▁substitution ▁al ph ab ets ▁that ▁frequency ▁counting ▁and ▁statistical ▁attacks ▁would ▁be ▁effectively ▁impossible . ▁En igma , ▁and ▁the ▁rot or ▁machines ▁generally , ▁were ▁just ▁what ▁was ▁needed ▁since ▁they ▁were ▁seriously ▁pol yal ph ab etic , ▁using ▁a ▁different ▁substitution ▁alphabet ▁for ▁each ▁letter ▁of ▁plain text , ▁and ▁automatic , ▁requiring ▁no ▁extraordinary ▁ab ilities ▁from ▁their ▁users . ▁Their ▁messages ▁were , ▁generally , ▁much ▁harder ▁to ▁break ▁than ▁any ▁previous ▁ci ph ers . ▁ ▁Mechan ization ▁It ▁is ▁straightforward ▁to ▁create ▁a ▁machine ▁for ▁performing ▁simple ▁substitution . ▁In ▁an ▁elect rical ▁system ▁with ▁ 2 6 ▁switch es ▁attached ▁to ▁ 2 6 ▁light ▁bul bs , ▁any ▁one ▁of ▁the ▁switch es ▁will ▁ill uminate ▁one ▁of ▁the ▁bul bs . ▁If ▁each ▁switch ▁is ▁operated ▁by ▁a ▁key ▁on ▁a ▁type writer , ▁and ▁the ▁bul bs ▁are ▁label led ▁with ▁letters , ▁then ▁such ▁a ▁system ▁can ▁be ▁used ▁for ▁encryption ▁by ▁choosing ▁the ▁w iring ▁between ▁the ▁keys ▁and ▁the ▁bul b : ▁for ▁example , ▁typing ▁the ▁letter ▁A ▁would ▁make ▁the ▁bul b ▁label led ▁Q ▁light ▁up . ▁However , ▁the ▁w iring ▁is ▁fixed , ▁providing ▁little ▁security . ▁ ▁Rot or ▁machines ▁change ▁the ▁inter connect ing ▁w iring ▁with ▁each ▁key ▁stroke . ▁The ▁w iring ▁is ▁placed ▁inside ▁a ▁rot or , ▁and ▁then ▁rot ated ▁with ▁a ▁g ear ▁every ▁time ▁a ▁letter ▁is ▁pressed . ▁ ▁So ▁while ▁pressing ▁A