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Štolba
Pneumatic rotor-based cipher machine - not in collection

Štolba 1 was a mechanical rotor-based cipher machine, developed in the mid-1930s by Josef Štolba 2 in Czechoslovakia. It features a pneumatic transmission system with six pneumatic cipher wheels, and has complex stepping rules. It was the first cipher machine used by the Czechoslovak Army in the late 1930s, and was later used in Slovakia during World War II [1]. Parts of the machine were made by the Prema Ing. Roudnický, Janáč a spol. company in Prague and by weapons manufacturer Československa Zbrojovka Brno in Brno — the capital of Moravia.

The machine weights ~ 45 kg [9] and looks like a typewriter. It has 26 keys, a printer with type-arms and a drum with six cipher rotors towards the rear. Unlike contemporary cipher machines – such as Enigma, Typex and Sigaba – it does not use electric current for its permutations, but air.

The keyboard comprises 26 pneumatic cylinders. When pressing a key, the air from the cylinder is pressed via narrow tubes, through the cipher rotors, and will eventually actuate a type arm of the Remington type mechanism at the centre. At the left is a retractable rotor-advance lever.
  
Stolba cipher machine. Photograph copyright Security Services Archive [8].

The advance lever operates 3 additional rotors that control the stepping of the 6 cipher rotors. The daily key consisted of the starting position of all 9 rotors. Many, but not all, characteristics of the machine are described by Eugen Antal and Pavol Zajac in the article The first Czechoslovak cipher machine, in Cryptologia (2021) [1]. Based on documents obtained from the Czech and Slovak archives, they have reconstructed the encryption algorithm with a high probability.

  1. Also written as 'Stolba'.
  2. Born on 5 July 1897 as Josef Sieber, he later changed his family name to Štolba. He was a Colonel and constructor of ciher machines at the Czech Ministry of Defence. He died on 16 May 1953 at the age of 55.

Stolba cipher machine. Photograph copyright Security Services Archive [8].
Remington Home Portable typewriter [5] of which the printing mechanism was very similar
Remongton 'Z' portable manufactured at Zbrojovka Brno. Photograph provided by the Moravian Provincial Archive [12].
Remington 'Z' typewriter of which the printing mechanism was used for the Štolba [4]
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Stolba cipher machine. Photograph copyright Security Services Archive [8].
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Remington Home Portable typewriter [5] of which the printing mechanism was very similar
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Remongton 'Z' portable manufactured at Zbrojovka Brno. Photograph provided by the Moravian Provincial Archive [12].
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Remington 'Z' typewriter of which the printing mechanism was used for the Štolba [4]

Features
The image below provides a quick overview of the features of the Štolba cipher machine. At the front is the keyboard which comprises 26 air cylinders, or pistons. To the left of the keyboard is a counter that shows the number of letters that have been entered. At the right side of the machine is a large knob that is used to select the desired mode of operation: plain, cipher or decipher.

Behind the keyboard is the printer which types the output directly onto a paper sheet. This was a standard OEM part from the American typewriter manufacturer E. Remington and Sons [3], and is identical to the printing mechanism of the Remington 'Z' typewriter [4] of which the outmost type arms have been removed. It was manufactured in Czechoslovakia by weapons manufacturer Československa Zbrojovka Brno 1 under licence from Remington [6][7]. It prints directly onto a paper sheet that is loaded onto a rubber roller (platen) at the heart of a carriage that moves from right to left whilst typing. The bay with the moving carriage is visible at the centre of the image:

Stolba cipher machine. Photograph copyright Security Services Archive [8].

The rotors are located behind the printer and are not visible in the image above. They can be accessed via two hinged lids in the top surface of the machine: a small one below which the 3 control rotors are located, and a wide one that gives access to the 6 cipher rotors. The rotors are mounted onto fixed spindles, and their order cannot be changed. The initial position of all nine rotors could be altered via the lids and form the cryptographic key, e.g.:
FUZ MILICA
[1 p.20]. 2

  1. Zbrojovka Brno was a manufacturer of weapons and tools, based in Brno (Czechoslovakia).  Wikipedia
  2. These are the key settings for 1 January 1939, as disclosed in [1 p.20].

Operation
The simplified block diagram below shows the basic operation of the machine. At the top left is the drum, which consists of six cipher rotors (1-6) embraced by two entry discs (ED1 and ED2). Each rotor has 25 air channels, or tubes, that connect the right side of the rotor to the left side, in a scrambled order. The air tubes of both entry discs are connected to a distribution board, that controls the direction of the air flow, depending on the selected mode: plain, cipher or decipher.

Simplified block diagram of the Štolba cipher machine

At the bottom left is the keyboard which comprises 26 pistons, or air cylinders (A-Z). In cipher or decipher mode, only 25 keys are used. The letter 'W' is omitted and must be replaced by 'VV' (the letter 'V' twice). When a key is pressed (Z), the air is pushed through the tube, via the rightmost entry disc (ED2) into one of the channels of the rightmost rotor (6). Rotor 6 passes the air onto rotor 5, etc., until it leaves the drum at the leftmost entry disc (ED1). Via the distribution board, the air in then passed to the printing mechanism, where it actuates one of the type arms of the Remington typewriter assembly, causing a letter to be printed onto a paper sheet.

The stepping of the cipher wheels is controlled by the stepping mechanism at the top right. This mechanism consists of three control rotors (7-9) that are similar to the cipher rotors. Each time the stepping lever (at the left side of the device) is operated, four pistons are activated. One of these pistons pushes air into the channel for the letter 'V' of the leftmost rotor (7). The air is then passed through rotors 7, 8 and 9, onto a selector (or demultiplexter) which causes precisely one cipher rotor to step forward or reverse. In practice however, reverse stepping was disabled [1].

The other three pistons advance the control rotors by one step, but only if the corresponding air vent is blocked by a blocking pin on the adjacent wheel. Rotor 7 controls the air vent blocking pin of rotor 8, rotor 8 controls that of rotor 9, and rotor 9 finally controls the air vent of rotor 7.

Distribution board
Štolba allows the following modes of operation:

  • Plain
  • Cipher (encryption)
  • Decipher (decryption)
The mode of operation is controlled entirely by the distribution board. Although the construction of this board is currently unknown, it is possible to make an educted guess. The MODE is selected with a 3-position knob at the right side of the machine. It is likely that the knob rotates a cylinder that is located below the keyboard, and runs from left to right. For each of the 26 keys, there are three air tubes. The cross-section below shows the air tubes in all 3 possible positions (modes).


In plain mode, only the middle tube is used and the air flows from the keyboard directly to the printer. In cipher mode, the keyboard is connected to the rightmost entry disc (ED2), whilst the lefmost one (ED1) is connected to the printer. In decipher mode, the keyboard is connected to the leftmost entry disc (ED1), whilst the rightmost entry disc (ED2) is connected to the printer.

Wheel stepping
Wheel stepping is controlled by rotors 7, 8 and 9, and by blocking pins on the circumference of the adjacent rotors. Although the wiring of the control rotors is known [1], the configuration of the air vent blocking pins is not. Furthermore, the exact configuration of the Selector (to the right of rotor 9) is currently unknown. Despite more than 170 thousand hours of computing time, the researchers were unable to reconstruct these from the limited information currently available [1].


Cryptographic keys
According to [1], two types of cryptographic keys were used:

  • Daily key
    This is a long term key that was changed only once a day. It was distributed on paper and consisted of two text strings: 3 letters for the offsets – or start positions – of the control rotors, and 6 letters for the start positions of the cipher rotors, e.g.
    FUZ MILICA
    .

  • Message key
    This key — also known as the individual key — must be different for each message. It consists of three random letters that are sent twice at the start of the ciphertext message, encrypted with the daily key. This is similar to the initial procedure of the Enigma cipher machine. Once the message key is encrypted (twice), the first three cipher rotors are set to the message key and the rest of the message is entered.
Wiring
Below is the wiring of the rotors and the entry discs, as recovered by [1], defining the left side of each rotor as the input. This means that the wiring of the cipher rotors (1-6) is for deciphering.

Rotor ABCDEFGHIJKLMNOPQRSTUVXYZ
1 ZYGCNRPKBUEFLHDTJXIMOQSAV
2 RXUJPMNFKVCEBTLDGOHYQIAZS
3 ULSXVPKTDGIBFJCEHMYNAZOQR
4 OIZPFKDMSQNJCURXBAVLGTYEH
5 JGDNKHECTAQSZVILOYPUXRMFB
6 NPRKGVIMEZHCOYXASBLDFJTUQ
7 BCOLRPZVATJHUXQFDIMSYEGKN
8 HZKROAMPFDTXSLECYVNIGBUQJ
9 TANVZQOIPYGDHSUJLCFXBKREM
ED1 DQKIGLORVUYBXTZCAJFMSNHEP
ED2 UZGTFREASYXDCVBNMQLKJHPOI
Manufacting
It is currently unknown which company or agency was responsible for the manfacturing of the Štolba cipher machine. It is known however, that parts of the machine were made by the Prema Ing. Roudnický, Janáč a spol. company in Prague — at the time the capital of Czechoslovakia.

It is also clear that the typing mechanism and the platen (the rubber roller holding the paper) were made by the company Československa Zbrojovka Brno in Brno (Moravia). At the time, Zbrojovka Brno was a weapons manufacturer who also built Remington typewriters under licence of E. Remington and Sons in the US [3].

The typing mechanism of the Štolba is very similar (if not identical) to that of the Remington 'Z' portable typewriter, which was also made at Zbrojovka Brno. The image on the right shows the manufacturing of this mechanism in Brno.
  
Manufacturing of parts for the Remington 'Z' typewriter. Photograph provided by the Moravian Provincial Archive [11].

A later version of the Remington 'Z' portable typewriter [4] even shows the name of the company — Československa Zbrojovka a.s. Brno — at its front edge. It is possible – but not certain – that Zbrojovka Brno also made other parts of the Štolba cipher machine.

Remongton 'Z' portable manufactured at Zbrojovka Brno. Photograph provided by the Moravian Provincial Archive [12].
Manufacturing of Remington typewriters at Zbrojovka Brno. Photograph provided by the Moravian Provincial Archive [11].
Manufacturing of parts for the Remington 'Z' typewriter. Photograph provided by the Moravian Provincial Archive [11].
Remington 'Z' typewriter of which the printing mechanism was used for the Štolba [4]
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Remongton 'Z' portable manufactured at Zbrojovka Brno. Photograph provided by the Moravian Provincial Archive [12].
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Manufacturing of Remington typewriters at Zbrojovka Brno. Photograph provided by the Moravian Provincial Archive [11].
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Manufacturing of parts for the Remington 'Z' typewriter. Photograph provided by the Moravian Provincial Archive [11].
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Remington 'Z' typewriter of which the printing mechanism was used for the Štolba [4]

References
  1. Eugen Antal & Pavol Zajac (2021): The first Czechoslovak cipher machine
    Cryptologia, DOI: 1080/01611194.201.1998809. 28 December 2021.

  2. Eugen Antal, Pavol Zajac & Otokar Grošek, Cryptology in the Slovak State During WWII
    Proceedings of the 2nd International Conference on Historical Cryptology, pp. 23-30.
    Mons (Belgium), 23-26 June 2019.

  3. Wikipedia, E. Remington and Sons
    Retrieved january 2022.

  4. Mr. & Mrs. Vintage Typewriters, Image of Remington 'Z'
    Retrieved January 2022. Reproduced here by kind permission.

  5. Bailiffgate Museum & Gallery, Adopt our Remington Portable Typewriter
    Retrieved January 2022.

  6. Wikipedia, Zbrojovka Brno
    Retrieved January 2022.

  7. Zbrojovka Brno, History of the company
    Retrieved January 2022.

  8. Archiv Bezpečnostnich Složek, Photograph of Stolba cipher machine
    Security Services Archive, founds of the Intelligence Department of the General Headquarters of the Czechoslovak Army, carton BF 395, part of the file 27-19/80-07.

  9. Captain Dufihol on Visit to CSR cipher section 1937
    Berlin, TICOM report 3607, PAAA, S8 (in French).

  10. Eugen Antal, Personal correspondence
    January - February 2022.

  11. Images of typewriter manufacturing at Zbrojovka Brno
    MZA v Brně, fond H 864 Zbrojovka, a.s., Brno, karton 892, inv.č. 2.

  12. Image of Remington portable typewriter at Zbrojovka Brno
    MZA v Brně, fond H 864 Zbrojovka, a.s., Brno, karton 927, inv.č. 1, 3, 4, 5, 6.
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Crypto Museum. Created: Wednesday 29 December 2021. Last changed: Friday, 04 March 2022 - 09:08 CET.
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