Abstract
Traditional quantum key distribution schemes arecarried out one-on-one. Both quantum and classical channels areneeded between any two users. This paper presents a quantumcryptographic network based on entanglement swapping and akey manage center. People can fulfill key distribution betweenany two users. Only channels between manage center and usersare needed while users need no communications between eachother. So it can save resource effectively and it is more reliableand flexible
Keywords-quantum cryptography; quantumcryptographic network; quantum key distribution;entanglement swapping; Bell measurement.t
I. INTRODUCTION
Quantum information science is the integration of quantummechanics with information science. One of the most importantfields in quantum information science is quantum cryptography.Unlike classical cryptography schemes based on thecomputation complexity, in quantum cryptography thesecurities of cryptograph schemes are guaranteed by thefundamental principle of quantum mechanics. So quantumcryptographic schemes can be unconditionally secure. Asknown how to distribute a key is the most important and mostdifficult problem in classical cryptography. In fact there aren'tunconditionally secure key distribution schemes through aninsecure channel existing at all. Quantum keydistribution(QKD) scheme is a good way to solve this problem.In QKD schemes we can achieve unconditional keydistribution by use of an insecure quantum channel and aninsecure but unjammed classical channel. The first quantumkey distribution scheme is proposed by C. H. Bennett and G.Brassard in 1984 ( so called BB84 scheme) [1]. Since thenmany quantum key distribution schemes have been establishedand their securities have been studied, such as the EPRschemes [2], B92 [3], the scheme of Lo-Chau [4], and so on [5-18]. On the other hand experimental work for OKD has alsosucceeded. In 1992 Bennett

Quantum cryptographic network using entanglement
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INTRODUCTION
In the early years of development of Internet protocols, stress was given more towards ubiquitous connectivity and guaranteed delivery of data. Once the Internet usage started increasing, the focus turned towards adding quality of service. Finally with the evolution of WWW back in 1991, the Internet has changed the human life phenomenally. People started participating in interactive environment, irrespective of geographical boundaries, within no time. As the Internet usage exploded, it became a medium even for financial transactions such as online banking. No doubt, the conveniences and the services provided by Internet are awesome but the inconveniences are ominous, really threatening.


OVERVIEW OF NETWORK SECURITY
Gaining access to Internet services is quite simple task. Depending upon user requirements or the application type he is running, one can either go for ISPs, dial-up connections using telephone line and modem or if he is simple PC owner, he can go for hourly based Internet access packages which are rightly now available in the market. In fact, statistically saying, it is expected that over 175 millions of computers are supposed to be on Internet by the end of 2003.See,”How people are really getting acquainted with the Internet usage! ”



CLASSICAL CRYPTOGRAPHY
In the last ten years, the Internet has enjoyed tremendous success connecting a large number of households and businesses with each other. This has created enormous economic possibilities. However, this economic potential can only be fully realized if the need for secure (i.e., safe against eavesdropping) transmission of data over the inherently insecure and open Internet can be satisfied. Cryptography addresses this need.


Symmetric Key Encryption:
Symmetric key encryption uses the same cryptographic algorithm and the same key to encipher and decipher messages. The key is chosen pseudo-randomly from a subset of all possible key values. As opposed to the one-time pad, symmetric key encryption uses the same key repeatedly to encipher and decipher messages. This makes it inherently less secure than the one-time pad since in its most straightforward implementation the same plaintext will result in the same ciphertext.


CONCLUSION
Quantum cryptography promises to revolutionize secure communication by providing security based on the fundamental laws of physics, instead of the current state of mathematical algorithms or computing technology.

Quantum cryptographic network using entanglement swapping


Abstract:

The question, “How to build a secure system?” baffled everyone who are currently enjoying the services provided by recent trends and technological developments achieved in the field of computers, especially the “Internet”. No doubt, gaining access to Internet and its services is quite simple, by just using gateways, dial-up connections, and ISP. But beneath this, the problems of security come as the information may be lost, stolen or corrupted. So, if the question “Why should one hack my PC?” is always backing at your mind, then there is a definite scope to challenge the “Bad guys” who want to break down the layers of security defenses. But there is no single foolproof solution for building such a secured system. Our security has to be a layered structure and that should start all the way from the selection of the Operating System even.
In this paper we mainly concentrated on Cryptography Science. We briefly discussed various Cryptographic Systems i.e., Symmetric and Asymmetric key Cryptography and their limitations. Owing to the drawbacks of basic Cryptographic Systems, our focus turned towards Quantum Cryptography whose strength, secrecy and privacy lies in the Laws of Physics than current state of unproven mathematical assumptions in Classical Cryptography. The core of the paper contains the detailed description of the fundamentals of Quantum Cryptography and how this concept overcomes the loopholes in Conventional Cryptographic System, especially “The Key Distribution Problem”. Finally we moved over to Commercial Implementations of Quantum Cryptography paving the path to Research Scope in this arena.