| The need for secure transmission in the fields of banking and defense has led to the interest in quantum cryptographic protocols which are theoretically more secure than any classical cryptographic protocol. However, the current implementations of the quantum cryptographic protocols have weaknesses. The main goal of this work is to find ways to strengthen quantum cryptographic protocols by using new implementation schemes. We present a method to improve the randomness of the sequence of polarization states used in BB84, the two-stage and the three-stage protocols. An analysis of quantum cryptography in the presence of noise is given. We also study a variant of the three-stage protocol where the intensity of the photons is tracked. We have developed a further improvement to this protocol where the state of the photons is also estimated. |
