RC2 uses "key-expansion algorithm" by which an expanded key consisting of 64 (16-bit words) is produces depending in a complicated way on every bit of the supplied ""variable-length"" input key. A mixing round consists of four applications of the ""mix-up"" transformation, as shown in the diagram. A round is ""mashed"" by adding to it one of the 16-bit words of the expanded key (RFC 2268).