Yardley's book (annotated by his arch rival Friedman no less!) referenced in the NSA document is here:<p><a href="https://archive.org/details/AmericanBlackChamber" rel="nofollow">https://archive.org/details/AmericanBlackChamber</a><p>"The cryptography historian David Kahn called the book "the most famous book on cryptology ever published."