Patent ID: 7280657

Claim:
A method of enciphering left and right input data blocks producing left and right output data blocks comprising: performing ( 214 ) a select function and a permuter function (PF) on a cipher round input data block ( 211 ) to produce a first interim data block; combining ( 216 ) the first interim data block with the left input data block to produce the right output data block; performing ( 220 ) a permuter function (Ef) on the left input data block to produce a second interim data block; combining ( 222 ) the second interim data block with a key from a key schedule to produce a third interim data block; performing ( 218 ) the permuter function (Ef) on the first interim data block to produce a fourth interim data block; and combining ( 224 ) the fourth interim data block with the third interim data block to produce a cipher round output data block ( 230 ), wherein the right input data block is set to be the left output data block, and the left output data block, right output data block and cipher round output data block correspond, respectively, with the left input data block, right input data block and cipher round input data block for use in subsequent rounds of ciphering.