▁first ▁ 3 2 ▁bits ▁of ▁these ▁two ▁sequences ▁to ▁match . ▁ ▁Thus ▁we ▁may ▁recover ▁the ▁key ▁for ▁L FS R - 3 ▁independently ▁of ▁the ▁keys ▁of ▁L FS R - 1 ▁and ▁L FS R - 2 . ▁ ▁At ▁this ▁stage ▁we ▁have ▁reduced ▁the ▁problem ▁of ▁br ute ▁forcing ▁a ▁system ▁of ▁ 3 ▁L FS R s ▁to ▁the ▁problem ▁of ▁br ute ▁forcing ▁a ▁single ▁L FS R ▁and ▁then ▁a ▁system ▁of ▁ 2 ▁L FS R s . ▁ ▁The ▁amount ▁of ▁effort ▁saved ▁here ▁depends ▁on ▁the ▁length ▁of ▁the ▁L FS R s . ▁ ▁For ▁real istic ▁values , ▁it ▁is ▁a ▁very ▁substantial ▁saving ▁and ▁can ▁make ▁br ute ▁force ▁attacks ▁very ▁practical . ▁ ▁We ▁do ▁not ▁need ▁to ▁stop ▁here . ▁ ▁Ob serve ▁in ▁the ▁table ▁above ▁that ▁ ▁also ▁agre es ▁with ▁the ▁generator ▁output ▁ 6 ▁times ▁out ▁of ▁ 8 , ▁again ▁a ▁correlation ▁of ▁ 7 5 % ▁correlation ▁between ▁ ▁and ▁the ▁generator ▁output . ▁▁ ▁We ▁may ▁begin ▁a ▁br ute ▁force ▁attack ▁against ▁L FS R - 2 ▁independently ▁of ▁the ▁keys ▁of ▁L FS R - 1 ▁and ▁L FS R - 3 , ▁leaving ▁only ▁L FS R - 1 ▁un bro ken . ▁ ▁Thus , ▁we ▁are ▁able ▁to ▁break ▁the ▁Ge ffe ▁generator ▁with ▁as ▁much ▁effort ▁as ▁required ▁to ▁br ute ▁force ▁ 3 ▁entirely ▁independent ▁L FS R s , ▁meaning ▁that