.; ▁the ▁letter ▁directly ▁to ▁the ▁far ▁left , ▁in ▁the ▁header ▁column , ▁is ▁the ▁corresponding ▁dec rypted ▁plain text ▁letter . ▁Assuming ▁a ▁standard ▁shift ▁of ▁ 1 ▁with ▁no ▁key ▁used , ▁the ▁encrypted ▁text ▁H F N OS ▁would ▁be ▁dec rypted ▁to ▁HE LL O ▁( H -> H , ▁F -> E , ▁N -> L , ▁O -> L , ▁S -> O ▁). ▁So , ▁for ▁example , ▁to ▁dec rypt ▁the ▁second ▁letter ▁of ▁this ▁text , ▁first ▁find ▁the ▁F ▁within ▁the ▁second ▁interior ▁column , ▁then ▁move ▁directly ▁to ▁the ▁left , ▁all ▁the ▁way ▁to ▁the ▁left most ▁header ▁column , ▁to ▁find ▁the ▁corresponding ▁plain text ▁letter : ▁E . ▁ ▁Data ▁is ▁encrypted ▁in ▁the ▁opposite ▁fashion , ▁by ▁first ▁loc ating ▁each ▁plain text ▁letter ▁of ▁the ▁message ▁in ▁the ▁left most ▁header ▁column ▁of ▁the ▁tab ula ▁rect a , ▁and ▁mapping ▁it ▁to ▁the ▁appropriate ▁corresponding ▁letter ▁in ▁the ▁interior ▁columns . ▁For ▁example , ▁the ▁first ▁letter ▁of ▁the ▁message ▁is ▁found ▁within ▁the ▁left ▁header ▁column , ▁and ▁then ▁mapped ▁to ▁the ▁letter ▁directly ▁across ▁in ▁the ▁column ▁head ed ▁by ▁" A ". ▁The ▁next ▁letter ▁is ▁then ▁mapped ▁to ▁the ▁corresponding ▁letter ▁in ▁the ▁column ▁head ed ▁by ▁" B ", ▁and ▁this ▁continues ▁until ▁the ▁entire ▁message ▁is ▁encrypted . ▁If ▁the ▁Tr ith em ius ▁ci pher ▁is ▁thought ▁of ▁as ▁having ▁the ▁key ▁ABC DEF G HI J K