AES is an encryption standard adopted by the US government. The standard comprises symmetric block cipher AES from a larger collection originally published as Rijndael. Rijndael supports a range of block and key sizes; whereas the AES adopts a 128-bit block size and a key size of 128, 192 or 256 bits which has 10/12/14 rounds. In the AES-128 shown as Figure 1, a state is a 4 × 4 array of bytes, and the AES operates on states. The AES includes 10 rounds, where each round includes 4 stages except the last round. The 128-bit (16 byte) block is depicted as a square matrix of 4 × 4 bytes. The block is copied into the state array. This state array is modified at each stage of encryption or decryption and copied into the output array at the end. In each round of encryption and decryption, four operations are performed. They are: substitute bytes, shift rows, mixcolumns, and add round key. The mixcolumns operation is omitted in the last round and an initial key addition is performance before the first round for whitening.

The state array is subject to four operations in each round. The first one is substitution bytes transformations. In the SubBytes step, each byte in the array is updated using an 8-bit substitution box, the Rijndael S-box (16 × 16) shown as in Figure 2. This operation provides the non-linearity in the cipher. The S-box used is derived from the multiplicative inverse over GF (2⁸), known to have good non-linearity properties. To avoid attacks based on simple algebraic properties, the S-box is constructed by combining the inverse function with an invertible affine transformation.

The ShiftRows step operates on the rows of the state; it cyclically shifts the bytes in each row by a certain offset shown in Figure 3. For AES, the first row is left unchanged. Each byte of the second row is shifted one to the left. Similarly, the third and fourth rows are shifted by offsets of two and three respectively.

In the MixColumns step, the four bytes of each column of the state are combined using an invertible linear transformation. The MixColumns function takes four bytes as input and outputs four bytes, where each input byte affects all four output bytes. Together with ShiftRows, MixColumns provides diffusion in the cipher. In Figure 4, each column is treated as a polynomial over GF (2⁸) and is then multiplied modulo x⁴ + 1 with a fixed polynomial c(x) = 03x³ + 02x² + 01x + 01.

In the AddRoundKey step shown as Figure 5, the subkey is combined with the state. For each round, a subkey is derived from the main key using Rijndael's key schedule; each subkey is the same size as the state. The subkey is added by combining each byte of the state with the corresponding byte of the subkey using bitwise XOR.

The key expansion algorithm, the 128-bit key is taken as a square matrix of bytes. The AES key encryption algorithm takes a 4-word key as input and gives a liner array of n_b(n_r + 1) words. The n_b is 4 (word key) and n_r is the number of rounds where n_r is 11 for AES-128, the key of which is then expanded into array of 44 key scheduled words asw[i] where 0 ≤ i ≤ n_b(n_r + 1). Initially the 4 word key is copied into the first four words of the expanded key. Then the remainder of the expanded key is filled in four words at a time. Each word is obtained by XORing the values of immediately preceding word and the word four positions back. In case of the position which is a multiple of 4, function Rot-word and function Subword are used, where the Rot-word performs a one-byte circular left shift on a word, and Sub-word is used to have a byte substitution on each byte of its input word using the S-box. The above two sub functions' results are XORed with a round constant. Round constant as Rcon[j], where 0 ≤ j ≤ 9, is a word in which three rightmost bytes are 0 so that the effect of an XOR with Round constant is performed on only the leftmost byte of the word. There is an example of the key expansion algorithm of AES-128 shown in Figure 6.

AES-Rijndael with 128/192/256 bit keys and 16 byte data treats data in 4 groups of 4 bytes, operating an entire block in every round. At that time, AES are considered not suitable for visual data such as digital image because of long computation process. Recent advances in hardware capability and improvement in software have led to achieve the optimal execution rate when we can find the size of input state by implementing our SEA algorithm system. The result shows that the size of input state among 20 × 20 to 30 × 30 can get the least execution time. In this paper, we proposed a novel encryption algorithm called SEA which is selective and improves the AES algorithm. The Architecture of SEA is shown in Figure 7. The Architecture allows one to perform core idea of our algorithm is a optional manner implemented by Selector component given in Figure 7. Since the current trend of medical image transmission over the network is more and more increasing. The digital visual data have some different types, like video, audio, Image, text file, and so on. As we known, many kinds of platforms from many kinds of devices are over the wire/wireless network. Therefore the selector component performs the selector function, where compression of the raw image or plain text noted as Cyn, the size of input state noted as InpS, the size of key noted as KeS and the number of round noted as Rn are optional and can be decided.

Recall that the resistance of AES-based encryption against cryptanalysis attacks depends entirely on the Rn used. The compression component using Huffman coding is proposed in our algorithm so as to reduce the Rn entirely used as well as keeping less implementation time. In the same breath, using compressed data as input state improves the resistance of AES against breaking attacks. The Huffman compressor component is shown in our algorithm architecture. The state-rotation function, a linear function lets input state do negative rotation by 90 degrees can be optional to add in our algorithm. Since many double circulation codes exist in the raw AES algorithm, it costs much time during it's implementation state. Therefore, our proposed algorithm performs unrolling and merging methods replacing the double circulation codes to keep its least implementation time, shown in Tables 1-3 [10].