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Fialka rotors
At the heart of each M-125 (Fialka) is a drum with 10 different electromechanical cipher rotors (wheels) that move in an irregular manner when entering a message. Each rotor has 30 contacts at either side and is identified by a letter of the Russian alphabet, as follows:

10 different Fialka rotors, each marked with a letter of the Russian alphabet.

A collection of 10 such unique rotors is called a rotor-set, or just: set. Each rotor is wired differently, and each country of the former Warsaw Pact had its own rotor-set (wired differently for each country). Such a country-specific rotor set is called a series, identified by a number and the letter 'K' (e.g. 3K for Poland). Direct communication between Warsaw Pact nations was strictly prohibited during peacetime and any messages had to be sent via the Russians. Only in the event of war with the West, a common rotor-set (known as the 0K-series) would be released.


Each rotor has 30 electric contacts at either side. The right side of the rotor is called the input, whilst the left side holds the output contacts. The input contacts are connected to the output contacts in a scrambled manner. As there are 30 contacts, each rotor has 30 possible positions. Each position is marked with a letter of the Russian alphabet on the index ring, in this order:

А Б В Г Д Е Ж З И К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ы Ь Ю Я Й

The 10 different rotors are placed on a spindle in the order dicatated by the daily key, similar to the rotors of the German Enigma. A retaining clip is used to keep the rotors locked to the spindle. The spindle is then placed inside the machine, after which the entry disc and the reflector are locked. After setting the rotors to their initial position, the machine is ready for use.

There are two different rotor types: fixed and adjustable. The fixed rotors were introduced with the first Fialka machines in 1956, whilst the adjustable rotors were supplied as an upgrade from 1978 onwards. They are known as the PROTON-2 upgrade. The adjustable rotors are commonly found with the later M-125-3 Fialka models, whilst fixed rotors remained in use with the older M-125 models. Although it is technically possible to use the adjustable rotors on the older M-125 model, no proof has been found so far to indicate that this was actually done.


Fixed rotors
Below are the original rotors that were distributed with the M-125 machines when they were first introduced in 1956. They were also supplied with the first M-125-3 machines when they were released in the mid-1960s. As these rotors are not adjustible, they are called the fixed rotors. The non-metal parts are made of brown bakelite with a fibre-strengthened outer ring with gaps.


Each rotor has 30 disc-shaped contacts at its left side and 30 spring-loaded contact pins on the right side. With each machine, a unique set of 10 different rotors was supplied, marked with 10 letters of the Russian alphabet as described above (Rotor ID). The number is printed at the right side of the disc; in the example below this is the letter 'A'. As the rotors are wired differently for each country, a series identification (Series ID) is also printed at the right side. In the example below this is '3K', which indicates that this rotor was used with the Polish Fialka variant.

Fialka cipher rotors with fixed wiring

Inside the rotor, the 30 contacts at the left are connected to the contacts on the right in some scrambled manner. This wiring can not be changed in the field. At the outer rim of each rotor are a number of metal pins. These pins control the irregular stepping of the rotors and are called the Advance Blocking Pins. Each rotor has a different number of such pins at different locations.


Each machine was supplied with two complete sets of rotors: an operational one and a spare one. The operational set usually resided inside the machine and had black lettering on the index ring. The spare rotors had red lettering and were kept in an metal container inside the dust cover.

The operational wheel set (front) and the spare wheels in an aluminum container
The spare cipher wheels in an aluminum container
The standard cipher wheels (left) and the spare wheels (right)
Standard and spare fixed wheels side-by-side
Two cipher wheels taken off the spindle
Opening the wheel
The inner wiring of a cipher wheel (wiring core)
Close-up of the fixed wiring
A
×
A
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The operational wheel set (front) and the spare wheels in an aluminum container
A
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The spare cipher wheels in an aluminum container
A
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The standard cipher wheels (left) and the spare wheels (right)
A
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Standard and spare fixed wheels side-by-side
A
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Two cipher wheels taken off the spindle
A
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Opening the wheel
A
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The inner wiring of a cipher wheel (wiring core)
A
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Close-up of the fixed wiring

Adjustable rotors   PROTON-2
In 1978 a new operating procedure for the Fialka was introduced, known as PROTON-2. At the same time a new set of cipher rotors was issued. For each individual country, the new PROTON-2 rotors were prepared by the Russians well in advance of the actual release date. They were shipped in carton boxes, such as the one shown here, which was discovered in Czechoslovakia.

The new rotors were much more complex than the earlier ones, and can be adjusted in a number of ways. This greatly increases the maximum number of permutations and, hence, the strength of the cipher, without making any modification to the machine whatsoever. In their basic setting, the adjustable rotors are compatible with the earlier fixed rotors. Although they can theoretically be used in the older M-125, no evidence has been found to indicate that this was actually done in practice. We therefore assume that the adjustable rotors belong to the M-125-3 machines.


The rotors that normally reside inside the machine, have black lettering on the index ring, with one letter in red to identify the rotor (Rotor ID). For example, on rotor 'A' the letter 'A' on the index ring is painted red, as shown in the image below. Inside the dust cover of the machine is a spare set of rotors, stored inside a cylindrical aluminium container. The letters on the spare rotors are all red, except for the letter that identifies the rotor, which is black.

Fialka cipher rotors with removable wire core

On the new adjustable rotors, the letter index ring is now movable, much like the Ring Setting (German: Ringstellung) of the Enigma. The ring is locked in place with the index release notch. Secondly, the wiring core can be now removed (see below) and can be re-inserted in 30 different orientations, plus 30 more if the core is flipped around (side 2 up). Furthermore, the wiring core of a particular rotor can be placed inside any of the other rotors as well.

In order to accomodate the removable wiring core, the thick circular spring-loaded contacts of the fixed rotors have been replaced by very thin U-shaped contacts that are made of spring-wire. On the inside of the rotor, the spring-wire is bended in such a way, that it makes contact with the reverse side of the core. The image on the right shows the interior of an adjustable rotor of which the wiring core has been removed.

These contacts have to be handled with care, as they are easily damaged. Spare springs were usually supplied with each maintenance kit.
  

If the correct core (i.e. the core with the same ID as the rotor) is inserted into the rotor, with side 1 up (i.e. side 1 visible from the left side of the rotor) and the white index line is lined up with the letter A on the index ring, and the index ring is set at the letter A, the rotor is backward compatible with the corresponding fixed rotor. This setting is known as the basic rotor setting.

Original carton box in which the Czech PROTON-2 wheels were distributed
Frontal view of the operational wheel set
Close-up of the operational wheel set
Close-up of an operational wheel
Wheels taken from the spindle
Fixed flat-faced contacts (left side)
Spring-loaded contacts (right side)
Close-up of the spring-loaded contacts of a bakelite adjustable wheel
Aluminium can with spare wheel set
Spare wheel set in aluminium can
Spare wheel set in aluminium can
Spare wheels (front) and operational wheels (rear)
Spare wheel set
Removing a spare wheel from the spindle
Spare wheels taken from the spindle
Close-up of the spare wheel set
The wiring core removed from a 5K wheel
The wiring core removed from the wheel
Wiring core removed from the wheel
Close-up of a 5K wiring core (wheel K, side 2)
The spring-contacts inside the adjustable wheel
Inserting the wiring core
Inserting core K with the mark at the letter 'A'
The ID and the side of the wiring core are printed in white on the side of the core
B
×
B
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Original carton box in which the Czech PROTON-2 wheels were distributed
B
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Frontal view of the operational wheel set
B
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Close-up of the operational wheel set
B
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Close-up of an operational wheel
B
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Wheels taken from the spindle
B
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Fixed flat-faced contacts (left side)
B
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Spring-loaded contacts (right side)
B
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Close-up of the spring-loaded contacts of a bakelite adjustable wheel
B
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Aluminium can with spare wheel set
B
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Spare wheel set in aluminium can
B
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Spare wheel set in aluminium can
B
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Spare wheels (front) and operational wheels (rear)
B
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Spare wheel set
B
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Removing a spare wheel from the spindle
B
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Spare wheels taken from the spindle
B
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Close-up of the spare wheel set
B
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The wiring core removed from a 5K wheel
B
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The wiring core removed from the wheel
B
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Wiring core removed from the wheel
B
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Close-up of a 5K wiring core (wheel K, side 2)
B
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The spring-contacts inside the adjustable wheel
B
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Inserting the wiring core
B
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Inserting core K with the mark at the letter 'A'
B
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The ID and the side of the wiring core are printed in white on the side of the core

Disassembly of an adjustable rotor
This image below shows how the adjustable PROTON-2 rotors can be disassembled. Originally, a special tool was supplied to open the rotor, but this can also be done manually by pressing the center disc down with both thumbs, and then rotating it until the center disc comes off. The wiring core can then be removed. Assembly of the rotor works just the other way around.


By flipping the core around, the wiring is effectively mirrored. This greatly increases the maximum number of settings. To make it even more complex, the core can be moved to another rotor, that has its Advance Blocking Pins at different positions. All this was part of the daily key. The Core ID and the Side ID (1 or 2) are printed in white in the centre part of the core, but also at the outer rim at both sides. This way the Core ID and the side number are always visible, even when the rotor is reassembled again and the metal centre disc covers the text on the core.

Fialka wheel opener
Fialka wheel opener
Fialka wheel opener
Fialka wheel opener
Holding the Fialka wheel opener
Holding the Fialka wheel opener
Fialka cipher wheel with special opener
Opening a wheel with a special tool
C
×
C
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Fialka wheel opener
C
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Fialka wheel opener
C
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Fialka wheel opener
C
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Fialka wheel opener
C
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Holding the Fialka wheel opener
C
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Holding the Fialka wheel opener
C
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Fialka cipher wheel with special opener
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Opening a wheel with a special tool

PROTON-2 key setting
The drawing below shows which parts of the PROTON-2 rotors can be adjusted and how it affects the setting of the daily key. For each day, a small printed card was supplied in a sealed bag. A two-digit number in the top right corner of the card identified the day of the month (e.g. 14).

Adjustable Fialka rotor taken apart

The card further contained 5 lines with 10 Russian characters each. The first line (1) gives the order in which the rotors should be placed on the spindle. Line (2) gives the setting of the index ring. The next line (3) tells us which wiring core should be used in each position, whilst line (4) shows which side of the core should be visible. Finally, line (5) defines the position of the white index line of the wiring core. Once all these settings have been carried out, the daily key is set.

Example of a card with the daily key


Manufacturing differences
There are two known manufacturing variants of the adjustable PROTON-2 rotors. Initially, the non-metal parts of the rotors were made of brown bakelite (phenol formaldehyde resin), one of the first plastics. These rotors are generally known as the brown rotors. When polymer plastics became mainstream, the production process was changed and from then on the non-metal parts were made of reinforced black plastic. These rotors are commonly called the black rotors.


In the image above, both types are shown side-by-side. The bakelite rotors (right) have a fibre-strengthened outer rim (i.e. the transport ring with the gaps). With the plastic rotors, the transport ring is reinforced with metal stubs, as is clearly visible in this close-up. More detailed images of the manufacturing differences can be found below. The first four images show the adjustable and fixed rotors side-by-side, whilst the last four images show plastic and bakelite adjustable rotors side-by-side. All types were available with either black or red lettering.

Fixed wheels (front) and adjustable wheels (rear)
Adjustable wheels (left) and fixed wheels (right)
Adjustable wheels (left) and fixed wheels (right)
Adjustable wheels (left) and fixed wheels (right)
Plastic (left) and bakelite adjustable wheels (right)
Plastic (left) and bakelite adjustable wheels (right)
Plastic (left) and bakelite adjustable wheels (right)
Bakelite (top) and plastic adjustable wheels (bottom)
D
×
D
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Fixed wheels (front) and adjustable wheels (rear)
D
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Adjustable wheels (left) and fixed wheels (right)
D
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Adjustable wheels (left) and fixed wheels (right)
D
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Adjustable wheels (left) and fixed wheels (right)
D
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Plastic (left) and bakelite adjustable wheels (right)
D
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Plastic (left) and bakelite adjustable wheels (right)
D
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Plastic (left) and bakelite adjustable wheels (right)
D
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Bakelite (top) and plastic adjustable wheels (bottom)

Documentation
  1. The Fialka M-125 Reference Manual
    Crypto Museum, Paul Reuvers and Marc Simons.
    ISBN 978-90-79991-01-3. First issued 2005.

  2. Fialka rotor opening tool — detailed drawing
    Crypto Museum, Paul Reuvers. 9 July 2023.
Further information
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Crypto Museum. Created: Sunday 06 July 2014. Last changed: Saturday, 15 July 2023 - 06:39 CET.
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