Chapter 7. Encryption — Symmetric Techniques

7.1 Introduction

Secrecy is at the heart of cryptography. Encryption is a practical means to achieve information secrecy. Modern encryption techniques are mathematical transformations (algorithms) which treat messages as numbers or algebraic elements in a space and transform them between a region of “meaningful messages” and a region of “unintelligible messages”. A messages in the meaningful region and input to an encryption algorithm is called cleartext and the unintelligible output from the encryption algorithm is called ciphertext. If we disregard the intelligibility of a message, then a message input to an encryption algorithm is conventionally called plaintext which may or may not be intelligible. ...

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