Chapter 1Introduction to Block Ciphers

1.1 Block Cipher in Cryptology

1.1.1 Introduction

Information includes our private data that we desire to protect from unwilling leakage depending on the application. Cryptology is a field of research that offers appropriate solutions for the data protection by exploring how to construct a secure communication for fair information exchange. Modern cryptology often deals with digitalized data rather than analog data that cannot be expressed simply with a series of 0s and 1s. In our daily life, information is exchanged by digital devices such as radio frequency identification (RFID) tags, smart cards, and smart phones, where a computational resource is limited. Therefore, it is one of the most important challenges in cryptology to realize an efficient implementation of cryptosystems.


Figure 1.1 Basic model for a symmetric-key cryptosystem

1.1.2 Symmetric-Key Ciphers

There are various ways to realize encryption that is a kind of computational process for information to be protected. In a symmetric-key cipher, information is encrypted with a secret key, and it is expected that the owner of the secret key can decrypt the encrypted information correctly. For instance, let us see the situation, where Alice would like to send a message to Bob in a secure way. If the secret key, K, is shared only with Alice and Bob, only Bob can decrypt the ...

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