This chapter is about a handful of people who made a business out of cryptography in the mid 1900s.
Three people stand out:
Gilbert S. Vernam > First to invent the the one time pad (1917). I say “first”, because at about the same time, some German lads also came up with the same technique. The one-time pad is notable because, if used properly, it is the only cipher to offer perfect security from cryptanalysis. The unfortunate downside is that using it is cumbersome. Your keys need to be (a) used at most once (b) be of the same length as the message you are transmitting and (c) distributed through some other means to anyone who is to read your encrypted messages.
Lester S. Hill > Applied algebraic techniques to allow for usable poly-graphic substitution (1929). If you squint, poly-graphic substitution looks a lot like modern block ciphers. Additionally his techniques brought mathematics closer to cryptography, just as Friedman had done with statistics.
Edward Hugh Hebern > Inventor of the first cipher rotor machine. Also owner of the first cipher machine company, Herbern Electric Code (started 1921), which did not do too well
Arthur Scherbius > Enigma (sometime in the 1920s?).
Boris Hagelin > Gained control of a failing Swedish cipher device company and turned its fate around, making him the first man to become a millionaire from cryptology. In 1948, he moved the company to Switzerland and incorporated it as Crypto Aktiengesellschaft, or CryptoAG as it is known today. Sometime between then and now, the company became jointly owned by the CIA and the BND. During this time, it manufactured compromised machines so that the US and Germany could snoop on enemy and ally communications. This was not discovered until much later and is an eye-opening story about the level secrecy that intelligence agencies maintain.