Fraunhofer Institute for Integrated Circuits IIS
Fraunhofer Institute for Integrated Circuits IIS

SG-41 cipher machine

© Fraunhofer IIS
The SG-41 cipher machine was badly corroded from being stored underground in the woods for decades. It was probably deliberately hidden there so that it could be dug back up after the end of World War II.

Date

1943

Origin

Manufacturer:Wanderer-Werke AG (Integrated Authority File (GND)), Chemnitz
Designer:Fritz Menzer

Inventory no.

2017–803

Client

Deutsches Museum

Technology

3D-CT

System

High-energy CT

Technical challenge

Detecting different materials with different absorption characteristics, from paper to iron

Task

Investigating the condition and internal structure of the cipher mechanism

The SG-41 cipher machine is regarded as the successor of the German military Enigma decoding machines. Thanks to an improved, irregular encryption algorithm, it had significantly more encryption combinations compared to the Enigmas.
By the end of the war, however, only very few of these machines had been manufactured, which is why there are only a handful that have survived to this day.

The SG-41 from the collection of the Deutsches Museum was discovered by an amateur treasure hunter in the forest near Ayin in 2017. Researchers at Fraunhofer EZRT used XXL CT to gain insights into the machine’s inner workings, reconstructing the entire encryption algorithm based on the scan data. 

Röntgenbild einer Chiffriermaschine SG-41, die als Nachfolger der Heeres-Enigma-Dechiffriergeräte gilt.
© Fraunhofer IIS
Das Schlüsselgerät SG-41 gilt als Nachfolger der Heeres-Enigma-Dechiffriergeräte.

The 3D CT technology revealed the cipher machine’s best kept secret: its internal mechanism. The Museum is using the visualizations to make the exhibit as accessible and engaging as possible, providing visitors with a tangible insight into the machine’s inner workings.

“3D-Cipher” research project

© Fraunhofer IIS

The digitalization of the SG-41 cipher machine is part of the larger “3D-Cipher” project in which approximately 60 cipher devices from the cryptography collection of the Deutsches Museum are being scanned and studied using the latest CT technology at Fraunhofer EZRT. The project results are being made available to the public in the form of open data.

This digitalization makes it possible to explore the encryption technologies hidden inside without opening the machines, which would cause irreparable damage. As a result, researchers are finally unraveling the remaining secrets of the cipher devices’ algorithms.

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