Friday, March 24, 2017

The Abwehr’s Enigma G cipher machine and Procedure 63

The Cryptologia article Mr. Twinn’s bombes is available from the Taylor and Francis website and it has some very interesting information on the Enigma G cipher machine, used in WWII by the German military intelligence service Abwehr.

The Enigma G was different from the version used by the German military since it did not have a plugboard. Also its stepping was more frequent due to the many notches in the rotors.

According to the article it was used by the following Abwehr networks:

1). Berlin, Madrid, Lisbon, Paris, Bordeaux

2). Berlin, Vienna, Budapest, Bucharest, Sofia, Salonika

3). Berlin, Vienna

4). Berlin with stations in Turkey

The device was issued with 3 rotors only (while the military version used 3 rotors from a set of 5). In some networks the rotors were rewired during the war.

Several indicator systems were used in the period 1941-44. Up to August 1942 the message key was enciphered twice on the Grundstellung (basic setting). The 8 letter sequence was the indicator at the start of the message. This was the same procedure used up to 1938 by the German Army and Airforce.

From August 1942 the double encipherment of the message key was dropped and instead it was enciphered on the Grundstellung only once.

In the period late 1943-early 1944 a new indicator procedure was introduced. This was part of new security regulations called Procedure 63 - ‘Verfahren 63’. The new system used two basic settings. One for the network and one for the station. The cipher clerk first enciphered the message key twice on the network’s basic setting and then enciphered the 8 letters again at the station’s basic setting.

It is interesting to note that an OKW/Chi report dated August 1944 says that Procedure 63 was not secure:

D) Agentenverkehr

Die Vorschrift Nr.63 genügt nur dann zeitgemässen Sicherheitsansprüchen, wenn auf jeder Linie nur wenig Verkehr auftritt. Es soll versucht werden eine bessere Vorschrift auszuarbeiten.

Es wird dafür gesorgt werden, dass alle anderen mit Enigma-Maschinen arbeitenden Behörden usw. nur die vom Ausschuss geprüften und zugelassenen Vorschriften benutzen.

Google translation:

D) Agent traffic

Regulation No.63 only meets current safety requirements if only little traffic occurs on each line. A better regulation is to be worked out.

It is necessary to ensure that all other authorities working with Enigma machines, etc., use only the regulations audited and approved by the Committee.


  1. If the abwehr enigma had been given a set of 5 rotors (instead of 3), AND had used a plugboard, would it have been categorically superior to other enigma models? The extra notches and more frequent stepping seems to be a big advantage. Would the allys have been able to crack it at all?

    Come to think of it, what operational mistakes by the abwehr led to their enigma model being broken at all?

    1. I’m not an expert but it seems that the use of a plugboard together with the irregular stepping system of the Enigma G would have been very hard to solve, at least with WWII technology.

      From the article it seems that the biggest mistake was enciphering the message key twice on the basic setting. This procedure was used by the German Army till May 1940 (double indicators, not on a basic setting though) and it allowed the British codebreakers to solve Enigma traffic.

      The basis of the solution is that the 1st and 5th, 2nd and 6th 3rd and 7th, 4th and 8th letters of the indicator represent the same initial letters (the example is for the Enigma G when the indicator had 8 letters).

      Also having a basic setting (grundstellung) was a mistake (shared by the German Navy!).