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Hand
Educational tool for alphabet substitution
One of the most elementary hand cipher
tools for learning the basics of cryptography is the blank Aristo 90197 slide rule.
It was used for training new
cryptanalists with the principles of alphabet substitution, shifting and
transposition, and is in fact the blank variant of a standard slide ruler.
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A slide rule, in the US also known as a slipstick,
is a mechanical analog computer 1 that was used for scientific calculations
like multiplication, division, roots, logarithms and trigoniometry.
Invented in 1622 by Reverend William Oughtred in the UK,
it was the most popular calculation device in science and education
before the arrival of the pocket calculator
around 1974 [1].
Over time, a wide variety of specialized slide rules were developed for
specific fields like navigation, engineering, antenna calculations, proof calculations,
education, photography, etc.
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Although the name may suggest otherwise, a slide rule was not used for taking
measurements. The most basic design consists of two fixed parts,
with a sliding section in the middle. By using a blank
variant of the slide rule, with evenly spaced cells, it becomes a useful practicing
tool for simple alphabet substitutions and transpositions;
two of the basic operations in cryptography.
The image above shows a typical blank slide rule made by Aristo in Germany,
one of the major manufacturers of educational tools in Europe.
The slide rule is made of plastic and is printed with vertical bars only,
allowing letters to be written inside the individual cells with a pencil.
Because of its simplicity it could be used for nearly every language. It was used
for the education of cryptanalists in Europe throughout the Cold War
and is very similar to the Dutch Caesar Box.
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The word computer should not be confused with a modern automatic programmable
digital computer.
Please note that a computer was initially a person that performed calculations
(calculator) and that the name was later also used for automated calculations,
both mechanically and electronically [2].
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© Crypto Museum. Created: Thursday 12 August 2010. Last changed: Sunday, 13 May 2018 - 06:57 CET.
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