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There are several modified in AES to improve speed the performance, increase the security and addition same complexity on algorithm steps. (Mohammad, et al., 2015) The reason development is appeared many different the implementation on software and hardware. Each implementation has need to modified AES according to the specific proposes.
In (Xu, et al., 2013) a modified AES by used longer key length and data matrix. That extended the data matrix to eight row and variable number of column (6, 8, 12 and 16) the input data block (48, 64, 96 and 128), and extended the key length to (384,512, 768 and 1024). This paper not change the first and fourth stages (substitution byte, Add Round Key), third stage shift row change from shift third row to seventh row shifted left and four stages (mix column) change the static matrix 3x3 to new matrix 8x8, should be calculate inverse static matrix used in Mix column on GF (28). This modification is increase robustness and use a few times for encryption and decryption processing.
In (Kaur, et al., 2014) modified the AES algorithm by reduce the calculation, computation overhead, and reduce the time encryption process. It replaces the mix column stage in AES algorithm into permutation stage (like the permutation table (IP) that used in DES algorithm) because the mix column is take large calculation time and that makes the encryption process are slow. The other stages in AES algorithm don’t change.
Finally, modification used simple S-box for encryption and decryption to reduce the computation amount, the new S-box has some properties, simple generation and same S-box used for encryption and decryption (Rashidi, 2014).