Kahn's is a quite interesting and entertaining book. Among other tales about Yardley and his admirable battles with the USG, Kahn tells how through hilarious Gonzales-grade legal shenanigans the only time a US law has been by enacted against revealing cryptological information, in 1933, to prevent Yardley from publishing a book, and the one-man-law it is still in effect. Chapter 15 A Law Aimed at Yardley, pp. 158-72: The law: An Act For the Protection of Government records Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That whoever, by virtue of his employment by the United States, shall obtain from another or shall have custody of or acess to, or shall have had custody of or access to, any official diplomatic code or any matter prepared in such code, or which purports to have been prepared in any such code, and shall willfully, without authorization or competent authority, publish or furnish to another any such code or matter, or any matter which was obtained while in the process of transmission between any foreign government and its diplomatic mission in the United States, shall be fined not more than $10,000 or imprisoned not more than ten years, or both. Approved June 10, 1933 Franklin D. Roosevelt See: USC Title 18 Section 952 http://assembler.law.cornell.edu/uscode/html/uscode18/usc_sec_18_00000952-- --000-.html Note the orignal $10,000 amount for the fine has been removed.