On the security of inclusion or omission of MixColumns in AES cipher

The Rijndael cipher or Advanced Encryption Standard (AES) is the most widely used block cipher these days. It is composed of a number of rounds of transformations. The transformations in each round are similar except for the last round where a linear mixing operation (called MixColumns) is omitted. Since its acceptance in 1999, the designers of the cipher had advocated, and it was widely believed, that the omission of the last round MixColumns has no security implications, and is left out for optimization reasons. However, in mid 2010, it was claimed that such an omission operation may have security implications as it may reduce the time complexity of the majority of attacks targeted against AES. This paper investigates both claims and evaluates the security of the AES when including and omitting the MixColumns operation in AES. The paper also studies the performance overhead when including the MixColumns operation.