A new 256-bits block cipher 舑 Twofish256

Twofish, proposed by Bruce Schneier et al., is a 128-bit block cipher that is constructed with Feistel Network. The cipher, one of the final candidate of AES, has a variable key length of 128, 192, and 256 bits. In this research, Twofish is expanded to a 256-bit block encryption algorithm. Besides maintaining the basic framework of Twofish, the number of rounds is reduced to 10 and improve the framework of F-function to a higher safety level. The new structure enables the 4 mutually-independent S-boxes in g-function to interact one another, and substantially raise complexity for the purpose of heightening avalanche effect. After the operations of S-box and maximum distance separable (MDS) operations, new byte-transformation is activated to elevate diffusion effect. The truncated differential probability of Twofish256 after 10 rounds is around 2^-81.2758, whose security is much higher than that of the Twofish on 16 rounds computed by S. Moriai.