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← USSR Cipher Mixer OTT
One-Time tape cipher machine
- wanted item
The M-105 (codename: AGAT) was a
Russian off-line cipher machine
that was developed and built in the USSR
in the late 1960s,
as the successor to the nearly identical M-104 (AMETYST and AMETYST-2).
The machines were used by all countries of the Warsaw Pact
and contained a built-in key tape mixer that was fed
with an 11-level punched paper tape with random data.
In East-Germany (DDR), the M-104 was introduced in 1966
and the M-105 was first used in 1968 [1].
The machine is also known as Agat (Russian: АГАТ) or Achat
and is a One-Time Tape cipher.
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At first sight, the machine somewhat resembles the
M-125 Fialka.
It has nearly the same size, is painted in grey hammerite, is driven
by an electric motor and has a latin/cyrillic keyboard at the front.
But that is where the similarity ends.
The M-105 prints it output directly to a sheet of paper that runs through
a carriage at the rear.
A sophisticated matrix-type print head allows
any of 30 characters (5 x 6) to be printed on the paper sheet.
Depending on the language, some hardly used characters or numbers
may have been omitted. The Polish variant is shown here.
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The M-105 has a built-in 5-level paper tape puncher at the right rear.
It accepts standard 5-level punched paper tape, but does not use the standard
Baudot encoding.
Instead, it uses the same coding scheme
as Fialka.
Just like Fialka,
the M-105 has a built-in 5-level paper tape reader at
the front right. The paper can be guided through a ruler that runs along
the full width of the machine, just above the keyboard.
It is started and stopped with the two keys at the front right.
In East-Germany (DDR), the M-105 was introduced in 1968 and was used
for communication with all partners of the Warsaw Pact and the Soviet Union.
It was also used by the DDR Government for exchanging messages at the highest
level, and by the East-German Intelligence Service – the MfS or Stasi 1 – until
at least 1982
for communication with their foreign radio monitoring stations [1].
Although the M-105 was succeeded in 1986 by the fully electronic
M-205 D,
many remained in use until the end of the DDR and the collapse of
the Soviet Union.
For communication between the DDR Government and Hungary, the M-105
was replaced by the T-353 (Dudek) in 1987.
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MfS = Ministerium für Staatssicherheit (Ministry for State Security).
Stasi = Staatssicherheit (state security).
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The image below shows the layout of the full keyboard. Each key cap has
two letters: A cyrillic one in black at the left, and a latin one in red
at the right. There are 30 normal keys, plus a black single-step key at
the bottom left and a black CR/LF key at the bottom right. There is also
a spacebar (at the bottom) which is shared with the
Й2
key at the top left.
When entering text in
cipher mode, the spacebar can be used and the
Й2
key is blocked (i.e. covered by a metal plate).
In decipher mode it is the other way around:
the spacebar is blocked and the
Й2
key is available.
When the machine is used in plain-text mode (MODE selector set to 'O'),
both the spacebar and the
Й2
key can be used.
The two black keys (single step and CR/LF) are not enciphered.
They are only used in plain-text mode for formatting of the output.
Loosing the Russian letter Й is not much of a problem, as it can
be replaced by the И without affecting readibility. Like with Fialka,
only the 30 most frequently used Cyrillic letters are present, whilst
3 have been dropped. Although they are commonly used, this does not
affect readibility.
Judging from the layout [1] the keyboard shown here suggest
this is probably the Polish variant of the machine. The following
Latin characters are available in this version:
ABCDEFGHIJKLMNOPQRSTUVWXYZ 2578
As not all numbers are present, they had to be spelled out in full.
When used in Cyrillic mode (Russian), numbers always had to be spelled out
in full. There are no punctuation marks, except for the SPACE character,
in which is swapped with the
Й
key at the top left.
Switching between Latin and Cyrillic (Russian), requires the
print head to be exchanged.
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Unlike Fialka,
which uses 10 configurable electrical cipher wheels for
creating a hard-to-predict pseudo-random key stream, the M-105 has a built-in
mechanical key stream generator that is programmed with an 11-level key tape.
The 11-level key tape is located on top of the machine.
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The key tape itself has two rows of sprocket holes: one along the top of the
tape and one just below the centre. Below the center sprocket hole are 5 data
holes. the Remaining 6 data holes are located in between the two sprocket
holes.
The key tape is fed into the reader from the right, like indicated in the
image on the right. A knurled knob at the front of the reader allows the
tape to be forwarded to the desired start position. To ensure that a key tape
could only be used once for encryption, a Control Hole is punched when
changing the mode of operation.
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Once this Control Hole is present, the key tape can no longer be used
for encryption. Decryption is still possible however, allowing a previously
encrypted text to be tested [1]. Key tapes that were intended for decryption
only, already had the Check Hole present when they were supplied, to prevent
accidental use as encryption key.
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The following key material was available for the M-105:
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- ТИ : Individual
This key material was used for one-on-one communication.
It consisted of two tapes: one for encryption and one for decryption.
This material was supplied in a package that contained a table
with 20 Indicator Groups (German: Kenngruppen) and 20 key tapes.
The Indicator informed the operator at the other end
about the key tape that was used.
- ТЦ : Group
For sending group messages (also known as NET), three or more
identical key tapes were used. Although this was less secure (i.e.
it didn't stricktly follow the rules of the One-Time Pad), it allowed
net messages to be sent to a number of recipients.
The key material was supplied in a Code Book that contained
a table with Indicators
and 25 key tapes, or a Cassette with an
Indicator table and 75 key tapes.
- Т-КПУ-М : Test
This material was intended for using the Test and Security Feature
of the M-105 (German: KSV, Kontroll- und Sicherungs-vorrichtung).
It consisted of a Code Book with 25 test key tapes.
As a security measure, the M-105 was able to test whether a key tape had
previously been used for encryption. This was done by punching an extra
hole in the key tape when switching from Cipher Mode (З)
to Plain Text Mode (O). Once this hole was present, the tape could no
longer be used for encryption. In decryption mode (Р), the tape could still
be used for verification, as the M-105 does not test for the hole in
that mode.
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Each key tape consisted of 500 groups of 5 letters each and was identified
by a tape number that was printed at the start of the tape.
A standard code book consisted of a table with 20 Indicators
and 20 key tapes. The following rules had to be followed:
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- Each key tape could only be used for encryption once.
- For each key tape, the matching Indicator had to be used.
- Each Indicator could only be used once and had to be ereased after use.
- A key tape had to be used immediately after it was taken from the code book.
- Unusued key tapes had to be accounted for.
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The M-105 accepts a standard 5-level punched paper tape, just like many
western telegraphic devices of the era, but does not use the standard
Baudot encoding for this. Instead, the machine uses the same encoding
as the M-125 Fialka. The 5-bit alphabet is illustrated in this diagram:
With 5 holes it is possible to create 25 = 32 different combinations.
30 of these are used for the standard 30 characters that are available on
the keyboard. The two ramaining positions are taken by the SPACE character
(10001) and the NULL character (00000), which is also known as STOP.
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At the front left of the machine, just behind the keyboard is a black
rotary knob that is used to select the required mode of operation.
There are three possible settings: 'O' for plain-text
(Открытый Текст),
'3' for ciphering
(ЗашифроватЬ)
and 'P' for deciphering (РасшифровыватЬ).
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In plain-text mode, the M-105 functions like a normal typewriter
or teleprinter. It can be used to print text and create 5-level
paper tape. In this mode, all keys can be used, including the
space bar, the single-step and the CR/LF key.
Setting the MODE selector to either cipher mode (3) or decipher
mode (P) results in a number of mechanical changes inside the machine.
In cipher mode, the
Й2
key
is blocked and the spacebar is available. In decipher mode,
this operation is reversed: the spacebar is blocked and the
Й2
key
can be used in the cipher text.
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In many ways the operation of the MODE selector is similar to the
MODE selector on other Russian cipher machines such as the
M-125 Fialka
or the M-130. The abbreviations used for the
various modes are identical on all machines, as shown in the
table below.
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At the front of the 11-level key tape reader is a
lever with three possible settings:
П,
ПК and
К. It is used to select the destination of the encoded, decoded or plain-text
output: to the puncher, to the printer or to both the puncher and printer.
The image on the right shows the front left of the machine. At the left is the
key tape reader. The output selection lever is mounted to the front of the key
tape reader, to the right of the kurdled knob.
At the right is another lever which is used to release
the motor (МОТОР / РУЧН.) in case of manual operation with the crank.
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Label
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Russian
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Phonetic
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English
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О
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Открытый Текст
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Otkrytyj Tekst
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Plain text
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З
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ЗашифроватЬ
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Zashifrovat
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Cipher
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Р
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РасшифровыватЬ
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Rasshifrovyvat'
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Decipher
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П
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Перфоратор
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Perforator
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Puncher
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К
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Карта
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Karta
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Sheet
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МОТОР
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МОТОР
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Motor
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Motor
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РУЧН.
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РУЧНОЙ
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Ruchnoy
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Manual
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There were several different ways to power the M-105, resulting in different
versions of the machine. The most common version has a built-in 24V DC motor that
can be powered by an external 24V source.
Especially for connection to a 110V DC network, a special
version with a 110V DC motor was available.
Existing 24V DC models could be modified for 110V DC.
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In the field, the 24V model could be powered directly by the battery of, say,
a truck. In most cases however, the unit was powered from the AC mains via
the standard Power Supply Unit (PSU)
that was supplied with each machine.
The image on the right shows the standard PSU that was used with the M-105.
It is suitable for a wide variety of mains voltages (typically in the 110V
or 220V range), so that it could be used virtually anywhere in the world.
The same PSU was used with the
M-125 Fialka cipher machine
in most Warsaw Pact countries, such as the DDR.
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The PSU came with several cables for connecting the M-105 to the AC mains
or to an externa 24V DC source. These cables were usually stored inside a
small storage compartment at the front of the PSU.
The hinged lid of this compartment
is held in place with two kurdled screws.
More...
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The M-105 is fitted with a fixed power cable that has a rather strange
3-pin plug at the end. It directly fits the 24V output socket
of the PSU.
The M-105 could be converted for use on 110V DC networks, by swapping
the existing 24V motor for a 110V one. Suitable conversion kits were
available for this at the time. The 110V motor was connected to a spare
socket (marked 110V) at the right right inside the machine.
➤ More about the PSU
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The M-105 internally uses a 5 x 6 matrix to address its 30 characters.
This is done by translating each 5-bit character into a a row (6 bits)
and column (5 bits). This result in 11 internal 'bits' that are used
to drive the mechanism. For this reason, the key tape has 11 bits as
well. If you closely examine the key tape,
only one of the row/column bits are used in each step.
The block diagram above should explain the operation of the M-105 AGAT.
At the left is the keyboard with its 30 keys that are mechanically
converted to a 5-bit binary code. It operates in parallel with the key
tape reader. The 5 data bits are then mechanically converted to an
11-bit row/column code (5 bits for the column and 6 bits for the row),
which is fed into the cipher unit.
In the example below, the letter 'V' generates the
column/row bit pattern 01000 000010.
The 11-bit code from the key tape is then added to the 11-bit data
stream and the result is converted back into 5-bit digital code. This 5-bit
code is then used to drive the 5-level paper tape puncher. The 5-bit
code is also electrically available from a
socket at the left rear.
At the moment it is not exactly known how the data from the key tape is
added to the data stream, but it seems likely that the column/row codes
from the key tape are used to shift the column/row codes from the data
stream by a number of positions. When deciphering, the shift-direction
could be reversed, or special deciphering key tapes had to be supplied.
The above diagram shows how it might have worked, but it is not guaranteed
that his is correct. It makes the M-105 effectively a
One-Time Pad,
or more precisely: a One-Time Tape machine (mixer).
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The top cover of the machine can be removed by loosening a couple
of screws in the outer case. This reveals the extremely complex
but well-built interior of the M-105. The image below shows a compact
mechanism with many cog-wheels at the center,
driven by a motor at the right.
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The printer mechanism and the paper carriage are barely visible at the
top of the image.
At the left is the 11-level key tape reader, whilst the 5-level tape
reader is located at the bottom right.
The 30 keys from the keyboard are mechanically converted into 5-level
code which is converted to electrical signals by means of
5 switches at the left rear.
The 5-level paper tape reader operates in parallel with the keyboard;
when a tape is played back, the keys automatically move up and down.
The machine has a hole at the right through which a crank can be inserted.
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The crank has several functions. It allows the machine to be
operated manually in case of a power failure. As the encryption process
is purely mechanical, the machine can read 5-level tapes and key tapes,
and can print to paper without any electricity. The crank was also used to free the mechanism in case it got jammed (e.g. when a key was pressed
whilst the motor wasn't running).
After encryption or decryption, the resulting 11 bits are (mechanically)
converted back to 5-bit binary data, so that an ordinary telegraphy paper
tape can be punched. The 5-bit data is also converted to electrical signals
by means of 5 sensing switches
at the left rear. These signals are available
on the socket at the left
of the machine (for which electricity is needed,
or course).
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© Crypto Museum. Created: Tuesday 06 May 2014. Last changed: Sunday, 22 December 2024 - 09:03 CET.
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