Science and Education Publishing American Journal of Computing Research Repository 2 2 2014 05 26 An Efficient Key Distribution Protocol Based on BB84 33 37 EN Parag K. Lala Department of Electrical Engineering, Texas A& M University-Texarkana, Texarkana, USA AJCRR2014222 10.12691/ajcrr-2-2-2 2014 05 07 2014 05 26 2014 05 26 Private key cryptography suffers from a major weakness - it requires sharing of a secret key between two parties. An intruder can copy the secret key as it is being exchanged, thereby severely compromising the security of the system. Thus a private key cryptographic system depends entirely on secrecy of the key. Public key cryptography does not have a key distribution problem but its security relies on the fact that determining the factors of a number that is the product of two very large prime numbers is not computationally feasible. It has been shown that a quantum computer can solve the prime factors of very large numbers in polynomial time which would otherwise take millions of years. Public key cryptography will therefore become insecure if quantum computing becomes a reality. Quantum cryptography, originally presented in BB84 protocol, avoids all these issues by encrypting the shared key using a series of photons. In this paper a key distribution protocol based on the concepts of BB84 is proposed It provides an additional layer of security by sending the key data bits twice; during the second transmission the original key bits or their complements are randomly chosen for transmission. The sender informs the receiver about the orientation of the key bits during the second round of transmission only after the data has been sent out.