At the midpoint of World War II, Field Marshall Erwin Rommel was on the verge of conquering the Middle East. Working in total secrecy, Allied codebreakers invented ways to crack the Germans' seemingly impregnable codes and provided the intelligence that led to the first great defeat of the Nazis - the turning point in the war. Gershom Gorenberg tells how they did it, and lays out lasting lessons for today's tech world.