Public key cryptosystems can well become void with the advent of incredibly high performance quantum computers. The underlying principles of these computers themselves, namely quantum mechanics, provide the solution to the key distribution problem. This paper explains how cryptography will be benefited from quantum mechanics, through a short introduction to classical cryptography, and the general principles of quantum cryptography and the BB84 protocol for key distribution. Then we review a modification to the BB84 protocol that is logically claimed to increase its efficiency. We then validate this claim by presenting our simulation results for BB84 and its improved protocols and show that the efficiency of the improved protocol could be doubled without undermining the security level of BB84 protocol.