International Association
for Cryptologic Research

Enlightened by the IDEA block cipher, the authors put forward the REESSE3+ block cipher (a symmetric key cryptosystem) based on three group arithmetics: addition modulo 2 (bit XOR), addition modulo 2 ^ 16, and multiplication modulo 2 ^ 16 + 1. Different from IDEA, REESSE3+ uses 128-bit block inputs, a 256-bit key, and a renovative round function. The authors describe the REESSE3+ cipher algorithm in the graph, and expound the encryption subkeys, encryption operation, decryption subkeys, and decryption operation. Further, demonstrate the correctness of the REESSE3+ cipher algorithm, and analyze the security of REESSE3+ from three aspects. The measures for assuring the security of REESSE3+ cover those for assuring the security of IDEA, and thus, the ability of REESSE3+ in resisting differential analysis is at least equivalent to that of IDEA.