Through the ages, the security of information has always been a major concern. Mankind has used simple, but interesting and sometimes artistic procedures in order to hide its information from eavesdroppers. With the advances in the field of information theory and cryptography a new approach was taken. Cryptography transitioned from an art form to a solid math based science and modern cryptography was born. Since the emergence of modern cryptography, symmetric key algorithms have been the main providers of information security. The main difficulty in using such algorithms is the problem of key sharing. Public key algorithms provide us with methods to share a key with a party via an insecure channel. The security of these algorithms is based on their computational complexity. The development of quantum information science has gravely endangered the security of public key algorithms. For instance, Shor algorithm has the ability to decrypt the RSA public key cryptosystem on a quantum computer in polynomial time. Employing quantum cryptography was the next logical step. Quantum cryptography guarantees the security of information by physical laws of quantum mechanics. BB84 was the first quantum key distribution protocol. This protocol offers the parties a method to securely share a key using quantum states in an insecure environment and in the presence of malicious parties. Eavesdropping will introduce disturbance in the process, which can easily be detected by the legitimate parties. In this dissertation, we propose a modified version of the BB84 protocol. In this protocol sender uses a group of quantum states and applies a non-local transformation to them and then starts sending them to the receiver, one by one. The parties use an authenticated ltr" Key Words: Quantum Cryptography, Quantum Key Distribution
