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.
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?
ReplyDeleteCome to think of it, what operational mistakes by the abwehr led to their enigma model being broken at all?
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.
DeleteFrom 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!).
Upon further reading, it seems that the abwehr was making even bigger mistakes with enigma. Wikipedia has this to say on the matter:
ReplyDelete“The spies that it placed in enemy countries used a lower level cipher (which was broken by Oliver Strachey's section at Bletchley Park) for their transmissions. However, the messages were often then re-transmitted word-for-word on the Abwehr's internal Enigma networks, which gave the best possible crib for deciphering that day's indicator setting.”