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The B-21 was the first cipher machine developed by Boris Hagelin.
He designed the machine in 1925 when he was working for the company
A.B. Cryptograph of Arvid Gerhard Damm in Stockholm (Sweden).
The B-21 was in production for many years, even after WWII when the company
had moved to Switzerland. It was available in many different versions and
variations.
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At the request of the invenstors - the Nobel family - Hagelin was placed in
the company in 1922 as a controller. From 1925 onwards, Hagelin was the
acting director, whilst Damm was persuing business in France.
When the Swedish Army wanted to buy Enigma machines
in 1925, Hagelin proposed his own machine: the B-21.
It was based on Damm's initial patented design of the B-18,
using two coding wheels. Hagelin improved the design by adding two of his
famous pin-wheels to each of the coding wheels
[1]
.
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Over the years, the design of the B-21 was changed and improved a number of
times. The image above shows one of the first versions and was probably
conceived in 1927, or shortly thereafter, as it still carries the original
company name: AB Cryptograph. It is battery powered and is
likely to have been modified at least once during its lifetime.
It was delivered to L.M. Ericsson (the phone company)
for use by its subsidaries in South America,
hence the presence of the Ericsson label
on the wooden transit case.
At the request of the French Army, an improved version of the B-21,
the B-211, was developed. It featured a printer instead of
the light bulbs. Eventually, the developments for the French Army led to a
range of power-less designs, the so-called C-machines, starting with the
C-35.
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At first glance,
it resembles the German Enigma machine.
It has a similar keyboard, is battery powered and uses a lamp panel for its
output. But that's where the similarity ends.
In order to avoid patent infringement, Hagelin used a completely
different operating principle. Rather than using alphabet substitution,
he used coding wheels to scramble a 5 x 5 matrix. This allowed only
25 letters to be used (5 x 5). As a result, the letter W was omitted.
Another difference with the Enigma was that the coding wheels were stepped
irregularly, whereas most of the Enigma variations featured regular stepping.
According to Hagelin, this made the machine far less predictable.
The B-21 was therefore considered more secure than the Enigma.
Although the latter isn't true - Arne Beurling of the Swedish Cipher Bureau
broke it in 1931 in less than 24 hours
[3]
- it was good enough for its time
and it was Hagelin's first commercially successful machine.
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The design of the B-21 is based on an earlier patient by Arvid
Gerhard Damm, modified by Boris Hagelin in 1925. It is based on
two electrical coding wheels and four so-called pin-wheels that
control the stepping of the coding wheels.
Although the actual circuit is far more complex, the simplified
circuit diagram below shows the situation when the machine is
in Ciphering Mode.
The keyboard consists of a mechanical matrix and two groups of
five electrical switches each. Pressing a key activates one switch
in each of the two groups. It also turns on power by activating
the ACT-switch for the duration of the key-press.
One group of switches is connected to the negative pole of the
battery (rows, marked 1 to 5). The other group is connected to
the positive pole (columns, I to V).
Each of the signals in then fed through a coding wheel, followd
by a programmable matrix. The outputs of the two programmable
matrices is then used to active a lamp on the lamp panel matrix.
In order to avoid current through all of the lamps, a diode is
connected in series with each lamp. In the B-21 shown here,
the diodes are mounted together as an
array of selenium diodes
at the right hand side of the machine.
The layout of the lamp-matrix is identical to the layout of the
keyboard-matrix.
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The machine described in the circuit diagram above is not reciproke.
For deciphering, a complex system of contacts and wires is used to
reverse the operation of each of the coding wheels and matrices.
This is mainly done by means of a cleverly designed switching mechanism,
controlled by a knob at the left,
that is combined with the slide contacts of the coding wheels.
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The image on the right shows a complex system of brushes and contacts
that form in fact five cross-switches. When in ciphering mode, the rearmost
brush contacts are touching the rings of the coding wheel.
The frontmost contacts are disengaged and are instead connected to a
fork-contact immediately below it.
The contacts are moved in tandem with the contacts of the other
coding wheel, so that they are always switched simultaneously.
Contrary to the Enigma,
the coding wheels are fixed in place and cannot be removed or replaced.
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Adding the cross-switches to the simplified circuit diagram
above, results in the slightly more complex
circuit diagram below.
This diagram is also available for download at the bottom of this
page.
The diagram shows the machine in Ciphering mode.
Switching to Deciphering, by rotating the C/D knob to the D-position,
reverses the path through each of the coding wheel/matrix
combinations. The operation of the cross-switches is illustrated at the centre.
Whether or not the selenium diodes are original parts
remains to be seen. In 1925, when the B-21 was developed,
selenium diodes had not yet been invented. Furthermore, Boris
Hagelin describes in the Hagelin Story
[2]
that he used electric relays in the initial design.
It is quite possible however, that the machine was overhauled
for diode-operation at a later date.
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Later version of the B-21
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The images below were taken during the presentation of
the book Mythos Enigma by Dominik Landwehr, in Basel in 2008.
Hagelin's first employee Oskar Stürzinger was present as the meeting and
demonstrated some historical Hagelin machines, including a variant
of the B-21.
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As becomes clear from the image on the right, the mechanical parts are
identical to the machine shown above, but electrically it is somewhat
different. The programmable matrix has been removed and is now situated
behind the coding wheels as a series of 10 plugs.
The space at the right is taken up by a mains transformer.
The serial number plate at the front shows the manufacturer name
A.B. Ingeniörsfirman Teknik, which was the name of the company
after it was taken over by Boris Hagelin in 1932.
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This particular machine is quite different from the one at the top of this
page, but carries the designation B-21 nevertheless.
The layout of the keyboard and the lamp panel is different and was probably
tailored for the Swedish language.
It features the standard Latin alphabet, but the letters W, X and Z
have been omitted. Instead, keys for Sk and Me have been added,
resulting in the maximum number of 25 keys.
In the image, there is no sign of a relay bank or a diode array, but it is
entirely possible that this is hidden under the lamp panel. The machine was
mains-powered and the external mains cable was present.
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A later variant of this machine is the B-211, which had a built-in
printer and was motor-driven. This machine became very popular in
France where it was used extensively during the Algerian war.
It was built in France by an Ericsson subsidary in Colombes (Paris)
under licence from the Swedish company.
The popularity of the machine within the French Army later led to
the development of the C-35.
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The Russians copied the design of the B-211 and adapated it to
contain a 5 x 6 matrix, allowing all characters of the larger
Cyrillic alphabet to be used.
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- Boris Hagelin, 100 Jahre Boris Hagelin 1892-1992
Memoires of Boris Hagelin (German).
Crypto A.G., Crypto Hauszeitung Nr. 11, September 1992.
- Boris Hagelin, The Story of Hagelin-Cryptos
Crypto A.G., Zug, Spring 1981.
- Bengt Beckman, Arne Beurling and the Swedish crypto program during WWII
2002, American Methematical Society (English translation).
p. 31-32.
(Original publication 1996.)
ISBN 0-8218-2889-4
- US Patent US1846105
Hagelin's patent for the B-21 filed in the US in 1928.
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© Copyright 2009-2012, Paul Reuvers & Marc Simons. Last changed: Mon,14 May 2012.09:38:58
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