[SOLVED] Week 3 Discussion Post - Information Systems

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. The initial post must be completed by Thursday at 11:59 eastern. . You must use at least one scholarly resource. Every discussion posting must be properly APA formatted.
500 words

Cryptography and Network Security:

Principles and Practice
Eighth Edition

Chapter 4

Block Ciphers and the Data

Encryption Standard

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

▪ 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

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

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

Figure 4.1 Stream Cipher and Block Cipher

Figure 4.2 General n-bit-n-bit Block

Substitution (shown with n = 4)

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

Feistel Cipher

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

permutations

• 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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[SOLVED] Week 3 Discussion Post – Information Systems

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