Intelligence Directive (NSCID) 9 on October 24, 1952, [ 10 ] and officially came into existence on November 4, 1952. President Truman's letter was itself classified and remained unknown to the public for more than a generation[ vague ]. Riverbank produced book on Bacon cipher http://books.google.com/books?id=dPwsAAAAYAAJ&printsec=frontcover&dq=riverbank+laboratories&source=bl&ots=0DnT5fZGfh&sig=C1QFk4f3hJ5_-Qw7ADgRQSnxsQE&hl=en&ei=NQu4TLGQGJG-sAP1zYGWDw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CB0Q6AEwAjgK#v=onepage&q&f=false TOP CODEBREAKERS William Frederick Friedman