Abstract: “The increasing ubiquity of information technologies in all aspects of human life makes security issues one of the most critical aspects of system design. In this paper we introduce a new symmetric cryptosystem based on IDEA system. The plaintext block is divided into basic sub-blocks each of thirty-two bits in length. The new Proposal can encrypt blocks of plaintext of length 512 bits into blocks of the same length. The key length is 1024 bits. The total number of rounds is 16. It uses modulo addition and thirty-two bits XORING are used followed by modulo multiplication. It uses new efficient MDS (Maximum Distance Separable) matrix which provides optimal diffusion mapping. In this system, we try to have maximum branch number for our new MDS matrix, we also try to get the minimum correlation between plaintext and ciphertext, highly avalanche effect and defeat the frequency analysis and most well-known attacks. The new algorithm is compared with IDEA and gives excellent results from the”

Keywords: IDEA cryptosystem, MDS matrix, Branch number, frequency analysis.