abstract:Hans-Thilo Schmidt (13 May 1888 – 1943) codenamed Asché or Source D, was a spy who, during the 1930s, sold secrets about the Germans' Enigma machine to the French. The materials he provided facilitated Polish mathematician Marian Rejewski's reconstruction of the wiring in the Enigma's rotors and reflector; thereafter the Poles were able to read a large proportion of Enigma-enciphered traffic.