**3. Hybrid graphical encryption**

The hybrid graphical encryption algorithm (HGEA) is a unique graphical encryption algorithm based on mathematical transformations and graphical pattern realization. It is a symmetric key encryption in which a single 64-bit key is shared between two parties for encryption and decryption of data.

### **3.1 Hybrid cubes encryption algorithm (HiSea)**

As the HGEA is inspired from hybrid cubes encryption algorithm (HiSea), it is explained here in brief.

Hybrid cubes encryption algorithm (HiSea) is the symmetric non-binary block cipher. The encryption and decryption keys, plaintext, ciphertext and internal operation in the encryption or decryption processes are based on the integer numbers. HiSea encryption algorithm was developed by Sapiee Jamel in 2011. The plaintext size for the encryption process is 64 bytes ASCII characters. Hybrid cube (HC) is generated based on the inner matrix multiplication of the layers between the two magic cubes (MCs). HC of order 4 4 is a matrix Hi,j, i {1, 2, 879} and j {1, 2, 3, 4}, defined as follows: Hi,j = MCi,j MCi + 1,j where the MCi,j is a jth layer of ith magic cube [17–19].

### **3.2 Hybrid graphical encryption algorithm (HGEA)**

HGEA performs the operation, like in HiSea, of generating 4 4 matrix, then mixing it with key and again mixing of rows and column. Further, the algorithm obtains decision parameters based on remainder value and exploit the correlation between distributions of two graphical patterns for manipulation of intermediate data.

The main concept of hybrid graphical encryption algorithm cipher is to realize the input data into 8 8 bit matrix pattern. Then, divide it into four 4 4 matrices by putting it up against XY axis quadrant graph. Again, each quadrant 4 4 matrix is expanded into four possible 16-bit 4 4 matrices by XOR operation with four 4 4 subkeys. Further quadrant selection operation selects one 4 4 bit matrix output for further processing. Finally, after the final XOR operation, each set of 4 4 bit matrix is plotted into XY axis plot (**Figure 4**).

Since this algorithm will be using the entire ASCII table for referencing, the case

After tabulating the plaintext in comparison with the ASCII table, ASCII and decimal values of the plaintext can be derived. Now, the decimal value has to be converted to binary value to move on to the next step. For binary values that do not reach the 8-bit mark, 0 s are added to the back. The obtained binary value is then

Since HGEA is a symmetric key encryption, a 64-bit binary key is shared for both encryption and decryption processes. These keys are also tabulated in the form

Consider key bits as 64 random bits tabulated in an 8 8 matrix form, similar to

In this step, initially the 8 8 matrix is divided into quadrant form as shown in **Table 4(a)**. The 8 8 matrix formed from plaintext is divided into four 4 4 matrices, that is, quarters named as M1, M2, M3 and M4 and generalized as Mi Similarly, the 8 8 matrix form key is also divided into four quarters named as

Again, Mi which is a 4 4 matrix is converted into 8 8 matrix by performing XOR operation of Mi with K1, K2, K3 and K4. M1 is XOR-ed with K1, K2, K3 and K4 and obtained value is populated to 1st, 2nd, 3rd and 4th quadrants,

*Reference XY axis and sample conversion of 8 8 matrix into 4 4 matrix.*

sensitivity of the message will play a very crucial part in output ciphertext.

tabulated in the form of an 8 8 matrix as shown in **Table 3**.

of an 8 8 matrix of message bits.

*Hybrid Approaches to Block Cipher*

*DOI: http://dx.doi.org/10.5772/intechopen.82272*

K1, K2, K3 and K4, generalized as Ki.

respectively, as shown in **Table 4(b)**.

*3.3.2 Step 2: transformation*

message bits.

**Table 3.**

**Table 4.**

**149**

*Conversion of plaintext to binary.*
