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Aes Final 2

The AES Cipher, designed by Rijmen-Daemen, is a block cipher that encrypts data in 128-bit blocks using key sizes of 128, 192, or 256 bits, with the number of rounds varying based on key length. The encryption process consists of four main sub-processes: byte substitution, shift rows, mix columns, and add round key, with each round employing a unique round key generated from the original key. AES decryption mirrors the encryption process but applies inverse operations and a different key schedule.

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15 views44 pages

Aes Final 2

The AES Cipher, designed by Rijmen-Daemen, is a block cipher that encrypts data in 128-bit blocks using key sizes of 128, 192, or 256 bits, with the number of rounds varying based on key length. The encryption process consists of four main sub-processes: byte substitution, shift rows, mix columns, and add round key, with each round employing a unique round key generated from the original key. AES decryption mirrors the encryption process but applies inverse operations and a different key schedule.

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aneru
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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The AES Cipher - Rijndael

 designed by Rijmen-Daemen in Belgium


 AES is a block cipher.
 The key size can be 128/192/256 bits.
 Encrypts data in blocks of 128 bits each.
 The number of rounds depends on the key
length as follows :
 128 bit key – 10 rounds
 192 bit key – 12 rounds
 256 bit key – 14 rounds
AES Encryption Process
AES
Encryption
Process
AES Structure
Encryption Process
 Each round comprise of four sub-processes.
AES Round
AES Structure
 data block of 4 columns of 4 bytes is state
 key is expanded to array of words
 Round operation

byte substitution (1 S-box used on every byte)

shift rows (permute bytes between groups/columns)

mix columns (subs using matrix multiply of groups)

add round key (XOR state with key material)
 Byte Substitution (SubBytes)
 The 16 input bytes are substituted by looking up a fixed table (S-
box) given in design. The result is in a matrix of four rows and four
columns.
Substitute Bytes
Substitute Bytes Example
Shift Rows
 a circular byte shift in each each

1st row is unchanged

2nd row does 1 byte circular shift to left

3rd row does 2 byte circular shift to left

4th row does 3 byte circular shift to left
 decrypt inverts using shifts to right
Shift Rows :

 This step is just as it sounds. Each row is shifted a


particular number of times.
 The first row is not shifted
 The second row is shifted once to the left.
 The third row is shifted twice to the left.
 The fourth row is shifted thrice to the left.
 (A left circular shift is performed.)
 [ b0 | b1 | b2 | b3 ] [ b0 | b1 | b2 | b3 ]
 | b4 | b5 | b6 | b7 | -> | b5 | b6 | b7 | b4 |
 | b8 | b9 | b10 | b11 | | b10 | b11 | b8 | b9 |
 [ b12 | b13 | b14 | b15 ] [ b15 | b12 | b13 | b14 ]
Shift Rows
Mix Columns
 each column is processed separately
 each byte is replaced by a value
dependent on all 4 bytes in the column
 effectively a matrix multiplication
Mix Columns
Mix Columns Example
Add Round Key
 XOR state with 128-bits of the round key
 again processed by column (though
effectively a series of byte operations)
Add Round Key
AES Round
AES Key Expansion
 Ittakes a single key up during the first
stage, which is later expanded to multiple
keys used in individual rounds.
AES Key Expansion
AES Decryption
 AES decryption is not identical to
encryption since steps done in reverse
 but can define an equivalent inverse
cipher with steps as for encryption

but using inverses of each step

with a different key schedule
AES Decryption
summary

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