Hans-Thilo Schmidt (13 May 1888 – 19 September 1943) codenamed Asché or Source D, was a German spy who sold secrets about the Enigma machine to the French during World War II. 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. He was the younger brother of Wehrmacht general Rudolf Schmidt.
Selling Enigma secrets
thumb|left|, born Rudolf Stallmann (1871–1946), served as his French point of contact as "Rex".
A former officer, Schmidt had been forced to leave the army having suffered from gas during the First World War. His brother, Rudolf Schmidt, secured him a civilian post at the German Armed Forces' cryptographic headquarters, the Cipher Office.