Cryptography - the art of secure communications, has been developed at leastover 2500 years. Still at present, no perfectly secure as well as practicallysuitable classical or quantum cryptosystems exist. Statistically encoding theindividual bit, here we present a practical key distribution technique which isabsolutely secure both for classical and quantum keys. To achieve perfectsecurity, noise has to be strategically introduced. Noise, a detrimentalfactor, which never becomes helpful anywhere in classical and quantuminformation theory, can be used as a gift of nature in our cryptosystem sincefundamentally the coding of this cipher system does not follow the standardtechnique of classical and quantum information processing.
Cryptography - the art of secure communications, has been developed at leastover 2500 years. Still at present, no perfectly secure as well as practicallysuitable classical or quantum cryptosystems exist. Statistically encoding theindividual bit, here we present a practical key distribution technique which isabsolutely secure both for classical and quantum keys. To achieve perfectsecurity, noise has to be strategically introduced. Noise, a detrimentalfactor, which never becomes helpful anywhere in classical and quantuminformation theory, can be used as a gift of nature in our cryptosystem sincefundamentally the coding of this cipher system does not follow the standardtechnique of classical and quantum information processing.
The practical implementation of quantum information technologies requires, for the most part, highly advanced and currently experimental procedures. One exception is quantum cryptography, or quantum key distribution, which has been successfully demonstrated in many laboratories and has reached an advanced level of development. It will probably become the first commercial application of quantum information. In quantum key distribution, Alice and Bob exploit a quantum channel to create a secret shared key comprising a random string of binary digits. This key can then be used to protect a subsequent communication between them. The principal idea is that the secrecy of the key distribution is ensured by the laws of quantum physics. Proving security for practical communication systems is a challenging problem and requires techniques that are beyond the scope of this book. At a fundamental level, however, the ideas are simple and may readily be understood with the knowledge we have already acquired. Quantum cryptography is the latest idea in the long history of secure (and not so secure) communications and, if it is to develop, it will have to compete with existing technologies. For this reason we begin with a brief survey of the history and current state of the art in secure communications before turning to the possibilities offered by quantum communications. The history of cryptography is a long and fascinating one. As a consequence of the success or, more spectacularly, the failure of ciphers, wars have been fought, battles decided, kingdoms won, and heads lost. In the information age, ciphers and cryptosystems have become part of everyday life; we use them to protect our computers, to shop over the Internet, and to access our money via an ATM (automated teller machine). One of the oldest and simplest of all ciphers is the transposition or Caesarean cipher (attributed to Julius Caesar), in which the letters are shifted by a known (and secret) number of places in the alphabet. If the shift is 1, for example, then A is enciphered as B, B→C, · · ·, Y→Z, Z→A. A shift of five places leads us to make the replacements A→F, B→G, · · ·, Y→D, Z→E.
Since it was noted that quantum computers could break public key cryptosystems based on number theory, extensive studies have been undertaken on Quantum Key Distribution (QKD). QKD or Quantum Cryptography solves the key distribution problem by allowing the exchange of a cryptographic key between two remote parties with absolute security, guaranteed by the laws of physics. Actually, the progress of research in this field allows the implementation of Quantum Cryptography outside of laboratories. Efforts are made to exploit this technology in the existing communication networks and to improve the performance and reliability of the implemented technologies. The cryptosystems based on QKD are very promising and also the technology is improving more and more to fulfill requirements. In this paper, we provide a state-of-the-art of practical Quantum Cryptography by exposing the popular works and projects on QKD implementation.
Following its etymology, the term cryptography denotes the techniques used to ensure the confidentiality of information in its storage or transmission. Besides confidentiality, cryptography also encompasses other important functions such as authentication, signature, non-repudiation or secret sharing, to name just a few. The purpose of this section is to give a short introduction to classical cryptography, but only for areas that are relevant to quantum cryptography. For our purposes, we will only deal with confidentiality and authentication. The former is the most important function that quantum key distribution helps to achieve, while the latter is a requirement for quantum key distribution to work. Also, we will cover some topics on the security of classical cryptographic schemes so as to give some insight when comparing classical and quantum cryptography. The study of cryptography ranges from the analysis of cryptographic algorithms (or primitives ) to the design of a solution to a security problem. A cryptographic algorithm is a mathematical tool that provides a solution to a very specific problem and may be based on premises or on other primitives. A solution can be designed by combining primitives, and the requirements and functions of the primitives have to be combined properly. We will first review the confidentiality provided by ciphers that use the same key for both encryption and decryption, hence called secret-key ciphers . Then, we will discuss authentication techniques. Finally, we will show some aspects of public-key cryptography .
Quantum cryptography is a new method of communication offering the security of the inviolability by using Law of Nature.Quantum Cryptography uses different secure communication by applying the phenomena of quantum physics. Unlike traditional classical cryptography, which uses mathematical techniques to restrict eavesdroppers, quantum cryptography is focused on the properties of physics of light for information. Quantum cryptography depends only on the validity of quantum theory, i.e., it is guarantied directly by the laws of physics. This is a different from any classical cryptographic techniques. This paper summarizes the current state of quantum cryptography and provides potential extensions of its feasibility as a mechanism for securing existing communication systems.
A common desire in today's world is that of security. Whether it is keeping your e-mail private or stopping the government from hacking into your computer, the idea behind cryptography is to communicate between two parties in different locations, and to secure this information from outsiders. During the last half century there have been numerous advances in encryption schemes and also in the machines that process such information. Modern encryption algorithms have become increasingly more complex with advances in computers and technology, and encryption algorithms such as RSA and DES have been presented as algorithms that have remained secure for decades. These recent advances in encryption schemes will be examined in the first part of this paper. On the other hand, because the security of classical ciphers relies on the secrecy of a key, advances in research and computing may begin to compromise the security of these cryptosystems, as quantum computers would be capable of mathematical calculations that could break many modern encryption algorithms. Unlike classical cryptosystems, quantum cryptography obeys the laws of quantum physics, resulting in a much stronger, provable security. Many great advances have come in recent decades, and the latter part of this paper deals with these advances as well as the phenomena of quantum physics, the evolution of quantum computing, and the study of quantum cryptography.