Networks (keys)

Keys:

Introduction

The German military forces before and during World War II consisted mainly, as in all other countries, of the army, air force and navy. Other small entities also existed: the police, the Gestapo, the SD, the management of travel by rail, ...

Obviously the components of these entities (small or large) needed to communicate securely. When land telegraph lines could not be used, the use of the radio was compulsory. In this case, encryption was also required. The most common means of encryption (especially at the start of the war) was the Enigma.

An Enigma network is therefore made up of different transmission centers which exchange messages. Each of these centers is associated with military entities. For example in the case of the Army, every army, every army corps, every division had a transmission center.

To improve security, each Enigma network used a specific configuration different from other networks. This setting (the key) was composed of the order of the rotors (Walzenlage), the position of the ring which allowed the advancement of the rotor located on the left (Ringstellung), the position of the steckers (Steckerverbindung) and finally the initial position of the rotors. This last setting (the position of the rotors) being specific for each message (Spruchschlüssel). Its value is transmitted to the correspondent according to specific network conventions. On the other hand, the Walzenlage, the Ringstellung and the Steckerverbindung. were identical for all members of the same network and were valid for a limited period of time, usually one day (daily key). All of the one-month settings were recorded on a key table (Schlüsseltafel) transmitted from hand to hand to each member of the network before the start of its validity period.

At the start of the war, there were basically three networks : army, air force and navy. But as new theaters of war and specialized units emerged, other networks appeared. The use of different keys is supposed to improve security. For example, at the start of the war the Air Force consisted of only two networks (one operational, the other for practice). By the end of the war, the Air Force consisted of around 40 networks. As the war progressed, certain keys would appear and then disappear. Thus in April 1940, the key associated with the Norwegian campaign appeared. This campaign ended in May 1940 and the associated key logically disappeared.

The British called an Enigma network a key. By January 1940, they were able to decipher part of the traffic of the various existing networks. It was the CG&CS, which was responsible at Bletchley Park (BP) to carry out these decipherments. Hut 6 took cares of army and air force keys, Hut 8 took cares of navy keys. Since a key was usually only valid for one day, English cryptologists had to renew their exploits every day for each network they mastered (and continuing to try to break new networks). During the war about a hundred air force networks were broken and at least as many for the army by Hut 6. On the other hand, the Hut 8 broke about twenty keys.

Keys that existed before the war

From 1932, the Poles began to read the messages of the German military forces encrypted with the Enigma. Several Enigma networks are identified and deciphered by Polish:

The Army Network (Heer). This is the main network.
The police network, from 1933.
The SD network (Sicherheitsdienst), from 1933 too.
The Air Force [Luftwaffe] network from 1935.
The network of the navy [Kriegsmarine] until 1937. Then this network changes procedure and becomes illegible.
The TGD network (of the Gestapo) is identified, but it was never deciphered.

The colors (keys deciphered by the British at the start of the war)

The start of the war, the red, green and blue keys

Just before the start of the war (in July 1939), the Poles transmitted their methods to the French and the British. The British started manufacturing Zygalski sheets for the five rotors in use.

Indeed, Zygalski sheets were the main method used by the Poles until the end of 1938 to decipher Enigma messages (based on the indicator method which ciphered twice the message key). Unfortunately the addition of 2 rotors (in all use of three rotors out of five) in December 1939 put an end to the Polish decipherments (except those associated with the SD network).

While the sheets were being made under Dilly Knox's control, Gordon Welchman was responsible for identifying the Enigma networks. He discerns three that he identifies with a color: Red, Green and Blue. This identification is based as much on Radio elements (frequency, D / F, chat) as on element present in the message headers (call signs, kenngruppe). Although several of these elements change every day (calls signs, kenngruppe, radio frequency, ...). Welchman manages to track these three networks every day.

January 1940, the start of deciphering

In January 1940 the Zygalski sheets were completed. The English use one set, the French and the Poles (who joined the French after the fall of Poland) use another. The first decryption takes place and the colors are associated with the various military forces:

Green corresponds to the army.
Red stands for air force (or GAF: German Air Force). It is an operational network.
Blue corresponds to an air force practice network.

The Norwegian campaign, the Yellow network

In April 1940, the Germans invaded Norway. Then the allies land in Norway to counter the Germans: it is the Norwegian campaign. The Germans create a new Enigma network for their expeditionary force (both air force and army). The allies name this network with a new color: Yellow.

The appearance of other networks (and therefore new colors)

Brown (Sept 1940), Special network for navigational beam experiments and operations (IV LN Versuchs Regiment).
Purple (May 1940): not broken
Violet (Dec 1940): general Luftgau network.
Orange (Dec 1940): SS.
Light Blue (Jan 1941): Operational network in Mediterranean area, allocated for North African campaign.
Pink (Feb 1941), the Luftwaffenführungsschlüssel, was the network intented for messages of the highest secrecy sent between the highest GAF commands.
Mustard (Jun 1941): German Y Service.

The naming of keys by the British

At the start of the war, the number of Enigma networks was low. It is possible to use the main colors to identify them, but from mid-1941 this is no longer possible. A nomenclature is set in place for the new networks!

Air force

a. Colors

Some networks keep their old name: Red, Blue, Pink. Later, some networks (Indigo and Puce) are named by a color.

b. Flowers

Flower names are used for Luftgau networks.

c. Vegetables

Vegetable names are used for weather networks as well as for technical networks.

d. Insects

Insect names are used to name Fliegerkorps networks.

e. Mammals

The names of mammals are used to name the Geschader networks.

f. Jungle Animals

The names of wild animals are used for Luftflotte networks. For example the Scorpion, Jaguar networks.

Army

The Hut 6 uses bird names for the Army keys:

Birds of prey are used for the eastern front (Vulture, Kite, Kestrel)
The Barnyards for the western front (Duck, Bantam, Chicken)

Remark: Green is renamed Greenshank. A greenshank is a bird (of the Scolopacidae family).

SS

The Hut 6 uses uses fruit names for SS keys. Remark: the Orange name is a fruit and a color.

Railway

It appears that Hut 6 did not use a cover name for the network used by German railways. It was simply called the Railway key.

Note: The Railway used a Commercial Enigma (without stecker) whose rotors were rewired.

Navy

The nomenclatures given above are used by Hut 6. Hut 8 which manages navy keys, follows its own rules and uses fish names to name the networks it attacks, eg Shark: the U-boat network.