For the NSA, which secretly controlled Crypto AG, this was an appalling prospect. The C52 was meant to keep its customers’ secrets secure from each other, not from the United States and its intelligence allies. “Foreign governments were paying good money to the U.S. and West Germany,” an internal CIA history recorded, “for the privilege of having their most secret communications read by at least two (and possibly as many as five or six) foreign countries.” The engineer’s son, also named Boris Hagelin, was now proposing shutting down the old production line and switching to making the more secure C52Y...