Abstract: It is known that the implementation of AES is asymmetrical, so it will cost more time and space resource. Based on the affine transformation and the MixColumn,an improved AES is presented to reduce the implementation cost. The whole architecture of Rijndael encryption and decryption is symmetrical except for the arranging sequence of the key. When calculating MixColumn or InvMixColumn, only 2 times Xtime multiplication and 4 times addition operation are needed. It slso has the advantage that the encryption and decryption can share the same logic implementation resource, which decreases the implementation cost.

Key words: AES, Rijndael, Sbox