NSA: A history of the U.S. Communications Security e-book
The free e-book consist in a series of lectures given by David G. Boak in 1966. This lecture, while fascinating in many aspects, presents NSA’s approach to different communication security issues, cryptography and even economics.
While many of the pages are redacted, it still has many pages left intact. Obviously, the lectures were given to new employed personnel by Mr Boak. I didn’t had time to completely read it, but I recommend this e-book to anyone.
Read or download the ‘NSA: A history of the U.S. Communications Security’ e-book