Using machinery to automate encryption permitted ciphers to be much more complicated than those which can reasonably be applied by hand without too many mistakes. And this was true even though machines had to be reliable and inexpensive, and this meant they could only carry out fairly simple operations. (Today, of course, the microchip has changed everything immensely!)
There are several types of cipher machine that we will examine in this section; and a few more that belong to another section, since they hint at the computer age to follow.
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