Declassified Cold War code-breaking manual on solving 'impossible' puzzles
Maybe I misunderstand something, but the article text says:<p>>  in 1992, the US Justice Department claimed releasing the third book could harm national security by revealing the NSA's "code-breaking prowess". It was finally released in December last year.<p>When we move to the first page of the linked book it says:<p>> This text constitutes the third in the series of six basic texts on the science of cryptanalytics.<p>So there is still book 4, 5 an 6?<p>(im probably on some list just for asking)