Loiss: A Byte-Oriented Stream Cipher

This paper presents a byte-oriented stream cipher – Loiss, which takes a 128-bit initial key and a 128-bit initial vector as inputs, and outputs a keystream in bytes. The algorithm is based on a linear feedback shift register, and uses a structure called BOMM in the filter generator, which has good property on resisting algebraic attacks, linear distinguishing attacks and fast correlation attacks. In order for the BOMM to be balanced, the S-boxes in the BOMM must be orthomorphic permutations. To further improve the capability in resisting against those attacks, the S-boxes in the BOMM must also possess some good cryptographic properties, for example, high algebraic immunity, high nonlinearity, and so on. However current researches on orthomorphic permutations pay little attention on their cryptographic properties, and we believe that the proposal of Loiss will enrich the application of orthomorphic permutations in cryptography, and also motivate the research on a variety of cryptographic properties of orthomorphic permutations.