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Mixer machines
One-Time Tape machines

Mixers are a class of cipher machines that are based on the Vernam Cipher. Plain text is mixed with a random key stream, hence the name mixer. If the mixer machine is used as intended, the key tape contains evenly-spread truely random characters and is therefore unbreakable. Such a key tape is commonly referred to as a One-Time Pad (OTP) or a One-Time Tape (OTT).

Mixer machines featured on this website:
 
The Siemens T-43 mixer machine T-43 Philips Ecolex I Ecolex 1 Philips Ecolex II Ecolex 2 Philips Ecolex IV Ecolex 4 Siemens M-190 M-190 Hagelin TC-52 TC-52 Hagelin C-446-RT, the OTP (OTT) version of the C-446 C-446-RT OTP/OTT version of the Hagelin CX-52 CX-52-RT
ATCRRM mixer machine used on the Washing-Moscow hotline ETCRRM Russian M-105 (AGAT) mixer machine M-105

Most of these machines use data from a teletype unit or from a paper-tape reader as input. Such data is generally stored in 5-bit digital format (e.g. in Baudot code), but other data formats are also possible. Plain text is either entered directly on the keyboard of a teletype machine (online), or is stored on a punched paper-tape first and sent later (offline).
<i>Mixing of the <b>plain text</b> and the <b>key</b></i>
The above illustration explains how the mixer works. Eacht letter from the Plain-text is added to a letter from a key tape, using an exclusive-OR (XOR) operation (sometimes called 'module-2 addition). The advantage of this operation is that it is reversable: adding the key stream to the cipher text, reveals the plain text again. For a detailed description of this principle, read our page about the Vernam Cipher.
 
Unclassified
It is often thought that, like most other cipher machines, the mixers were classified. However, due to the way the mixer works, there is nothing secret about the machine at all. Besides, when the machine is used correctly, the code is unbreakable anyway. Most mixer machines were therefore unclassified, although circuit diagrams and user manuals may have been restricted at the time.

With machines in this class, it is the key tape that protects the secret. This is the reason why the key tapes were only used once and were destroyed immediately after use, so that they could not fall into the wrong hands. Operational key tapes were always classified. They often carried labels like NATO Secret. Placing a classified key tape on a machine, makes the entire system classified.
 
Mixer machines featured on this website

Futher information

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Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Monday, 12 May 2014 - 18:38 CET
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