Algorithm 1: Algorithm of the encryption process

Input: plain color image $P$ of size $256\times 256$ Output: cipher image $C$ Step 1: Block scrambling is applied on $P$, which is split into 64 blocks each of size 32 × 32 represented as $C_1$. Step 2: Modified zigzag transform (ZT) is performed on the scrambled blocks $C_1$ to obtain $C_2$. Step 3: $C_2$ is split into RGB channels each of size $256\times 256$. Step 4: Using ELM, the intermediate key is generated with initial values are taken as $X_0=0.790,Y_0=0.889,Z_0=0.590$, respectively. Step 5: The final key is generated by applying the chosen values from image and external user as initial condition and parameters. Step 6: The secret key K is EX-OR-ed with the RGB channels received after modified ZT to obtain $C$.