Declassified Cold War code-breaking manual has lessons for solving ‘impossible’ puzzles
Richard Bean does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
The United States National Security Agency — the country’s premier signals intelligence organisation — recently declassified a Cold War-era document about code-breaking.
The 1977 book, written by cryptologist Lambros Callimahos, is the last in a trilogy called Military Cryptanalytics. It’s significant in the history of cryptography, as it explains how to break all types of codes, including military codes, or puzzles — which are created solely for the purpose of a challenge.
The first two parts of the trilogy were published publicly in the 1980s and covered solving well-known types of classical cipher.
But 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.
