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So for exampe the letter “A” might be moved two places and become the letter “C”, similarly the letter “H” would become “J”, and the letters at the end looping back around so “Y” would become “A”. Under this change “HELLO ALICE” becomes “JGNNQ CNKEG”. The problem with this sort of ancient approach is that if you do this sort of encryption long enough it becomes obvious by what number you're moving all the letters forward in the alphabet.