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Table of contents
1.
Introduction
2.
Operations of Advanced Encryption Standard
3.
Encryption Process
3.1.
Byte Substitution
3.2.
Row Shifting
3.3.
Column Shuffling
3.4.
Round Key Addition
4.
Decryption Process
5.
FAQs
6.
Key Takeaways
Last Updated: Mar 27, 2024

Advanced Encryption Standard

Author Prachi Singh
1 upvote
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23 Jul, 2024 @ 01:30 PM

Introduction

The most adaptive and dominant encryption algorithm used nowadays is Advanced Encryption Standard. It has been estimated that it is six times faster than the triple Data Encryption Standard.

An alternative for DES was needed as it characterizes itself with a small key size. Advanced Encryption Standard came into existence to enhance the computational efficiency of symmetric encryption algorithms.

Operations of Advanced Encryption Standard

Unlike Data Encryption Standard, Advanced Encryption Standard is an iterative Cipher. The algorithm comprises of interconnected operations. The corresponding functions include replacing inputs with some outputs and permutating other bits.

Hence, Advanced Encryption Standard performs operations on 128 bits of a plain text equivalent to 16 bytes. The representation of 16 bytes is along with the matrix of four rows and four columns. 

The variation in iterative rounds in Advanced Encryption Standard is variable, and its value depends on the size of the key.

The relation between the number of iterative rounds and cypher key is as below:

ROUND

KEY SIZE

10

128

12

192

14

256

 

The Advanced Encryption Structure is represented as:

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Encryption Process

Each encryption process is divided into four sub-tasks. The first round process is as shown below:

Byte Substitution

The input bytes are shuffled using a fixed table(s-box). The result obtained is a matrix with four rows and four columns.

Row Shifting

Each of the four rows obtained in the substitution process is made to shift one step to the left.

The shifting needs to be implemented on the basis of the following criteria:

  1. The first row is kept static.
  2. The second row is moved one step to the left.
  3. The third row is moved two steps to the left.
  4. The fourth row is moved three steps to the left.
  5. The result obtained is the new matrix with the same bytes but only change in the position with respect to the other.

Column Shuffling

A special mathematical function shuffles all the four bytes of each and every column. The new four bytes of the column as the output are replacing the original input values of the column. Hence, the resultant is another matrix consisting of new 16 bytes.

Round Key Addition

The new matrix with 16 bytes is to be implemented over an XOR operator of 128 bytes. The result obtained is the ciphertext.

If not, then the same process is repeated again.

Decryption Process

The decryption Process for Advanced Encryption Standard is the same as Encryption Process for Advanced Encryption Standard but is always performed in reverse order. The four different sub-processes involved are as follows:

  1. Round Key Addition
  2. Column Shuffling
  3. Row Shifting
  4. Byte Substitution

The encryption and decryption processes are carried out separately since sub-tasks are carried out in reverse order.

FAQs

  1. What is the size of the block in the Advanced Encryption Standard?
    The size of the block in Advanced Encryption Standard is 128-Bit.
     
  2. What is the size of the key in the Advanced Encryption Standard?
    The size of the key in the Advanced Encryption Standard is 128, 192 or 256 Bits. 
     
  3. How many iterative rounds does Advanced Encryption Standard 192 perform?
    Advanced Encryption Standard 192 performs 12 rounds.
     
  4. How many iterative rounds does Advanced Encryption Standard 256 perform?
    Advanced Encryption Standard 192 performs 14 rounds.
     
  5. What are States in AES?
    The 4*4 matrices in the Advanced Encryption Standard algorithm are called States.

Key Takeaways

Congratulations on finishing the blog!! After reading this blog, you will grasp the concept of the Advanced Encryption Standard.

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