IOSR Journal of Computer Engineering (IOSR-JCE) e-ISSN: 2278-0661, p- ISSN: 2278-8727Volume 16, Issue 2, Ver. XI (Mar-Apr. 2014), PP 01-09 www.iosrjournals.org www.iosrjournals.org 1 | Page Quantum Key Distribution Protocols: A Review Hitesh Singh 1, D.L. Gupta 2 A.K Singh 3 1 M.tech, Department of Computer Science Engineering, KNIT, Sultanpur, UP, India 2 Member IEEE, Assistant Professor, Department of Computer Science Engineering, KNIT, Sultanpur, UP, India 3 Associate Professor, Department of Electronics Engineering, KNIT, Sultanpur, UP, India Abstract : Quantum key distribution (QKD) provides a way for distribution of secure key in at least two parties which they initially share. And there are many protocols for providing a secure key i.e. BB84 protocol, SARG04 protocol, E91 protocol and many more. In this paper all the concerned protocols that share a secret key is explained and comparative study of all protocols shown. Keywords : Quantum key distribution, BB84 protocol, BB92 protocol, SARG04 protocol, E91 protocol, COW protocol, DPS protocol, KMB09 Protocol, S09 protocol, S13 protocol. I. INTRODUCTION Quantum key distribution (QKD) [1] [2] provides a way for two parties to expand a secure key that they initially share. The best known QKD is the BB84 protocol published by Bennett and Brassard in 1984 [1]. The security of BB84 was not proved until many years after its introduction. Among the proofs [3] [4] [5] [6], the one by Shor and Preskill [6] is relevant to this paper. Their simple proof essentially converts an entanglement distillation protocol (EDP) based QKD proposed by Lo and Chau [5] to the BB84 Protocol. The EDP-based QKD has already been shown to be secure by [5] and the conversion successively leads to the security of BB84 protocol. Security proofs of QKD protocols were further extended to explicitly accommodate the imperfection in practical devices [7] [8]. One important imperfection is that the laser sources used in practice and coherent sources that occasionally emit more than one photon in each signal. Thus they are not single –photon sources that the other security proofs [3] [4] [6] of BB84 assumed. In particular, BB84 may become insecure when coherent sources with strong intensity are used. For instance Eve can launch a photon-number-splitting (PNS) attack puts severe limits on the distance and the key generation rate of unconditionally secure QKD. A novel solution to the problem of imperfect devices in BB84 protocol was proposed by Hwang [9]. Which uses extra test states called the decoy states to learn the properties of the channel and/or eavesdropping on the key- generating signal states. An unconditional security proof of decoy-state QKD [10] [11] is presented. Another method to combat PNS attack was by Scarani et.al. [12], who introduced a new protocol called SARG04, which is very similar to the BB84 protocol. The quantum state transmission phase and the measurement phase of SARG04 are the same as that of BB84, as both use the same four quantum state and the same experimental measurement. The only difference between the two protocols is the classical post-processing phase, the protocol becomes secure even when Alice emits two photon, a situation under which BB84 is insecure .This protocol was proved by [13] who also proved the security of SARG04 with a single-photon source. They also proposed a modified SARG04 protocol that uses same six states as the original six state protocols [14] [15]. The security of SAG04 with a single-photon source was also proved by Branciard et.al [16]. They considered SARG04 protocol implemented with single-sources and with realistic sources. For the single- photon source case, they provided upper and lower bounds of the bit error rate with one-way classical communications. For the realistic source case they considered only incoherent attack by Eve and showed that SARG04 can achieve higher secret key rate and greater source distance than BB84. Another protocol that is similar to SARG04 is the B92 Protocol [17] which uses two nonorthogonal quantum states. The security of B92 with a single-photon source was proved by Tamaki et al [18] [19]. On the other hand Koashi [20] proposed an implementation of B92 with strong phase-reference coherent light that was proved secure. The Focus of this paper is to survey the most prominent quantum key distribution protocols and their security. In this paper we briefly describe the necessary principles of quantum mechanics from which the protocols are divided in to two categories those based on the Heisenberg Uncertainty Principles and others are based on quantum entanglement Rest of the paper is organised as: In section II description of quantum cryptography and there mechanism is explained. Section III depicts all the Quantum key distribution protocols used Heisenberg‟s uncertainty principles. IV depicts all the Quantum key distribution protocols used quantum entanglement principles and in