Classical and Quantum Components of Quantum Key Distribution Protocol

Abstract

Quantum Key Distribution Protocol (QKD) is a type of quantum cryptography, i.e., it uses the concepts related to quantum mechanics to establish security in the communication channel. It is a key generation protocol and is used for generating a shared secret key between two parties, commonly known as Alice and Bob. Any QKD protocol uses two communication channels for the key generation. The first one is a quantum channel for the transmission of qubits. The other one is a classical channel for the transmission of random classical bits. The two major processes of any QKD protocol involve key generation algorithm and classical post processing phase. For the key generation process, algorithms like BB84 protocol or Eckart E91 protocol is used. These algorithms use polarisation, entanglement, and measurement concepts of quantum mechanics for generating the key. The key generated in the final step of the key generation algorithm of the QKD protocol is made up of classical bits. Because of the inherent noisy nature of quantum channels, the keys generated at both ends after classical reconciliation can still be wrong. This defeats the purpose of key sharing. To overcome this adversities classical post processing is used. In this phase the keys generated at the two ends are processed via an error correcting scheme to potentially reach a common key without any public sharing of the data. To this end we have studied the behavior of various error correction schemes, both block based and convolutional schemes and later used them as part of the post processing phase of the BB84 QKD protocol. Then we studied the efficiency of these coding schemes with and without the interruption of a malicious third party.