**1.1 Byte substitution**

The 16 input bytes are substituted by using fixed lookup table known as s-box. **Figure 2** shows s-box of AES algorithm. This s-box consists of all possible combinations of 8-bit sequence. The resulting new 16 bytes are organized in a matrix having four rows and four columns.

**Figure 3** shows byte substitution stage in AES algorithm.


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**Figure 4.** *Shift row stage.*

**1.2 Shift row**

*Byte substitution stage.*

**Figure 3.**

**1.3 Mix column**

*High-Speed Area-Efficient Implementation of AES Algorithm on Reconfigurable Platform*

Each row from the matrix generated from the byte substitution is cyclically shifted to the left. Any entry that is dropped off is reinserted to the right side. The first row is kept as it is, the second row is shifted by one-byte position to the left, the third row is shifted by two-byte position to the left, and the fourth row is shifted by three-byte position to the left. The resultant matrix consists of same 16 bytes but at

Each column of four bytes is now transformed using special arithmetical function

of Galois field (GF) 28. This function takes four bytes of the column as input and

different position. **Figure 4** shows shift row stage in AES algorithm.

*DOI: http://dx.doi.org/10.5772/intechopen.82434*

**Figure 2.** *S-box of AES algorithm.* *High-Speed Area-Efficient Implementation of AES Algorithm on Reconfigurable Platform DOI: http://dx.doi.org/10.5772/intechopen.82434*

### **1.2 Shift row**

*Computer and Network Security*

**1.1 Byte substitution**

*Structure of AES algorithm.*

**Figure 1.**

four rows and four columns.

this algorithm is designed with 128 bits of block size and key size, respectively, that is, AES generates cipher text of 128 bits for 128 bits of plaintext. After the initial round, plaintext processes through ten rounds. Each round contains processes like

The 16 input bytes are substituted by using fixed lookup table known as s-box. **Figure 2** shows s-box of AES algorithm. This s-box consists of all possible combinations of 8-bit sequence. The resulting new 16 bytes are organized in a matrix having

byte substitution, shift rows, mix columns, and add round key.

**Figure 3** shows byte substitution stage in AES algorithm.

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**Figure 2.**

*S-box of AES algorithm.*

Each row from the matrix generated from the byte substitution is cyclically shifted to the left. Any entry that is dropped off is reinserted to the right side. The first row is kept as it is, the second row is shifted by one-byte position to the left, the third row is shifted by two-byte position to the left, and the fourth row is shifted by three-byte position to the left. The resultant matrix consists of same 16 bytes but at different position. **Figure 4** shows shift row stage in AES algorithm.

#### **1.3 Mix column**

Each column of four bytes is now transformed using special arithmetical function of Galois field (GF) 28. This function takes four bytes of the column as input and

**Figure 4.** *Shift row stage.*

outputs completely new four bytes that replaces the original four bytes. **Figure 5** shows mix column stage in AES algorithm.
