After reading chapter 4, evaluate the history of the Data Encryption Standard (DES) and then how it has transformed cryptography with the advancement of triple DES. You must use at least one scholarly resource.  Discussion posting must be properly APA formatted. 
Read the PPT and also research other sources in online to answer. need high quality work. 

Week 3 OverviewThe objective of this chapter is to illustrate the principles of modern symmetric ciphers. For this purpose, we focus on the most widely used symmetric cipher: the Data Encryption Standard (DES). Although numerous symmetric ciphers have been developed since the introduction of DES, and although it is destined to be replaced by the Advanced Encryption Standard (AES), DES remains the most important such algorithm. Furthermore, a detailed study of DES provides an understanding of the principles used in other symmetric ciphers.
 you should be able to:

Understand the difference between stream ciphers and block ciphers.
Present an overview of Data Encryption Standard (DES).
Discuss the cryptographic strength of DES.

Cryptography and Network Security:

Principles and Practice
Eighth Edition

Chapter 4

Block Ciphers and the Data

Encryption Standard

Copyright © 2020 Pearson Education, Inc. All Rights Reserved.

Copyright © 2020 Pearson Education, Inc. All Rights Reserved.

Stream Cipher (1 of 2)

• Encrypts a digital data stream one bit or one byte at a time

– Examples:

▪ Autokeyed Vigenère cipher

▪ Vernam cipher

• In the ideal case, a one-time pad version of the Vernam cipher

would be used, in which the keystream is as long as the

plaintext bit stream

– If the cryptographic keystream is random, then this cipher is

unbreakable by any means other than acquiring the


▪ Keystream must be provided to both users in advance

via some independent and secure channel

▪ This introduces insurmountable logistical problems if the

intended data traffic is very large

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Stream Cipher (2 of 2)

• For practical reasons the bit-stream generator must be

implemented as an algorithmic procedure so that the

cryptographic bit stream can be produced by both users

– It must be computationally impractical to predict future

portions of the bit stream based on previous portions of

the bit stream

– The two users need only share the generating key and

each can produce the keystream

Copyright © 2020 Pearson Education, Inc. All Rights Reserved.

Block Cipher

• A block of plaintext is treated as a whole and used to

produce a ciphertext block of equal length

• Typically a block size of 64 or 128 bits is used

• As with a stream cipher, the two users share a symmetric

encryption key

• The majority of network-based symmetric cryptographic

applications make use of block ciphers

Copyright © 2020 Pearson Education, Inc. All Rights Reserved.

Figure 4.1 Stream Cipher and Block Cipher

Copyright © 2020 Pearson Education, Inc. All Rights Reserved.

Figure 4.2 General n-bit-n-bit Block

Substitution (shown with n = 4)

Copyright © 2020 Pearson Education, Inc. All Rights Reserved.

Table 4.1 Encryption and Decryption Tables for

Substitution Cipher of Figure 4.2

Plaintext Ciphertext

0000 1110

0001 0100

0010 1101

0011 0001

0100 0010

0101 1111

0110 1011

0111 1000

1000 0011

1001 1010

1010 0110

1011 1100

1100 0101

1101 1001

1110 0000

1111 0111

Ciphertext Plaintext

0000 1110

0001 0011

0010 0100

0011 1000

0100 0001

0101 1100

0110 1010

0111 1111

1000 0111

1001 1101

1010 1001

1011 0110

1100 1011

1101 0010

1110 0000

1111 0101

Copyright © 2020 Pearson Education, Inc. All Rights Reserved.

Feistel Cipher

• Feistel proposed the use of a cipher that alternates substitutions and


• Substitutions

– Each plaintext element or group of elements is uniquely replaced

by a corresponding ciphertext element or group of elements

• Permutation

– No elements are added or deleted or replaced in the sequence,

rather the order in whic

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