AES Cipher

1. ADVANCED ENCRYPTION STANDARD (AES)
Name: Md Fazle Rabbi
ID:16CSE057

2. CONTENTS
 What is AES?
 AES features
 Operation of AES
 AES security

3. WHAT IS AES?
 The Advanced Encryption Standard (AES) is a symmetric
block cipher chosen by the U.S. government to protect
classified information.
 The more popular and widely adopted symmetric encryption
algorithm likely to be encountered nowadays is the Advanced
Encryption Standard (AES).
 It is found at least six time faster than triple DES.
 AES is implemented in software and hardware throughout the
world to encrypt sensitive data.
 It is essential for government computer security, cyber security
and electronic data protection

4. AES FEATURES
AES algorithm must be a block cipher capable of handling 128-bit
blocks, using keys sized at 128, 192 and 256 bits. Other criteria for
being chosen as the next AES algorithm included the following:
 Security. Competing algorithms were to be judged on their ability to
resist attack -- as compared to other submitted ciphers. Security strength
was to be considered the most important factor in the competition.
 Cost. Intended to be released on a global, nonexclusive and royalty-free
basis, the candidate algorithms were to be evaluated on computational
and memory efficiency.
 Implementation. Factors to be considered included the algorithm's
flexibility, suitability for hardware or software implementation, and
overall simplicity.

5. OPERATION OF AES
 The number of rounds in AES is variable and depends on
the length of the key. AES uses 10 rounds for 128-bit
keys, 12 rounds for 192-bit keys and 14 rounds for 256-
bit keys. Each of these rounds uses a different 128-bit
round key, which is calculated from the original AES key.

6. THE SCHEMATIC OF AES STRUCTURE IS GIVEN IN THE FOLLOWING
ILLUSTRATION −

7. HOW DOES AES ENCRYPTION WORK?
1. Dividing data into blocks
 First, we have to keep in mind that AES is a block cipher.
Unlike stream ciphers, it encrypts data in blocks of
bits instead of bit-by-bit.
 Each of its blocks contains a column of 16 bytes in a layout of
four-by-four. As one byte contains 8 bits, we get 128-bit block
size (16×8=128).
 Thus, the very first step of AES encryption is dividing the
plaintext (text that is not written in code) into these blocks.
 So, let’s choose the text you want to encrypt. For example, it
can be “better late than never”.

8.  Applying the advanced encryption standard would
turn the beginning of this phrase into the following
block:

9. 2.ADDING ROUND KEY
 This is the very first round of AES encryption. Here, the
algorithm adds the initial key to our phrase, which was
previously turned into a 4×4 block:
+
=
Adding two blocks of text might seem impossible. However, remember that
AES actually uses binary code, and what you now see is just a visual
representation of what is actually happening in the binary language.

10. ENCRYPTION PROCESS
 Here, we restrict to description of a typical round of
AES encryption. Each round comprise of four sub-
processes. The first round process is depicted
below −

11. I) BYTE SUBSTITUTION
The 16 input bytes (128-bit) are substituted based
on a predetermined table. The result is a matrix of
four rows and four columns where the data is altered
in a non-linear way to add confusion

12. II) SHIFT ROWS
Shift Row is carried out in four parts:
 First row is not shifted
 Second row is shifted one (byte) position to the left
 Third row is shifted two positions to the left
 Fourth row is shifted three positions to the left
In the end, a new matrix is formed based on the same 16 bytes.

13. III)) MIX-COLUMNS
This operation is the most difficult, both to explain and
perform. Each column of the state array is processed
separately to produce a new column. The new
column replaces the old one. The processing involves
a matrix multiplication.

14. IV) XOR-ROUND KEY
 After the Mix-Columns operation, the Xor-Round Key is very
simple indeed and hardly needs its own name. This operation
simply takes the existing state array, XORs the value of the
appropriate round key, and replaces the state array with the
result.

15. AES SECURITY
 Security experts maintain that AES is secure when
implemented properly. However, AES encryption keys need
to be protected. Even the most extensive cryptographic
systems can be vulnerable if a hacker gains access to the
encryption key.
 Use of strong passwords, password managers, multifactor
authentication (MFA), firewalls and antivirus software is
critical to enterprise security. Employees should also be
trained in ways to prevent social engineering and phishing
attacks.

16. THE END