SLIDE 1
1
Content
Introduction Methods AddRoundKey SubBytes ShiftRows MixColumns Key Expansion Conclusion
AES Group | The Feather Beamer Theme
Advanced Encryption Standard (AES) AES Group March 3, 2019 - - PowerPoint PPT Presentation
Advanced Encryption Standard (AES) AES Group March 3, 2019 - - PowerPoint PPT Presentation
Faculty of Information Engineering and Technology Advanced Encryption Standard (AES) AES Group March 3, 2019 Content 1 Introduction Methods AddRoundKey SubBytes ShiftRows MixColumns Key Expansion Conclusion AES Group | The Feather
SLIDE 2
SLIDE 3
2
Introduction
◮ Internet
AES Group | The Feather Beamer Theme
SLIDE 4
3
Introduction
◮ What is Encryption?
AES Group | The Feather Beamer Theme
SLIDE 5
4
Introduction
◮ Idea Of Encryption
AES Group | The Feather Beamer Theme
SLIDE 6
5
Introduction
Types of Encryption:
◮ Blowfish ◮ RSA ◮ 3DES ◮ AES
AES Group | The Feather Beamer Theme
SLIDE 7
6
Introduction
◮ The National institute of standards and technology and AES:
AES Group | The Feather Beamer Theme
SLIDE 8
7
Introduction
◮ What is good about AES?
AES Group | The Feather Beamer Theme
SLIDE 9
8
Methods
AddRoundKey
LET’S SAY FOR EXAPMLE WE HAVE THE FOLLOWING:
AES Group | The Feather Beamer Theme
SLIDE 10
9
Methods
AddRoundKey
ENCRYPTION PROCESS:
Figure: Encryption process
AES Group | The Feather Beamer Theme
SLIDE 11
10
Methods
AddRoundKey
The previous figure shows the steps of the encryption process, first you get your input array of binary digits and X-OR it with the array of the Cipher key this step is called AddRoundKey Method, then you pass by 4 stages 9 times then you have a final round. Each of the 9 stages consist of the same 4 methods:
◮ AddRoundKey ◮ SubBytes ◮ ShiftRows ◮ MixColumns
At Round 1 after passing by the 4 methods, we X-OR it with the Cipher Key again, then at Round 2 we pass by the same 4 methods but here we X-OR the output Round 2 with the Output of Round 1 and so on until Round 9, we keep X-OR-ing with the result of the previous round, whereas Round 10 doesn’t include MixColumns.
AES Group | The Feather Beamer Theme
SLIDE 12
11
Methods
AddRoundKey
Figure: Encryption process explained
AES Group | The Feather Beamer Theme
SLIDE 13
12
Methods
AddRoundKey
Figure: Encryption process explained
AES Group | The Feather Beamer Theme
SLIDE 14
13
Methods
SubBytes
The State:
◮ It is Matrix of size 4x4 ◮ Hexadecimal bits ◮ Digits
AES Group | The Feather Beamer Theme
SLIDE 15
14
Methods
SubBytes
◮ SECOND transformation ◮ Substitute a byte ◮ Using S-Box
Figure: SubBytes method
AES Group | The Feather Beamer Theme
SLIDE 16
15
Methods
SubBytes
◮ 16x16 Array ◮ rows and columns indexed by hexadecimal bits array
AES Group | The Feather Beamer Theme
SLIDE 17
16
Methods
SubBytes
Figure: S-box
AES Group | The Feather Beamer Theme
SLIDE 18
17
Methods
SubBytes
◮ Two Digits representation ◮ The new byte from S-Box ◮ The content change ◮ No change in arrangement of bytes
AES Group | The Feather Beamer Theme
SLIDE 19
18
Methods
ShiftRows
Figure: ShiftRows method
AES Group | The Feather Beamer Theme
SLIDE 20
19
Methods
MixColumns
Figure: MixColumns method
First result byte is calculated by multiplying 4 elements in the first column of the state by the first 4 elements in the row of multiplication matrix (c) B1 = (b1 ∗ 2)xor(b2 ∗ 3)xor(b3 ∗ 1)xor(b4 ∗ 1) (1) Second result byte is calculated by multiplying 4 elements in the first column of the state by the second 4 elements in the row of multiplication matrix (c)
AES Group | The Feather Beamer Theme
SLIDE 21
20
Methods
MixColumns
B2 = (b1 ∗ 1)xor(b2 ∗ 2)xor(b3 ∗ 3)xor(b4 ∗ 1) (2) Third result byte is calculated by multiplying 4 elements in the first column of the state by the Third 4 elements in the row of multiplication matrix (c) B3 = (b1 ∗ 1)xor(b2 ∗ 1)xor(b3 ∗ 2)xor(b4 ∗ 3) (3) Forth result byte is calculated by multiplying 4 elements in the first column of the state by the fourth 4 elements in the row of multiplication matrix (c) B4 = (b1 ∗ 3)xor(b2 ∗ 1)xor(b3 ∗ 1)xor(b4 ∗ 2) (4)
AES Group | The Feather Beamer Theme
SLIDE 22
21
Methods
Key Expansion
◮ This phase is crucial because it protects the key from being
vulnerable to attacks.
◮ This phase takes place where expansion of the cipher key into
11 partial keys, used in the initial round, the 9 main rounds and the final round.
AES Group | The Feather Beamer Theme
SLIDE 23
22
Methods
Key Expansion
◮ The Process goes as follows:
a) Applying the RotWord and SubBytes transformation to the previous word (wi-1). b) Adding (XOR) this result to the word 4 position earlier (wi-4), plus a round constant Rcon.
AES Group | The Feather Beamer Theme
SLIDE 24
23
Methods
Key Expansion
Figure: Key expansion method
AES Group | The Feather Beamer Theme
SLIDE 25
24
Methods
Key Expansion
Figure: Key expansion method
AES Group | The Feather Beamer Theme
SLIDE 26
25
Methods
Key Expansion
Figure: Key expansion method
AES Group | The Feather Beamer Theme
SLIDE 27
26
Methods
Key Expansion
Figure: Key expansion method
AES Group | The Feather Beamer Theme
SLIDE 28
27
Methods
Key Expansion
◮ The remaining 32-bit words (wi) are calculated by adding (XOR)
the previous word (wi-1) with the word4 positions earlier (wi-4).
Figure: Key expansion method
AES Group | The Feather Beamer Theme
SLIDE 29
28
Methods
Key Expansion
Figure: Key expansion method
AES Group | The Feather Beamer Theme
SLIDE 30
29
Conclusion
◮ In Conclusion , AES is a symmetric block cipher algorithm that
consists of 4 rounds.
◮ ADDRoundKey in which the cipher key is combined with state
using bitwise XOR.
◮ SubBytes where we substitute every byte in the state into the
corresponding byte in the ASCII code(S-Box ).
◮ ShiftRows where we shift the bytes in a cyclic manner to the left
in each row other than the number 0 row.
◮ MixColumns where multiplication is carried out between each
byte of a row by each byte in the state column and the output is XORED to produce 4 new bytes.
◮ And finally , Key expansion where the cipher key is expanded to
11 partial keys used in each round.
AES Group | The Feather Beamer Theme
SLIDE 31