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
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].