1.
AES KEY EXPANSION

2.
AES ENCRYPTION AND DECRYPTION DIAGRAM

3.
AES KEY EXPANSION
The AES algorithm which
takes 128 bits (16 bytes)
key as input, four-word
key as input and produce a
linear array of 44 words.
(In AES 4 Bytes = 1 Word).
Figure describe the steps
of key expansion.
Figure : 1. Four word round 2. AES Encryption Process

4.
AES KEY EXPANSION
A four-word round key is
acceptable for the initial stage.
The initial stage is Add Round
Key and each of the 10 rounds
of cipher. So, total 11 rounds =
44 words. The key is added
into the first four words of the
expanded key.
Figure : 1. Four word round 2. AES Encryption Process

5.
AES KEY EXPANSION
• The function g defines the complex
and that function consist of some sub
function as follow:
• Step-1: This function performs the
one-byte circular left shift.
• Step-2: Using S-box each sub word
performs a byte substitution.
• Step-3: Finally result of Rot word and
step 2 is XORed with the round
constant called as Rcon[Round].
Figure : Function g

6.
AES KEY EXPANSION
• The function g defines the complex
and that function consist of some sub
function as follow:
• Step-1: This function performs the
one-byte circular left shift.
• Step-2: Using S-box each sub word
performs a byte substitution.
• Step-3: Finally result of Rot word and
step 2 is XORed with the round
constant called as Rconst[j].
Figure : STEP-1
W3 Left
Shift
AF 7F
7F 67
67 98
98 AF
W0 w1 w2 w3
0F 47 0C AF
15 D9 B7 7F
71 E8 AD 67
C9 59 D6 98

7.
AES KEY EXPANSION
Figure : STEP-2
Left Shift
7F
67
98
AF

8.
AES KEY EXPANSION
Figure : STEP-2
Left
Shift
S-box
7F
67
98
AF
ROW COLUMN

9.
AES KEY EXPANSION
Figure : STEP-2
Left
Shift
S-box
7F
67
98
AF
ROW COLUMN

10.
AES KEY EXPANSION
Figure : STEP-2
Left
Shift
S-box
7F D2
67
98
AF
ROW COLUMN

11.
AES KEY EXPANSION
Figure : STEP-2
Left
Shift
S-box
7F D2
67
98
AF

12.
AES KEY EXPANSION
Figure : STEP-2
Left
Shift
S-box
7F D2
67 85
98
AF

13.
AES KEY EXPANSION
Figure : STEP-2
Left
Shift
S-box
7F D2
67 85
98 46
AF

14.
AES KEY EXPANSION
Figure : STEP-2
Left
Shift
S-box
7F D2
67 85
98 46
AF 79

15.
AES KEY EXPANSION
• The function g defines the complex
and that function consist of some sub
function as follow:
• Step-1: This function performs the
one-byte circular left shift.
• Step-2: Using S-box each sub word
performs a byte substitution.
• Step-3: Finally result of Rot word and
step 2 is XORed with the round
constant called as Rcon[Round].

16.
AES KEY EXPANSION
w0 w1 w2 w3
0F 47 0C AF
15 D9 B7 7F
71 E8 AD 67
C9 59 D6 98
Left Shift
(Step-1)
S-box
(Step-2)
7F D2
67 85
98 46
AF 79
S-box
(Step-2)
D2
85
46
79
Rcon(Round)
01
00
00
00
w0
0F
15
71
C9
W4
DC
90
37
B0
Step-3: Finally result of Rot word
and step 2 is XORed with the
round constant called as
Rcon[Round].

17.
AES KEY EXPANSION
w0 w1 w2 w3 w4 w5 w6 w7
0F 47 0C AF DC 9B
15 D9 B7 7F 90 49
71 E8 AD 67 37 DF
C9 59 D6 98 B0 E9

18.
AES KEY EXPANSION
w0 w1 w2 w3 w4 w5 w6 w7
0F 47 0C AF DC 9B 97
15 D9 B7 7F 90 49 FE
71 E8 AD 67 37 DF 72
C9 59 D6 98 B0 E9 3F

19.
AES KEY EXPANSION
w0 w1 w2 w3 w4 w5 w6 w7
0F 47 0C AF DC 9B 97 38
15 D9 B7 7F 90 49 FE 81
71 E8 AD 67 37 DF 72 15
C9 59 D6 98 B0 E9 3F A7

20.
AES EXAMPLE

21.
AES EXAMPLE
Initial
Round
Round 1
Round 2
Round 3
Round 4
Round 5
Round 6
Round 7
Round 8

22.
AES EXAMPLE

23.
AES EXAMPLE