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 .
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 .
Cryptography has long been an essential tool in safeguarding digital communication and securing sensitive information. As technology has progressed, so has the complexity of the methods used to protect our data. In the wake of quantum computing's rise, traditional cryptographic systems face serious challenges, demanding a new understanding of how quantum algorithms could both undermine and enhance security. Chapter 1 deals with the Basics of Cryptography lays the groundwork by introducing classical cryptography, tracing its evolution from ancient ciphers to modern cryptosystems. In Chapter 2, readers are introduced to Quantum Algorithms, the principles of quantum mechanics relevant to computing, including qubits, superposition, and entanglement. The Chapter 3 focuses on Shor’s algorithm, a landmark quantum algorithm that threatens the security of widely used public-key cryptosystems like RSA and ECC. In Chapter 4 Grover’s Algorithm is examined in the context of brute-force attacks on symmetric key cryptography. Chapter 5 focusing on Simon’s Algorithm and its role in breaking cryptographic primitives through structure exploitation. In Chapter 6 a broader discussion about Cryptographic Implications of Quantum Computing is given on how quantum computing affects modern cryptographic systems. Finally, in Chapter 7, the future of cryptography in the quantum era is discussed.
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 .
Cryptography is not for secure the sensitive data but now days it is compulsory in many applications like IoT, Cloud Platform, business systems and so on. A new area of advanced information technology called quantum-computing uses the unique characteristics of quantum physics to solve complex problems, which are beyond the powers of even the most robust classical/powerful computers. Security is the major concern in the area of quantum computing environment. Quantum cryptography, in addition, merely practices the ideologies of quantum mechanism to encrypt/decrypt data and transmit it in a way that cannot be hacked by anyone. This chapter explores the area of quantum public key cryptography, which seeks to create cryptographic building blocks that can withstand attacks from a quantum computing-enabled adversary. Chapter begins with fundamental principles of quantum mechanics, cryptography, quantum cryptography, quantum public key cryptography and, core families of quantum-resistant public key schemes.
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.
Cryptography is the process of encrypting data or transforming plain text to ciphertext so that it can be deciphered only by appropriate key. Quantum cryptography employs quantum physics principles to encrypt and transport data in an unpackable manner. Quantum key distribution (QKD) is a technique for creating and exchanging private keys over quantum channels between two parties. Then, using standard cryptography, the keys can be used to encrypt and decrypt messages. Unbreakable encryption is something we really must have. The integrity of encrypted data is now in danger due to the impending development of quantum computers. Fortunately, quantum cryptography, via QKD, provides the answer we require to protect our information for a very long time to come. This is all based on the intricate principles of quantum mechanics. This chapter is discussing the various algorithms used and the applications of quantum cryptography.
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 .