Twofish's distinctive features are the use of pre-computed key-dependent S-boxes, and a relatively complex key schedule.

Other AES contest entrants included Stefan Lucks, Tadayoshi Kohno, and Mike Stay.

It was designed to allow for several layers of performance trade offs, depending on the importance of encryption speed, memory usage, hardware gate count, key setup and other parameters.

In 1999, Niels Ferguson published an impossible differential attack that breaks 6 rounds out of 16 of the 256-bit key version using 2256 steps.

[6] Bruce Schneier responded in a 2005 blog entry that this paper did not present a full cryptanalytic attack, but only some hypothesized differential characteristics: "But even from a theoretical perspective, Twofish isn't even remotely broken.