We proposed a new block cipher, Serpent, as a candidate for the Advanced Encryption Standard. This algorithm uses a new structure that simultaneously allows a more rapid avalanche, a more efficient bitslice implementation, and an easy analysis that enables us to demonstrate its security against all known types of attack. Although designed primarily for efficient implementation on Intel Pentium/MMX platforms, it is also suited for implementation on smartcards and other 8-bit processors. In this note we describe why. We also describe why many other candidates are not suitable.