1. An apparatus for encrypting block data comprising: encrypting sections connected in series, each of the encrypting sections comprising: a first unit configured to randomize first subblock data which are obtained by dividing the block data; and a second unit configured to diffuse data output from the first unit with respect to a range which is wider than a range of the first subblock data and supply a result of diffusion to a first unit in a succeeding encrypting section, at least one bit of data input to the first unit in own encrypting section being transmitted to at least one bit of data input to the first unit in the succeeding encrypting section via at least two routes.