed information towards QKD. It starts with the basic architecture algorithm of the quantum cryptography system and details each components of the architecture. Later we focus on the security analysis specifically for the B92 protocol. Finally in the chapter, we will make some finite element analysis for the B92 protocol with uninformative states. In Chapter Four and onwards, we are discussing the experimental implementation and analysis. We begin with the heart of our system which is the field programmable gate array (FPGA) system. We explain the detailed architecture of our FPGA system and how the system works. The module that we develop in our FPGA system in order to work inside the QKD system is also explained in detail. We reserve the modification and advanced work of this system for the future by giving the original codes in the Appendix A. Chapter Five is one of the shortest chapters in this thesis. This chapter explains our electronic development and the opto-electronic device which are used in the QKD system. The main device that we develop for the QKD system is our Mezzanine board for FPGA. This mezzanine board supports some functions that are not available from the FPGA in order to make the system functional. Other developments include opto-electronic board and proportional-integral-derivative (PID) controller with the current driver. Chapter Six is the main experimental part. In this Chapter we start to give the introduction to our optical setup. We detail out our configuration of the setup and finally show our results taken from experimental work. Finally in Chapter Seven we conclude our work and purposed future work which actually need to done for the system.