▁ 5 1 2 ▁bits ; ▁block ▁ci ph ers ▁typically ▁have ▁much ▁smaller ▁keys , ▁rarely ▁exceed ing ▁ 2 5 6 ▁bits . ▁Most ▁of ▁the ▁key ▁material ▁is ▁used ▁to ▁construct ▁the ▁ci pher ' s ▁S - box es . ▁Because ▁the ▁key - setup ▁time ▁is ▁quite ▁time ▁cons uming , ▁Kh uf u ▁is ▁not ▁well ▁su ited ▁to ▁situations ▁in ▁which ▁many ▁small ▁messages ▁are ▁handled . ▁It ▁is ▁better ▁su ited ▁to ▁bulk ▁encryption ▁of ▁large ▁amounts ▁of ▁data . ▁ ▁Kh uf u ▁is ▁a ▁Fe ist el ▁ci pher ▁with ▁ 1 6 ▁r ounds ▁by ▁default ▁( other ▁multi ples ▁of ▁eight ▁between ▁ 8 ▁and ▁ 6 4 ▁are ▁allowed ). ▁Each ▁set ▁of ▁eight ▁r ounds ▁is ▁term ed ▁an ▁oct et ; ▁a ▁different ▁S - box ▁is ▁used ▁in ▁each ▁oct et . ▁In ▁a ▁round , ▁the ▁least ▁significant ▁byte ▁of ▁half ▁of ▁the ▁block ▁is ▁passed ▁into ▁the ▁ 8 × 3 2 - bit ▁S - box . ▁The ▁S - box ▁output ▁is ▁then ▁combined ▁( using ▁X OR ) ▁with ▁the ▁other ▁ 3 2 - bit ▁half . ▁The ▁left ▁half ▁is ▁rot ated ▁to ▁bring ▁a ▁new ▁byte ▁into ▁position , ▁and ▁the ▁hal ves ▁are ▁sw apped . ▁At ▁the ▁start ▁and ▁end ▁of ▁the ▁algorithm , ▁extra ▁key ▁material ▁is ▁X OR ed ▁with ▁the ▁block ▁( key ▁wh iten ing ). ▁Other ▁than ▁this , ▁all ▁the ▁key