Karl Stein received his doctorate with his dissertation on the topic Zur Theorie der Funktionen mehrerer komplexer Veränderlichen; Die Regularitätshüllen niederdimensionaler Mannigfaltigkeiten at the University of Münster under the supervision of Heinrich Behnke in 1937. Karl Stein was conscripted into the Wehrmacht sometime before 1942, and trained as a cryptographer to work at OKW/Chi, the Cipher Department of the High Command of the Wehrmacht. He was assigned to manage the OKW/Chi IV, Subsection a, which was a unit responsible for security of own processes, cipher devices testing, and invention of new cipher devices. He managed a staff of 11[1] In 1955 he became professor at the Ludwig Maximilian University of Munich and emeritated in 1981. In 1990 he received the first Cantor medal.[2]