Cryptography Reference
In-Depth Information
Yet another problem involved authentication of encrypted messages.
Encryption between parties relied on a shared secret key. If enciphering
material and keys were seized by the enemy, one could be fed false infor-
mation, in what the Germans called a
funkspiel
. To authenticate encrypted
material, and thus prevent funkspiels, two distinct methods were used.
The first relied on inserting within the message itself an
authenticator
, a
security check agreed upon in advance—for example, an additional
x
after
every tenth letter of plaintext. The absence of an authenticator was meant
as a “silent alarm,” indicating to the receiving party that something was
amiss.
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The second method took advantage of the fact that Morse operators
could not help but identify themselves in the process of keying informa-
tion. The radio signal itself embedded biometric information uniquely
identifying its human operator—its “fist,” or “sending touch,” “as disti-
nctive as handwriting.”
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Such biometrics provided another layer of
authentication, one much more difficult to defeat: Kahn explains that “Nazi
radio spies were trained in a school near Hamburg . . . each agent's 'fist' was
recorded to make radiotelegraph forgery by the Allies that much more
difficult.”29
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Electromechanical Devices
In the aftermath of the Great War, technological advances made possible
the development of ciphers both remarkably powerful and simple to oper-
ate—the
Enigma machines
used by Germany during World War II and the
Vernam one-time pad
, used in diplomatic communications. These would
spur corresponding advances in both theory and practice of cryptanalysis
and eventually pave the way for Alan Turing's foundational work in digital
computing and Claude Shannon's mathematical theory of information
and communication.
Enigma and Hagelin Machines
In 1918 and 1919, several inventors developed, refined, and commercial-
ized a series of electromechanical devices that provided extremely powerful
encryption capabilities: One of these inventors, Swede Boris Hagelin, was
to become cryptography's first millionaire; another one, German Arthur
Scherbius, commercialized a portable, battery-powered machine called the