An important algorithm commonly used in a typical e-commerce transaction is the Advanced Encryption Standard (AES). The following diagram shows the basic structure of AES.
(a) Describe the mathematical operation and function of each stage shown in a round in this diagram, briefly but concisely.
Plaintext
Key
Plaintext
Add round key
w[0,3]
Add round key 4
Inverse sub bytes 4
Inverse shift rows
Substitute bytes
Expand key
Round 10
Inverse mix columns
Add round key
Shift rows
Mix columns
Add round key
w[4,7]
A
Inverse sub bytes 4
Inverse shift rows
A
Substitute bytes
Shift rows 6
Mix columns
Inverse mix columns 4
Add round key
Add round key
w[36,39]
Substitute bytes
Inverse sub bytes
Round 10
Shift rows
Add round key
T
Inverse shift rows
w[40,43]
Add round key 1
Ciphertext
Ciphertext
(b) Encryption
(b) Decryption