Cryptography Reference
In-Depth Information
chapter 5
EARLY MANUAL
AND MECHANICAL
CRYPTOGRAPHY
The first well-defined phase in the history of cryptol-
ogy was the period of manual cryptography, starting
with the origins of the subject in antiquity and continuing
through World War I. Throughout this phase cryptogra-
phy was limited by the complexity of what a code clerk
could reasonably do aided by simple mnemonic devices.
As a result, ciphers were limited to at most a few pages in
size, i.e., to only a few thousands of characters. General
principles for both cryptography and cryptanalysis were
known, but the security that could be achieved was always
limited by what could be done manually. Most systems
could be cryptanalyzed, therefore, given sufficient cipher-
text and effort. One way to think of this phase is that any
cryptography scheme devised during those two millennia
could have equally well been used by the ancients if they
had known of it.
A second phase came with the mechanization of cryp-
tography, which began shortly after World War I and
continues even today. The applicable technology involved
either telephone and telegraph communications (employ-
ing punched paper tape, telephone switches, and relays) or
calculating machines such as the Brunsvigas, Marchants,
Facits, and Friedens (employing gears, sprockets, ratchets,
pawls, and cams). This resulted in the rotor machines used
by all participants in World War II. These machines could
 
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