TUNNY codebreaking machine
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Heath Robinson was an electronic machine that was used as an aid in breaking
the German Lorenz SZ-40/42 cipher machine
It was designed by Tommy Flowers
and Frank Morell of the General Post
Office (GPO) research stations at Dollis Hill (north-west London).
It was the first machine produced by
Tommy Flowers and his team
after he was introduced to codebreaker Max Newman
at Bletchley Park
by fellow codebreaker/mathematician
The machine is equipped with two tape readers, one of which is used
for generating the wheel sequences of the Lorenz SZ-40/42 machine.
In recent years, the Heath Robinson has been rebuilt by a team of
volunteers, and is now on public display at The national Museum of Computing
(TNMOC) at Bletchley Park (UK).
The machine was named after Heath Robinson, a World War I cartoonist
and illustrator who was known for his drawings of fantastic but ridiculously
complex machines that were used for simple tasks,
pretty my like Rube Goldberg did in the US . As a result, the term
Heath Robinson, or Heath Robinson Contraption
was induced in the English language.
In US English, such a design is often called a Rube Goldberg machine.
Development of the Heath Robinson started in January 1943 and the first
prototype was delivered at Bletchley Park in June 1943. It was put to
work soon afterwards. At the heart of the machine is an electronic
valve-based circuit, designed by Tommy Flowers,
that performs the boolean XOR function (Modulo-2 addition)
on a digital 5-bit teleprinter signal (as in
the Vernam cipher).
One paper tape reader is loaded with the cipher text that had
to be at least 2000 characters long. The other reader was loaded with
a tape that contained the possible Chi-wheel start patterns of the Lorenz.
It had to be exactly one character longer than the cipher text tape,
so that it would be displaced by one character on each pass.
The tapes were read at 1000 characters per second.
It was vitally important to keep the two tapes 'in sync' with
each other, but this appeared to be difficult in practice due to
tape stretching. Several mechanical solutions were tested and applied
to solve this tape synchronisation problem.
After several improvements, the Heath Robinson eventually led
to the development of Colossus,
the first electronic programmable
computer, which was also used to break the Lorenz cipher.
Colossus did not suffer from the synchronisation problem as it used
only one tape reader, whilst the Chi-wheel start patterns were
generated internally by Colossus, using the spocket hole to
synchronise the machine.
Nevertheless, the Heath Robinson remained in service as it appeared
to be usefull for some dedicated tasks. Several design variants
and 'specials' were derived from it.
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