Page 39 - DCAP516_COMPUTER_SECURITY

Avinash Bhagat, Lovely Professional University
Unit 4: Cryptography

Unit 4: Cryptography Notes

CONTENTS
Objectives
Introduction

4.1 What is Cryptography
4.1.1 Substitution Ciphers
4.1.2 Transposition Ciphers

4.2 Two Fundamental Cryptographic Principles
4.3 Data Encryption Standard
4.4 The AES Encryption Algorithm
4.5 Public-Key Algorithms
4.6 Uses of Encryption

4.7 Summary
4.8 Keywords
4.9 Review Questions

4.10 Further Readings
Objectives

After studying this unit, you will be able to:
Familiarize with the concepts of cryptography
Discuss the concept of substitution ciphers and transposition

Understand the methodology of making good encryption algorithm
Describe the concepts of AES and DES algorithms
Know about the uses of encryption

Introduction

In pre-computer days, military, diplomats, diarists and lovers used the art of cryptography for
hiding data or message from intruders. The message to be encrypted known as “plaintext”, are
transformed by a function that is parametrized by “key”. The output of the encryption process,
known as the ciphertext or cryptograph is then transmitted by some medium (messenger, radio
or wire). Suppose, an intruder, hears and accurately copies the ciphertext. Unlike the intended
recipient, he does not know the key and so cannot decrypt the ciphertext easily.
Sometimes an active intruder can record message and modify message before they get to the
intended recipient. The art of breaking ciphers is called cryptanalysis. The art of devising ciphers
and breaking them is collectively known as ‘cryptology’. To achieve security the cryptographer
should make sure that the system is unbreakable even if his opponent can encrypt arbitrary
amount of plaintext.

LOVELY PROFESSIONAL UNIVERSITY 33