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Mixer Vernam USA
One-time tape cipher machine
- this page is a stub
Telekrypton was an electromechanical
one-time tape cipher machine,
built around 1933 in the United States
by the Western Union Telegraph Company.
Built in small quantities it was based on the so-called
Vernam Cipher,
invented in 1918 by Gilbert Sandford Vernam (1890-1960)
and described in US Patent 1310719 [2].
It is further described in an AIEE journal in February 1926 [3].
In order to prove the concept, the Western Union Telegraph Company
built a limited number of machines that were marketed for several years
uner the name Telekrypton. The machine was commercially not very successful
and had two major weaknesses. First of all it was extremely large.
Consisting of a table full of equipment, it would in practice be very
difficult to maintain. More importantly however, was the fact that the
keystream tape was looped, presenting a major cryptographic flaw.
Due to its repetitive nature, the keystream tape could be reconstructed.
In his paper of 1926 [3 p. 16] Vernam descibes a way of improving security
by using two looped keystream tapes of approx. 7 feet,
each of which has a different length (that should not share a common factor
with the number of characters on the other tape).
The image above shows the system that was described in his paper.
Although the increased cipher period greatly improves the cryptographic
strength of the system, it still is not a true
one-time pad system.
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In 1940, The
British Security Coordination (BSC)
was looking for a machine that could be used to send secure messages
in pre-war America,
between the BSC in Washington and the BSC in New York.
Canadian communications expert Benjamin deForest Bayly was asked
to find a solution.
Bayly took the existing Telekrypton machine, of which Western
Union still had two left in its warehouse, and reworked them for the BSC.
Unnecessary parts were removed and a much longer random tape was introduced.
By using a random tape that had the same length as the message (or more)
and allowing only two identical tapes to exist, Bayly had in fact created
an unbreakable OTP cipher.
He also instructed the key tapes at both ends
to be destroyed immediately after use.
Using hand-punched keystream tapes, the first Telekrypton line between
the BSC in New York and the BSC in Washington became operational in
January 1942. In May 1942 an additional line was opened between the BSC and
Ottawa and finally in July between the BSC and the transatlantic transmitter
at Camp X in Whitby 1 (Ontario, Canada) [1].
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During WWII, Camp X was the unofficial name of a paramilitary, clandestine
and commando training installation of the BSC,
located in Ontario (Canada) between Whitby and Oshawa. It is known today
as Intrepid Park.
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In the following year, Bayly fixed a number of security weaknesses in the
Telekrypton design and modified the combining logic so that only the 26 letters
of the Latin alphabet appeared in the encrypted output, allowing the ciphertext
to be nicely formatted in groups of five letters each,
separated by automatically inserted spaces and linefeeds.
The modified machine became known as Rockex
and was first used in 1943
on the transatlantic link between Camp X and the UK.
➤ More about Rockex
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The American Institute of Electrical Engineers (AIEE) was merged
with the Institute of Electrical and Electronics Engineers (IEEE)
on 1 January 1963 and is now known as IEEE. The document cited here
is located off-site and is reproduced there by permission of the IEEE
(read the enclosed copyright notice).
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© Crypto Museum. Created: Tuesday 27 January 2015. Last changed: Saturday, 30 April 2022 - 08:55 CET.
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![Photograph from Vernam's paper of 1926 [2] describing the machine](img/vernam.png)