Homepage
Crypto
Index
Glossary
Enigma
Hagelin
Fialka
Siemens
Philips
Nema
Racal
Motorola
STK
Transvertex
Gretag
OMI
HELL
Telsy
Teltron
TST
Mils
AT&T
Tadiran
USA
USSR
UK
Yugoslavia
Voice
Hand
OTP
Mixers
Phones
FILL
Codebooks
Spy radio
Burst encoders
Intercept
Covert
Radio
PC
Telex
People
Agencies
Manufacturers
• • • Donate • • •
Kits
Shop
News
Events
Wanted
Contact
About
Links
   Logo (click for homepage)
Mixers
One-Time Tape cipher machines

Mixers are a class of cipher machines that are based on the Vernam Cipher in which Plain text is mixed with a random key stream (hence the name mixer). If the mixer is used with a key tape that contains evenly-spread truely random characters, the cipher is guaranteed to be unbreakable. Such a key tape is commonly referred to as a One-Time Pad (OTP) or a One-Time Tape (OTT).
 
Mixers on this website   one-time tape machines
The Siemens T-43 mixer machine T-43 British/Canadion one-time tape cipher machine used during and after WWII Rockex British 5-UCO (BID/30) OTT cipher machine 5-UCO ATCRRM mixer machine used on the Washington-Moscow hotline ETCRRM British one-time tape cipher machine compatible with Rockex Noreen Philips Ecolex I Ecolex 1 Philips Ecolex II Ecolex 2 Philips Ecolex IV Ecolex 4
Siemens Schlüsselgerät D D Siemens M-190 OTT cipher machine, used on the Washington-Moscow hotline 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 Russian M-105 (AGAT) mixer machine M-105 DUDEK StG-1 (T-352 / T-353) one-time tape cipher machine developed in Poland DUDEK Mils Elektronik one-time tape cipher machine, developed in the mid-1970s. ME-620
Mils Elektronik one-time tape cipher machine, with key generator ME-640

 
Unclassified
It is often thought that, like most cipher machines, mixers are classified items. 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 of 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.
 
Principle
Most mixers, or OTT machines, use data from a teleprinter machine or from a paper-tape reader as input. Such data is generally stored in 5-bit digital format, commonly in ITA2 code (baudot), but other data formats are also possible. Plain text is either entered directly on the keyboard of the teleprinter (online), or is stored on a punched paper-tape first and replayed later (offline).

<i>Mixing of the <b>plain text</b> and the <b>key</b></i>

The above illustration explains how the mixer works. Each letter of the Plaintext is added to a letter from a Key tape, using an exclusive-OR, or XOR, operation. In mathematics this is known as modulo-2 addition. In cryptography it is known as the Vernam Cipher. It has the advantage of being reversible: by adding the key stream to the ciphertext, the original plaintext is retrieved.

 More about the Vernam Cipher.
 
Invention
Many companies and countries claim the invention of the One-Time Tape cipher machine (mixer). Although the Philips Ecolex was definitely not the first machine in this class, its 'inventor' was payed for his patents for many years. STK (now: Thales) claims that it was a Norwegian invention, but their patent of 1952 is predated by the Siemens T-43, the British 5-UCO and the British-Canadian Rockex, all of which were developed during WWII and were introduced in 1943.

Although all mixers are based on the so-called Vernam Cipher, an invention of Gilbert Sandford Vernam in 1918, and that Vernam is also the (co)inventor of the One-Time Pad (OTP), the first machine that was based on the Vernam Cipher (1926, Telekrypton) used a looped key tape and was therefore not a One-Time Tape machine. This means that, based on the currently available information, the Siemens T-43, the British Rockex and the 5-UCO should be recognised as firsts.
 
Futher information

Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
© Crypto Museum. Last changed: Thursday, 31 March 2016 - 13:19 CET.
Click for homepage