Part I: MATHEMATICAL PRELIMINARIES
CHAPTER 6
Basic Concepts of Cryptography
6.1 THE LEXICON OF CRYPTOGRAPHY
The word cryptography is derived from the Greek word kryptos, which means hidden, and graphien, which means to write. David Kahn’s book [Kahn 1967] provide extensive accounts of cryptography and its influence on history.
Every scientific discipline develops its own lexicon and cryptography is no exception. We begin with a brief summary of the principal terms used in cryptography.
An alphabet 
= {a0, a1, … , am−1} is a finite set of letters; for our purposes, the most natural alphabets are
Binary (m = 2r): (0,1)-sequences of fixed length r: Zr,2 = {x = (x0, x1, … , xr−1)}.
American Standard Code for Information Interchange (ASCII)/Extended Binary Coded Decimal Interchange (EBCDIC) (m = 27/m = 28).
Text is formed by concatenating letters of ; an n-gram (a0 a1 … an−1) is the concatenation of n letters. We do not require that the text be understandable nor that it be grammatically correct relative to a natural language; thus, examples of ASCII text include both GoodMorning and vUI* 9Uiing8.
Encipherment (or encryption) is a transformation process T the plaintext x = (x0, x1, … , xn−1) is enciphered to the ciphertext y = (y0, y1, … , ym−1).
is an example of encipherment introduced ...
