Cryptologist [Lambros Callimahos] was a victim of his own success. He wrote a trilogy of books called Military Cryptanalytics covering code breaking in 1977. The first two volumes were eventually published, but the NSA blocked the public release of the third volume back in 1992. But last December, it finally saw the light of day.
Of course, some parts of the book are redacted, including parts of the table of contents. That’s pretty bad when even your chapter headings can be classified. [Richard Bean] over on Phys.org has some notes about the book along with some examples of hard-to-solve crypto puzzles.
One key part of the book, apparently, is cryptodiagnosis which is the approach to solving a message encrypted using an unknown method. In other words, while it is hard to break, say, an Enigma message, just knowing it is an Enigma message is a pretty big hint. If you get some random encoded message, where do you start? The answer is in the book.
We always think it is interesting that looking at what’s in a book that has been released can give you clues about what is still secret, just like smoke might show an invisible being by highlighting where they are not. However, we imagine the intelligence community has the same thought and throws some red herrings in just to confuse us.