Improving Diffusion Power of AES Rijndael with 8x8 MDS Matrix

AES Rijndael is a block cipher developed by NIST as the Advanced Encryption Standard (AES) replacing DES and published as FIPS 197 in November 2001 [5] to address the threatened key size of Data Encryption Standard (DES). AES-Rijndael was developed by Joan Daemen and Vincent Rijmen, Rijndael [4, 5] and was selected from five finalists. Advancement in computation speed every day puts lots of pressure on AES and AES may not with stand attack for longer time. This work focuses on improving security of an encryption algorithm, beyond AES. Though there are various techniques available to enhance the security, an attempt is made to improve the diffusion strength of an algorithm. For enhancing the diffusion power AES Rijndael in MixColumn operation the branch number of MDS matrix is raised from 5 to 9 using a new 8X8 MDS matrix with trade off of speed [8, 9] and implemented on R8C microcontroller. Keywordsdiffusion, MDS matrix, AES Rijndael, security