From Newsgroup: sci.crypt
There was a time when you could just go out and buy an Enigma machine.
In the early nineteen-twenties, any organization with a need to keep
its communications secret could order a few of those brand-new devices
from Germany and rest assured that any messages encoded using them
would be safe from prying eyes. It didn't take long for the military to
catch on to the Enigma's usefulness. Just a few years after the machine
came on the market, it had been adopted by the German Navy, Army, and
Air Force, and made possible the rapid, secret coordination central to
the technique we now call blitzkrieg. When World War II began, Axis
forces were confident, as anyone in possession of an unbreakable code
might well be.
As history played out, of course, that code turned out to be breakable.
That this came as a surprise to the Nazis makes sense if you watch the
new video above from Veritasium, which opens up an actual Enigma
machine and explains its inner workings. Each letter typed into its
keyboard passes through a series of interchangeable rotors wired
together, then comes back through in the opposite direction, resulting
in a particular substitute letter.
Each character entered advances at least one of the rotors, each of
which turns at a different speed, meaning that the already complex substitution cipher constantly changes. To make it even trickier, the
Nazis made modifications to their Enigma machines, including a telephone-operator-style plugboard that expanded the possible
encryption keys to 7 x 1018: an infinite-seeming number that fairly
cried out for the mathematical services of Alan Turing.
Already famous for having come up with the "Turing machine," which
could theoretically manipulate strings of symbols in what we'd now call
an algorithmic fashion, he was recruited by Britain's wartime
codebreaking headquarters at Bletchley Park, where experts were already
hard at work reverse-engineering the Enigma machine. There he
considered flaws in the design of the device, such as its inability to
encrypt any given letter as itself, and the ways in which its human
operators used it, such as making predictable weather reports.
Exploiting these weaknesses required building a non-theoretical
computation engine, the Bombe, to grind through all possibilities at
what would then have seemed an unfathomable speed. The intelligence the
Bombe produced contributed to the success of the surprise D|ore4rCyDay invasion and may have taken years off the potential ravages of World
War II. It wouldn't have happened without Turing's formidable
intelligence - or his understanding that you need a machine to outsmart
a machine.
https://www.openculture.com/2026/09/how-alan-turing-and-his-fellow-codebreakers-broke-the-nazis-unbreakable-enigma-code.html
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