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Cambridge University Press eBooks

Cryptography

Noson S. Yanofsky, Mirco A. Mannucci

Published Aug 11, 2008• 1 citation
Publisher

Abstract

We dance round in a ring and suppose, But the Secret sits in the middle and knows. Robert Frost, The Secret Sits (1942) In this chapter we explore the merging of quantum computation and classical cryptography. This is a new and exciting field of pure and applied research known as quantum cryptography . We begin with the basics of classical cryptography in Section 9.1. Section 9.2 demonstrates a quantum cryptographic protocol that uses two different bases. We improve on this in Section 9.3, where a protocol with one basis is employed. Section 9.4 shows how to use entanglement to secretly send a message. We conclude with Section 9.5, in which teleportation is demonstrated. CLASSICAL CRYPTOGRAPHY Before delving into quantum cryptography, we need to familiarize ourselves with the core ideas of classical cryptography. A good place to start is the following definition. Definition 9.1.1 Cryptography is the art of concealing messages . Indeed, this is precisely what the etymology reveals: “Cryptography” is a compound of two Greek words, crypton and graphein , which mean, respectively, hidden and writing. Turning an ordinary message into an indecipherable one is called encryption . The opposite action, i.e., restoring the original message, is decryption . The original message is generally referred to as the plaintext , and the encrypted message is the ciphertext . A method for encryption is often referred to as an encryption protocol .

DOI
10.1017/cbo9780511813887.011

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We dance round in a ring and suppose, But the Secret sits in the middle and knows. Robert Frost, The Secret Sits (1942) In this chapter we explore the merging of quantum computation and classical cryptography. This is a new and exciting field of pure and applied research known as quantum cryptography . We begin with the basics of classical cryptography in Section 9.1. Section 9.2 demonstrates a quantum cryptographic protocol that uses two different bases. We improve on this in Section 9.3, where a protocol with one basis is employed. Section 9.4 shows how to use entanglement to secretly send a message. We conclude with Section 9.5, in which teleportation is demonstrated. CLASSICAL CRYPTOGRAPHY Before delving into quantum cryptography, we need to familiarize ourselves with the core ideas of classical cryptography. A good place to start is the following definition. Definition 9.1.1 Cryptography is the art of concealing messages . Indeed, this is precisely what the etymology reveals: “Cryptography” is a compound of two Greek words, crypton and graphein , which mean, respectively, hidden and writing. Turning an ordinary message into an indecipherable one is called encryption . The opposite action, i.e., restoring the original message, is decryption . The original message is generally referred to as the plaintext , and the encrypted message is the ciphertext . A method for encryption is often referred to as an encryption protocol .
The word cryptography originates from two Greek words: kryptos (secret) and graphein (writing). Thus cryptography is the art of communicating a message in secret manner or in other words, it is the art of rendering a message unintelligible to any unauthorized party. Its history is very old and exciting. From the beginning of human civilization there was a need to hide information from unauthorized people. This need gave birth to cryptography. Initial cryptographic protocols were very simple. With time they have become much more sophisticated and secure. However, all the classical cryptographic protocols developed so far are secure under some assumptions. In contrast, the protocols of quantum cryptography are unconditionally secure. This particular aspect of quantum cryptography makes it very interesting. This chapter aims to provide a flavor of the intrinsic beauty of various aspects of secure quantum communication. Before we start a journey into the fascinating world of secure quantum communication, it would be apt to become familiar with the jargon used in this field and also with some interesting protocols of classical cryptography. Let us first do that.
This final chapter concerns cryptography , the principle of securing information against access or tampering by third parties. Classical cryptography refers to the manipulation of classical bits for this purpose, while quantum cryptography can be viewed as doing the same with qubits . I describe these two approaches in the same chapter, as in my view the field of cryptography should be understood as a whole and appreciated within such a broader framework, as opposed to focusing on the specific applications offered by the quantum approach. I, thus, begin by introducing the notions of message encryption , message decryption , and code breaking , the action of retrieving the message information contents without knowledge of the code's secret algorithm or secret key . I then consider the basic algorithms to achieve encryption and decryption with binary numbers, which leads to the early IBM concept of the Lucifer cryptosystem , which is the ancestor of the first data encryption standard (DES). The principle of double-key encryption , which alleviates the problem of key exchange , is first considered as an elegant solution but it is unsafe against code-breaking. Then the revolutionary principles of cryptography without key exchange and public-key cryptography (PKC) are considered, the latter also being known as RSA . The PKC–RSA cryptosystem is based on the extreme difficulty of factorizing large numbers . This is the reason for the description made earlier in Chapter 20 concerning Shor's factorization algorithm .
Classical cryptography is the process of hiding information and it manages the secret knowledge by encrypting the plain text message through the translation of it to an unintelligible message. Quantum cryptography is also hiding the plain text through encryption and it works based on the law of quantum physics for providing absolute security of data communication. It uses the idea of quantum mechanics to gadget a cryptographic system and the key problems are solved by intrusion detection including the Eavesdropping detection using quantum expertise. On the contrary, principles of secured communication protocol systems are demonstrated with classical quantum cryptography where the keys are distributed securely and are applied in quantum key distribution as well. In this paper, we provide a survey of works on classical cryptography and quantum cryptography and compare them with respect to time, security level and the classification of the data. Moreover, we perform a concise analysis of perspective classical cryptography and the conception of Quantum cryptography with various protocols and highlight the benefits of classical cryptography and Quantum cryptography in different applications. Finally, we provide a set of recommendations for selecting the suitable encryption model for securing the communication.
Cryptography literally means “The art & science of secret writing & sending a message between two parties in such a way that its contents cannot be understood by someone other than the intended recipient. ” and Quantum word is related with “Light”. Thus, Quantum Cryptography is a way of descripting any information in the form of quantum particles. There are no classical cryptographic systems which are perfectly secure. In contrast to Classical cryptography which depends upon Mathematics, Quantum Cryptography utilizes the concepts of Quantum Physics which provides us the security against the cleverest marauders of the present age. In the view of increasing need of Network and Information Security, we do require methods to overcome the Molecular Computing technologies (A future technology) and other techniques of the various codebrakers. Both the parts i.e. Quantum Key distribution and Information transference from Sender to Receiver are much efficient and secure. It is based upon BB84 protocol. It can be of great use for Govt. agencies such as Banks, Insurance, Brokerages firms, financial institutions, e-commerce and most important is the Defense & security of any country. It is a Cryptographic communication system in which the original users can detect unauthorized eavesdropper and in addition it gives a guarantee of no eavesdropping. It proves to be the ultra secure mode of communication b/w two intended parties.
Quantum cryptography uses physics to develop a cryptosystem completely secure against being compromised, without the sender or the receiver of messages being known. The word quantum itself refers to the most fundamental behavior of the smallest particles of matter and energy. Quantum cryptography is different from traditional cryptographic systems in that it relies more on physics, rather than mathematics, as a key aspect of its security model. Essentially, quantum cryptography is based on the usage of individual particles/waves of light (photon) and their intrinsic quantum properties to develop an unbreakable cryptosystem (because it is impossible to measure the quantum state of any system without disturbing that system). Regular, non-quantum encryption can work in a variety of ways but generally a message is scrambled and can only be unscrambled using a secret key. The trick is to make sure that whomever you’re trying to hide your communication from doesn’t get their hands on your secret key.
Cryptography is a word derived from the Greek that is approximately translated as hidden writing. There are various forms and styles of cryptography; however, since ancient times the aim of cryptography has been the same: secure the transmission of information from an emitter to a receiver. A classical form of cryptography involves the sharing of a code between the emitter and the receiver. A different algorithmic approach allows the use of a public key and is known as public key cryptography. This approach uses a public key and a secured key, both of which are mathematically connected. Quantum cryptography was first introduced by Weisner in 1983 and then by C. H. Bennett and G. Brassard. A refined protocol was introduced by Bennett et al. The Bennett and Brassard approach relies on the straightforward polarization property of single photons. An alternative method, based on the quantum entanglement of pairs of photons, was introduced by A. K. Ekert.